first commit

core/modules/workspaces/css/workspaces.off-canvas.css

@@ -0,0 +1,205 @@
+/*
+ * DO NOT EDIT THIS FILE.
+ * See the following change record for more information,
+ * https://www.drupal.org/node/3084859
+ * @preserve
+ */
+
+/**
+ * @file
+ * Styling for the Workspaces off-canvas user interface.
+ */
+
+#drupal-off-canvas-wrapper.workspaces-dialog {
+  padding-bottom: calc(var(--off-canvas-padding) / 2);
+}
+
+@media (min-width: 47.9375rem) {
+  #drupal-off-canvas-wrapper.workspaces-dialog .ui-dialog-content > div {
+    display: flex;
+    align-items: flex-end;
+    width: 100%;
+    height: 100%;
+  }
+}
+
+@media (max-width: 47.9375rem) {
+  #drupal-off-canvas-wrapper.workspaces-dialog + .ui-dialog .ui-dialog-content {
+    max-height: unset !important; /* Override the max-height added by JS. */
+  }
+}
+
+/**
+   * The Workspace UI hides the titlebar, but we need to show and correctly
+   * position the close button that is nested within it.
+   */
+
+#drupal-off-canvas-wrapper.workspaces-dialog .ui-dialog-titlebar {
+  all: revert;
+}
+
+#drupal-off-canvas-wrapper.workspaces-dialog .ui-dialog-titlebar::before {
+  content: none;
+}
+
+#drupal-off-canvas-wrapper.workspaces-dialog .ui-dialog-titlebar .ui-dialog-title {
+  display: none;
+}
+
+#drupal-off-canvas-wrapper.workspaces-dialog .ui-dialog-titlebar .ui-dialog-titlebar-close {
+  inset-block-start: 1em;
+  inset-inline-end: 1em;
+  z-index: 1;
+  transform: none;
+}
+
+#drupal-off-canvas-wrapper.workspaces-dialog .active-workspace {
+  padding: 0 var(--off-canvas-padding);
+}
+
+@media (min-width: 47.9375rem) {
+  #drupal-off-canvas-wrapper.workspaces-dialog .active-workspace {
+    display: flex;
+    flex-direction: column;
+    flex-basis: 12.5rem;
+    flex-grow: 2;
+    align-self: stretch;
+    order: 1;
+    padding: var(--off-canvas-padding) var(--off-canvas-padding) 0;
+  }
+}
+
+#drupal-off-canvas-wrapper.workspaces-dialog .active-workspace__title {
+  font-size: 0.8125rem;
+  font-weight: bold;
+}
+
+#drupal-off-canvas-wrapper.workspaces-dialog .active-workspace__label {
+  position: relative; /* Anchor icon pseudo-element. */
+  padding: 1.125rem 3.125rem 0;
+  color: #fff;
+  font-size: 1.125rem;
+  font-weight: bold;
+  line-height: 1.2;
+}
+
+#drupal-off-canvas-wrapper.workspaces-dialog .active-workspace__label::before {
+  position: absolute;
+  inset-inline-start: 0;
+  display: block;
+  width: 1.25rem;
+  height: 1.25rem;
+  content: "";
+  background: url("data:image/svg+xml,%3csvg xmlns='http://www.w3.org/2000/svg' width='40' height='40' viewBox='0 0 40 40'%3e  %3cpath fill='%23F0A100' fill-rule='evenodd' d='M38,0 L2.002,0 C0.896716337,-1.37884559e-07 0.000552089742,0.895716475 0,2.001 L0,38.003 C0,39.105 0.899,40.003 2,40.003 L38,40.003 C39.103,40.003 40,39.103 40,38.003 L40,2.001 C40.000531,1.47031248 39.7900198,0.961193334 39.4148607,0.585846626 C39.0397016,0.210499918 38.5306877,-0.000265742306 38,0 Z M34.003,4 C35.105,4 36.003,4.899 36.003,6 C36.003,7.102 35.103,7.998 34.003,7.998 C32.9235903,7.96385326 32.0662376,7.07894966 32.0662376,5.999 C32.0662376,4.91905034 32.9235903,4.03414674 34.003,4 Z M26.003,4 C27.105,4 28.002,4.899 28.002,6 C28.002,7.102 27.102,7.998 26.002,7.998 C24.9225903,7.96385326 24.0652376,7.07894966 24.0652376,5.999 C24.0652376,4.91905034 24.9225903,4.03414674 26.002,4 L26.003,4 Z M18.002,4 C19.104,4 20.002,4.899 20.002,6 C20.002,7.102 19.102,7.998 18.002,7.998 C16.899,7.998 16.002,7.1 16.002,5.999 C16.0025521,4.89482104 16.8978209,3.99999986 18.002,4 Z M36.002,36.002 L4,36.002 L4,12.001 L36.002,12.001 L36.002,36.002 Z M8.805,32.002 L15.196,32.002 C15.4092125,32.0030667 15.6140295,31.9189775 15.764983,31.7683995 C15.9159365,31.6178215 16.0005357,31.4132145 16,31.2 L16,16.805 C16.0005341,16.5919596 15.916072,16.3875055 15.7653354,16.2369566 C15.6145988,16.0864077 15.4100395,16.0022004 15.197,16.003 L8.794,16.003 C8.581215,16.0027342 8.37706868,16.087145 8.22660684,16.2376068 C8.07614501,16.3880687 7.99173418,16.592215 7.992,16.805 L7.992,31.208 C7.99966319,31.6507223 8.36222028,32.0048063 8.805,32.002 Z M20.803,24.002 L31.206,24.002 C31.4190404,24.0025341 31.6234945,23.918072 31.7740434,23.7673354 C31.9245923,23.6165988 32.0087996,23.4120395 32.008,23.199 L32.008,16.797 C32.0085328,16.5841335 31.9242078,16.3798319 31.7736879,16.2293121 C31.6231681,16.0787922 31.4188665,15.9944672 31.206,15.995 L20.803,15.995 C20.5901335,15.9944672 20.3858319,16.0787922 20.2353121,16.2293121 C20.0847922,16.3798319 20.0004672,16.5841335 20.001,16.797 L20.001,23.199 C20.001,23.646 20.356,24.001 20.803,24.001 L20.803,24.002 Z M20.803,32.002 L31.206,32.002 C31.4188665,32.0025328 31.6231681,31.9182078 31.7736879,31.7676879 C31.9242078,31.6171681 32.0085328,31.4128665 32.008,31.2 L32.008,28.797 C32.0085328,28.5841335 31.9242078,28.3798319 31.7736879,28.2293121 C31.6231681,28.0787922 31.4188665,27.9944672 31.206,27.995 L20.803,27.995 C20.5901335,27.9944672 20.3858319,28.0787922 20.2353121,28.2293121 C20.0847922,28.3798319 20.0004672,28.5841335 20.001,28.797 L20.001,31.2 C20.001,31.647 20.356,32.002 20.803,32.002 Z'/%3e%3c/svg%3e") center center no-repeat;
+  background-size: contain;
+}
+
+@media (min-width: 47.9375rem) {
+  #drupal-off-canvas-wrapper.workspaces-dialog .active-workspace__label::before {
+    width: 2.5rem;
+    height: 2.5rem;
+  }
+}
+
+/* This is the "Manage workspace" link that appears when you're on a non-default workspace. */
+
+#drupal-off-canvas-wrapper.workspaces-dialog .active-workspace__manage {
+  display: block;
+  font-size: 0.8125rem;
+}
+
+/* This is the link to "View all workspaces". */
+
+#drupal-off-canvas-wrapper.workspaces-dialog .all-workspaces {
+  display: inline-block;
+  padding: var(--off-canvas-padding);
+  font-size: 0.875rem;
+}
+
+@media (min-width: 47.9375rem) {
+  #drupal-off-canvas-wrapper.workspaces-dialog .all-workspaces {
+    grid-row: 1;
+    grid-column: 2;
+    justify-self: end;
+    padding: 0;
+  }
+}
+
+#drupal-off-canvas-wrapper.workspaces-dialog .workspaces > h3 {
+  margin-top: 0;
+}
+
+#drupal-off-canvas-wrapper.workspaces-dialog .workspaces ul {
+  display: flex;
+  flex-direction: column;
+  grid-row: 2;
+  grid-column: 1 / -1;
+  margin: 0;
+  padding: 0;
+  list-style: none;
+  gap: 2px;
+}
+
+@media (min-width: 47.9375rem) {
+  #drupal-off-canvas-wrapper.workspaces-dialog .workspaces ul {
+    flex-direction: row;
+  }
+}
+
+#drupal-off-canvas-wrapper.workspaces-dialog .workspaces li {
+  flex: 1;
+}
+
+@media (min-width: 47.9375rem) {
+  #drupal-off-canvas-wrapper.workspaces-dialog .workspaces {
+    display: grid;
+    flex-grow: 8;
+    grid-template-columns: 1fr 1fr;
+  }
+}
+
+/* This is the link to the workspace. */
+
+#drupal-off-canvas-wrapper.workspaces-dialog .workspaces__item {
+  position: relative;
+  display: block;
+  min-height: 4.6875rem;
+  padding-block-start: var(--off-canvas-padding);
+  padding-inline-start: 3.125rem;
+  color: var(--off-canvas-text-color);
+  outline-offset: -2px; /* Ensure focus outline doesn't overflow. */
+  background-color: var(--off-canvas-background-color-light);
+  font-size: 0.875rem;
+  font-weight: bold;
+}
+
+#drupal-off-canvas-wrapper.workspaces-dialog .workspaces__item:hover,
+#drupal-off-canvas-wrapper.workspaces-dialog .workspaces__item:focus {
+  background-color: #666;
+}
+
+#drupal-off-canvas-wrapper.workspaces-dialog .workspaces__item::before {
+  position: absolute;
+  inset-inline-start: var(--off-canvas-padding);
+  display: block;
+  width: 1.25rem;
+  height: 1.25rem;
+  content: "";
+  background: url("data:image/svg+xml,%3csvg xmlns='http://www.w3.org/2000/svg' width='40' height='40' viewBox='0 0 40 40'%3e  %3cpath fill='%23F0A100' fill-rule='evenodd' d='M38,0 L2.002,0 C0.896716337,-1.37884559e-07 0.000552089742,0.895716475 0,2.001 L0,38.003 C0,39.105 0.899,40.003 2,40.003 L38,40.003 C39.103,40.003 40,39.103 40,38.003 L40,2.001 C40.000531,1.47031248 39.7900198,0.961193334 39.4148607,0.585846626 C39.0397016,0.210499918 38.5306877,-0.000265742306 38,0 Z M34.003,4 C35.105,4 36.003,4.899 36.003,6 C36.003,7.102 35.103,7.998 34.003,7.998 C32.9235903,7.96385326 32.0662376,7.07894966 32.0662376,5.999 C32.0662376,4.91905034 32.9235903,4.03414674 34.003,4 Z M26.003,4 C27.105,4 28.002,4.899 28.002,6 C28.002,7.102 27.102,7.998 26.002,7.998 C24.9225903,7.96385326 24.0652376,7.07894966 24.0652376,5.999 C24.0652376,4.91905034 24.9225903,4.03414674 26.002,4 L26.003,4 Z M18.002,4 C19.104,4 20.002,4.899 20.002,6 C20.002,7.102 19.102,7.998 18.002,7.998 C16.899,7.998 16.002,7.1 16.002,5.999 C16.0025521,4.89482104 16.8978209,3.99999986 18.002,4 Z M36.002,36.002 L4,36.002 L4,12.001 L36.002,12.001 L36.002,36.002 Z M8.805,32.002 L15.196,32.002 C15.4092125,32.0030667 15.6140295,31.9189775 15.764983,31.7683995 C15.9159365,31.6178215 16.0005357,31.4132145 16,31.2 L16,16.805 C16.0005341,16.5919596 15.916072,16.3875055 15.7653354,16.2369566 C15.6145988,16.0864077 15.4100395,16.0022004 15.197,16.003 L8.794,16.003 C8.581215,16.0027342 8.37706868,16.087145 8.22660684,16.2376068 C8.07614501,16.3880687 7.99173418,16.592215 7.992,16.805 L7.992,31.208 C7.99966319,31.6507223 8.36222028,32.0048063 8.805,32.002 Z M20.803,24.002 L31.206,24.002 C31.4190404,24.0025341 31.6234945,23.918072 31.7740434,23.7673354 C31.9245923,23.6165988 32.0087996,23.4120395 32.008,23.199 L32.008,16.797 C32.0085328,16.5841335 31.9242078,16.3798319 31.7736879,16.2293121 C31.6231681,16.0787922 31.4188665,15.9944672 31.206,15.995 L20.803,15.995 C20.5901335,15.9944672 20.3858319,16.0787922 20.2353121,16.2293121 C20.0847922,16.3798319 20.0004672,16.5841335 20.001,16.797 L20.001,23.199 C20.001,23.646 20.356,24.001 20.803,24.001 L20.803,24.002 Z M20.803,32.002 L31.206,32.002 C31.4188665,32.0025328 31.6231681,31.9182078 31.7736879,31.7676879 C31.9242078,31.6171681 32.0085328,31.4128665 32.008,31.2 L32.008,28.797 C32.0085328,28.5841335 31.9242078,28.3798319 31.7736879,28.2293121 C31.6231681,28.0787922 31.4188665,27.9944672 31.206,27.995 L20.803,27.995 C20.5901335,27.9944672 20.3858319,28.0787922 20.2353121,28.2293121 C20.0847922,28.3798319 20.0004672,28.5841335 20.001,28.797 L20.001,31.2 C20.001,31.647 20.356,32.002 20.803,32.002 Z'/%3e%3c/svg%3e") center center no-repeat;
+  background-size: 100% auto;
+}
+
+#drupal-off-canvas-wrapper.workspaces-dialog .active-workspace--default .active-workspace__label::before,
+#drupal-off-canvas-wrapper.workspaces-dialog .workspaces__item--default::before {
+  background-image: url("data:image/svg+xml,%3csvg xmlns='http://www.w3.org/2000/svg' width='20' height='20' viewBox='0 0 20 20'%3e  %3cpath fill='%2381C071' fill-rule='evenodd' d='M19,0 L1,0 C0.449,0 0,0.448 0,1 L0,19 C0,19.552 0.45,20 1,20 L19,20 C19.552,20 20,19.55 20,19 L20,1 C20,0.44771525 19.5522847,3.38176876e-17 19,0 Z M17.001,2 C17.553,2 18.001,2.45 18.001,3 C18.001,3.55 17.551,3.999 17.001,3.999 C16.451,3.999 16.001,3.549 16.001,2.999 C16.001,2.44671525 16.4487153,1.999 17.001,1.999 L17.001,2 Z M13.001,2 C13.552,2 14.001,2.45 14.001,3 C14.001,3.55 13.551,3.999 13.001,3.999 C12.4487153,3.999 12.001,3.55128475 12.001,2.999 C12.001,2.44671525 12.4487153,1.999 13.001,1.999 L13.001,2 Z M9.001,2 C9.552,2 10.001,2.45 10.001,3 C10.001,3.55 9.551,3.999 9.001,3.999 C8.44871525,3.999 8.001,3.55128475 8.001,2.999 C8.001,2.44671525 8.44871525,1.999 9.001,1.999 L9.001,2 Z M18.001,18 L2,18 L2,6 L18.001,6 L18.001,18 Z M4.402,16 L7.598,16 C7.70460623,16.0005334 7.80701477,15.9584887 7.88249152,15.8831997 C7.95796827,15.8079107 8.00026785,15.7056072 8,15.599 L8,8.402 C8.00026565,8.29574025 7.95824022,8.19374159 7.88319685,8.11851062 C7.80815349,8.04327965 7.70626008,8.00099967 7.6,8.001 L4.396,8.001 C4.28956674,8.00073358 4.18741595,8.04289612 4.11215603,8.11815603 C4.03689612,8.19341595 3.99473358,8.29556674 3.995,8.402 L3.995,15.603 C3.999,15.823 4.177,16 4.401,16 L4.402,16 Z M10.402,12 L15.603,12 C15.7094333,12.0002664 15.811584,11.9581039 15.886844,11.882844 C15.9621039,11.807584 16.0042664,11.7054333 16.004,11.599 L16.004,8.398 C16.0042664,8.29156674 15.9621039,8.18941595 15.886844,8.11415603 C15.811584,8.03889612 15.7094333,7.99673358 15.603,7.997 L10.402,7.997 C10.2957402,7.99673435 10.1937416,8.03875978 10.1185106,8.11380315 C10.0432796,8.18884651 10.0009997,8.29073992 10.001,8.397 L10.001,11.6 C10.001,11.824 10.178,12 10.401,12 L10.402,12 Z M10.402,16 L15.603,16 C15.7094333,16.0002664 15.811584,15.9581039 15.886844,15.882844 C15.9621039,15.807584 16.0042664,15.7054333 16.004,15.599 L16.004,14.398 C16.0042664,14.2915667 15.9621039,14.189416 15.886844,14.114156 C15.811584,14.0388961 15.7094333,13.9967336 15.603,13.997 L10.402,13.997 C10.2957402,13.9967343 10.1937416,14.0387598 10.1185106,14.1138031 C10.0432796,14.1888465 10.0009997,14.2907399 10.001,14.397 L10.001,15.6 C10.001,15.824 10.178,16 10.401,16 L10.402,16 Z'/%3e%3c/svg%3e"); /* Green icon. */
+}
+
+#drupal-off-canvas-wrapper.workspaces-dialog .active-workspace__actions .button {
+  margin: 0.625rem 0 0;
+}
+
+@media (max-width: 47.9375rem) {
+  #drupal-off-canvas-wrapper.workspaces-dialog {
+    height: 100% !important;
+  }
+}

core/modules/workspaces/css/workspaces.off-canvas.pcss.css

@@ -0,0 +1,187 @@
+/**
+ * @file
+ * Styling for the Workspaces off-canvas user interface.
+ */
+
+@custom-media --workspace-layout-small (max-width: 767px);
+@custom-media --workspace-layout-large (min-width: 767px);
+
+#drupal-off-canvas-wrapper.workspaces-dialog {
+  padding-bottom: calc(var(--off-canvas-padding) / 2);
+
+  & .ui-dialog-content > div {
+    @media (--workspace-layout-large) {
+      display: flex;
+      align-items: flex-end;
+      width: 100%;
+      height: 100%;
+    }
+  }
+
+  & + .ui-dialog .ui-dialog-content {
+    @media (--workspace-layout-small) {
+      max-height: unset !important; /* Override the max-height added by JS. */
+    }
+  }
+
+  /**
+   * The Workspace UI hides the titlebar, but we need to show and correctly
+   * position the close button that is nested within it.
+   */
+  & .ui-dialog-titlebar {
+    all: revert;
+
+    &::before {
+      content: none;
+    }
+
+    & .ui-dialog-title {
+      display: none;
+    }
+
+    & .ui-dialog-titlebar-close {
+      inset-block-start: 1em;
+      inset-inline-end: 1em;
+      z-index: 1;
+      transform: none;
+    }
+  }
+
+  & .active-workspace {
+    padding: 0 var(--off-canvas-padding);
+
+    @media (--workspace-layout-large) {
+      display: flex;
+      flex-direction: column;
+      flex-basis: 200px;
+      flex-grow: 2;
+      align-self: stretch;
+      order: 1;
+      padding: var(--off-canvas-padding) var(--off-canvas-padding) 0;
+    }
+  }
+
+  & .active-workspace__title {
+    font-size: 13px;
+    font-weight: bold;
+  }
+
+  & .active-workspace__label {
+    position: relative; /* Anchor icon pseudo-element. */
+    padding: 18px 50px 0;
+    color: #fff;
+    font-size: 18px;
+    font-weight: bold;
+    line-height: 1.2;
+
+    &::before {
+      position: absolute;
+      inset-inline-start: 0;
+      display: block;
+      width: 20px;
+      height: 20px;
+      content: "";
+      background: url("../icons/f0a100/ws_icon.svg") center center no-repeat;
+      background-size: contain;
+
+      @media (--workspace-layout-large) {
+        width: 40px;
+        height: 40px;
+      }
+    }
+  }
+
+  /* This is the "Manage workspace" link that appears when you're on a non-default workspace. */
+  & .active-workspace__manage {
+    display: block;
+    font-size: 13px;
+  }
+
+  /* This is the link to "View all workspaces". */
+  & .all-workspaces {
+    display: inline-block;
+    padding: var(--off-canvas-padding);
+    font-size: 14px;
+
+    @media (--workspace-layout-large) {
+      grid-row: 1;
+      grid-column: 2;
+      justify-self: end;
+      padding: 0;
+    }
+  }
+
+  & .workspaces {
+    & > h3 {
+      margin-top: 0;
+    }
+
+    & ul {
+      display: flex;
+      flex-direction: column;
+      grid-row: 2;
+      grid-column: 1 / -1;
+      margin: 0;
+      padding: 0;
+      list-style: none;
+      gap: 2px;
+
+      @media (--workspace-layout-large) {
+        flex-direction: row;
+      }
+    }
+
+    & li {
+      flex: 1;
+    }
+
+    @media (--workspace-layout-large) {
+      display: grid;
+      flex-grow: 8;
+      grid-template-columns: 1fr 1fr;
+    }
+  }
+
+  /* This is the link to the workspace. */
+  & .workspaces__item {
+    position: relative;
+    display: block;
+    min-height: 75px;
+    padding-block-start: var(--off-canvas-padding);
+    padding-inline-start: 50px;
+    color: var(--off-canvas-text-color);
+    outline-offset: -2px; /* Ensure focus outline doesn't overflow. */
+    background-color: var(--off-canvas-background-color-light);
+    font-size: 14px;
+    font-weight: bold;
+
+    &:hover,
+    &:focus {
+      background-color: #666;
+    }
+
+    &::before {
+      position: absolute;
+      inset-inline-start: var(--off-canvas-padding);
+      display: block;
+      width: 20px;
+      height: 20px;
+      content: "";
+      background: url("../icons/f0a100/ws_icon.svg") center center no-repeat;
+      background-size: 100% auto;
+    }
+  }
+
+  & .active-workspace--default .active-workspace__label::before,
+  & .workspaces__item--default::before {
+    background-image: url("../icons/81c071/ws_icon.svg"); /* Green icon. */
+  }
+
+  & .active-workspace__actions .button {
+    margin: 10px 0 0;
+  }
+
+  @media (--workspace-layout-small) {
+    height: 100% !important;
+  }
+}

core/modules/workspaces/css/workspaces.overview.css

@@ -0,0 +1,17 @@
+/*
+ * DO NOT EDIT THIS FILE.
+ * See the following change record for more information,
+ * https://www.drupal.org/node/3084859
+ * @preserve
+ */
+
+/**
+ * @file
+ * Styling for the Workspaces overview table.
+ */
+
+/** @todo Move to Claro theme before Workspaces is marked stable. */
+
+tr.active-workspace {
+  background-color: #ebeae4;
+}

core/modules/workspaces/css/workspaces.overview.pcss.css

@@ -0,0 +1,9 @@
+/**
+ * @file
+ * Styling for the Workspaces overview table.
+ */
+
+/** @todo Move to Claro theme before Workspaces is marked stable. */
+tr.active-workspace {
+  background-color: #ebeae4;
+}

core/modules/workspaces/css/workspaces.toolbar.css

@@ -0,0 +1,96 @@
+/*
+ * DO NOT EDIT THIS FILE.
+ * See the following change record for more information,
+ * https://www.drupal.org/node/3084859
+ * @preserve
+ */
+
+/**
+ * @file
+ * Styling for Workspaces module's toolbar tab.
+ */
+
+/* Toolbar tab */
+
+.toolbar .toolbar-bar .workspaces-toolbar-tab {
+  color: #000;
+  background-color: #e09600;
+}
+
+.toolbar .toolbar-bar .workspaces-toolbar-tab--is-default {
+  background-color: #81c071;
+}
+
+.toolbar-oriented .toolbar-bar .workspaces-toolbar-tab {
+  float: right; /* LTR */
+
+  /**
+   * Chromium and Webkit do not yet support flow relative logical properties,
+   * such as float: inline-end. However, PostCSS Logical does not compile this
+   * value, so we accommodate by not using these.
+   *
+   * @see https://caniuse.com/mdn-css_properties_clear_flow_relative_values
+   * @see https://github.com/csstools/postcss-plugins/issues/632
+   */
+}
+
+[dir="rtl"] .toolbar-oriented .toolbar-bar .workspaces-toolbar-tab {
+  float: left;
+}
+
+@media (min-width: 16.5rem) {
+  .toolbar:not(.toolbar-oriented) .toolbar-bar .workspaces-toolbar-tab {
+    float: right; /* LTR */
+
+    /**
+     * Chromium and Webkit do not yet support flow relative logical properties,
+     * such as float: inline-end. However, PostCSS Logical does not compile this
+     * value, so we accommodate by not using these.
+     *
+     * @see https://caniuse.com/mdn-css_properties_clear_flow_relative_values
+     * @see https://github.com/csstools/postcss-plugins/issues/632
+     */
+  }
+  [dir="rtl"] .toolbar:not(.toolbar-oriented) .toolbar-bar .workspaces-toolbar-tab {
+    float: left;
+  }
+}
+
+/* Link within the toolbar tab. */
+
+.toolbar .toolbar-bar .workspaces-toolbar-tab .toolbar-item {
+  width: 100%;
+  margin: 0;
+  text-align: start;
+  color: inherit;
+}
+
+.toolbar-oriented :is(.toolbar .toolbar-bar .workspaces-toolbar-tab .toolbar-item) {
+  width: auto;
+  text-align: initial;
+}
+
+.toolbar .toolbar-icon-workspace::before {
+  background-image: url("data:image/svg+xml,%3csvg xmlns='http://www.w3.org/2000/svg' width='16' height='16' viewBox='0 0 16 16'%3e  %3cpath d='M14,12 L16,12 L16,0 L4,0 L4,2 L14,2 L14,12 Z M0,4 L12,4 L12,16 L0,16 L0,4 Z'/%3e%3c/svg%3e");
+}
+
+@media all and (max-width: 47.875rem) {
+  .toolbar-oriented .toolbar-bar .workspaces-toolbar-tab .toolbar-icon-workspace {
+    width: auto;
+    max-width: 8em;
+  }
+
+  .toolbar .toolbar-bar .workspaces-toolbar-tab .toolbar-icon-workspace {
+    overflow: hidden;
+    padding-inline: 2.75em 1.3333em;
+    white-space: nowrap;
+    text-indent: 0;
+    text-overflow: ellipsis;
+  }
+
+  .toolbar .toolbar-bar .workspaces-toolbar-tab .toolbar-icon-workspace::before {
+    inset-inline-start: 0.6667em;
+    width: 1.25rem;
+    background-size: 100% auto;
+  }
+}

core/modules/workspaces/css/workspaces.toolbar.pcss.css

@@ -0,0 +1,84 @@
+/**
+ * @file
+ * Styling for Workspaces module's toolbar tab.
+ */
+
+/* Toolbar tab */
+.toolbar .toolbar-bar .workspaces-toolbar-tab {
+  color: #000;
+  background-color: #e09600;
+}
+.toolbar .toolbar-bar .workspaces-toolbar-tab--is-default {
+  background-color: #81c071;
+}
+.toolbar-oriented .toolbar-bar .workspaces-toolbar-tab {
+  float: right; /* LTR */
+
+  /**
+   * Chromium and Webkit do not yet support flow relative logical properties,
+   * such as float: inline-end. However, PostCSS Logical does not compile this
+   * value, so we accommodate by not using these.
+   *
+   * @see https://caniuse.com/mdn-css_properties_clear_flow_relative_values
+   * @see https://github.com/csstools/postcss-plugins/issues/632
+   */
+  &:dir(rtl) {
+    float: left;
+  }
+}
+
+@media (min-width: 264px) {
+  .toolbar:not(.toolbar-oriented) .toolbar-bar .workspaces-toolbar-tab {
+    float: right; /* LTR */
+
+    /**
+     * Chromium and Webkit do not yet support flow relative logical properties,
+     * such as float: inline-end. However, PostCSS Logical does not compile this
+     * value, so we accommodate by not using these.
+     *
+     * @see https://caniuse.com/mdn-css_properties_clear_flow_relative_values
+     * @see https://github.com/csstools/postcss-plugins/issues/632
+     */
+    &:dir(rtl) {
+      float: left;
+    }
+  }
+}
+
+/* Link within the toolbar tab. */
+.toolbar .toolbar-bar .workspaces-toolbar-tab .toolbar-item {
+  width: 100%;
+  margin: 0;
+  text-align: start;
+  color: inherit;
+
+  @nest .toolbar-oriented & {
+    width: auto;
+    text-align: initial;
+  }
+}
+
+.toolbar .toolbar-icon-workspace::before {
+  background-image: url("../icons/000000/workspaces.svg");
+}
+
+@media all and (max-width: 766px) {
+  .toolbar-oriented .toolbar-bar .workspaces-toolbar-tab .toolbar-icon-workspace {
+    width: auto;
+    max-width: 8em;
+  }
+
+  .toolbar .toolbar-bar .workspaces-toolbar-tab .toolbar-icon-workspace {
+    overflow: hidden;
+    padding-inline: 2.75em 1.3333em;
+    white-space: nowrap;
+    text-indent: 0;
+    text-overflow: ellipsis;
+  }
+
+  .toolbar .toolbar-bar .workspaces-toolbar-tab .toolbar-icon-workspace::before {
+    inset-inline-start: 0.6667em;
+    width: 20px;
+    background-size: 100% auto;
+  }
+}

core/modules/workspaces/icons/000000/workspaces.svg

@@ -0,0 +1,3 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="16" height="16" viewBox="0 0 16 16">
+  <path d="M14,12 L16,12 L16,0 L4,0 L4,2 L14,2 L14,12 Z M0,4 L12,4 L12,16 L0,16 L0,4 Z"/>
+</svg>

core/modules/workspaces/icons/81c071/ws_icon.svg

@@ -0,0 +1,3 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="20" height="20" viewBox="0 0 20 20">
+  <path fill="#81C071" fill-rule="evenodd" d="M19,0 L1,0 C0.449,0 0,0.448 0,1 L0,19 C0,19.552 0.45,20 1,20 L19,20 C19.552,20 20,19.55 20,19 L20,1 C20,0.44771525 19.5522847,3.38176876e-17 19,0 Z M17.001,2 C17.553,2 18.001,2.45 18.001,3 C18.001,3.55 17.551,3.999 17.001,3.999 C16.451,3.999 16.001,3.549 16.001,2.999 C16.001,2.44671525 16.4487153,1.999 17.001,1.999 L17.001,2 Z M13.001,2 C13.552,2 14.001,2.45 14.001,3 C14.001,3.55 13.551,3.999 13.001,3.999 C12.4487153,3.999 12.001,3.55128475 12.001,2.999 C12.001,2.44671525 12.4487153,1.999 13.001,1.999 L13.001,2 Z M9.001,2 C9.552,2 10.001,2.45 10.001,3 C10.001,3.55 9.551,3.999 9.001,3.999 C8.44871525,3.999 8.001,3.55128475 8.001,2.999 C8.001,2.44671525 8.44871525,1.999 9.001,1.999 L9.001,2 Z M18.001,18 L2,18 L2,6 L18.001,6 L18.001,18 Z M4.402,16 L7.598,16 C7.70460623,16.0005334 7.80701477,15.9584887 7.88249152,15.8831997 C7.95796827,15.8079107 8.00026785,15.7056072 8,15.599 L8,8.402 C8.00026565,8.29574025 7.95824022,8.19374159 7.88319685,8.11851062 C7.80815349,8.04327965 7.70626008,8.00099967 7.6,8.001 L4.396,8.001 C4.28956674,8.00073358 4.18741595,8.04289612 4.11215603,8.11815603 C4.03689612,8.19341595 3.99473358,8.29556674 3.995,8.402 L3.995,15.603 C3.999,15.823 4.177,16 4.401,16 L4.402,16 Z M10.402,12 L15.603,12 C15.7094333,12.0002664 15.811584,11.9581039 15.886844,11.882844 C15.9621039,11.807584 16.0042664,11.7054333 16.004,11.599 L16.004,8.398 C16.0042664,8.29156674 15.9621039,8.18941595 15.886844,8.11415603 C15.811584,8.03889612 15.7094333,7.99673358 15.603,7.997 L10.402,7.997 C10.2957402,7.99673435 10.1937416,8.03875978 10.1185106,8.11380315 C10.0432796,8.18884651 10.0009997,8.29073992 10.001,8.397 L10.001,11.6 C10.001,11.824 10.178,12 10.401,12 L10.402,12 Z M10.402,16 L15.603,16 C15.7094333,16.0002664 15.811584,15.9581039 15.886844,15.882844 C15.9621039,15.807584 16.0042664,15.7054333 16.004,15.599 L16.004,14.398 C16.0042664,14.2915667 15.9621039,14.189416 15.886844,14.114156 C15.811584,14.0388961 15.7094333,13.9967336 15.603,13.997 L10.402,13.997 C10.2957402,13.9967343 10.1937416,14.0387598 10.1185106,14.1138031 C10.0432796,14.1888465 10.0009997,14.2907399 10.001,14.397 L10.001,15.6 C10.001,15.824 10.178,16 10.401,16 L10.402,16 Z"/>
+</svg>

core/modules/workspaces/icons/f0a100/ws_icon.svg

@@ -0,0 +1,3 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="40" height="40" viewBox="0 0 40 40">
+  <path fill="#F0A100" fill-rule="evenodd" d="M38,0 L2.002,0 C0.896716337,-1.37884559e-07 0.000552089742,0.895716475 0,2.001 L0,38.003 C0,39.105 0.899,40.003 2,40.003 L38,40.003 C39.103,40.003 40,39.103 40,38.003 L40,2.001 C40.000531,1.47031248 39.7900198,0.961193334 39.4148607,0.585846626 C39.0397016,0.210499918 38.5306877,-0.000265742306 38,0 Z M34.003,4 C35.105,4 36.003,4.899 36.003,6 C36.003,7.102 35.103,7.998 34.003,7.998 C32.9235903,7.96385326 32.0662376,7.07894966 32.0662376,5.999 C32.0662376,4.91905034 32.9235903,4.03414674 34.003,4 Z M26.003,4 C27.105,4 28.002,4.899 28.002,6 C28.002,7.102 27.102,7.998 26.002,7.998 C24.9225903,7.96385326 24.0652376,7.07894966 24.0652376,5.999 C24.0652376,4.91905034 24.9225903,4.03414674 26.002,4 L26.003,4 Z M18.002,4 C19.104,4 20.002,4.899 20.002,6 C20.002,7.102 19.102,7.998 18.002,7.998 C16.899,7.998 16.002,7.1 16.002,5.999 C16.0025521,4.89482104 16.8978209,3.99999986 18.002,4 Z M36.002,36.002 L4,36.002 L4,12.001 L36.002,12.001 L36.002,36.002 Z M8.805,32.002 L15.196,32.002 C15.4092125,32.0030667 15.6140295,31.9189775 15.764983,31.7683995 C15.9159365,31.6178215 16.0005357,31.4132145 16,31.2 L16,16.805 C16.0005341,16.5919596 15.916072,16.3875055 15.7653354,16.2369566 C15.6145988,16.0864077 15.4100395,16.0022004 15.197,16.003 L8.794,16.003 C8.581215,16.0027342 8.37706868,16.087145 8.22660684,16.2376068 C8.07614501,16.3880687 7.99173418,16.592215 7.992,16.805 L7.992,31.208 C7.99966319,31.6507223 8.36222028,32.0048063 8.805,32.002 Z M20.803,24.002 L31.206,24.002 C31.4190404,24.0025341 31.6234945,23.918072 31.7740434,23.7673354 C31.9245923,23.6165988 32.0087996,23.4120395 32.008,23.199 L32.008,16.797 C32.0085328,16.5841335 31.9242078,16.3798319 31.7736879,16.2293121 C31.6231681,16.0787922 31.4188665,15.9944672 31.206,15.995 L20.803,15.995 C20.5901335,15.9944672 20.3858319,16.0787922 20.2353121,16.2293121 C20.0847922,16.3798319 20.0004672,16.5841335 20.001,16.797 L20.001,23.199 C20.001,23.646 20.356,24.001 20.803,24.001 L20.803,24.002 Z M20.803,32.002 L31.206,32.002 C31.4188665,32.0025328 31.6231681,31.9182078 31.7736879,31.7676879 C31.9242078,31.6171681 32.0085328,31.4128665 32.008,31.2 L32.008,28.797 C32.0085328,28.5841335 31.9242078,28.3798319 31.7736879,28.2293121 C31.6231681,28.0787922 31.4188665,27.9944672 31.206,27.995 L20.803,27.995 C20.5901335,27.9944672 20.3858319,28.0787922 20.2353121,28.2293121 C20.0847922,28.3798319 20.0004672,28.5841335 20.001,28.797 L20.001,31.2 C20.001,31.647 20.356,32.002 20.803,32.002 Z"/>
+</svg>

core/modules/workspaces/src/Access/ActiveWorkspaceCheck.php

@@ -0,0 +1,50 @@
+<?php
+
+namespace Drupal\workspaces\Access;
+
+use Drupal\Core\Access\AccessResult;
+use Drupal\Core\Routing\Access\AccessInterface;
+use Drupal\workspaces\WorkspaceManagerInterface;
+use Symfony\Component\Routing\Route;
+
+/**
+ * Determines access to routes based on the presence of an active workspace.
+ */
+class ActiveWorkspaceCheck implements AccessInterface {
+
+  /**
+   * The workspace manager.
+   *
+   * @var \Drupal\workspaces\WorkspaceManagerInterface
+   */
+  protected $workspaceManager;
+
+  /**
+   * Constructs a new ActiveWorkspaceCheck.
+   *
+   * @param \Drupal\workspaces\WorkspaceManagerInterface $workspace_manager
+   *   The workspace manager.
+   */
+  public function __construct(WorkspaceManagerInterface $workspace_manager) {
+    $this->workspaceManager = $workspace_manager;
+  }
+
+  /**
+   * Checks access.
+   *
+   * @param \Symfony\Component\Routing\Route $route
+   *   The route to check against.
+   *
+   * @return \Drupal\Core\Access\AccessResultInterface
+   *   The access result.
+   */
+  public function access(Route $route) {
+    if (!$route->hasRequirement('_has_active_workspace')) {
+      return AccessResult::neutral();
+    }
+
+    $required_value = filter_var($route->getRequirement('_has_active_workspace'), FILTER_VALIDATE_BOOLEAN);
+    return AccessResult::allowedIf($required_value === $this->workspaceManager->hasActiveWorkspace())->addCacheContexts(['workspace']);
+  }
+
+}

core/modules/workspaces/src/Controller/WorkspacesHtmlEntityFormController.php

@@ -0,0 +1,97 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\workspaces\Controller;
+
+use Drupal\Core\Controller\FormController;
+use Drupal\Core\DependencyInjection\DependencySerializationTrait;
+use Drupal\Core\Form\FormInterface;
+use Drupal\Core\Routing\RouteMatchInterface;
+use Drupal\Core\StringTranslation\StringTranslationTrait;
+use Drupal\Core\TypedData\TypedDataManagerInterface;
+use Drupal\workspaces\Plugin\Validation\Constraint\EntityWorkspaceConflictConstraint;
+use Drupal\workspaces\WorkspaceInformationInterface;
+use Drupal\workspaces\WorkspaceManagerInterface;
+use Symfony\Component\HttpFoundation\Request;
+
+/**
+ * Overrides the entity form controller service for workspaces operations.
+ */
+class WorkspacesHtmlEntityFormController extends FormController {
+
+  use DependencySerializationTrait;
+  use StringTranslationTrait;
+
+  public function __construct(
+    protected readonly FormController $entityFormController,
+    protected readonly WorkspaceManagerInterface $workspaceManager,
+    protected readonly WorkspaceInformationInterface $workspaceInfo,
+    protected readonly TypedDataManagerInterface $typedDataManager,
+  ) {}
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getContentResult(Request $request, RouteMatchInterface $route_match): array {
+    $form_arg = $this->getFormArgument($route_match);
+    $form_object = $this->getFormObject($route_match, $form_arg);
+
+    /** @var \Drupal\Core\Entity\EntityInterface $entity */
+    $entity = $form_object->getEntity();
+    if ($this->workspaceInfo->isEntitySupported($entity)) {
+      $active_workspace = $this->workspaceManager->getActiveWorkspace();
+
+      // Prepare a minimal render array in case we need to return it.
+      $build['#cache']['contexts'] = $entity->getCacheContexts();
+      $build['#cache']['tags'] = $entity->getCacheTags();
+      $build['#cache']['max-age'] = $entity->getCacheMaxAge();
+
+      // Prevent entities from being edited if they're tracked in workspace.
+      if ($form_object->getOperation() !== 'delete') {
+        $constraints = array_values(array_filter($entity->getTypedData()->getConstraints(), function ($constraint) {
+          return $constraint instanceof EntityWorkspaceConflictConstraint;
+        }));
+
+        if (!empty($constraints)) {
+          $violations = $this->typedDataManager->getValidator()->validate(
+            $entity->getTypedData(),
+            $constraints[0]
+          );
+          if (count($violations)) {
+            $build['#markup'] = $violations->get(0)->getMessage();
+
+            return $build;
+          }
+        }
+      }
+
+      // Prevent entities from being deleted in a workspace if they have a
+      // published default revision.
+      if ($form_object->getOperation() === 'delete' && $active_workspace && !$this->workspaceInfo->isEntityDeletable($entity, $active_workspace)) {
+        $build['#markup'] = $this->t('This @entity_type_label can only be deleted in the Live workspace.', [
+          '@entity_type_label' => $entity->getEntityType()->getSingularLabel(),
+        ]);
+
+        return $build;
+      }
+    }
+
+    return $this->entityFormController->getContentResult($request, $route_match);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function getFormArgument(RouteMatchInterface $route_match): string {
+    return $this->entityFormController->getFormArgument($route_match);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function getFormObject(RouteMatchInterface $route_match, $form_arg): FormInterface {
+    return $this->entityFormController->getFormObject($route_match, $form_arg);
+  }
+
+}

core/modules/workspaces/src/Entity/Handler/BlockContentWorkspaceHandler.php

@@ -0,0 +1,24 @@
+<?php
+
+namespace Drupal\workspaces\Entity\Handler;
+
+use Drupal\Core\Entity\EntityInterface;
+
+/**
+ * Provides a custom workspace handler for block_content entities.
+ *
+ * @internal
+ */
+class BlockContentWorkspaceHandler extends DefaultWorkspaceHandler {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function isEntitySupported(EntityInterface $entity): bool {
+    // Only reusable blocks can be tracked individually. Non-reusable or inline
+    // blocks are tracked as part of the entity they are a composite of.
+    /** @var \Drupal\block_content\BlockContentInterface $entity */
+    return $entity->isReusable();
+  }
+
+}

core/modules/workspaces/src/Entity/Handler/DefaultWorkspaceHandler.php

@@ -0,0 +1,31 @@
+<?php
+
+namespace Drupal\workspaces\Entity\Handler;
+
+use Drupal\Core\Entity\EntityHandlerInterface;
+use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Entity\EntityTypeInterface;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Common customizations for most entity types.
+ *
+ * @internal
+ */
+class DefaultWorkspaceHandler implements WorkspaceHandlerInterface, EntityHandlerInterface {
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function createInstance(ContainerInterface $container, EntityTypeInterface $entity_type) {
+    return new static();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function isEntitySupported(EntityInterface $entity): bool {
+    return TRUE;
+  }
+
+}

core/modules/workspaces/src/Entity/Handler/IgnoredWorkspaceHandler.php

@@ -0,0 +1,31 @@
+<?php
+
+namespace Drupal\workspaces\Entity\Handler;
+
+use Drupal\Core\Entity\EntityHandlerInterface;
+use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Entity\EntityTypeInterface;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Defines a handler for entity types that are ignored by workspaces.
+ *
+ * @internal
+ */
+class IgnoredWorkspaceHandler implements WorkspaceHandlerInterface, EntityHandlerInterface {
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function createInstance(ContainerInterface $container, EntityTypeInterface $entity_type) {
+    return new static();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function isEntitySupported(EntityInterface $entity): bool {
+    return FALSE;
+  }
+
+}

core/modules/workspaces/src/Entity/Handler/WorkspaceHandlerInterface.php

@@ -0,0 +1,30 @@
+<?php
+
+namespace Drupal\workspaces\Entity\Handler;
+
+use Drupal\Core\Entity\EntityInterface;
+
+/**
+ * Defines workspace operations that need to vary by entity type.
+ *
+ * @internal
+ */
+interface WorkspaceHandlerInterface {
+
+  /**
+   * Determines if an entity should be tracked in a workspace.
+   *
+   * At the general level, workspace support is determined for the entire entity
+   * type. If an entity type is supported, there may be further decisions each
+   * entity type can make to evaluate if a given entity is appropriate to be
+   * tracked in a workspace.
+   *
+   * @param \Drupal\Core\Entity\EntityInterface $entity
+   *   The entity we may be tracking.
+   *
+   * @return bool
+   *   TRUE if this entity should be tracked in a workspace, FALSE otherwise.
+   */
+  public function isEntitySupported(EntityInterface $entity): bool;
+
+}

core/modules/workspaces/src/Entity/Workspace.php

@@ -0,0 +1,201 @@
+<?php
+
+namespace Drupal\workspaces\Entity;
+
+use Drupal\Core\Entity\ContentEntityBase;
+use Drupal\Core\Entity\EntityChangedTrait;
+use Drupal\Core\Entity\EntityStorageInterface;
+use Drupal\Core\Entity\EntityTypeInterface;
+use Drupal\Core\Field\BaseFieldDefinition;
+use Drupal\Core\StringTranslation\TranslatableMarkup;
+use Drupal\user\EntityOwnerTrait;
+use Drupal\workspaces\WorkspaceInterface;
+
+/**
+ * The workspace entity class.
+ *
+ * @ContentEntityType(
+ *   id = "workspace",
+ *   label = @Translation("Workspace"),
+ *   label_collection = @Translation("Workspaces"),
+ *   label_singular = @Translation("workspace"),
+ *   label_plural = @Translation("workspaces"),
+ *   label_count = @PluralTranslation(
+ *     singular = "@count workspace",
+ *     plural = "@count workspaces"
+ *   ),
+ *   handlers = {
+ *     "list_builder" = "\Drupal\workspaces\WorkspaceListBuilder",
+ *     "view_builder" = "Drupal\workspaces\WorkspaceViewBuilder",
+ *     "access" = "Drupal\workspaces\WorkspaceAccessControlHandler",
+ *     "views_data" = "Drupal\views\EntityViewsData",
+ *     "route_provider" = {
+ *       "html" = "\Drupal\Core\Entity\Routing\AdminHtmlRouteProvider",
+ *     },
+ *     "form" = {
+ *       "default" = "\Drupal\workspaces\Form\WorkspaceForm",
+ *       "add" = "\Drupal\workspaces\Form\WorkspaceForm",
+ *       "edit" = "\Drupal\workspaces\Form\WorkspaceForm",
+ *       "delete" = "\Drupal\workspaces\Form\WorkspaceDeleteForm",
+ *       "activate" = "\Drupal\workspaces\Form\WorkspaceActivateForm",
+ *     },
+ *     "workspace" = "\Drupal\workspaces\Entity\Handler\IgnoredWorkspaceHandler",
+ *   },
+ *   admin_permission = "administer workspaces",
+ *   base_table = "workspace",
+ *   revision_table = "workspace_revision",
+ *   data_table = "workspace_field_data",
+ *   revision_data_table = "workspace_field_revision",
+ *   field_ui_base_route = "entity.workspace.collection",
+ *   entity_keys = {
+ *     "id" = "id",
+ *     "revision" = "revision_id",
+ *     "uuid" = "uuid",
+ *     "label" = "label",
+ *     "uid" = "uid",
+ *     "owner" = "uid",
+ *   },
+ *   links = {
+ *     "canonical" = "/admin/config/workflow/workspaces/manage/{workspace}",
+ *     "add-form" = "/admin/config/workflow/workspaces/add",
+ *     "edit-form" = "/admin/config/workflow/workspaces/manage/{workspace}/edit",
+ *     "delete-form" = "/admin/config/workflow/workspaces/manage/{workspace}/delete",
+ *     "activate-form" = "/admin/config/workflow/workspaces/manage/{workspace}/activate",
+ *     "collection" = "/admin/config/workflow/workspaces",
+ *   },
+ * )
+ */
+class Workspace extends ContentEntityBase implements WorkspaceInterface {
+
+  use EntityChangedTrait;
+  use EntityOwnerTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function baseFieldDefinitions(EntityTypeInterface $entity_type) {
+    $fields = parent::baseFieldDefinitions($entity_type);
+    $fields += static::ownerBaseFieldDefinitions($entity_type);
+
+    $fields['id'] = BaseFieldDefinition::create('string')
+      ->setLabel(new TranslatableMarkup('Workspace ID'))
+      ->setDescription(new TranslatableMarkup('The workspace ID.'))
+      ->setSetting('max_length', 128)
+      ->setRequired(TRUE)
+      ->addConstraint('UniqueField')
+      ->addConstraint('DeletedWorkspace')
+      ->addPropertyConstraints('value', ['Regex' => ['pattern' => '/^[a-z0-9_]+$/']]);
+
+    $fields['label'] = BaseFieldDefinition::create('string')
+      ->setLabel(new TranslatableMarkup('Workspace name'))
+      ->setDescription(new TranslatableMarkup('The workspace name.'))
+      ->setRevisionable(TRUE)
+      ->setSetting('max_length', 128)
+      ->setRequired(TRUE);
+
+    $fields['uid']
+      ->setLabel(new TranslatableMarkup('Owner'))
+      ->setDescription(new TranslatableMarkup('The workspace owner.'))
+      ->setDisplayOptions('form', [
+        'type' => 'entity_reference_autocomplete',
+        'weight' => 5,
+      ])
+      ->setDisplayConfigurable('form', TRUE);
+
+    $fields['parent'] = BaseFieldDefinition::create('entity_reference')
+      ->setLabel(new TranslatableMarkup('Parent'))
+      ->setDescription(new TranslatableMarkup('The parent workspace.'))
+      ->setSetting('target_type', 'workspace')
+      ->setReadOnly(TRUE)
+      ->setDisplayConfigurable('form', TRUE)
+      ->setDisplayOptions('form', [
+        'type' => 'options_select',
+        'weight' => 10,
+      ]);
+
+    $fields['changed'] = BaseFieldDefinition::create('changed')
+      ->setLabel(new TranslatableMarkup('Changed'))
+      ->setDescription(new TranslatableMarkup('The time that the workspace was last edited.'))
+      ->setRevisionable(TRUE);
+
+    $fields['created'] = BaseFieldDefinition::create('created')
+      ->setLabel(new TranslatableMarkup('Created'))
+      ->setDescription(new TranslatableMarkup('The time that the workspace was created.'));
+
+    return $fields;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function publish() {
+    return \Drupal::service('workspaces.operation_factory')->getPublisher($this)->publish();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getCreatedTime() {
+    return $this->get('created')->value;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function setCreatedTime($created) {
+    return $this->set('created', (int) $created);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function hasParent() {
+    return !$this->get('parent')->isEmpty();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function preDelete(EntityStorageInterface $storage, array $entities) {
+    parent::preDelete($storage, $entities);
+
+    $workspace_tree = \Drupal::service('workspaces.repository')->loadTree();
+
+    // Ensure that workspaces that have descendants can not be deleted.
+    foreach ($entities as $entity) {
+      if (!empty($workspace_tree[$entity->id()]['descendants'])) {
+        throw new \InvalidArgumentException("The {$entity->label()} workspace can not be deleted because it has child workspaces.");
+      }
+    }
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function postDelete(EntityStorageInterface $storage, array $entities) {
+    parent::postDelete($storage, $entities);
+
+    /** @var \Drupal\workspaces\WorkspaceManagerInterface $workspace_manager */
+    $workspace_manager = \Drupal::service('workspaces.manager');
+    // Disable the currently active workspace if it has been deleted.
+    if ($workspace_manager->hasActiveWorkspace()
+      && in_array($workspace_manager->getActiveWorkspace()->id(), array_keys($entities), TRUE)) {
+      $workspace_manager->switchToLive();
+    }
+
+    // Ensure that workspace batch purging does not happen inside a workspace.
+    $workspace_manager->executeOutsideWorkspace(function () use ($workspace_manager, $entities) {
+      // Add the IDs of the deleted workspaces to the list of workspaces that will
+      // be purged on cron.
+      $state = \Drupal::state();
+      $deleted_workspace_ids = $state->get('workspace.deleted', []);
+      $deleted_workspace_ids += array_combine(array_keys($entities), array_keys($entities));
+      $state->set('workspace.deleted', $deleted_workspace_ids);
+
+      // Trigger a batch purge to allow empty workspaces to be deleted
+      // immediately.
+      $workspace_manager->purgeDeletedWorkspacesBatch();
+    });
+  }
+
+}

core/modules/workspaces/src/EntityAccess.php

@@ -0,0 +1,152 @@
+<?php
+
+namespace Drupal\workspaces;
+
+use Drupal\Core\Access\AccessResult;
+use Drupal\Core\DependencyInjection\ContainerInjectionInterface;
+use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Entity\EntityTypeManagerInterface;
+use Drupal\Core\Session\AccountInterface;
+use Drupal\Core\StringTranslation\StringTranslationTrait;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Service wrapper for hooks relating to entity access control.
+ *
+ * @internal
+ */
+class EntityAccess implements ContainerInjectionInterface {
+
+  use StringTranslationTrait;
+
+  /**
+   * The entity type manager service.
+   *
+   * @var \Drupal\Core\Entity\EntityTypeManagerInterface
+   */
+  protected $entityTypeManager;
+
+  /**
+   * The workspace manager service.
+   *
+   * @var \Drupal\workspaces\WorkspaceManagerInterface
+   */
+  protected $workspaceManager;
+
+  /**
+   * The workspace information service.
+   *
+   * @var \Drupal\workspaces\WorkspaceInformationInterface
+   */
+  protected $workspaceInfo;
+
+  /**
+   * Constructs a new EntityAccess instance.
+   *
+   * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
+   *   The entity type manager service.
+   * @param \Drupal\workspaces\WorkspaceManagerInterface $workspace_manager
+   *   The workspace manager service.
+   * @param \Drupal\workspaces\WorkspaceInformationInterface $workspace_information
+   *   The workspace information service.
+   */
+  public function __construct(EntityTypeManagerInterface $entity_type_manager, WorkspaceManagerInterface $workspace_manager, WorkspaceInformationInterface $workspace_information) {
+    $this->entityTypeManager = $entity_type_manager;
+    $this->workspaceManager = $workspace_manager;
+    $this->workspaceInfo = $workspace_information;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container) {
+    return new static(
+      $container->get('entity_type.manager'),
+      $container->get('workspaces.manager'),
+      $container->get('workspaces.information')
+    );
+  }
+
+  /**
+   * Implements a hook bridge for hook_entity_access().
+   *
+   * @param \Drupal\Core\Entity\EntityInterface $entity
+   *   The entity to check access for.
+   * @param string $operation
+   *   The operation being performed.
+   * @param \Drupal\Core\Session\AccountInterface $account
+   *   The user account making the to check access for.
+   *
+   * @return \Drupal\Core\Access\AccessResult
+   *   The result of the access check.
+   *
+   * @see hook_entity_access()
+   */
+  public function entityOperationAccess(EntityInterface $entity, $operation, AccountInterface $account) {
+    // Workspaces themselves are handled by their own access handler and we
+    // should not try to do any access checks for entity types that can not
+    // belong to a workspace.
+    if (!$this->workspaceInfo->isEntitySupported($entity) || !$this->workspaceManager->hasActiveWorkspace()) {
+      return AccessResult::neutral();
+    }
+
+    // Prevent the deletion of entities with a published default revision.
+    if ($operation === 'delete') {
+      $active_workspace = $this->workspaceManager->getActiveWorkspace();
+      $is_deletable = $this->workspaceInfo->isEntityDeletable($entity, $active_workspace);
+
+      return AccessResult::forbiddenIf(!$is_deletable)
+        ->addCacheableDependency($entity)
+        ->addCacheableDependency($active_workspace);
+    }
+
+    return $this->bypassAccessResult($account);
+  }
+
+  /**
+   * Implements a hook bridge for hook_entity_create_access().
+   *
+   * @param \Drupal\Core\Session\AccountInterface $account
+   *   The user account making the to check access for.
+   * @param array $context
+   *   The context of the access check.
+   * @param string $entity_bundle
+   *   The bundle of the entity.
+   *
+   * @return \Drupal\Core\Access\AccessResult
+   *   The result of the access check.
+   *
+   * @see hook_entity_create_access()
+   */
+  public function entityCreateAccess(AccountInterface $account, array $context, $entity_bundle) {
+    // Workspaces themselves are handled by their own access handler and we
+    // should not try to do any access checks for entity types that can not
+    // belong to a workspace.
+    $entity_type = $this->entityTypeManager->getDefinition($context['entity_type_id']);
+    if (!$this->workspaceInfo->isEntityTypeSupported($entity_type) || !$this->workspaceManager->hasActiveWorkspace()) {
+      return AccessResult::neutral();
+    }
+
+    return $this->bypassAccessResult($account);
+  }
+
+  /**
+   * Checks the 'bypass' permissions.
+   *
+   * @param \Drupal\Core\Session\AccountInterface $account
+   *   The user account making the to check access for.
+   *
+   * @return \Drupal\Core\Access\AccessResult
+   *   The result of the access check.
+   */
+  protected function bypassAccessResult(AccountInterface $account) {
+    // This approach assumes that the current "global" active workspace is
+    // correct, i.e. if you're "in" a given workspace then you get ALL THE PERMS
+    // to ALL THE THINGS! That's why this is a dangerous permission.
+    $active_workspace = $this->workspaceManager->getActiveWorkspace();
+
+    return AccessResult::allowedIf($active_workspace->getOwnerId() == $account->id())->cachePerUser()->addCacheableDependency($active_workspace)
+      ->andIf(AccessResult::allowedIfHasPermission($account, 'bypass entity access own workspace'));
+  }
+
+}

core/modules/workspaces/src/EntityOperations.php

@@ -0,0 +1,351 @@
+<?php
+
+namespace Drupal\workspaces;
+
+use Drupal\Core\DependencyInjection\ContainerInjectionInterface;
+use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Entity\EntityTypeManagerInterface;
+use Drupal\Core\Entity\RevisionableInterface;
+use Drupal\Core\Form\FormStateInterface;
+use Drupal\Core\StringTranslation\StringTranslationTrait;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Defines a class for reacting to entity events.
+ *
+ * @internal
+ */
+class EntityOperations implements ContainerInjectionInterface {
+
+  use StringTranslationTrait;
+
+  /**
+   * The entity type manager service.
+   *
+   * @var \Drupal\Core\Entity\EntityTypeManagerInterface
+   */
+  protected $entityTypeManager;
+
+  /**
+   * The workspace manager service.
+   *
+   * @var \Drupal\workspaces\WorkspaceManagerInterface
+   */
+  protected $workspaceManager;
+
+  /**
+   * The workspace association service.
+   *
+   * @var \Drupal\workspaces\WorkspaceAssociationInterface
+   */
+  protected $workspaceAssociation;
+
+  /**
+   * The workspace information service.
+   *
+   * @var \Drupal\workspaces\WorkspaceInformationInterface
+   */
+  protected $workspaceInfo;
+
+  /**
+   * Constructs a new EntityOperations instance.
+   *
+   * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
+   *   The entity type manager service.
+   * @param \Drupal\workspaces\WorkspaceManagerInterface $workspace_manager
+   *   The workspace manager service.
+   * @param \Drupal\workspaces\WorkspaceAssociationInterface $workspace_association
+   *   The workspace association service.
+   * @param \Drupal\workspaces\WorkspaceInformationInterface $workspace_information
+   *   The workspace information service.
+   */
+  public function __construct(EntityTypeManagerInterface $entity_type_manager, WorkspaceManagerInterface $workspace_manager, WorkspaceAssociationInterface $workspace_association, WorkspaceInformationInterface $workspace_information) {
+    $this->entityTypeManager = $entity_type_manager;
+    $this->workspaceManager = $workspace_manager;
+    $this->workspaceAssociation = $workspace_association;
+    $this->workspaceInfo = $workspace_information;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container) {
+    return new static(
+      $container->get('entity_type.manager'),
+      $container->get('workspaces.manager'),
+      $container->get('workspaces.association'),
+      $container->get('workspaces.information')
+    );
+  }
+
+  /**
+   * Acts on entity IDs before they are loaded.
+   *
+   * @see hook_entity_preload()
+   */
+  public function entityPreload(array $ids, $entity_type_id) {
+    $entities = [];
+
+    $entity_type = $this->entityTypeManager->getDefinition($entity_type_id);
+    if (!$this->workspaceInfo->isEntityTypeSupported($entity_type) || !$this->workspaceManager->hasActiveWorkspace()) {
+      return $entities;
+    }
+
+    // Get a list of revision IDs for entities that have a revision set for the
+    // current active workspace. If an entity has multiple revisions set for a
+    // workspace, only the one with the highest ID is returned.
+    if ($tracked_entities = $this->workspaceAssociation->getTrackedEntities($this->workspaceManager->getActiveWorkspace()->id(), $entity_type_id, $ids)) {
+      // Bail out early if there are no tracked entities of this type.
+      if (!isset($tracked_entities[$entity_type_id])) {
+        return $entities;
+      }
+
+      /** @var \Drupal\Core\Entity\RevisionableStorageInterface $storage */
+      $storage = $this->entityTypeManager->getStorage($entity_type_id);
+
+      // Swap out every entity which has a revision set for the current active
+      // workspace.
+      foreach ($storage->loadMultipleRevisions(array_keys($tracked_entities[$entity_type_id])) as $revision) {
+        $entities[$revision->id()] = $revision;
+      }
+    }
+
+    return $entities;
+  }
+
+  /**
+   * Acts on an entity before it is created or updated.
+   *
+   * @param \Drupal\Core\Entity\EntityInterface $entity
+   *   The entity being saved.
+   *
+   * @see hook_entity_presave()
+   */
+  public function entityPresave(EntityInterface $entity) {
+    if ($this->shouldSkipOperations($entity)) {
+      return;
+    }
+
+    // Disallow any change to an unsupported entity when we are not in the
+    // default workspace.
+    if (!$this->workspaceInfo->isEntitySupported($entity)) {
+      throw new \RuntimeException('This entity can only be saved in the default workspace.');
+    }
+
+    /** @var \Drupal\Core\Entity\ContentEntityInterface|\Drupal\Core\Entity\EntityPublishedInterface $entity */
+    if (!$entity->isNew() && !$entity->isSyncing()) {
+      // Force a new revision if the entity is not replicating.
+      $entity->setNewRevision(TRUE);
+
+      // All entities in the non-default workspace are pending revisions,
+      // regardless of their publishing status. This means that when creating
+      // a published pending revision in a non-default workspace it will also be
+      // a published pending revision in the default workspace, however, it will
+      // become the default revision only when it is replicated to the default
+      // workspace.
+      $entity->isDefaultRevision(FALSE);
+    }
+
+    // In ::entityFormEntityBuild() we mark the entity as a non-default revision
+    // so that validation constraints can rely on $entity->isDefaultRevision()
+    // always returning FALSE when an entity form is submitted in a workspace.
+    // However, after validation has run, we need to revert that flag so the
+    // first revision of a new entity is correctly seen by the system as the
+    // default revision.
+    if ($entity->isNew()) {
+      $entity->isDefaultRevision(TRUE);
+    }
+
+    // Track the workspaces in which the new revision was saved.
+    if (!$entity->isSyncing()) {
+      $field_name = $entity->getEntityType()->getRevisionMetadataKey('workspace');
+      $entity->{$field_name}->target_id = $this->workspaceManager->getActiveWorkspace()->id();
+    }
+
+    // When a new published entity is inserted in a non-default workspace, we
+    // actually want two revisions to be saved:
+    // - An unpublished default revision in the default ('live') workspace.
+    // - A published pending revision in the current workspace.
+    if ($entity->isNew() && $entity->isPublished()) {
+      // Keep track of the publishing status in a dynamic property for
+      // ::entityInsert(), then unpublish the default revision.
+      // @todo Remove this dynamic property once we have an API for associating
+      //   temporary data with an entity: https://www.drupal.org/node/2896474.
+      $entity->_initialPublished = TRUE;
+      $entity->setUnpublished();
+    }
+  }
+
+  /**
+   * Responds to the creation of a new entity.
+   *
+   * @param \Drupal\Core\Entity\EntityInterface $entity
+   *   The entity that was just saved.
+   *
+   * @see hook_entity_insert()
+   */
+  public function entityInsert(EntityInterface $entity) {
+    if ($this->shouldSkipOperations($entity) || !$this->workspaceInfo->isEntitySupported($entity)) {
+      return;
+    }
+
+    $this->workspaceAssociation->trackEntity($entity, $this->workspaceManager->getActiveWorkspace());
+
+    // When a published entity is created in a workspace, it should remain
+    // published only in that workspace, and unpublished in the live workspace.
+    // It is first saved as unpublished for the default revision, then
+    // immediately a second revision is created which is published and attached
+    // to the workspace. This ensures that the initial version of the entity
+    // does not 'leak' into the live site. This differs from edits to existing
+    // entities where there is already a valid default revision for the live
+    // workspace.
+    if (isset($entity->_initialPublished)) {
+      $entity->setPublished();
+      $entity->isDefaultRevision(FALSE);
+      $entity->save();
+    }
+  }
+
+  /**
+   * Responds to updates to an entity.
+   *
+   * @param \Drupal\Core\Entity\EntityInterface $entity
+   *   The entity that was just saved.
+   *
+   * @see hook_entity_update()
+   */
+  public function entityUpdate(EntityInterface $entity) {
+    if ($this->shouldSkipOperations($entity) || !$this->workspaceInfo->isEntitySupported($entity)) {
+      return;
+    }
+
+    // Only track new revisions.
+    /** @var \Drupal\Core\Entity\RevisionableInterface $entity */
+    if ($entity->getLoadedRevisionId() != $entity->getRevisionId()) {
+      $this->workspaceAssociation->trackEntity($entity, $this->workspaceManager->getActiveWorkspace());
+    }
+  }
+
+  /**
+   * Acts after an entity translation has been added.
+   *
+   * @param \Drupal\Core\Entity\EntityInterface $translation
+   *   The translation that was added.
+   *
+   * @see hook_entity_translation_insert()
+   */
+  public function entityTranslationInsert(EntityInterface $translation): void {
+    if ($this->shouldSkipOperations($translation)
+      || !$this->workspaceInfo->isEntitySupported($translation)
+      || $translation->isSyncing()
+    ) {
+      return;
+    }
+
+    // When a new translation is added to an existing entity, we need to add
+    // that translation to the default revision as well, otherwise the new
+    // translation wouldn't show up in entity queries or views which use the
+    // field data table as the base table.
+    $this->workspaceManager->executeOutsideWorkspace(function () use ($translation) {
+      $storage = $this->entityTypeManager->getStorage($translation->getEntityTypeId());
+      $default_revision = $storage->load($translation->id());
+
+      $langcode = $translation->language()->getId();
+      if (!$default_revision->hasTranslation($langcode)) {
+        $default_revision_translation = $default_revision->addTranslation($langcode, $translation->toArray());
+        $default_revision_translation->setUnpublished();
+        $default_revision_translation->setSyncing(TRUE);
+        $default_revision_translation->save();
+      }
+    });
+  }
+
+  /**
+   * Acts on an entity before it is deleted.
+   *
+   * @param \Drupal\Core\Entity\EntityInterface $entity
+   *   The entity being deleted.
+   *
+   * @see hook_entity_predelete()
+   */
+  public function entityPredelete(EntityInterface $entity) {
+    if ($this->shouldSkipOperations($entity)) {
+      return;
+    }
+
+    // Prevent the entity from being deleted if the entity type does not have
+    // support for workspaces, or if the entity has a published default
+    // revision.
+    $active_workspace = $this->workspaceManager->getActiveWorkspace();
+    if (!$this->workspaceInfo->isEntitySupported($entity) || !$this->workspaceInfo->isEntityDeletable($entity, $active_workspace)) {
+      throw new \RuntimeException("This {$entity->getEntityType()->getSingularLabel()} can only be deleted in the Live workspace.");
+    }
+  }
+
+  /**
+   * Alters entity forms to disallow concurrent editing in multiple workspaces.
+   *
+   * @param array $form
+   *   An associative array containing the structure of the form.
+   * @param \Drupal\Core\Form\FormStateInterface $form_state
+   *   The current state of the form.
+   * @param string $form_id
+   *   The form ID.
+   *
+   * @see hook_form_alter()
+   */
+  public function entityFormAlter(array &$form, FormStateInterface $form_state, $form_id) {
+    $entity = $form_state->getFormObject()->getEntity();
+    if (!$this->workspaceInfo->isEntitySupported($entity) && !$this->workspaceInfo->isEntityIgnored($entity)) {
+      return;
+    }
+
+    // For supported and ignored entity types, signal the fact that this form is
+    // safe to use in a workspace.
+    // @see \Drupal\workspaces\FormOperations::validateForm()
+    $form_state->set('workspace_safe', TRUE);
+
+    // There is nothing more to do for ignored entity types.
+    if ($this->workspaceInfo->isEntityIgnored($entity)) {
+      return;
+    }
+
+    // Add an entity builder to the form which marks the edited entity object as
+    // a pending revision. This is needed so validation constraints like
+    // \Drupal\path\Plugin\Validation\Constraint\PathAliasConstraintValidator
+    // know in advance (before hook_entity_presave()) that the new revision will
+    // be a pending one.
+    if ($this->workspaceManager->hasActiveWorkspace()) {
+      $form['#entity_builders'][] = [static::class, 'entityFormEntityBuild'];
+    }
+  }
+
+  /**
+   * Entity builder that marks all supported entities as pending revisions.
+   */
+  public static function entityFormEntityBuild($entity_type_id, RevisionableInterface $entity, &$form, FormStateInterface &$form_state) {
+    // Ensure that all entity forms are signaling that a new revision will be
+    // created.
+    $entity->setNewRevision(TRUE);
+
+    // Set the non-default revision flag so that validation constraints are also
+    // aware that a pending revision is about to be created.
+    $entity->isDefaultRevision(FALSE);
+  }
+
+  /**
+   * Determines whether we need to react on entity operations.
+   *
+   * @param \Drupal\Core\Entity\EntityInterface $entity
+   *   The entity to check.
+   *
+   * @return bool
+   *   Returns TRUE if entity operations should not be altered, FALSE otherwise.
+   */
+  protected function shouldSkipOperations(EntityInterface $entity) {
+    // We should not react on entity operations when the entity is ignored or
+    // when we're not in a workspace context.
+    return $this->workspaceInfo->isEntityIgnored($entity) || !$this->workspaceManager->hasActiveWorkspace();
+  }
+
+}

core/modules/workspaces/src/EntityQuery/PgsqlQueryFactory.php

@@ -0,0 +1,12 @@
+<?php
+
+namespace Drupal\workspaces\EntityQuery;
+
+/**
+ * Workspaces PostgreSQL-specific entity query implementation.
+ *
+ * @internal
+ */
+class PgsqlQueryFactory extends QueryFactory {
+
+}

core/modules/workspaces/src/EntityQuery/Query.php

@@ -0,0 +1,45 @@
+<?php
+
+namespace Drupal\workspaces\EntityQuery;
+
+use Drupal\Core\Entity\Query\Sql\Query as BaseQuery;
+
+/**
+ * Alters entity queries to use a workspace revision instead of the default one.
+ */
+class Query extends BaseQuery {
+
+  use QueryTrait {
+    prepare as traitPrepare;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function prepare() {
+    $this->traitPrepare();
+
+    // If the prepare() method from the trait decided that we need to alter this
+    // query, we need to re-define the key fields for fetchAllKeyed() as SQL
+    // expressions.
+    if ($this->sqlQuery->getMetaData('active_workspace_id')) {
+      $id_field = $this->entityType->getKey('id');
+      $revision_field = $this->entityType->getKey('revision');
+
+      // Since the query is against the base table, we have to take into account
+      // that the revision ID might come from the workspace_association
+      // relationship, and, as a consequence, the revision ID field is no longer
+      // a simple SQL field but an expression.
+      $this->sqlFields = [];
+      $this->sqlQuery->addExpression("COALESCE([workspace_association].[target_entity_revision_id], [base_table].[$revision_field])", $revision_field);
+      $this->sqlQuery->addExpression("[base_table].[$id_field]", $id_field);
+
+      $this->sqlGroupBy['workspace_association.target_entity_revision_id'] = 'workspace_association.target_entity_revision_id';
+      $this->sqlGroupBy["base_table.$id_field"] = "base_table.$id_field";
+      $this->sqlGroupBy["base_table.$revision_field"] = "base_table.$revision_field";
+    }
+
+    return $this;
+  }
+
+}

core/modules/workspaces/src/EntityQuery/QueryAggregate.php

@@ -0,0 +1,31 @@
+<?php
+
+namespace Drupal\workspaces\EntityQuery;
+
+use Drupal\Core\Entity\Query\Sql\QueryAggregate as BaseQueryAggregate;
+
+/**
+ * Alters aggregate entity queries to use a workspace revision if possible.
+ */
+class QueryAggregate extends BaseQueryAggregate {
+
+  use QueryTrait {
+    prepare as traitPrepare;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function prepare() {
+    // Aggregate entity queries do not return an array of entity IDs keyed by
+    // revision IDs, they only return the values of the aggregated fields, so we
+    // don't need to add any expressions like we do in
+    // \Drupal\workspaces\EntityQuery\Query::prepare().
+    $this->traitPrepare();
+
+    // Throw away the ID fields.
+    $this->sqlFields = [];
+    return $this;
+  }
+
+}

core/modules/workspaces/src/EntityQuery/QueryFactory.php

@@ -0,0 +1,44 @@
+<?php
+
+namespace Drupal\workspaces\EntityQuery;
+
+use Drupal\Core\Database\Connection;
+use Drupal\Core\Entity\EntityTypeInterface;
+use Drupal\Core\Entity\Query\QueryBase;
+use Drupal\Core\Entity\Query\Sql\QueryFactory as BaseQueryFactory;
+use Drupal\workspaces\WorkspaceInformationInterface;
+use Drupal\workspaces\WorkspaceManagerInterface;
+
+/**
+ * Workspaces-specific entity query implementation.
+ *
+ * @internal
+ */
+class QueryFactory extends BaseQueryFactory {
+
+  public function __construct(
+    Connection $connection,
+    protected readonly WorkspaceManagerInterface $workspaceManager,
+    protected readonly WorkspaceInformationInterface $workspaceInfo,
+  ) {
+    $this->connection = $connection;
+    $this->namespaces = QueryBase::getNamespaces($this);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function get(EntityTypeInterface $entity_type, $conjunction) {
+    $class = QueryBase::getClass($this->namespaces, 'Query');
+    return new $class($entity_type, $conjunction, $this->connection, $this->namespaces, $this->workspaceManager, $this->workspaceInfo);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getAggregate(EntityTypeInterface $entity_type, $conjunction) {
+    $class = QueryBase::getClass($this->namespaces, 'QueryAggregate');
+    return new $class($entity_type, $conjunction, $this->connection, $this->namespaces, $this->workspaceManager, $this->workspaceInfo);
+  }
+
+}

core/modules/workspaces/src/EntityQuery/QueryTrait.php

@@ -0,0 +1,99 @@
+<?php
+
+namespace Drupal\workspaces\EntityQuery;
+
+use Drupal\Core\Database\Connection;
+use Drupal\Core\Entity\EntityTypeInterface;
+use Drupal\workspaces\WorkspaceInformationInterface;
+use Drupal\workspaces\WorkspaceManagerInterface;
+
+/**
+ * Provides workspaces-specific helpers for altering entity queries.
+ *
+ * @internal
+ */
+trait QueryTrait {
+
+  /**
+   * The workspace manager.
+   *
+   * @var \Drupal\workspaces\WorkspaceManagerInterface
+   */
+  protected $workspaceManager;
+
+  /**
+   * The workspace information service.
+   *
+   * @var \Drupal\workspaces\WorkspaceInformationInterface
+   */
+  protected $workspaceInfo;
+
+  /**
+   * Constructs a Query object.
+   *
+   * @param \Drupal\Core\Entity\EntityTypeInterface $entity_type
+   *   The entity type definition.
+   * @param string $conjunction
+   *   - AND: all of the conditions on the query need to match.
+   *   - OR: at least one of the conditions on the query need to match.
+   * @param \Drupal\Core\Database\Connection $connection
+   *   The database connection to run the query against.
+   * @param array $namespaces
+   *   List of potential namespaces of the classes belonging to this query.
+   * @param \Drupal\workspaces\WorkspaceManagerInterface $workspace_manager
+   *   The workspace manager.
+   * @param \Drupal\workspaces\WorkspaceInformationInterface $workspace_information
+   *   The workspace information service.
+   */
+  public function __construct(EntityTypeInterface $entity_type, $conjunction, Connection $connection, array $namespaces, WorkspaceManagerInterface $workspace_manager, WorkspaceInformationInterface $workspace_information) {
+    parent::__construct($entity_type, $conjunction, $connection, $namespaces);
+
+    $this->workspaceManager = $workspace_manager;
+    $this->workspaceInfo = $workspace_information;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function prepare() {
+    parent::prepare();
+
+    // Do not alter entity revision queries.
+    // @todo How about queries for the latest revision? Should we alter them to
+    //   look for the latest workspace-specific revision?
+    if ($this->allRevisions) {
+      return $this;
+    }
+
+    // Only alter the query if the active workspace is not the default one and
+    // the entity type is supported.
+    if ($this->workspaceInfo->isEntityTypeSupported($this->entityType) && $this->workspaceManager->hasActiveWorkspace()) {
+      $active_workspace = $this->workspaceManager->getActiveWorkspace();
+      $this->sqlQuery->addMetaData('active_workspace_id', $active_workspace->id());
+      $this->sqlQuery->addMetaData('simple_query', FALSE);
+
+      // LEFT JOIN 'workspace_association' to the base table of the query so we
+      // can properly include live content along with a possible workspace
+      // revision.
+      $id_field = $this->entityType->getKey('id');
+      $this->sqlQuery->leftJoin('workspace_association', 'workspace_association', "[%alias].[target_entity_type_id] = '{$this->entityTypeId}' AND [%alias].[target_entity_id] = [base_table].[$id_field] AND [%alias].[workspace] = '{$active_workspace->id()}'");
+    }
+
+    return $this;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function isSimpleQuery() {
+    // We declare that this is not a simple query in
+    // \Drupal\workspaces\EntityQuery\QueryTrait::prepare(), but that's not
+    // enough because the parent method can return TRUE in some circumstances.
+    if ($this->sqlQuery->getMetaData('active_workspace_id')) {
+      return FALSE;
+    }
+
+    return parent::isSimpleQuery();
+  }
+
+}

core/modules/workspaces/src/EntityQuery/Tables.php

@@ -0,0 +1,157 @@
+<?php
+
+namespace Drupal\workspaces\EntityQuery;
+
+use Drupal\Core\Database\Query\SelectInterface;
+use Drupal\Core\Entity\EntityType;
+use Drupal\Core\Entity\Query\Sql\Tables as BaseTables;
+use Drupal\Core\Field\FieldStorageDefinitionInterface;
+
+/**
+ * Alters entity queries to use a workspace revision instead of the default one.
+ */
+class Tables extends BaseTables {
+
+  /**
+   * The workspace information service.
+   *
+   * @var \Drupal\workspaces\WorkspaceInformationInterface
+   */
+  protected $workspaceInfo;
+
+  /**
+   * Workspace association table array, key is base table name, value is alias.
+   *
+   * @var array
+   */
+  protected $contentWorkspaceTables = [];
+
+  /**
+   * Keeps track of the entity type IDs for each base table of the query.
+   *
+   * The array is keyed by the base table alias and the values are entity type
+   * IDs.
+   *
+   * @var array
+   */
+  protected $baseTablesEntityType = [];
+
+  /**
+   * {@inheritdoc}
+   */
+  public function __construct(SelectInterface $sql_query) {
+    parent::__construct($sql_query);
+
+    $this->workspaceInfo = \Drupal::service('workspaces.information');
+
+    // The join between the first 'workspace_association' table and base table
+    // of the query is done in
+    // \Drupal\workspaces\EntityQuery\QueryTrait::prepare(), so we need to
+    // initialize its entry manually.
+    if ($this->sqlQuery->getMetaData('active_workspace_id')) {
+      $this->contentWorkspaceTables['base_table'] = 'workspace_association';
+      $this->baseTablesEntityType['base_table'] = $this->sqlQuery->getMetaData('entity_type');
+    }
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function addField($field, $type, $langcode) {
+    // The parent method uses shared and dedicated revision tables only when the
+    // entity query is instructed to query all revisions. However, if we are
+    // looking for workspace-specific revisions, we have to force the parent
+    // method to always pick the revision tables if the field being queried is
+    // revisionable.
+    if ($this->sqlQuery->getMetaData('active_workspace_id')) {
+      $previous_all_revisions = $this->sqlQuery->getMetaData('all_revisions');
+      $this->sqlQuery->addMetaData('all_revisions', TRUE);
+    }
+
+    $alias = parent::addField($field, $type, $langcode);
+
+    // Restore the 'all_revisions' metadata because we don't want to interfere
+    // with the rest of the query.
+    if (isset($previous_all_revisions)) {
+      $this->sqlQuery->addMetaData('all_revisions', $previous_all_revisions);
+    }
+
+    return $alias;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function addJoin($type, $table, $join_condition, $langcode, $delta = NULL) {
+    if ($this->sqlQuery->getMetaData('active_workspace_id')) {
+      // The join condition for a shared or dedicated field table is in the form
+      // of "%alias.$id_field = $base_table.$id_field". Whenever we join a field
+      // table we have to check:
+      // 1) if $base_table is of an entity type that can belong to a workspace;
+      // 2) if $id_field is the revision key of that entity type or the special
+      // 'revision_id' string used when joining dedicated field tables.
+      // If those two conditions are met, we have to update the join condition
+      // to also look for a possible workspace-specific revision using COALESCE.
+      $condition_parts = explode(' = ', $join_condition);
+      $condition_parts_1 = str_replace(['[', ']'], '', $condition_parts[1]);
+      [$base_table, $id_field] = explode('.', $condition_parts_1);
+
+      if (isset($this->baseTablesEntityType[$base_table])) {
+        $entity_type_id = $this->baseTablesEntityType[$base_table];
+        $revision_key = $this->entityTypeManager->getActiveDefinition($entity_type_id)->getKey('revision');
+
+        if ($id_field === $revision_key || $id_field === 'revision_id') {
+          $workspace_association_table = $this->contentWorkspaceTables[$base_table];
+          $join_condition = "{$condition_parts[0]} = COALESCE($workspace_association_table.target_entity_revision_id, {$condition_parts[1]})";
+        }
+      }
+    }
+
+    return parent::addJoin($type, $table, $join_condition, $langcode, $delta);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function addNextBaseTable(EntityType $entity_type, $table, $sql_column, FieldStorageDefinitionInterface $field_storage) {
+    $next_base_table_alias = parent::addNextBaseTable($entity_type, $table, $sql_column, $field_storage);
+
+    $active_workspace_id = $this->sqlQuery->getMetaData('active_workspace_id');
+    if ($active_workspace_id && $this->workspaceInfo->isEntityTypeSupported($entity_type)) {
+      $this->addWorkspaceAssociationJoin($entity_type->id(), $next_base_table_alias, $active_workspace_id);
+    }
+
+    return $next_base_table_alias;
+  }
+
+  /**
+   * Adds a new join to the 'workspace_association' table for an entity base table.
+   *
+   * This method assumes that the active workspace has already been determined
+   * to be a non-default workspace.
+   *
+   * @param string $entity_type_id
+   *   The ID of the entity type whose base table we are joining.
+   * @param string $base_table_alias
+   *   The alias of the entity type's base table.
+   * @param string $active_workspace_id
+   *   The ID of the active workspace.
+   *
+   * @return string
+   *   The alias of the joined table.
+   */
+  public function addWorkspaceAssociationJoin($entity_type_id, $base_table_alias, $active_workspace_id) {
+    if (!isset($this->contentWorkspaceTables[$base_table_alias])) {
+      $entity_type = $this->entityTypeManager->getActiveDefinition($entity_type_id);
+      $id_field = $entity_type->getKey('id');
+
+      // LEFT join the Workspace association entity's table so we can properly
+      // include live content along with a possible workspace-specific revision.
+      $this->contentWorkspaceTables[$base_table_alias] = $this->sqlQuery->leftJoin('workspace_association', NULL, "[%alias].[target_entity_type_id] = '$entity_type_id' AND [%alias].[target_entity_id] = [$base_table_alias].[$id_field] AND [%alias].[workspace] = '$active_workspace_id'");
+
+      $this->baseTablesEntityType[$base_table_alias] = $entity_type->id();
+    }
+    return $this->contentWorkspaceTables[$base_table_alias];
+  }
+
+}

core/modules/workspaces/src/EntityTypeInfo.php

@@ -0,0 +1,152 @@
+<?php
+
+namespace Drupal\workspaces;
+
+use Drupal\Core\DependencyInjection\ContainerInjectionInterface;
+use Drupal\Core\Entity\EntityPublishedInterface;
+use Drupal\Core\Entity\EntityTypeInterface;
+use Drupal\Core\Field\BaseFieldDefinition;
+use Drupal\Core\StringTranslation\TranslatableMarkup;
+use Drupal\workspaces\Entity\Handler\BlockContentWorkspaceHandler;
+use Drupal\workspaces\Entity\Handler\DefaultWorkspaceHandler;
+use Drupal\workspaces\Entity\Handler\IgnoredWorkspaceHandler;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Manipulates entity type information.
+ *
+ * This class contains primarily bridged hooks for compile-time or
+ * cache-clear-time hooks. Runtime hooks should be placed in EntityOperations.
+ *
+ * @internal
+ */
+class EntityTypeInfo implements ContainerInjectionInterface {
+
+  public function __construct(
+    protected readonly WorkspaceInformationInterface $workspaceInfo,
+  ) {
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container) {
+    return new static(
+      $container->get('workspaces.information')
+    );
+  }
+
+  /**
+   * Adds workspace support info to eligible entity types.
+   *
+   * @param \Drupal\Core\Entity\EntityTypeInterface[] $entity_types
+   *   An associative array of all entity type definitions, keyed by the entity
+   *   type name. Passed by reference.
+   *
+   * @see hook_entity_type_build()
+   */
+  public function entityTypeBuild(array &$entity_types) {
+    foreach ($entity_types as $entity_type) {
+      if ($entity_type->hasHandlerClass('workspace')) {
+        continue;
+      }
+
+      // Revisionable and publishable entity types are always supported.
+      if ($entity_type->entityClassImplements(EntityPublishedInterface::class) && $entity_type->isRevisionable()) {
+        $entity_type->setHandlerClass('workspace', DefaultWorkspaceHandler::class);
+
+        // Support for custom blocks has to be determined on a per-entity
+        // basis.
+        if ($entity_type->id() === 'block_content') {
+          $entity_type->setHandlerClass('workspace', BlockContentWorkspaceHandler::class);
+        }
+      }
+
+      // The 'file' entity type is allowed to perform CRUD operations inside a
+      // workspace without being tracked.
+      if ($entity_type->id() === 'file') {
+        $entity_type->setHandlerClass('workspace', IgnoredWorkspaceHandler::class);
+      }
+
+      // Internal entity types are allowed to perform CRUD operations inside a
+      // workspace.
+      if ($entity_type->isInternal()) {
+        $entity_type->setHandlerClass('workspace', IgnoredWorkspaceHandler::class);
+      }
+    }
+  }
+
+  /**
+   * Adds Workspace configuration to appropriate entity types.
+   *
+   * @param \Drupal\Core\Entity\EntityTypeInterface[] $entity_types
+   *   An array of entity types.
+   *
+   * @see hook_entity_type_alter()
+   */
+  public function entityTypeAlter(array &$entity_types) {
+    foreach ($entity_types as $entity_type) {
+      if (!$this->workspaceInfo->isEntityTypeSupported($entity_type)) {
+        continue;
+      }
+
+      // Workspace-support status has been declared in the "build" phase, now we
+      // can use that information and add additional configuration in the
+      // "alter" phase.
+      $entity_type->addConstraint('EntityWorkspaceConflict');
+      $entity_type->setRevisionMetadataKey('workspace', 'workspace');
+
+      // Non-default workspaces display the active revision on the canonical
+      // route of an entity, so the latest version route is no longer needed.
+      $link_templates = $entity_type->get('links');
+      unset($link_templates['latest-version']);
+      $entity_type->set('links', $link_templates);
+    }
+  }
+
+  /**
+   * Alters field plugin definitions.
+   *
+   * @param array[] $definitions
+   *   An array of field plugin definitions.
+   *
+   * @see hook_field_info_alter()
+   */
+  public function fieldInfoAlter(&$definitions) {
+    if (isset($definitions['entity_reference'])) {
+      $definitions['entity_reference']['constraints']['EntityReferenceSupportedNewEntities'] = [];
+    }
+
+    // Allow path aliases to be changed in workspace-specific pending revisions.
+    if (isset($definitions['path'])) {
+      unset($definitions['path']['constraints']['PathAlias']);
+    }
+  }
+
+  /**
+   * Provides custom base field definitions for a content entity type.
+   *
+   * @param \Drupal\Core\Entity\EntityTypeInterface $entity_type
+   *   The entity type definition.
+   *
+   * @return \Drupal\Core\Field\FieldDefinitionInterface[]
+   *   An array of field definitions, keyed by field name.
+   *
+   * @see hook_entity_base_field_info()
+   */
+  public function entityBaseFieldInfo(EntityTypeInterface $entity_type) {
+    if ($this->workspaceInfo->isEntityTypeSupported($entity_type)) {
+      $field_name = $entity_type->getRevisionMetadataKey('workspace');
+      $fields[$field_name] = BaseFieldDefinition::create('entity_reference')
+        ->setLabel(new TranslatableMarkup('Workspace'))
+        ->setDescription(new TranslatableMarkup('Indicates the workspace that this revision belongs to.'))
+        ->setSetting('target_type', 'workspace')
+        ->setInternal(TRUE)
+        ->setTranslatable(FALSE)
+        ->setRevisionable(TRUE);
+
+      return $fields;
+    }
+  }
+
+}

core/modules/workspaces/src/Event/WorkspacePostPublishEvent.php

@@ -0,0 +1,9 @@
+<?php
+
+namespace Drupal\workspaces\Event;
+
+/**
+ * Defines the post-publish event class.
+ */
+class WorkspacePostPublishEvent extends WorkspacePublishEvent {
+}

core/modules/workspaces/src/Event/WorkspacePrePublishEvent.php

@@ -0,0 +1,9 @@
+<?php
+
+namespace Drupal\workspaces\Event;
+
+/**
+ * Defines the pre-publish event class.
+ */
+class WorkspacePrePublishEvent extends WorkspacePublishEvent {
+}

core/modules/workspaces/src/Event/WorkspacePublishEvent.php

@@ -0,0 +1,112 @@
+<?php
+
+namespace Drupal\workspaces\Event;
+
+use Drupal\Core\StringTranslation\TranslatableMarkup;
+use Drupal\workspaces\WorkspaceInterface;
+use Drupal\Component\EventDispatcher\Event;
+
+/**
+ * Defines the workspace publish event.
+ */
+abstract class WorkspacePublishEvent extends Event {
+
+  /**
+   * The IDs of the entities that are being published.
+   */
+  protected readonly array $publishedRevisionIds;
+
+  /**
+   * Whether an event subscriber requested the publishing to be stopped.
+   */
+  protected bool $publishingStopped = FALSE;
+
+  /**
+   * The reason why publishing stopped. For use in messages.
+   */
+  protected string $publishingStoppedReason = '';
+
+  /**
+   * Constructs a new WorkspacePublishEvent.
+   *
+   * @param \Drupal\workspaces\WorkspaceInterface $workspace
+   *   The workspace.
+   * @param array $published_revision_ids
+   *   The IDs of the entities that are being published.
+   */
+  public function __construct(
+    protected readonly WorkspaceInterface $workspace,
+    array $published_revision_ids,
+  ) {
+    $this->publishedRevisionIds = $published_revision_ids;
+  }
+
+  /**
+   * Gets the workspace.
+   *
+   * @return \Drupal\workspaces\WorkspaceInterface
+   *   The workspace.
+   */
+  public function getWorkspace(): WorkspaceInterface {
+    return $this->workspace;
+  }
+
+  /**
+   * Gets the entity IDs that are being published as part of the workspace.
+   *
+   * @return array
+   *   Returns a multidimensional array where the first level keys are entity
+   *   type IDs and the values are an array of entity IDs keyed by revision IDs.
+   */
+  public function getPublishedRevisionIds(): array {
+    return $this->publishedRevisionIds;
+  }
+
+  /**
+   * Determines whether a subscriber requested the publishing to be stopped.
+   *
+   * @return bool
+   *   TRUE if the publishing of the workspace should be stopped, FALSE
+   *   otherwise.
+   */
+  public function isPublishingStopped(): bool {
+    return $this->publishingStopped;
+  }
+
+  /**
+   * Signals that the workspace publishing should be aborted.
+   *
+   * @return $this
+   */
+  public function stopPublishing(): static {
+    $this->publishingStopped = TRUE;
+
+    return $this;
+  }
+
+  /**
+   * Gets the reason for stopping the workspace publication.
+   *
+   * @return string|\Drupal\Core\StringTranslation\TranslatableMarkup
+   *   The reason for stopping the workspace publication or an empty string if
+   *   no reason is provided.
+   */
+  public function getPublishingStoppedReason(): string|TranslatableMarkup {
+    return $this->publishingStoppedReason;
+  }
+
+  /**
+   * Sets the reason for stopping the workspace publication.
+   *
+   * @param string|\Stringable $reason
+   *   The reason for stopping the workspace publication.
+   *
+   * @return $this
+   */
+  public function setPublishingStoppedReason(string|\Stringable $reason): static {
+    $this->publishingStoppedReason = $reason;
+
+    return $this;
+  }
+
+}

core/modules/workspaces/src/EventSubscriber/EntitySchemaSubscriber.php

@@ -0,0 +1,161 @@
+<?php
+
+namespace Drupal\workspaces\EventSubscriber;
+
+use Drupal\Core\Entity\EntityDefinitionUpdateManagerInterface;
+use Drupal\Core\Entity\EntityLastInstalledSchemaRepositoryInterface;
+use Drupal\Core\Entity\EntityTypeEventSubscriberTrait;
+use Drupal\Core\Entity\EntityTypeInterface;
+use Drupal\Core\Entity\EntityTypeListenerInterface;
+use Drupal\Core\Field\BaseFieldDefinition;
+use Drupal\Core\StringTranslation\StringTranslationTrait;
+use Drupal\workspaces\WorkspaceInformationInterface;
+use Symfony\Component\EventDispatcher\EventSubscriberInterface;
+
+/**
+ * Defines a class for listening to entity schema changes.
+ */
+class EntitySchemaSubscriber implements EntityTypeListenerInterface, EventSubscriberInterface {
+
+  use EntityTypeEventSubscriberTrait;
+  use StringTranslationTrait;
+
+  /**
+   * The definition update manager.
+   *
+   * @var \Drupal\Core\Entity\EntityDefinitionUpdateManagerInterface
+   */
+  protected $entityDefinitionUpdateManager;
+
+  /**
+   * The last installed schema definitions.
+   *
+   * @var \Drupal\Core\Entity\EntityLastInstalledSchemaRepositoryInterface
+   */
+  protected $entityLastInstalledSchemaRepository;
+
+  /**
+   * The workspace information service.
+   *
+   * @var \Drupal\workspaces\WorkspaceInformationInterface
+   */
+  protected $workspaceInfo;
+
+  /**
+   * Constructs a new EntitySchemaSubscriber.
+   *
+   * @param \Drupal\Core\Entity\EntityDefinitionUpdateManagerInterface $entityDefinitionUpdateManager
+   *   Definition update manager.
+   * @param \Drupal\Core\Entity\EntityLastInstalledSchemaRepositoryInterface $entityLastInstalledSchemaRepository
+   *   Last definitions.
+   * @param \Drupal\workspaces\WorkspaceInformationInterface $workspace_information
+   *   The workspace information service.
+   */
+  public function __construct(EntityDefinitionUpdateManagerInterface $entityDefinitionUpdateManager, EntityLastInstalledSchemaRepositoryInterface $entityLastInstalledSchemaRepository, WorkspaceInformationInterface $workspace_information) {
+    $this->entityDefinitionUpdateManager = $entityDefinitionUpdateManager;
+    $this->entityLastInstalledSchemaRepository = $entityLastInstalledSchemaRepository;
+    $this->workspaceInfo = $workspace_information;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function getSubscribedEvents(): array {
+    return static::getEntityTypeEvents();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function onEntityTypeCreate(EntityTypeInterface $entity_type) {
+    // If the entity type is supported by Workspaces, add the revision metadata
+    // field.
+    if ($this->workspaceInfo->isEntityTypeSupported($entity_type)) {
+      $this->addRevisionMetadataField($entity_type);
+    }
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function onFieldableEntityTypeCreate(EntityTypeInterface $entity_type, array $field_storage_definitions) {
+    $this->onEntityTypeCreate($entity_type);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function onEntityTypeUpdate(EntityTypeInterface $entity_type, EntityTypeInterface $original) {
+    // If the entity type is now supported by Workspaces, add the revision
+    // metadata field.
+    if ($this->workspaceInfo->isEntityTypeSupported($entity_type) && !$this->workspaceInfo->isEntityTypeSupported($original)) {
+      $this->addRevisionMetadataField($entity_type);
+    }
+
+    // If the entity type is no longer supported by Workspaces, remove the
+    // revision metadata field.
+    if ($this->workspaceInfo->isEntityTypeSupported($original) && !$this->workspaceInfo->isEntityTypeSupported($entity_type)) {
+      $revision_metadata_keys = $original->get('revision_metadata_keys');
+      $field_storage_definition = $this->entityLastInstalledSchemaRepository->getLastInstalledFieldStorageDefinitions($entity_type->id())[$revision_metadata_keys['workspace']];
+      $this->entityDefinitionUpdateManager->uninstallFieldStorageDefinition($field_storage_definition);
+
+      // We are only removing a revision metadata key so we don't need to go
+      // through the entity update process.
+      $entity_type->setRevisionMetadataKey('workspace', NULL);
+      $this->entityLastInstalledSchemaRepository->setLastInstalledDefinition($entity_type);
+    }
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function onFieldableEntityTypeUpdate(EntityTypeInterface $entity_type, EntityTypeInterface $original, array $field_storage_definitions, array $original_field_storage_definitions, ?array &$sandbox = NULL) {
+    $this->onEntityTypeUpdate($entity_type, $original);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function onEntityTypeDelete(EntityTypeInterface $entity_type) {
+    // Nothing to do here.
+  }
+
+  /**
+   * Adds the 'workspace' revision metadata field to an entity type.
+   *
+   * @param \Drupal\Core\Entity\EntityTypeInterface $entity_type
+   *   The entity type that has been installed or updated.
+   */
+  protected function addRevisionMetadataField(EntityTypeInterface $entity_type) {
+    if (!$entity_type->hasRevisionMetadataKey('workspace')) {
+      // Bail out if there's an existing field called 'workspace'.
+      if ($this->entityDefinitionUpdateManager->getFieldStorageDefinition('workspace', $entity_type->id())) {
+        throw new \RuntimeException("An existing 'workspace' field was found for the '{$entity_type->id()}' entity type. Set the 'workspace' revision metadata key to use a different field name and run this update function again.");
+      }
+
+      // We are only adding a revision metadata key so we don't need to go
+      // through the entity update process.
+      $entity_type->setRevisionMetadataKey('workspace', 'workspace');
+      $this->entityLastInstalledSchemaRepository->setLastInstalledDefinition($entity_type);
+    }
+
+    $this->entityDefinitionUpdateManager->installFieldStorageDefinition($entity_type->getRevisionMetadataKey('workspace'), $entity_type->id(), 'workspaces', $this->getWorkspaceFieldDefinition());
+  }
+
+  /**
+   * Gets the base field definition for the 'workspace' revision metadata field.
+   *
+   * @return \Drupal\Core\Field\BaseFieldDefinition
+   *   The base field definition.
+   */
+  protected function getWorkspaceFieldDefinition() {
+    return BaseFieldDefinition::create('entity_reference')
+      ->setLabel($this->t('Workspace'))
+      ->setDescription($this->t('Indicates the workspace that this revision belongs to.'))
+      ->setSetting('target_type', 'workspace')
+      ->setInternal(TRUE)
+      ->setTranslatable(FALSE)
+      ->setRevisionable(TRUE);
+  }
+
+}

core/modules/workspaces/src/EventSubscriber/WorkspaceRequestSubscriber.php

@@ -0,0 +1,47 @@
+<?php
+
+namespace Drupal\workspaces\EventSubscriber;
+
+use Drupal\Core\Routing\CacheableRouteProviderInterface;
+use Drupal\Core\Routing\RouteProviderInterface;
+use Drupal\workspaces\WorkspaceManagerInterface;
+use Symfony\Component\EventDispatcher\EventSubscriberInterface;
+use Symfony\Component\HttpKernel\Event\RequestEvent;
+use Symfony\Component\HttpKernel\KernelEvents;
+
+/**
+ * Provides a event subscriber for setting workspace-specific cache keys.
+ *
+ * @internal
+ */
+class WorkspaceRequestSubscriber implements EventSubscriberInterface {
+
+  public function __construct(
+    protected readonly RouteProviderInterface $routeProvider,
+    protected readonly WorkspaceManagerInterface $workspaceManager,
+  ) {}
+
+  /**
+   * Adds the active workspace as a cache key part to the route provider.
+   *
+   * @param \Symfony\Component\HttpKernel\Event\RequestEvent $event
+   *   An event object.
+   */
+  public function onKernelRequest(RequestEvent $event) {
+    if ($this->workspaceManager->hasActiveWorkspace() && $this->routeProvider instanceof CacheableRouteProviderInterface) {
+      $this->routeProvider->addExtraCacheKeyPart('workspace', $this->workspaceManager->getActiveWorkspace()->id());
+    }
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function getSubscribedEvents(): array {
+    // Use a priority of 33 in order to run before Symfony's router listener.
+    // @see \Symfony\Component\HttpKernel\EventListener\RouterListener::getSubscribedEvents()
+    $events[KernelEvents::REQUEST][] = ['onKernelRequest', 33];
+
+    return $events;
+  }
+
+}

core/modules/workspaces/src/Form/SwitchToLiveForm.php

@@ -0,0 +1,80 @@
+<?php
+
+namespace Drupal\workspaces\Form;
+
+use Drupal\Core\DependencyInjection\ContainerInjectionInterface;
+use Drupal\Core\Form\ConfirmFormBase;
+use Drupal\Core\Form\FormStateInterface;
+use Drupal\Core\Form\WorkspaceSafeFormInterface;
+use Drupal\Core\Url;
+use Drupal\workspaces\WorkspaceManagerInterface;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Provides a form that switches to the live version of the site.
+ */
+class SwitchToLiveForm extends ConfirmFormBase implements ContainerInjectionInterface, WorkspaceSafeFormInterface {
+
+  /**
+   * The workspace manager.
+   *
+   * @var \Drupal\workspaces\WorkspaceManagerInterface
+   */
+  protected $workspaceManager;
+
+  /**
+   * Constructs a new SwitchToLiveForm.
+   *
+   * @param \Drupal\workspaces\WorkspaceManagerInterface $workspace_manager
+   *   The workspace manager.
+   */
+  public function __construct(WorkspaceManagerInterface $workspace_manager) {
+    $this->workspaceManager = $workspace_manager;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container) {
+    return new static(
+      $container->get('workspaces.manager')
+    );
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getFormId() {
+    return 'switch_to_live_form';
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getQuestion() {
+    return $this->t('Would you like to switch to the live version of the site?');
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getDescription() {
+    return $this->t('Switch to the live version of the site.');
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getCancelUrl() {
+    return new Url('<current>');
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function submitForm(array &$form, FormStateInterface $form_state) {
+    $this->workspaceManager->switchToLive();
+    $this->messenger()->addMessage($this->t('You are now viewing the live version of the site.'));
+  }
+
+}

core/modules/workspaces/src/Form/WorkspaceActivateForm.php

@@ -0,0 +1,144 @@
+<?php
+
+namespace Drupal\workspaces\Form;
+
+use Drupal\Core\Access\AccessResult;
+use Drupal\Core\Entity\EntityConfirmFormBase;
+use Drupal\Core\Form\FormStateInterface;
+use Drupal\Core\Form\WorkspaceSafeFormInterface;
+use Drupal\Core\Messenger\MessengerInterface;
+use Drupal\Core\Routing\RouteMatchInterface;
+use Drupal\workspaces\WorkspaceAccessException;
+use Drupal\workspaces\WorkspaceManagerInterface;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Handle activation of a workspace on administrative pages.
+ */
+class WorkspaceActivateForm extends EntityConfirmFormBase implements WorkspaceSafeFormInterface {
+
+  /**
+   * The workspace entity.
+   *
+   * @var \Drupal\workspaces\WorkspaceInterface
+   */
+  protected $entity;
+
+  /**
+   * The workspace replication manager.
+   *
+   * @var \Drupal\workspaces\WorkspaceManagerInterface
+   */
+  protected $workspaceManager;
+
+  /**
+   * The messenger service.
+   *
+   * @var \Drupal\Core\Messenger\MessengerInterface
+   */
+  protected $messenger;
+
+  /**
+   * Constructs a new WorkspaceActivateForm.
+   *
+   * @param \Drupal\workspaces\WorkspaceManagerInterface $workspace_manager
+   *   The workspace manager.
+   * @param \Drupal\Core\Messenger\MessengerInterface $messenger
+   *   The messenger service.
+   */
+  public function __construct(WorkspaceManagerInterface $workspace_manager, MessengerInterface $messenger) {
+    $this->workspaceManager = $workspace_manager;
+    $this->messenger = $messenger;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container) {
+    return new static(
+      $container->get('workspaces.manager'),
+      $container->get('messenger')
+    );
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getQuestion() {
+    return $this->t('Would you like to activate the %workspace workspace?', ['%workspace' => $this->entity->label()]);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getDescription() {
+    return $this->t('Activate the %workspace workspace.', ['%workspace' => $this->entity->label()]);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getCancelUrl() {
+    return $this->entity->toUrl('collection');
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function buildForm(array $form, FormStateInterface $form_state) {
+    $form = parent::buildForm($form, $form_state);
+
+    // Content entity forms do not use the parent's #after_build callback.
+    unset($form['#after_build']);
+
+    return $form;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function actions(array $form, FormStateInterface $form_state) {
+    $actions = parent::actions($form, $form_state);
+    $actions['cancel']['#attributes']['class'][] = 'dialog-cancel';
+    return $actions;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function submitForm(array &$form, FormStateInterface $form_state) {
+    try {
+      $this->workspaceManager->setActiveWorkspace($this->entity);
+      $this->messenger->addMessage($this->t('%workspace_label is now the active workspace.', ['%workspace_label' => $this->entity->label()]));
+    }
+    catch (WorkspaceAccessException $e) {
+      $this->messenger->addError($this->t('You do not have access to activate the %workspace_label workspace.', ['%workspace_label' => $this->entity->label()]));
+    }
+
+    // Redirect to the workspace manage page by default.
+    if (!$this->getRequest()->query->has('destination')) {
+      $form_state->setRedirectUrl($this->entity->toUrl());
+    }
+  }
+
+  /**
+   * Checks access for the workspace activate form.
+   *
+   * @param \Drupal\Core\Routing\RouteMatchInterface $route_match
+   *   The route match.
+   *
+   * @return \Drupal\Core\Access\AccessResult
+   *   The access result.
+   */
+  public function checkAccess(RouteMatchInterface $route_match) {
+    /** @var \Drupal\workspaces\WorkspaceInterface $workspace */
+    $workspace = $route_match->getParameter('workspace');
+    $active_workspace = $this->workspaceManager->getActiveWorkspace();
+
+    $access = AccessResult::allowedIf(!$active_workspace || ($active_workspace && $active_workspace->id() != $workspace->id()))
+      ->addCacheableDependency($workspace);
+
+    return $access;
+  }
+
+}

core/modules/workspaces/src/Form/WorkspaceDeleteForm.php

@@ -0,0 +1,115 @@
+<?php
+
+namespace Drupal\workspaces\Form;
+
+use Drupal\Component\Datetime\TimeInterface;
+use Drupal\Core\Entity\ContentEntityDeleteForm;
+use Drupal\Core\Entity\EntityRepositoryInterface;
+use Drupal\Core\Entity\EntityTypeBundleInfoInterface;
+use Drupal\Core\Form\FormStateInterface;
+use Drupal\workspaces\WorkspaceAssociationInterface;
+use Drupal\workspaces\WorkspaceRepositoryInterface;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Provides a form for deleting a workspace.
+ *
+ * @internal
+ */
+class WorkspaceDeleteForm extends ContentEntityDeleteForm {
+
+  /**
+   * The workspace entity.
+   *
+   * @var \Drupal\workspaces\WorkspaceInterface
+   */
+  protected $entity;
+
+  /**
+   * The workspace association service.
+   *
+   * @var \Drupal\workspaces\WorkspaceAssociationInterface
+   */
+  protected $workspaceAssociation;
+
+  /**
+   * The workspace repository service.
+   *
+   * @var \Drupal\workspaces\WorkspaceRepositoryInterface
+   */
+  protected $workspaceRepository;
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container) {
+    return new static(
+      $container->get('entity.repository'),
+      $container->get('workspaces.association'),
+      $container->get('workspaces.repository'),
+      $container->get('entity_type.bundle.info'),
+      $container->get('datetime.time')
+    );
+  }
+
+  /**
+   * Constructs a WorkspaceDeleteForm object.
+   *
+   * @param \Drupal\Core\Entity\EntityRepositoryInterface $entity_repository
+   *   The entity repository service.
+   * @param \Drupal\workspaces\WorkspaceAssociationInterface $workspace_association
+   *   The workspace association service to check how many revisions will be
+   *   deleted.
+   * @param \Drupal\workspaces\WorkspaceRepositoryInterface $workspace_repository
+   *   The workspace repository service.
+   * @param \Drupal\Core\Entity\EntityTypeBundleInfoInterface $entity_type_bundle_info
+   *   The entity type bundle service.
+   * @param \Drupal\Component\Datetime\TimeInterface $time
+   *   The time service.
+   */
+  public function __construct(EntityRepositoryInterface $entity_repository, WorkspaceAssociationInterface $workspace_association, WorkspaceRepositoryInterface $workspace_repository, ?EntityTypeBundleInfoInterface $entity_type_bundle_info = NULL, ?TimeInterface $time = NULL) {
+    parent::__construct($entity_repository, $entity_type_bundle_info, $time);
+    $this->workspaceAssociation = $workspace_association;
+    $this->workspaceRepository = $workspace_repository;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function buildForm(array $form, FormStateInterface $form_state) {
+    $form = parent::buildForm($form, $form_state);
+
+    $workspace_tree = $this->workspaceRepository->loadTree();
+    if (!empty($workspace_tree[$this->entity->id()]['descendants'])) {
+      $form['description']['#markup'] = $this->t('The %label workspace can not be deleted because it has child workspaces.', [
+        '%label' => $this->entity->label(),
+      ]);
+      $form['actions']['submit']['#disabled'] = TRUE;
+
+      return $form;
+    }
+
+    $tracked_entities = $this->workspaceAssociation->getTrackedEntities($this->entity->id());
+    $items = [];
+    foreach ($tracked_entities as $entity_type_id => $entity_ids) {
+      $revision_ids = $this->workspaceAssociation->getAssociatedRevisions($this->entity->id(), $entity_type_id, $entity_ids);
+      $label = $this->entityTypeManager->getDefinition($entity_type_id)->getLabel();
+      $items[] = $this->formatPlural(count($revision_ids), '1 @label revision.', '@count @label revisions.', ['@label' => $label]);
+    }
+    $form['revisions'] = [
+      '#theme' => 'item_list',
+      '#title' => $this->t('The following will also be deleted:'),
+      '#items' => $items,
+    ];
+
+    return $form;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getDescription() {
+    return $this->t('This action cannot be undone, and will also delete all content created in this workspace.');
+  }
+
+}

core/modules/workspaces/src/Form/WorkspaceForm.php

@@ -0,0 +1,169 @@
+<?php
+
+namespace Drupal\workspaces\Form;
+
+use Drupal\Core\Entity\ContentEntityForm;
+use Drupal\Core\Entity\EntityConstraintViolationListInterface;
+use Drupal\Core\Form\FormStateInterface;
+use Drupal\Core\Url;
+use Drupal\workspaces\WorkspaceManagerInterface;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Form controller for the workspace edit forms.
+ */
+class WorkspaceForm extends ContentEntityForm {
+
+  /**
+   * The workspace entity.
+   *
+   * @var \Drupal\workspaces\WorkspaceInterface
+   */
+  protected $entity;
+
+  /**
+   * The workspace manager.
+   */
+  protected WorkspaceManagerInterface $workspaceManager;
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container) {
+    $instance = parent::create($container);
+    $instance->workspaceManager = $container->get('workspaces.manager');
+    return $instance;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function form(array $form, FormStateInterface $form_state) {
+    $workspace = $this->entity;
+
+    if ($this->operation == 'edit') {
+      $form['#title'] = $this->t('Edit workspace %label', ['%label' => $workspace->label()]);
+    }
+    $form['label'] = [
+      '#type' => 'textfield',
+      '#title' => $this->t('Label'),
+      '#maxlength' => 255,
+      '#default_value' => $workspace->label(),
+      '#required' => TRUE,
+    ];
+
+    $form['id'] = [
+      '#type' => 'machine_name',
+      '#title' => $this->t('Workspace ID'),
+      '#maxlength' => 255,
+      '#default_value' => $workspace->id(),
+      '#disabled' => !$workspace->isNew(),
+      '#machine_name' => [
+        'exists' => '\Drupal\workspaces\Entity\Workspace::load',
+      ],
+      '#element_validate' => [],
+    ];
+
+    return parent::form($form, $form_state);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function getEditedFieldNames(FormStateInterface $form_state) {
+    return array_merge([
+      'label',
+      'id',
+    ], parent::getEditedFieldNames($form_state));
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function flagViolations(EntityConstraintViolationListInterface $violations, array $form, FormStateInterface $form_state) {
+    // Manually flag violations of fields not handled by the form display. This
+    // is necessary as entity form displays only flag violations for fields
+    // contained in the display.
+    $field_names = [
+      'label',
+      'id',
+    ];
+    foreach ($violations->getByFields($field_names) as $violation) {
+      [$field_name] = explode('.', $violation->getPropertyPath(), 2);
+      $form_state->setErrorByName($field_name, $violation->getMessage());
+    }
+    parent::flagViolations($violations, $form, $form_state);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function actions(array $form, FormStateInterface $form_state): array {
+    $actions = parent::actions($form, $form_state);
+
+    // When adding a new workspace, the default action should also activate it.
+    if ($this->entity->isNew()) {
+      $actions['submit']['#value'] = $this->t('Save and switch');
+      $actions['submit']['#submit'] = ['::submitForm', '::save', '::activate'];
+
+      $actions['save'] = [
+        '#type' => 'submit',
+        '#value' => $this->t('Save'),
+        '#submit' => ['::submitForm', '::save'],
+      ];
+    }
+
+    return $actions;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function save(array $form, FormStateInterface $form_state) {
+    $workspace = $this->entity;
+    $workspace->setNewRevision(TRUE);
+    $status = $workspace->save();
+
+    $info = ['%info' => $workspace->label()];
+    $context = ['@type' => $workspace->bundle(), '%info' => $workspace->label()];
+    $logger = $this->logger('workspaces');
+
+    if ($status == SAVED_UPDATED) {
+      $logger->notice('@type: updated %info.', $context);
+      $this->messenger()->addMessage($this->t('Workspace %info has been updated.', $info));
+    }
+    else {
+      $logger->notice('@type: added %info.', $context);
+      $this->messenger()->addMessage($this->t('Workspace %info has been created.', $info));
+    }
+
+    if ($workspace->id()) {
+      $form_state->setValue('id', $workspace->id());
+      $form_state->set('id', $workspace->id());
+
+      $collection_url = $workspace->toUrl('collection');
+      $redirect = $collection_url->access() ? $collection_url : Url::fromRoute('<front>');
+      $form_state->setRedirectUrl($redirect);
+    }
+    else {
+      $this->messenger()->addError($this->t('The workspace could not be saved.'));
+      $form_state->setRebuild();
+    }
+  }
+
+  /**
+   * Form submission handler for the 'submit' action.
+   *
+   * @param array $form
+   *   An associative array containing the structure of the form.
+   * @param \Drupal\Core\Form\FormStateInterface $form_state
+   *   The current state of the form.
+   */
+  public function activate(array $form, FormStateInterface $form_state): void {
+    $this->workspaceManager->setActiveWorkspace($this->entity);
+    $this->messenger()->addMessage($this->t('%label is now the active workspace.', [
+      '%label' => $this->entity->label(),
+    ]));
+  }
+
+}

core/modules/workspaces/src/Form/WorkspaceFormInterface.php

@@ -0,0 +1,18 @@
+<?php
+
+namespace Drupal\workspaces\Form;
+
+use Drupal\Core\Form\FormInterface;
+
+/**
+ * Defines interface for workspace forms so they can be easily distinguished.
+ *
+ * @internal
+ *
+ * @deprecated in drupal:10.3.0 and is removed from drupal:11.0.0. Use
+ *   \Drupal\Core\Form\WorkspaceSafeFormInterface or
+ *   \Drupal\Core\Form\WorkspaceDynamicSafeFormInterface instead.
+ *
+ * @see https://www.drupal.org/node/3229111
+ */
+interface WorkspaceFormInterface extends FormInterface {}

core/modules/workspaces/src/Form/WorkspaceMergeForm.php

@@ -0,0 +1,154 @@
+<?php
+
+namespace Drupal\workspaces\Form;
+
+use Drupal\Core\DependencyInjection\ContainerInjectionInterface;
+use Drupal\Core\Entity\EntityTypeManagerInterface;
+use Drupal\Core\Form\ConfirmFormBase;
+use Drupal\Core\Form\FormStateInterface;
+use Drupal\Core\Form\WorkspaceSafeFormInterface;
+use Drupal\Core\Url;
+use Drupal\workspaces\WorkspaceInterface;
+use Drupal\workspaces\WorkspaceOperationFactory;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Provides a form that merges the contents for a workspace into another one.
+ */
+class WorkspaceMergeForm extends ConfirmFormBase implements ContainerInjectionInterface, WorkspaceSafeFormInterface {
+
+  /**
+   * The source workspace entity.
+   *
+   * @var \Drupal\workspaces\WorkspaceInterface
+   */
+  protected $sourceWorkspace;
+
+  /**
+   * The target workspace entity.
+   *
+   * @var \Drupal\workspaces\WorkspaceInterface
+   */
+  protected $targetWorkspace;
+
+  /**
+   * The workspace operation factory.
+   *
+   * @var \Drupal\workspaces\WorkspaceOperationFactory
+   */
+  protected $workspaceOperationFactory;
+
+  /**
+   * The entity type manager.
+   *
+   * @var \Drupal\Core\Entity\EntityTypeManagerInterface
+   */
+  protected $entityTypeManager;
+
+  /**
+   * Constructs a new WorkspaceMergeForm.
+   *
+   * @param \Drupal\workspaces\WorkspaceOperationFactory $workspace_operation_factory
+   *   The workspace operation factory service.
+   * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
+   *   The entity type manager.
+   */
+  public function __construct(WorkspaceOperationFactory $workspace_operation_factory, EntityTypeManagerInterface $entity_type_manager) {
+    $this->workspaceOperationFactory = $workspace_operation_factory;
+    $this->entityTypeManager = $entity_type_manager;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container) {
+    return new static(
+      $container->get('workspaces.operation_factory'),
+      $container->get('entity_type.manager')
+    );
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getFormId() {
+    return 'workspace_merge_form';
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function buildForm(array $form, FormStateInterface $form_state, ?WorkspaceInterface $source_workspace = NULL, ?WorkspaceInterface $target_workspace = NULL) {
+    $this->sourceWorkspace = $source_workspace;
+    $this->targetWorkspace = $target_workspace;
+
+    $form = parent::buildForm($form, $form_state);
+
+    $workspace_merger = $this->workspaceOperationFactory->getMerger($this->sourceWorkspace, $this->targetWorkspace);
+
+    $args = [
+      '%source_label' => $this->sourceWorkspace->label(),
+      '%target_label' => $this->targetWorkspace->label(),
+    ];
+
+    // List the changes that can be merged into the target.
+    if ($source_rev_diff = $workspace_merger->getDifferringRevisionIdsOnSource()) {
+      $total_count = $workspace_merger->getNumberOfChangesOnSource();
+      $form['merge'] = [
+        '#theme' => 'item_list',
+        '#title' => $this->formatPlural($total_count, 'There is @count item that can be merged from %source_label to %target_label', 'There are @count items that can be merged from %source_label to %target_label', $args),
+        '#items' => [],
+        '#total_count' => $total_count,
+      ];
+      foreach ($source_rev_diff as $entity_type_id => $revision_difference) {
+        $form['merge']['#items'][$entity_type_id] = $this->entityTypeManager->getDefinition($entity_type_id)->getCountLabel(count($revision_difference));
+      }
+    }
+
+    // If there are no changes to merge, show an informational message.
+    if (!isset($form['merge'])) {
+      $form['description'] = [
+        '#markup' => $this->t('There are no changes that can be merged from %source_label to %target_label.', $args),
+      ];
+      $form['actions']['submit']['#disabled'] = TRUE;
+    }
+
+    return $form;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getQuestion() {
+    return $this->t('Would you like to merge the contents of the %source_label workspace into %target_label?', [
+      '%source_label' => $this->sourceWorkspace->label(),
+      '%target_label' => $this->targetWorkspace->label(),
+    ]);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getDescription() {
+    return $this->t('Merge workspace contents.');
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getCancelUrl() {
+    return Url::fromRoute('entity.workspace.collection', [], ['query' => $this->getDestinationArray()]);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function submitForm(array &$form, FormStateInterface $form_state) {
+    $this->workspaceOperationFactory->getMerger($this->sourceWorkspace, $this->targetWorkspace)->merge();
+    $this->messenger()->addMessage($this->t('The contents of the %source_label workspace have been merged into %target_label.', [
+      '%source_label' => $this->sourceWorkspace->label(),
+      '%target_label' => $this->targetWorkspace->label(),
+    ]));
+  }
+
+}

core/modules/workspaces/src/Form/WorkspacePublishForm.php

@@ -0,0 +1,159 @@
+<?php
+
+namespace Drupal\workspaces\Form;
+
+use Drupal\Core\DependencyInjection\ContainerInjectionInterface;
+use Drupal\Core\Entity\EntityTypeManagerInterface;
+use Drupal\Core\Form\ConfirmFormBase;
+use Drupal\Core\Form\FormStateInterface;
+use Drupal\Core\Form\WorkspaceSafeFormInterface;
+use Drupal\Core\Url;
+use Drupal\workspaces\WorkspaceAccessException;
+use Drupal\workspaces\WorkspaceInterface;
+use Drupal\workspaces\WorkspaceOperationFactory;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Provides the workspace publishing form.
+ */
+class WorkspacePublishForm extends ConfirmFormBase implements ContainerInjectionInterface, WorkspaceSafeFormInterface {
+
+  /**
+   * The workspace that will be published.
+   *
+   * @var \Drupal\workspaces\WorkspaceInterface
+   */
+  protected $workspace;
+
+  /**
+   * The workspace operation factory.
+   *
+   * @var \Drupal\workspaces\WorkspaceOperationFactory
+   */
+  protected $workspaceOperationFactory;
+
+  /**
+   * The entity type manager.
+   *
+   * @var \Drupal\Core\Entity\EntityTypeManagerInterface
+   */
+  protected $entityTypeManager;
+
+  /**
+   * Constructs a new WorkspacePublishForm.
+   *
+   * @param \Drupal\workspaces\WorkspaceOperationFactory $workspace_operation_factory
+   *   The workspace operation factory service.
+   * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
+   *   The entity type manager.
+   */
+  public function __construct(WorkspaceOperationFactory $workspace_operation_factory, EntityTypeManagerInterface $entity_type_manager) {
+    $this->workspaceOperationFactory = $workspace_operation_factory;
+    $this->entityTypeManager = $entity_type_manager;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container) {
+    return new static(
+      $container->get('workspaces.operation_factory'),
+      $container->get('entity_type.manager')
+    );
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getFormId() {
+    return 'workspace_publish_form';
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function buildForm(array $form, FormStateInterface $form_state, ?WorkspaceInterface $workspace = NULL) {
+    $this->workspace = $workspace;
+
+    $form = parent::buildForm($form, $form_state);
+
+    $workspace_publisher = $this->workspaceOperationFactory->getPublisher($this->workspace);
+
+    $args = [
+      '%source_label' => $this->workspace->label(),
+      '%target_label' => $workspace_publisher->getTargetLabel(),
+    ];
+    $form['#title'] = $this->t('Publish %source_label workspace', $args);
+
+    // List the changes that can be pushed.
+    if ($source_rev_diff = $workspace_publisher->getDifferringRevisionIdsOnSource()) {
+      $total_count = $workspace_publisher->getNumberOfChangesOnSource();
+      $form['description'] = [
+        '#theme' => 'item_list',
+        '#title' => $this->formatPlural($total_count, 'There is @count item that can be published from %source_label to %target_label', 'There are @count items that can be published from %source_label to %target_label', $args),
+        '#items' => [],
+        '#total_count' => $total_count,
+      ];
+      foreach ($source_rev_diff as $entity_type_id => $revision_difference) {
+        $form['description']['#items'][$entity_type_id] = $this->entityTypeManager->getDefinition($entity_type_id)->getCountLabel(count($revision_difference));
+      }
+
+      $form['actions']['submit']['#value'] = $this->formatPlural($total_count, 'Publish @count item to @target', 'Publish @count items to @target', ['@target' => $workspace_publisher->getTargetLabel()]);
+    }
+    else {
+      // If there are no changes to push or pull, show an informational message.
+      $form['help'] = [
+        '#markup' => $this->t('There are no changes that can be published from %source_label to %target_label.', $args),
+      ];
+
+      // Do not allow the 'Publish' operation if there's nothing to publish.
+      $form['actions']['submit']['#value'] = $this->t('Publish');
+      $form['actions']['submit']['#disabled'] = TRUE;
+    }
+
+    return $form;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getQuestion() {
+    return $this->t('Would you like to publish the contents of the %label workspace?', [
+      '%label' => $this->workspace->label(),
+    ]);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getDescription() {
+    return $this->t('Publish workspace contents.');
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getCancelUrl() {
+    return Url::fromRoute('entity.workspace.collection', [], ['query' => $this->getDestinationArray()]);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function submitForm(array &$form, FormStateInterface $form_state) {
+    $workspace = $this->workspace;
+
+    try {
+      $workspace->publish();
+      $this->messenger()->addMessage($this->t('Successful publication.'));
+    }
+    catch (WorkspaceAccessException $e) {
+      $this->messenger()->addMessage($e->getMessage(), 'error');
+    }
+    catch (\Exception $e) {
+      $this->messenger()->addMessage($this->t('Publication failed. All errors have been logged.'), 'error');
+      $this->getLogger('workspaces')->error($e->getMessage());
+    }
+  }
+
+}

core/modules/workspaces/src/Form/WorkspaceSwitcherForm.php

@@ -0,0 +1,156 @@
+<?php
+
+namespace Drupal\workspaces\Form;
+
+use Drupal\Core\Entity\EntityTypeManagerInterface;
+use Drupal\Core\Form\FormBase;
+use Drupal\Core\Form\FormStateInterface;
+use Drupal\Core\Form\WorkspaceSafeFormInterface;
+use Drupal\Core\Messenger\MessengerInterface;
+use Drupal\workspaces\WorkspaceAccessException;
+use Drupal\workspaces\WorkspaceManagerInterface;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Provides a form that activates a different workspace.
+ */
+class WorkspaceSwitcherForm extends FormBase implements WorkspaceSafeFormInterface {
+
+  /**
+   * The workspace manager.
+   *
+   * @var \Drupal\workspaces\WorkspaceManagerInterface
+   */
+  protected $workspaceManager;
+
+  /**
+   * The workspace entity storage handler.
+   *
+   * @var \Drupal\Core\Entity\EntityStorageInterface
+   */
+  protected $workspaceStorage;
+
+  /**
+   * The messenger service.
+   *
+   * @var \Drupal\Core\Messenger\MessengerInterface
+   */
+  protected $messenger;
+
+  /**
+   * Constructs a new WorkspaceSwitcherForm.
+   *
+   * @param \Drupal\workspaces\WorkspaceManagerInterface $workspace_manager
+   *   The workspace manager.
+   * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
+   *   The entity type manager.
+   * @param \Drupal\Core\Messenger\MessengerInterface $messenger
+   *   The messenger service.
+   */
+  public function __construct(WorkspaceManagerInterface $workspace_manager, EntityTypeManagerInterface $entity_type_manager, MessengerInterface $messenger) {
+    $this->workspaceManager = $workspace_manager;
+    $this->workspaceStorage = $entity_type_manager->getStorage('workspace');
+    $this->messenger = $messenger;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container) {
+    return new static(
+      $container->get('workspaces.manager'),
+      $container->get('entity_type.manager'),
+      $container->get('messenger')
+    );
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getFormId() {
+    return 'workspace_switcher_form';
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function buildForm(array $form, FormStateInterface $form_state) {
+    $workspaces = $this->workspaceStorage->loadMultiple();
+    $workspace_labels = [];
+    foreach ($workspaces as $workspace) {
+      $workspace_labels[$workspace->id()] = $workspace->label();
+    }
+
+    $active_workspace = $this->workspaceManager->getActiveWorkspace();
+    if ($active_workspace) {
+      unset($workspace_labels[$active_workspace->id()]);
+    }
+
+    $form['current'] = [
+      '#type' => 'item',
+      '#title' => $this->t('Current workspace'),
+      '#markup' => $active_workspace ? $active_workspace->label() : $this->t('None'),
+      '#wrapper_attributes' => [
+        'class' => ['container-inline'],
+      ],
+    ];
+
+    $form['workspace_id'] = [
+      '#type' => 'select',
+      '#title' => $this->t('Select workspace'),
+      '#required' => TRUE,
+      '#options' => $workspace_labels,
+      '#wrapper_attributes' => [
+        'class' => ['container-inline'],
+      ],
+      '#access' => !empty($workspace_labels),
+    ];
+
+    $form['actions']['#type'] = 'actions';
+    $form['actions']['submit'] = [
+      '#type' => 'submit',
+      '#value' => $this->t('Activate'),
+      '#button_type' => 'primary',
+      '#access' => !empty($workspace_labels),
+    ];
+
+    if ($active_workspace) {
+      $form['actions']['switch_to_live'] = [
+        '#type' => 'submit',
+        '#submit' => ['::submitSwitchToLive'],
+        '#value' => $this->t('Switch to Live'),
+        '#limit_validation_errors' => [],
+        '#button_type' => 'primary',
+      ];
+    }
+
+    return $form;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function submitForm(array &$form, FormStateInterface $form_state) {
+    $id = $form_state->getValue('workspace_id');
+
+    /** @var \Drupal\workspaces\WorkspaceInterface $workspace */
+    $workspace = $this->workspaceStorage->load($id);
+
+    try {
+      $this->workspaceManager->setActiveWorkspace($workspace);
+      $this->messenger->addMessage($this->t('%workspace_label is now the active workspace.', ['%workspace_label' => $workspace->label()]));
+    }
+    catch (WorkspaceAccessException $e) {
+      $this->messenger->addError($this->t('You do not have access to activate the %workspace_label workspace.', ['%workspace_label' => $workspace->label()]));
+    }
+  }
+
+  /**
+   * Submit handler for switching to the live version of the site.
+   */
+  public function submitSwitchToLive(array &$form, FormStateInterface $form_state) {
+    $this->workspaceManager->switchToLive();
+    $this->messenger->addMessage($this->t('You are now viewing the live version of the site.'));
+  }
+
+}

core/modules/workspaces/src/FormOperations.php

@@ -0,0 +1,108 @@
+<?php
+
+namespace Drupal\workspaces;
+
+use Drupal\Core\DependencyInjection\ContainerInjectionInterface;
+use Drupal\Core\Form\FormStateInterface;
+use Drupal\Core\Form\WorkspaceDynamicSafeFormInterface;
+use Drupal\Core\Form\WorkspaceSafeFormInterface;
+use Drupal\Core\Render\Element;
+use Drupal\Core\StringTranslation\TranslatableMarkup;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Defines a class for reacting to form operations.
+ *
+ * @internal
+ */
+class FormOperations implements ContainerInjectionInterface {
+
+  /**
+   * The workspace manager service.
+   *
+   * @var \Drupal\workspaces\WorkspaceManagerInterface
+   */
+  protected $workspaceManager;
+
+  /**
+   * Constructs a new FormOperations instance.
+   *
+   * @param \Drupal\workspaces\WorkspaceManagerInterface $workspace_manager
+   *   The workspace manager service.
+   */
+  public function __construct(WorkspaceManagerInterface $workspace_manager) {
+    $this->workspaceManager = $workspace_manager;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container) {
+    return new static(
+      $container->get('workspaces.manager')
+    );
+  }
+
+  /**
+   * Alters forms to disallow editing in non-default workspaces.
+   *
+   * @param array $form
+   *   An associative array containing the structure of the form.
+   * @param \Drupal\Core\Form\FormStateInterface $form_state
+   *   The current state of the form.
+   * @param string $form_id
+   *   The form ID.
+   *
+   * @see hook_form_alter()
+   */
+  public function formAlter(array &$form, FormStateInterface $form_state, $form_id) {
+    // No alterations are needed if we're not in a workspace context.
+    if (!$this->workspaceManager->hasActiveWorkspace()) {
+      return;
+    }
+
+    // Add a validation step for every form if we are in a workspace.
+    $this->addWorkspaceValidation($form);
+
+    // If a form has already been marked as safe or not to submit in a
+    // workspace, we don't have anything else to do.
+    if ($form_state->has('workspace_safe')) {
+      return;
+    }
+
+    $form_object = $form_state->getFormObject();
+    $workspace_safe = $form_object instanceof WorkspaceSafeFormInterface
+      || ($form_object instanceof WorkspaceDynamicSafeFormInterface && $form_object->isWorkspaceSafeForm($form, $form_state));
+
+    $form_state->set('workspace_safe', $workspace_safe);
+  }
+
+  /**
+   * Adds our validation handler recursively on each element of a form.
+   *
+   * @param array &$element
+   *   An associative array containing the structure of the form.
+   */
+  protected function addWorkspaceValidation(array &$element) {
+    // Recurse through all children and add our validation handler if needed.
+    foreach (Element::children($element) as $key) {
+      if (isset($element[$key]) && $element[$key]) {
+        $this->addWorkspaceValidation($element[$key]);
+      }
+    }
+
+    if (isset($element['#validate'])) {
+      $element['#validate'][] = [static::class, 'validateDefaultWorkspace'];
+    }
+  }
+
+  /**
+   * Validation handler which sets a validation error for all unsupported forms.
+   */
+  public static function validateDefaultWorkspace(array &$form, FormStateInterface $form_state) {
+    if ($form_state->get('workspace_safe') !== TRUE) {
+      $form_state->setError($form, new TranslatableMarkup('This form can only be submitted in the default workspace.'));
+    }
+  }
+
+}

core/modules/workspaces/src/Negotiator/QueryParameterWorkspaceNegotiator.php

@@ -0,0 +1,52 @@
+<?php
+
+namespace Drupal\workspaces\Negotiator;
+
+use Drupal\Component\Utility\Crypt;
+use Drupal\Core\Site\Settings;
+use Symfony\Component\HttpFoundation\Request;
+
+/**
+ * Defines the query parameter workspace negotiator.
+ */
+class QueryParameterWorkspaceNegotiator extends SessionWorkspaceNegotiator {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function applies(Request $request) {
+    return is_string($request->query->get('workspace'))
+      && is_string($request->query->get('token'))
+      && parent::applies($request);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getActiveWorkspaceId(Request $request): ?string {
+    $workspace_id = (string) $request->query->get('workspace');
+    $token = (string) $request->query->get('token');
+    $is_valid_token = hash_equals($this->getQueryToken($workspace_id), $token);
+
+    // This negotiator receives a workspace ID from user input, so a minimal
+    // validation is needed to ensure that we protect against fake input before
+    // the workspace manager fully validates the negotiated workspace ID.
+    // @see \Drupal\workspaces\WorkspaceManager::getActiveWorkspace()
+    return $is_valid_token ? $workspace_id : NULL;
+  }
+
+  /**
+   * Calculates a token based on a workspace ID.
+   *
+   * @param string $workspace_id
+   *   The workspace ID.
+   *
+   * @return string
+   *   An 8 char token based on the given workspace ID.
+   */
+  protected function getQueryToken(string $workspace_id): string {
+    // Return the first 8 characters.
+    return substr(Crypt::hmacBase64($workspace_id, Settings::getHashSalt()), 0, 8);
+  }
+
+}

core/modules/workspaces/src/Negotiator/SessionWorkspaceNegotiator.php

@@ -0,0 +1,64 @@
+<?php
+
+namespace Drupal\workspaces\Negotiator;
+
+use Drupal\Core\Entity\EntityTypeManagerInterface;
+use Drupal\Core\Session\AccountInterface;
+use Drupal\workspaces\WorkspaceInterface;
+use Symfony\Component\HttpFoundation\Request;
+use Symfony\Component\HttpFoundation\Session\Session;
+
+/**
+ * Defines the session workspace negotiator.
+ */
+class SessionWorkspaceNegotiator implements WorkspaceNegotiatorInterface, WorkspaceIdNegotiatorInterface {
+
+  public function __construct(
+    protected readonly AccountInterface $currentUser,
+    protected readonly Session $session,
+    protected readonly EntityTypeManagerInterface $entityTypeManager,
+  ) {}
+
+  /**
+   * {@inheritdoc}
+   */
+  public function applies(Request $request) {
+    // This negotiator only applies if the current user is authenticated.
+    return $this->currentUser->isAuthenticated();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getActiveWorkspaceId(Request $request): ?string {
+    return $this->session->get('active_workspace_id');
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getActiveWorkspace(Request $request) {
+    $workspace_id = $this->getActiveWorkspaceId($request);
+
+    if ($workspace_id && ($workspace = $this->entityTypeManager->getStorage('workspace')->load($workspace_id))) {
+      return $workspace;
+    }
+
+    return NULL;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function setActiveWorkspace(WorkspaceInterface $workspace) {
+    $this->session->set('active_workspace_id', $workspace->id());
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function unsetActiveWorkspace() {
+    $this->session->remove('active_workspace_id');
+  }
+
+}

core/modules/workspaces/src/Negotiator/WorkspaceIdNegotiatorInterface.php

@@ -0,0 +1,23 @@
+<?php
+
+namespace Drupal\workspaces\Negotiator;
+
+use Symfony\Component\HttpFoundation\Request;
+
+/**
+ * Interface for workspace negotiators that return only the negotiated ID.
+ */
+interface WorkspaceIdNegotiatorInterface {
+
+  /**
+   * Performs workspace negotiation.
+   *
+   * @param \Symfony\Component\HttpFoundation\Request $request
+   *   The HTTP request.
+   *
+   * @return string|null
+   *   A valid workspace ID if the negotiation was successful, NULL otherwise.
+   */
+  public function getActiveWorkspaceId(Request $request): ?string;
+
+}

core/modules/workspaces/src/Negotiator/WorkspaceNegotiatorInterface.php

@@ -0,0 +1,40 @@
+<?php
+
+namespace Drupal\workspaces\Negotiator;
+
+use Drupal\workspaces\WorkspaceInterface;
+use Symfony\Component\HttpFoundation\Request;
+
+/**
+ * Workspace negotiators provide a way to get the active workspace.
+ *
+ * \Drupal\workspaces\WorkspaceManager acts as the service collector for
+ * Workspace negotiators.
+ */
+interface WorkspaceNegotiatorInterface {
+
+  /**
+   * Checks whether the negotiator applies to the current request or not.
+   *
+   * @param \Symfony\Component\HttpFoundation\Request $request
+   *   The HTTP request.
+   *
+   * @return bool
+   *   TRUE if the negotiator applies for the current request, FALSE otherwise.
+   */
+  public function applies(Request $request);
+
+  /**
+   * Notifies the negotiator that the workspace ID returned has been accepted.
+   *
+   * @param \Drupal\workspaces\WorkspaceInterface $workspace
+   *   The negotiated workspace entity.
+   */
+  public function setActiveWorkspace(WorkspaceInterface $workspace);
+
+  /**
+   * Unsets the negotiated workspace.
+   */
+  public function unsetActiveWorkspace();
+
+}

core/modules/workspaces/src/Plugin/Block/WorkspaceSwitcherBlock.php

@@ -0,0 +1,99 @@
+<?php
+
+namespace Drupal\workspaces\Plugin\Block;
+
+use Drupal\Core\Access\AccessResult;
+use Drupal\Core\Access\AccessResultInterface;
+use Drupal\Core\Block\Attribute\Block;
+use Drupal\Core\Block\BlockBase;
+use Drupal\Core\Entity\EntityTypeManagerInterface;
+use Drupal\Core\Form\FormBuilderInterface;
+use Drupal\Core\Plugin\ContainerFactoryPluginInterface;
+use Drupal\Core\Session\AccountInterface;
+use Drupal\Core\StringTranslation\TranslatableMarkup;
+use Drupal\workspaces\Form\WorkspaceSwitcherForm;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Provides a 'Workspace switcher' block.
+ */
+#[Block(
+  id: "workspace_switcher",
+  admin_label: new TranslatableMarkup("Workspace switcher"),
+  category: new TranslatableMarkup("Workspace")
+)]
+class WorkspaceSwitcherBlock extends BlockBase implements ContainerFactoryPluginInterface {
+
+  /**
+   * The form builder.
+   *
+   * @var \Drupal\Core\Form\FormBuilderInterface
+   */
+  protected $formBuilder;
+
+  /**
+   * The entity type manager.
+   *
+   * @var \Drupal\Core\Entity\EntityTypeManagerInterface
+   */
+  protected $entityTypeManager;
+
+  /**
+   * Constructs a new WorkspaceSwitcherBlock instance.
+   *
+   * @param array $configuration
+   *   The plugin configuration.
+   * @param string $plugin_id
+   *   The plugin ID.
+   * @param mixed $plugin_definition
+   *   The plugin definition.
+   * @param \Drupal\Core\Form\FormBuilderInterface $form_builder
+   *   The form builder.
+   * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
+   *   The entity type manager.
+   */
+  public function __construct(array $configuration, $plugin_id, $plugin_definition, FormBuilderInterface $form_builder, EntityTypeManagerInterface $entity_type_manager) {
+    parent::__construct($configuration, $plugin_id, $plugin_definition);
+    $this->formBuilder = $form_builder;
+    $this->entityTypeManager = $entity_type_manager;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition) {
+    return new static(
+      $configuration,
+      $plugin_id,
+      $plugin_definition,
+      $container->get('form_builder'),
+      $container->get('entity_type.manager')
+    );
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function build() {
+    $build = [
+      'form' => $this->formBuilder->getForm(WorkspaceSwitcherForm::class),
+      '#cache' => [
+        'contexts' => $this->entityTypeManager->getDefinition('workspace')->getListCacheContexts(),
+        'tags' => $this->entityTypeManager->getDefinition('workspace')->getListCacheTags(),
+      ],
+    ];
+    return $build;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function blockAccess(AccountInterface $account): AccessResultInterface {
+    return AccessResult::allowedIfHasPermissions($account, [
+      'view own workspace',
+      'view any workspace',
+      'administer workspaces',
+    ], 'OR');
+  }
+
+}

core/modules/workspaces/src/Plugin/EntityReferenceSelection/WorkspaceSelection.php

@@ -0,0 +1,103 @@
+<?php
+
+namespace Drupal\workspaces\Plugin\EntityReferenceSelection;
+
+use Drupal\Component\Utility\Html;
+use Drupal\Core\Entity\Attribute\EntityReferenceSelection;
+use Drupal\Core\Entity\Plugin\EntityReferenceSelection\DefaultSelection;
+use Drupal\Core\Form\FormStateInterface;
+use Drupal\Core\StringTranslation\TranslatableMarkup;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Provides specific access control for the workspace entity type.
+ */
+#[EntityReferenceSelection(
+  id: "default:workspace",
+  label: new TranslatableMarkup("Workspace selection"),
+  entity_types: ["workspace"],
+  group: "default",
+  weight: 1
+)]
+class WorkspaceSelection extends DefaultSelection {
+
+  /**
+   * The workspace repository service.
+   *
+   * @var \Drupal\workspaces\WorkspaceRepositoryInterface
+   */
+  protected $workspaceRepository;
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition) {
+    $instance = parent::create($container, $configuration, $plugin_id, $plugin_definition);
+    $instance->workspaceRepository = $container->get('workspaces.repository');
+    return $instance;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function defaultConfiguration() {
+    return [
+      'sort' => [
+        'field' => 'label',
+        'direction' => 'asc',
+      ],
+    ] + parent::defaultConfiguration();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function buildConfigurationForm(array $form, FormStateInterface $form_state) {
+    $form = parent::buildConfigurationForm($form, $form_state);
+
+    // Sorting is not possible for workspaces because we always sort them by
+    // depth and label.
+    $form['sort']['#access'] = FALSE;
+
+    return $form;
+
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getReferenceableEntities($match = NULL, $match_operator = 'CONTAINS', $limit = 0) {
+    // Get all the workspace entities and sort them in tree order.
+    $storage = $this->entityTypeManager->getStorage('workspace');
+    $workspace_tree = $this->workspaceRepository->loadTree();
+    $entities = array_replace($workspace_tree, $storage->loadMultiple());
+
+    // If we need to restrict the list of workspaces by searching only a part of
+    // their label ($match) or by a number of results ($limit), the workspace
+    // tree would be mangled because it wouldn't contain all the tree items.
+    if ($match || $limit) {
+      $options = parent::getReferenceableEntities($match, $match_operator, $limit);
+    }
+    else {
+      $options = [];
+      foreach ($entities as $entity) {
+        $options[$entity->bundle()][$entity->id()] = str_repeat('-', $workspace_tree[$entity->id()]['depth']) . Html::escape($this->entityRepository->getTranslationFromContext($entity)->label());
+      }
+    }
+
+    $restricted_access_entities = [];
+    foreach ($options as $bundle => $bundle_options) {
+      foreach (array_keys($bundle_options) as $id) {
+        // If a user can not view a workspace, we need to prevent them from
+        // referencing that workspace as well as its descendants.
+        if (in_array($id, $restricted_access_entities) || !$entities[$id]->access('view', $this->currentUser)) {
+          $restricted_access_entities += $workspace_tree[$id]['descendants'];
+          unset($options[$bundle][$id]);
+        }
+      }
+    }
+
+    return $options;
+  }
+
+}

core/modules/workspaces/src/Plugin/Validation/Constraint/DeletedWorkspaceConstraint.php

@@ -0,0 +1,25 @@
+<?php
+
+namespace Drupal\workspaces\Plugin\Validation\Constraint;
+
+use Drupal\Core\StringTranslation\TranslatableMarkup;
+use Drupal\Core\Validation\Attribute\Constraint;
+use Symfony\Component\Validator\Constraint as SymfonyConstraint;
+
+/**
+ * Deleted workspace constraint.
+ */
+#[Constraint(
+  id: 'DeletedWorkspace',
+  label: new TranslatableMarkup('Deleted workspace', [], ['context' => 'Validation'])
+)]
+class DeletedWorkspaceConstraint extends SymfonyConstraint {
+
+  /**
+   * The default violation message.
+   *
+   * @var string
+   */
+  public $message = 'A workspace with this ID has been deleted but data still exists for it.';
+
+}

core/modules/workspaces/src/Plugin/Validation/Constraint/DeletedWorkspaceConstraintValidator.php

@@ -0,0 +1,58 @@
+<?php
+
+namespace Drupal\workspaces\Plugin\Validation\Constraint;
+
+use Drupal\Core\DependencyInjection\ContainerInjectionInterface;
+use Drupal\Core\State\StateInterface;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+use Symfony\Component\Validator\Constraint;
+use Symfony\Component\Validator\ConstraintValidator;
+
+/**
+ * Checks if data still exists for a deleted workspace ID.
+ */
+class DeletedWorkspaceConstraintValidator extends ConstraintValidator implements ContainerInjectionInterface {
+
+  /**
+   * The state service.
+   *
+   * @var \Drupal\Core\State\StateInterface
+   */
+  protected $state;
+
+  /**
+   * Creates a new DeletedWorkspaceConstraintValidator instance.
+   *
+   * @param \Drupal\Core\State\StateInterface $state
+   *   The state service.
+   */
+  public function __construct(StateInterface $state) {
+    $this->state = $state;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container) {
+    return new static(
+      $container->get('state')
+    );
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function validate($value, Constraint $constraint) {
+    /** @var \Drupal\Core\Field\FieldItemListInterface $value */
+    // This constraint applies only to newly created workspace entities.
+    if (!isset($value) || !$value->getEntity()->isNew()) {
+      return;
+    }
+
+    $deleted_workspace_ids = $this->state->get('workspace.deleted', []);
+    if (isset($deleted_workspace_ids[$value->getEntity()->id()])) {
+      $this->context->addViolation($constraint->message);
+    }
+  }
+
+}

core/modules/workspaces/src/Plugin/Validation/Constraint/EntityReferenceSupportedNewEntitiesConstraint.php

@@ -0,0 +1,25 @@
+<?php
+
+namespace Drupal\workspaces\Plugin\Validation\Constraint;
+
+use Drupal\Core\StringTranslation\TranslatableMarkup;
+use Drupal\Core\Validation\Attribute\Constraint;
+use Symfony\Component\Validator\Constraint as SymfonyConstraint;
+
+/**
+ * The entity reference supported new entities constraint.
+ */
+#[Constraint(
+  id: 'EntityReferenceSupportedNewEntities',
+  label: new TranslatableMarkup('Entity Reference Supported New Entities', [], ['context' => 'Validation'])
+)]
+class EntityReferenceSupportedNewEntitiesConstraint extends SymfonyConstraint {
+
+  /**
+   * The default violation message.
+   *
+   * @var string
+   */
+  public $message = '%collection_label can only be created in the default workspace.';
+
+}

core/modules/workspaces/src/Plugin/Validation/Constraint/EntityReferenceSupportedNewEntitiesConstraintValidator.php

@@ -0,0 +1,76 @@
+<?php
+
+namespace Drupal\workspaces\Plugin\Validation\Constraint;
+
+use Drupal\Core\DependencyInjection\ContainerInjectionInterface;
+use Drupal\Core\Entity\EntityTypeManagerInterface;
+use Drupal\workspaces\WorkspaceInformationInterface;
+use Drupal\workspaces\WorkspaceManagerInterface;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+use Symfony\Component\Validator\Constraint;
+use Symfony\Component\Validator\ConstraintValidator;
+
+/**
+ * Checks if new entities created for entity reference fields are supported.
+ */
+class EntityReferenceSupportedNewEntitiesConstraintValidator extends ConstraintValidator implements ContainerInjectionInterface {
+
+  /**
+   * The workspace manager.
+   *
+   * @var \Drupal\workspaces\WorkspaceManagerInterface
+   */
+  protected $workspaceManager;
+
+  /**
+   * The entity type manager.
+   *
+   * @var \Drupal\Core\Entity\EntityTypeManagerInterface
+   */
+  protected $entityTypeManager;
+
+  /**
+   * The workspace information service.
+   *
+   * @var \Drupal\workspaces\WorkspaceInformationInterface
+   */
+  protected $workspaceInfo;
+
+  /**
+   * Creates a new EntityReferenceSupportedNewEntitiesConstraintValidator instance.
+   */
+  public function __construct(WorkspaceManagerInterface $workspaceManager, EntityTypeManagerInterface $entityTypeManager, WorkspaceInformationInterface $workspace_information) {
+    $this->workspaceManager = $workspaceManager;
+    $this->entityTypeManager = $entityTypeManager;
+    $this->workspaceInfo = $workspace_information;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container) {
+    return new static(
+      $container->get('workspaces.manager'),
+      $container->get('entity_type.manager'),
+      $container->get('workspaces.information')
+    );
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function validate($value, Constraint $constraint) {
+    // The validator should run only if we are in a active workspace context.
+    if (!$this->workspaceManager->hasActiveWorkspace()) {
+      return;
+    }
+
+    $target_entity_type_id = $value->getFieldDefinition()->getFieldStorageDefinition()->getSetting('target_type');
+    $target_entity_type = $this->entityTypeManager->getDefinition($target_entity_type_id);
+
+    if ($value->hasNewEntity() && !$this->workspaceInfo->isEntityTypeSupported($target_entity_type)) {
+      $this->context->addViolation($constraint->message, ['%collection_label' => $target_entity_type->getCollectionLabel()]);
+    }
+  }
+
+}

core/modules/workspaces/src/Plugin/Validation/Constraint/EntityWorkspaceConflictConstraint.php

@@ -0,0 +1,26 @@
+<?php
+
+namespace Drupal\workspaces\Plugin\Validation\Constraint;
+
+use Drupal\Core\StringTranslation\TranslatableMarkup;
+use Drupal\Core\Validation\Attribute\Constraint;
+use Symfony\Component\Validator\Constraint as SymfonyConstraint;
+
+/**
+ * Validation constraint for an entity being edited in multiple workspaces.
+ */
+#[Constraint(
+  id: 'EntityWorkspaceConflict',
+  label: new TranslatableMarkup('Entity workspace conflict', [], ['context' => 'Validation']),
+  type: ['entity']
+)]
+class EntityWorkspaceConflictConstraint extends SymfonyConstraint {
+
+  /**
+   * The default violation message.
+   *
+   * @var string
+   */
+  public $message = 'The content is being edited in the @label workspace. As a result, your changes cannot be saved.';
+
+}

core/modules/workspaces/src/Plugin/Validation/Constraint/EntityWorkspaceConflictConstraintValidator.php

@@ -0,0 +1,61 @@
+<?php
+
+namespace Drupal\workspaces\Plugin\Validation\Constraint;
+
+use Drupal\Core\DependencyInjection\ContainerInjectionInterface;
+use Drupal\Core\Entity\EntityTypeManagerInterface;
+use Drupal\workspaces\WorkspaceAssociationInterface;
+use Drupal\workspaces\WorkspaceManagerInterface;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+use Symfony\Component\Validator\Constraint;
+use Symfony\Component\Validator\ConstraintValidator;
+
+/**
+ * Validates the EntityWorkspaceConflict constraint.
+ *
+ * @internal
+ */
+class EntityWorkspaceConflictConstraintValidator extends ConstraintValidator implements ContainerInjectionInterface {
+
+  public function __construct(
+    protected readonly EntityTypeManagerInterface $entityTypeManager,
+    protected readonly WorkspaceManagerInterface $workspaceManager,
+    protected readonly WorkspaceAssociationInterface $workspaceAssociation,
+  ) {}
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container) {
+    return new static(
+      $container->get('entity_type.manager'),
+      $container->get('workspaces.manager'),
+      $container->get('workspaces.association'),
+    );
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function validate($entity, Constraint $constraint) {
+    /** @var \Drupal\Core\Entity\EntityInterface $entity */
+    if (isset($entity) && !$entity->isNew()) {
+      $active_workspace = $this->workspaceManager->getActiveWorkspace();
+
+      // If the entity is tracked in a workspace, it can only be edited in
+      // that workspace or one of its descendants.
+      if ($tracking_workspace_ids = $this->workspaceAssociation->getEntityTrackingWorkspaceIds($entity, TRUE)) {
+        if (!$active_workspace || !in_array($active_workspace->id(), $tracking_workspace_ids, TRUE)) {
+          $first_tracking_workspace_id = reset($tracking_workspace_ids);
+          $workspace = $this->entityTypeManager->getStorage('workspace')
+            ->load($first_tracking_workspace_id);
+
+          $this->context->buildViolation($constraint->message)
+            ->setParameter('@label', $workspace->label())
+            ->addViolation();
+        }
+      }
+    }
+  }
+
+}

core/modules/workspaces/src/ViewsQueryAlter.php

@@ -0,0 +1,462 @@
+<?php
+
+namespace Drupal\workspaces;
+
+use Drupal\Core\DependencyInjection\ContainerInjectionInterface;
+use Drupal\Core\Entity\EntityFieldManagerInterface;
+use Drupal\Core\Entity\EntityTypeInterface;
+use Drupal\Core\Entity\EntityTypeManagerInterface;
+use Drupal\Core\Language\LanguageManagerInterface;
+use Drupal\views\Plugin\views\query\QueryPluginBase;
+use Drupal\views\Plugin\views\query\Sql;
+use Drupal\views\Plugin\ViewsHandlerManager;
+use Drupal\views\ViewExecutable;
+use Drupal\views\ViewsData;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Defines a class for altering views queries.
+ *
+ * @internal
+ */
+class ViewsQueryAlter implements ContainerInjectionInterface {
+
+  /**
+   * The entity type manager service.
+   *
+   * @var \Drupal\Core\Entity\EntityTypeManagerInterface
+   */
+  protected $entityTypeManager;
+
+  /**
+   * The entity field manager.
+   *
+   * @var \Drupal\Core\Entity\EntityFieldManagerInterface
+   */
+  protected $entityFieldManager;
+
+  /**
+   * The workspace manager service.
+   *
+   * @var \Drupal\workspaces\WorkspaceManagerInterface
+   */
+  protected $workspaceManager;
+
+  /**
+   * The views data.
+   *
+   * @var \Drupal\views\ViewsData
+   */
+  protected $viewsData;
+
+  /**
+   * A plugin manager which handles instances of views join plugins.
+   *
+   * @var \Drupal\views\Plugin\ViewsHandlerManager
+   */
+  protected $viewsJoinPluginManager;
+
+  /**
+   * The language manager.
+   *
+   * @var \Drupal\Core\Language\LanguageManagerInterface
+   */
+  protected $languageManager;
+
+  /**
+   * The workspace information service.
+   *
+   * @var \Drupal\workspaces\WorkspaceInformationInterface
+   */
+  protected WorkspaceInformationInterface $workspaceInfo;
+
+  /**
+   * An array of tables adjusted for workspace_association join.
+   *
+   * @var \WeakMap
+   */
+  protected \WeakMap $adjustedTables;
+
+  /**
+   * Constructs a new ViewsQueryAlter instance.
+   *
+   * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
+   *   The entity type manager service.
+   * @param \Drupal\Core\Entity\EntityFieldManagerInterface $entity_field_manager
+   *   The entity field manager.
+   * @param \Drupal\workspaces\WorkspaceManagerInterface $workspace_manager
+   *   The workspace manager service.
+   * @param \Drupal\views\ViewsData $views_data
+   *   The views data.
+   * @param \Drupal\views\Plugin\ViewsHandlerManager $views_join_plugin_manager
+   *   The views join plugin manager.
+   * @param \Drupal\Core\Language\LanguageManagerInterface $language_manager
+   *   The language manager.
+   * @param \Drupal\workspaces\WorkspaceInformationInterface $workspace_information
+   *   The workspace information service.
+   */
+  public function __construct(EntityTypeManagerInterface $entity_type_manager, EntityFieldManagerInterface $entity_field_manager, WorkspaceManagerInterface $workspace_manager, ViewsData $views_data, ViewsHandlerManager $views_join_plugin_manager, LanguageManagerInterface $language_manager, WorkspaceInformationInterface $workspace_information) {
+    $this->entityTypeManager = $entity_type_manager;
+    $this->entityFieldManager = $entity_field_manager;
+    $this->workspaceManager = $workspace_manager;
+    $this->viewsData = $views_data;
+    $this->viewsJoinPluginManager = $views_join_plugin_manager;
+    $this->languageManager = $language_manager;
+    $this->workspaceInfo = $workspace_information;
+    $this->adjustedTables = new \WeakMap();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container) {
+    return new static(
+      $container->get('entity_type.manager'),
+      $container->get('entity_field.manager'),
+      $container->get('workspaces.manager'),
+      $container->get('views.views_data'),
+      $container->get('plugin.manager.views.join'),
+      $container->get('language_manager'),
+      $container->get('workspaces.information')
+    );
+  }
+
+  /**
+   * Implements a hook bridge for hook_views_query_alter().
+   *
+   * @see hook_views_query_alter()
+   */
+  public function alterQuery(ViewExecutable $view, QueryPluginBase $query) {
+    // Don't alter any views queries if we're not in a workspace context.
+    if (!$this->workspaceManager->hasActiveWorkspace()) {
+      return;
+    }
+
+    // Don't alter any non-sql views queries.
+    if (!$query instanceof Sql) {
+      return;
+    }
+
+    // Find out what entity types are represented in this query.
+    $entity_type_ids = [];
+    foreach ($query->relationships as $info) {
+      $table_data = $this->viewsData->get($info['base']);
+      if (empty($table_data['table']['entity type'])) {
+        continue;
+      }
+      $entity_type_id = $table_data['table']['entity type'];
+      // This construct ensures each entity type exists only once.
+      $entity_type_ids[$entity_type_id] = $entity_type_id;
+    }
+
+    $entity_type_definitions = $this->entityTypeManager->getDefinitions();
+    foreach ($entity_type_ids as $entity_type_id) {
+      if ($this->workspaceInfo->isEntityTypeSupported($entity_type_definitions[$entity_type_id])) {
+        $this->alterQueryForEntityType($query, $entity_type_definitions[$entity_type_id]);
+      }
+    }
+  }
+
+  /**
+   * Alters the entity type tables for a Views query.
+   *
+   * This should only be called after determining that this entity type is
+   * involved in the query, and that a non-default workspace is in use.
+   *
+   * @param \Drupal\views\Plugin\views\query\Sql $query
+   *   The query plugin object for the query.
+   * @param \Drupal\Core\Entity\EntityTypeInterface $entity_type
+   *   The entity type definition.
+   */
+  protected function alterQueryForEntityType(Sql $query, EntityTypeInterface $entity_type) {
+    /** @var \Drupal\Core\Entity\Sql\DefaultTableMapping $table_mapping */
+    $table_mapping = $this->entityTypeManager->getStorage($entity_type->id())->getTableMapping();
+    $field_storage_definitions = $this->entityFieldManager->getFieldStorageDefinitions($entity_type->id());
+    $dedicated_field_storage_definitions = array_filter($field_storage_definitions, function ($definition) use ($table_mapping) {
+      return $table_mapping->requiresDedicatedTableStorage($definition);
+    });
+    $dedicated_field_data_tables = array_map(function ($definition) use ($table_mapping) {
+      return $table_mapping->getDedicatedDataTableName($definition);
+    }, $dedicated_field_storage_definitions);
+
+    $move_workspace_tables = [];
+    $table_queue =& $query->getTableQueue();
+    foreach ($table_queue as $alias => &$table_info) {
+      // If we reach the workspace_association array item before any candidates,
+      // then we do not need to move it.
+      if ($table_info['table'] == 'workspace_association') {
+        break;
+      }
+
+      // Any dedicated field table is a candidate.
+      if ($field_name = array_search($table_info['table'], $dedicated_field_data_tables, TRUE)) {
+        $relationship = $table_info['relationship'];
+
+        // There can be reverse relationships used. If so, Workspaces can't do
+        // anything with them. Detect this and skip.
+        if ($table_info['join']->field != 'entity_id') {
+          continue;
+        }
+
+        // Get the dedicated revision table name.
+        $new_table_name = $table_mapping->getDedicatedRevisionTableName($field_storage_definitions[$field_name]);
+
+        // Now add the workspace_association table.
+        $workspace_association_table = $this->ensureWorkspaceAssociationTable($entity_type->id(), $query, $relationship);
+
+        // Update the join to use our COALESCE.
+        $revision_field = $entity_type->getKey('revision');
+        $table_info['join']->leftFormula = "COALESCE($workspace_association_table.target_entity_revision_id, $relationship.$revision_field)";
+
+        // Update the join and the table info to our new table name, and to join
+        // on the revision key.
+        $table_info['table'] = $new_table_name;
+        $table_info['join']->table = $new_table_name;
+        $table_info['join']->field = 'revision_id';
+
+        // Finally, if we added the workspace_association table we have to move
+        // it in the table queue so that it comes before this field.
+        if (empty($move_workspace_tables[$workspace_association_table])) {
+          $move_workspace_tables[$workspace_association_table] = $alias;
+        }
+      }
+    }
+
+    // JOINs must be in order. i.e, any tables you mention in the ON clause of a
+    // JOIN must appear prior to that JOIN. Since we're modifying a JOIN in
+    // place, and adding a new table, we must ensure that the new table appears
+    // prior to this one. So we recorded at what index we saw that table, and
+    // then use array_splice() to move the workspace_association table join to
+    // the correct position.
+    foreach ($move_workspace_tables as $workspace_association_table => $alias) {
+      $this->moveEntityTable($query, $workspace_association_table, $alias);
+    }
+
+    $base_entity_table = $entity_type->isTranslatable() ? $entity_type->getDataTable() : $entity_type->getBaseTable();
+
+    $base_fields = array_diff($table_mapping->getFieldNames($entity_type->getBaseTable()), [$entity_type->getKey('langcode')]);
+    $revisionable_fields = array_diff($table_mapping->getFieldNames($entity_type->getRevisionDataTable()), $base_fields);
+
+    // Go through and look to see if we have to modify fields and filters.
+    foreach ($query->fields as &$field_info) {
+      // Some fields don't actually have tables, meaning they're formulae and
+      // whatnot. At this time we are going to ignore those.
+      if (empty($field_info['table'])) {
+        continue;
+      }
+
+      // Dereference the alias into the actual table.
+      $table = $table_queue[$field_info['table']]['table'];
+      if ($table == $base_entity_table && in_array($field_info['field'], $revisionable_fields)) {
+        $relationship = $table_queue[$field_info['table']]['alias'];
+        $alias = $this->ensureRevisionTable($entity_type, $query, $relationship);
+        if ($alias) {
+          // Change the base table to use the revision table instead.
+          $field_info['table'] = $alias;
+        }
+      }
+    }
+
+    $relationships = [];
+    // Build a list of all relationships that might be for our table.
+    foreach ($query->relationships as $relationship => $info) {
+      if ($info['base'] == $base_entity_table) {
+        $relationships[] = $relationship;
+      }
+    }
+
+    // Now we have to go through our where clauses and modify any of our fields.
+    foreach ($query->where as &$clauses) {
+      foreach ($clauses['conditions'] as &$where_info) {
+        // Build a matrix of our possible relationships against fields we need
+        // to switch.
+        foreach ($relationships as $relationship) {
+          foreach ($revisionable_fields as $field) {
+            if (is_string($where_info['field']) && $where_info['field'] == "$relationship.$field") {
+              $alias = $this->ensureRevisionTable($entity_type, $query, $relationship);
+              if ($alias) {
+                // Change the base table to use the revision table instead.
+                $where_info['field'] = "$alias.$field";
+              }
+            }
+          }
+        }
+      }
+    }
+
+    // @todo Handle $query->orderby, $query->groupby, $query->having and
+    //   $query->count_field in https://www.drupal.org/node/2968165.
+  }
+
+  /**
+   * Adds the 'workspace_association' table to a views query.
+   *
+   * @param string $entity_type_id
+   *   The ID of the entity type to join.
+   * @param \Drupal\views\Plugin\views\query\Sql $query
+   *   The query plugin object for the query.
+   * @param string $relationship
+   *   The primary table alias this table is related to.
+   *
+   * @return string
+   *   The alias of the 'workspace_association' table.
+   */
+  protected function ensureWorkspaceAssociationTable($entity_type_id, Sql $query, $relationship) {
+    if (isset($query->tables[$relationship]['workspace_association'])) {
+      return $query->tables[$relationship]['workspace_association']['alias'];
+    }
+
+    $table_data = $this->viewsData->get($query->relationships[$relationship]['base']);
+
+    // Construct the join.
+    $definition = [
+      'table' => 'workspace_association',
+      'field' => 'target_entity_id',
+      'left_table' => $relationship,
+      'left_field' => $table_data['table']['base']['field'],
+      'extra' => [
+        [
+          'field' => 'target_entity_type_id',
+          'value' => $entity_type_id,
+        ],
+        [
+          'field' => 'workspace',
+          'value' => $this->workspaceManager->getActiveWorkspace()->id(),
+        ],
+      ],
+      'type' => 'LEFT',
+    ];
+
+    $join = $this->viewsJoinPluginManager->createInstance('standard', $definition);
+    $join->adjusted = TRUE;
+
+    return $query->queueTable('workspace_association', $relationship, $join);
+  }
+
+  /**
+   * Adds the revision table of an entity type to a query object.
+   *
+   * @param \Drupal\Core\Entity\EntityTypeInterface $entity_type
+   *   The entity type definition.
+   * @param \Drupal\views\Plugin\views\query\Sql $query
+   *   The query plugin object for the query.
+   * @param string $relationship
+   *   The name of the relationship.
+   *
+   * @return string
+   *   The alias of the relationship.
+   */
+  protected function ensureRevisionTable(EntityTypeInterface $entity_type, Sql $query, $relationship) {
+    // Get the alias for the 'workspace_association' table we chain off of in
+    // the COALESCE.
+    $workspace_association_table = $this->ensureWorkspaceAssociationTable($entity_type->id(), $query, $relationship);
+
+    // Get the name of the revision table and revision key.
+    $base_revision_table = $entity_type->isTranslatable() ? $entity_type->getRevisionDataTable() : $entity_type->getRevisionTable();
+    $revision_field = $entity_type->getKey('revision');
+
+    // If the table was already added and has a join against the same field on
+    // the revision table, reuse that rather than adding a new join.
+    if (isset($query->tables[$relationship][$base_revision_table])) {
+      $table_queue =& $query->getTableQueue();
+      $alias = $query->tables[$relationship][$base_revision_table]['alias'];
+      if (isset($table_queue[$alias]['join']->field) && $table_queue[$alias]['join']->field == $revision_field) {
+        // If this table previously existed, but was not added by us, we need
+        // to modify the join and make sure that 'workspace_association' comes
+        // first.
+        if (!$this->adjustedTables->offsetExists($table_queue[$alias]['join'])) {
+          $table_queue[$alias]['join'] = $this->getRevisionTableJoin($relationship, $base_revision_table, $revision_field, $workspace_association_table, $entity_type);
+          // We also have to ensure that our 'workspace_association' comes before
+          // this.
+          $this->moveEntityTable($query, $workspace_association_table, $alias);
+        }
+
+        return $alias;
+      }
+    }
+
+    // Construct a new join.
+    $join = $this->getRevisionTableJoin($relationship, $base_revision_table, $revision_field, $workspace_association_table, $entity_type);
+    return $query->queueTable($base_revision_table, $relationship, $join);
+  }
+
+  /**
+   * Fetches a join for a revision table using the workspace_association table.
+   *
+   * @param string $relationship
+   *   The relationship to use in the view.
+   * @param string $table
+   *   The table name.
+   * @param string $field
+   *   The field to join on.
+   * @param string $workspace_association_table
+   *   The alias of the 'workspace_association' table joined to the main entity
+   *   table.
+   * @param \Drupal\Core\Entity\EntityTypeInterface $entity_type
+   *   The entity type that is being queried.
+   *
+   * @return \Drupal\views\Plugin\views\join\JoinPluginInterface
+   *   An adjusted views join object to add to the query.
+   *
+   * @throws \Drupal\Component\Plugin\Exception\PluginException
+   */
+  protected function getRevisionTableJoin($relationship, $table, $field, $workspace_association_table, EntityTypeInterface $entity_type) {
+    $definition = [
+      'table' => $table,
+      'field' => $field,
+      'left_table' => $relationship,
+      'left_formula' => "COALESCE($workspace_association_table.target_entity_revision_id, $relationship.$field)",
+    ];
+
+    if ($entity_type->isTranslatable() && $this->languageManager->isMultilingual()) {
+      $langcode_field = $entity_type->getKey('langcode');
+      $definition['extra'] = [
+        ['field' => $langcode_field, 'left_field' => $langcode_field],
+      ];
+    }
+
+    /** @var \Drupal\views\Plugin\views\join\JoinPluginInterface $join */
+    $join = $this->viewsJoinPluginManager->createInstance('standard', $definition);
+    $join->adjusted = TRUE;
+    $this->adjustedTables[$join] = TRUE;
+
+    return $join;
+  }
+
+  /**
+   * Moves a 'workspace_association' table to appear before the given alias.
+   *
+   * Because Workspace chains possibly pre-existing tables onto the
+   * 'workspace_association' table, we have to ensure that the
+   * 'workspace_association' table appears in the query before the alias it's
+   * chained on or the SQL is invalid.
+   *
+   * @param \Drupal\views\Plugin\views\query\Sql $query
+   *   The SQL query object.
+   * @param string $workspace_association_table
+   *   The alias of the 'workspace_association' table.
+   * @param string $alias
+   *   The alias of the table it needs to appear before.
+   */
+  protected function moveEntityTable(Sql $query, $workspace_association_table, $alias) {
+    $table_queue =& $query->getTableQueue();
+    $keys = array_keys($table_queue);
+    $current_index = array_search($workspace_association_table, $keys);
+    $index = array_search($alias, $keys);
+
+    // If it's already before our table, we don't need to move it, as we could
+    // accidentally move it forward.
+    if ($current_index < $index) {
+      return;
+    }
+    $splice = [$workspace_association_table => $table_queue[$workspace_association_table]];
+    unset($table_queue[$workspace_association_table]);
+
+    // Now move the item to the proper location in the array. Don't use
+    // array_splice() because that breaks indices.
+    $table_queue = array_slice($table_queue, 0, $index, TRUE) +
+      $splice +
+      array_slice($table_queue, $index, NULL, TRUE);
+  }
+
+}

core/modules/workspaces/src/WorkspaceAccessControlHandler.php

@@ -0,0 +1,69 @@
+<?php
+
+namespace Drupal\workspaces;
+
+use Drupal\Core\Access\AccessResult;
+use Drupal\Core\Entity\EntityAccessControlHandler;
+use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Session\AccountInterface;
+
+/**
+ * Defines the access control handler for the workspace entity type.
+ *
+ * @see \Drupal\workspaces\Entity\Workspace
+ */
+class WorkspaceAccessControlHandler extends EntityAccessControlHandler {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function checkAccess(EntityInterface $entity, $operation, AccountInterface $account) {
+    /** @var \Drupal\workspaces\WorkspaceInterface $entity */
+    if ($operation === 'publish' && $entity->hasParent()) {
+      $message = $this->t('Only top-level workspaces can be published.');
+      return AccessResult::forbidden((string) $message)->addCacheableDependency($entity);
+    }
+
+    if ($account->hasPermission('administer workspaces')) {
+      return AccessResult::allowed()->cachePerPermissions();
+    }
+
+    // @todo Consider adding explicit "publish any|own workspace" permissions in
+    //   https://www.drupal.org/project/drupal/issues/3084260.
+    switch ($operation) {
+      case 'update':
+      case 'publish':
+        $permission_operation = 'edit';
+        break;
+
+      case 'view all revisions':
+        $permission_operation = 'view';
+        break;
+
+      default:
+        $permission_operation = $operation;
+        break;
+    }
+
+    // Check if the user has permission to access all workspaces.
+    $access_result = AccessResult::allowedIfHasPermission($account, $permission_operation . ' any workspace');
+
+    // Check if it's their own workspace, and they have permission to access
+    // their own workspace.
+    if ($access_result->isNeutral() && $account->isAuthenticated() && $account->id() === $entity->getOwnerId()) {
+      $access_result = AccessResult::allowedIfHasPermission($account, $permission_operation . ' own workspace')
+        ->cachePerUser()
+        ->addCacheableDependency($entity);
+    }
+
+    return $access_result;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function checkCreateAccess(AccountInterface $account, array $context, $entity_bundle = NULL) {
+    return AccessResult::allowedIfHasPermissions($account, ['administer workspaces', 'create workspace'], 'OR');
+  }
+
+}

core/modules/workspaces/src/WorkspaceAccessException.php

@@ -0,0 +1,12 @@
+<?php
+
+namespace Drupal\workspaces;
+
+use Drupal\Core\Access\AccessException;
+
+/**
+ * Exception thrown when trying to switch to an inaccessible workspace.
+ */
+class WorkspaceAccessException extends AccessException {
+
+}

core/modules/workspaces/src/WorkspaceAssociation.php

@@ -0,0 +1,445 @@
+<?php
+
+namespace Drupal\workspaces;
+
+use Drupal\Core\Database\Connection;
+use Drupal\Core\Database\Query\PagerSelectExtender;
+use Drupal\Core\Entity\EntityTypeManagerInterface;
+use Drupal\Core\Entity\RevisionableInterface;
+use Drupal\Core\Entity\Sql\SqlContentEntityStorage;
+use Drupal\Core\Utility\Error;
+use Drupal\workspaces\Event\WorkspacePostPublishEvent;
+use Drupal\workspaces\Event\WorkspacePublishEvent;
+use Psr\Log\LoggerInterface;
+use Symfony\Component\EventDispatcher\EventSubscriberInterface;
+
+/**
+ * Provides a class for CRUD operations on workspace associations.
+ */
+class WorkspaceAssociation implements WorkspaceAssociationInterface, EventSubscriberInterface {
+
+  /**
+   * The table for the workspace association storage.
+   */
+  const TABLE = 'workspace_association';
+
+  /**
+   * The database connection.
+   *
+   * @var \Drupal\Core\Database\Connection
+   */
+  protected $database;
+
+  /**
+   * The entity type manager.
+   *
+   * @var \Drupal\Core\Entity\EntityTypeManagerInterface
+   */
+  protected $entityTypeManager;
+
+  /**
+   * The workspace repository service.
+   *
+   * @var \Drupal\workspaces\WorkspaceRepositoryInterface
+   */
+  protected $workspaceRepository;
+
+  /**
+   * A multidimensional array of entity IDs that are associated to a workspace.
+   *
+   * The first level keys are workspace IDs, the second level keys are entity
+   * type IDs, and the third level array are entity IDs, keyed by revision IDs.
+   *
+   * @var array
+   */
+  protected array $associatedRevisions = [];
+
+  /**
+   * A multidimensional array of entity IDs that were created in a workspace.
+   *
+   * The first level keys are workspace IDs, the second level keys are entity
+   * type IDs, and the third level array are entity IDs, keyed by revision IDs.
+   *
+   * @var array
+   */
+  protected array $associatedInitialRevisions = [];
+
+  /**
+   * Constructs a WorkspaceAssociation object.
+   *
+   * @param \Drupal\Core\Database\Connection $connection
+   *   A database connection for reading and writing path aliases.
+   * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
+   *   The entity type manager for querying revisions.
+   * @param \Drupal\workspaces\WorkspaceRepositoryInterface $workspace_repository
+   *   The Workspace repository service.
+   * @param \Psr\Log\LoggerInterface|null $logger
+   *   The logger.
+   */
+  public function __construct(Connection $connection, EntityTypeManagerInterface $entity_type_manager, WorkspaceRepositoryInterface $workspace_repository, protected ?LoggerInterface $logger = NULL) {
+    $this->database = $connection;
+    $this->entityTypeManager = $entity_type_manager;
+    $this->workspaceRepository = $workspace_repository;
+    if ($this->logger === NULL) {
+      @trigger_error('Calling ' . __METHOD__ . '() without the $logger argument is deprecated in drupal:10.1.0 and it will be required in drupal:11.0.0. See https://www.drupal.org/node/2932520', E_USER_DEPRECATED);
+      $this->logger = \Drupal::service('logger.channel.workspaces');
+    }
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function trackEntity(RevisionableInterface $entity, WorkspaceInterface $workspace) {
+    // Determine all workspaces that might be affected by this change.
+    $affected_workspaces = $this->workspaceRepository->getDescendantsAndSelf($workspace->id());
+
+    // Get the currently tracked revision for this workspace.
+    $tracked = $this->getTrackedEntities($workspace->id(), $entity->getEntityTypeId(), [$entity->id()]);
+
+    $tracked_revision_id = NULL;
+    if (isset($tracked[$entity->getEntityTypeId()])) {
+      $tracked_revision_id = key($tracked[$entity->getEntityTypeId()]);
+    }
+
+    try {
+      $transaction = $this->database->startTransaction();
+      // Update all affected workspaces that were tracking the current revision.
+      // This means they are inheriting content and should be updated.
+      if ($tracked_revision_id) {
+        $this->database->update(static::TABLE)
+          ->fields([
+            'target_entity_revision_id' => $entity->getRevisionId(),
+          ])
+          ->condition('workspace', $affected_workspaces, 'IN')
+          ->condition('target_entity_type_id', $entity->getEntityTypeId())
+          ->condition('target_entity_id', $entity->id())
+          // Only update descendant workspaces if they have the same initial
+          // revision, which means they are currently inheriting content.
+          ->condition('target_entity_revision_id', $tracked_revision_id)
+          ->execute();
+      }
+
+      // Insert a new index entry for each workspace that is not tracking this
+      // entity yet.
+      $missing_workspaces = array_diff($affected_workspaces, $this->getEntityTrackingWorkspaceIds($entity));
+      if ($missing_workspaces) {
+        $insert_query = $this->database->insert(static::TABLE)
+          ->fields([
+            'workspace',
+            'target_entity_revision_id',
+            'target_entity_type_id',
+            'target_entity_id',
+          ]);
+        foreach ($missing_workspaces as $workspace_id) {
+          $insert_query->values([
+            'workspace' => $workspace_id,
+            'target_entity_type_id' => $entity->getEntityTypeId(),
+            'target_entity_id' => $entity->id(),
+            'target_entity_revision_id' => $entity->getRevisionId(),
+          ]);
+        }
+        $insert_query->execute();
+      }
+    }
+    catch (\Exception $e) {
+      if (isset($transaction)) {
+        $transaction->rollBack();
+      }
+      Error::logException($this->logger, $e);
+      throw $e;
+    }
+
+    $this->associatedRevisions = $this->associatedInitialRevisions = [];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function workspaceInsert(WorkspaceInterface $workspace) {
+    // When a new workspace has been saved, we need to copy all the associations
+    // of its parent.
+    if ($workspace->hasParent()) {
+      $this->initializeWorkspace($workspace);
+    }
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getTrackedEntities($workspace_id, $entity_type_id = NULL, $entity_ids = NULL) {
+    $query = $this->database->select(static::TABLE);
+    $query
+      ->fields(static::TABLE, ['target_entity_type_id', 'target_entity_id', 'target_entity_revision_id'])
+      ->orderBy('target_entity_revision_id', 'ASC')
+      ->condition('workspace', $workspace_id);
+
+    if ($entity_type_id) {
+      $query->condition('target_entity_type_id', $entity_type_id, '=');
+
+      if ($entity_ids) {
+        $query->condition('target_entity_id', $entity_ids, 'IN');
+      }
+    }
+
+    $tracked_revisions = [];
+    foreach ($query->execute() as $record) {
+      $tracked_revisions[$record->target_entity_type_id][$record->target_entity_revision_id] = $record->target_entity_id;
+    }
+
+    return $tracked_revisions;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getTrackedEntitiesForListing($workspace_id, ?int $pager_id = NULL, int|false $limit = 50): array {
+    $query = $this->database->select(static::TABLE)
+      ->extend(PagerSelectExtender::class)
+      ->limit($limit);
+    if ($pager_id) {
+      $query->element($pager_id);
+    }
+
+    $query
+      ->fields(static::TABLE, ['target_entity_type_id', 'target_entity_id', 'target_entity_revision_id'])
+      ->orderBy('target_entity_type_id', 'ASC')
+      ->orderBy('target_entity_revision_id', 'DESC')
+      ->condition('workspace', $workspace_id);
+
+    $tracked_revisions = [];
+    foreach ($query->execute() as $record) {
+      $tracked_revisions[$record->target_entity_type_id][$record->target_entity_revision_id] = $record->target_entity_id;
+    }
+
+    return $tracked_revisions;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getAssociatedRevisions($workspace_id, $entity_type_id, $entity_ids = NULL) {
+    if (isset($this->associatedRevisions[$workspace_id][$entity_type_id])) {
+      if ($entity_ids) {
+        return array_intersect($this->associatedRevisions[$workspace_id][$entity_type_id], $entity_ids);
+      }
+      else {
+        return $this->associatedRevisions[$workspace_id][$entity_type_id];
+      }
+    }
+
+    /** @var \Drupal\Core\Entity\EntityStorageInterface $storage */
+    $storage = $this->entityTypeManager->getStorage($entity_type_id);
+
+    // If the entity type is not using core's default entity storage, we can't
+    // assume the table mapping layout so we have to return only the latest
+    // tracked revisions.
+    if (!$storage instanceof SqlContentEntityStorage) {
+      return $this->getTrackedEntities($workspace_id, $entity_type_id, $entity_ids)[$entity_type_id];
+    }
+
+    $entity_type = $storage->getEntityType();
+    $table_mapping = $storage->getTableMapping();
+    $workspace_field = $table_mapping->getColumnNames($entity_type->get('revision_metadata_keys')['workspace'])['target_id'];
+    $id_field = $table_mapping->getColumnNames($entity_type->getKey('id'))['value'];
+    $revision_id_field = $table_mapping->getColumnNames($entity_type->getKey('revision'))['value'];
+
+    $workspace_tree = $this->workspaceRepository->loadTree();
+    if (isset($workspace_tree[$workspace_id])) {
+      $workspace_candidates = array_merge([$workspace_id], $workspace_tree[$workspace_id]['ancestors']);
+    }
+    else {
+      $workspace_candidates = [$workspace_id];
+    }
+
+    $query = $this->database->select($entity_type->getRevisionTable(), 'revision');
+    $query->leftJoin($entity_type->getBaseTable(), 'base', "[revision].[$id_field] = [base].[$id_field]");
+
+    $query
+      ->fields('revision', [$revision_id_field, $id_field])
+      ->condition("revision.$workspace_field", $workspace_candidates, 'IN')
+      ->where("[revision].[$revision_id_field] >= [base].[$revision_id_field]")
+      ->orderBy("revision.$revision_id_field", 'ASC');
+
+    // Restrict the result to a set of entity ID's if provided.
+    if ($entity_ids) {
+      $query->condition("revision.$id_field", $entity_ids, 'IN');
+    }
+
+    $result = $query->execute()->fetchAllKeyed();
+
+    // Cache the list of associated entity IDs if the full list was requested.
+    if (!$entity_ids) {
+      $this->associatedRevisions[$workspace_id][$entity_type_id] = $result;
+    }
+
+    return $result;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getAssociatedInitialRevisions(string $workspace_id, string $entity_type_id, array $entity_ids = []) {
+    if (isset($this->associatedInitialRevisions[$workspace_id][$entity_type_id])) {
+      if ($entity_ids) {
+        return array_intersect($this->associatedInitialRevisions[$workspace_id][$entity_type_id], $entity_ids);
+      }
+      else {
+        return $this->associatedInitialRevisions[$workspace_id][$entity_type_id];
+      }
+    }
+
+    /** @var \Drupal\Core\Entity\EntityStorageInterface $storage */
+    $storage = $this->entityTypeManager->getStorage($entity_type_id);
+
+    // If the entity type is not using core's default entity storage, we can't
+    // assume the table mapping layout so we have to return only the latest
+    // tracked revisions.
+    if (!$storage instanceof SqlContentEntityStorage) {
+      return $this->getTrackedEntities($workspace_id, $entity_type_id, $entity_ids)[$entity_type_id];
+    }
+
+    $entity_type = $storage->getEntityType();
+    $table_mapping = $storage->getTableMapping();
+    $workspace_field = $table_mapping->getColumnNames($entity_type->get('revision_metadata_keys')['workspace'])['target_id'];
+    $id_field = $table_mapping->getColumnNames($entity_type->getKey('id'))['value'];
+    $revision_id_field = $table_mapping->getColumnNames($entity_type->getKey('revision'))['value'];
+
+    $query = $this->database->select($entity_type->getBaseTable(), 'base');
+    $query->leftJoin($entity_type->getRevisionTable(), 'revision', "[base].[$revision_id_field] = [revision].[$revision_id_field]");
+
+    $query
+      ->fields('base', [$revision_id_field, $id_field])
+      ->condition("revision.$workspace_field", $workspace_id, '=')
+      ->orderBy("base.$revision_id_field", 'ASC');
+
+    // Restrict the result to a set of entity ID's if provided.
+    if ($entity_ids) {
+      $query->condition("base.$id_field", $entity_ids, 'IN');
+    }
+
+    $result = $query->execute()->fetchAllKeyed();
+
+    // Cache the list of associated entity IDs if the full list was requested.
+    if (!$entity_ids) {
+      $this->associatedInitialRevisions[$workspace_id][$entity_type_id] = $result;
+    }
+
+    return $result;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getEntityTrackingWorkspaceIds(RevisionableInterface $entity, bool $latest_revision = FALSE) {
+    $query = $this->database->select(static::TABLE, 'wa')
+      ->fields('wa', ['workspace'])
+      ->condition('[wa].[target_entity_type_id]', $entity->getEntityTypeId())
+      ->condition('[wa].[target_entity_id]', $entity->id());
+
+    // Use a self-join to get only the workspaces in which the latest revision
+    // of the entity is tracked.
+    if ($latest_revision) {
+      $inner_select = $this->database->select(static::TABLE, 'wai')
+        ->condition('[wai].[target_entity_type_id]', $entity->getEntityTypeId())
+        ->condition('[wai].[target_entity_id]', $entity->id());
+      $inner_select->addExpression('MAX([wai].[target_entity_revision_id])', 'max_revision_id');
+
+      $query->join($inner_select, 'waj', '[wa].[target_entity_revision_id] = [waj].[max_revision_id]');
+    }
+
+    $result = $query->execute()->fetchCol();
+
+    // Return early if the entity is not tracked in any workspace.
+    if (empty($result)) {
+      return [];
+    }
+
+    // Return workspace IDs sorted in tree order.
+    $tree = $this->workspaceRepository->loadTree();
+    return array_keys(array_intersect_key($tree, array_flip($result)));
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function postPublish(WorkspaceInterface $workspace) {
+    @trigger_error(__METHOD__ . '() is deprecated in drupal:10.1.0 and is removed from drupal:11.0.0. Use the \Drupal\workspaces\Event\WorkspacePostPublishEvent event instead. See https://www.drupal.org/node/3242573', E_USER_DEPRECATED);
+    $this->deleteAssociations($workspace->id());
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function deleteAssociations($workspace_id = NULL, $entity_type_id = NULL, $entity_ids = NULL, $revision_ids = NULL) {
+    if (!$workspace_id && !$entity_type_id) {
+      throw new \InvalidArgumentException('A workspace ID or an entity type ID must be provided.');
+    }
+
+    $query = $this->database->delete(static::TABLE);
+
+    if ($workspace_id) {
+      $query->condition('workspace', $workspace_id);
+    }
+
+    if ($entity_type_id) {
+      if (!$entity_ids && !$revision_ids) {
+        throw new \InvalidArgumentException('A list of entity IDs or revision IDs must be provided for an entity type.');
+      }
+
+      $query->condition('target_entity_type_id', $entity_type_id, '=');
+
+      if ($entity_ids) {
+        $query->condition('target_entity_id', $entity_ids, 'IN');
+      }
+
+      if ($revision_ids) {
+        $query->condition('target_entity_revision_id', $revision_ids, 'IN');
+      }
+    }
+
+    $query->execute();
+
+    $this->associatedRevisions = $this->associatedInitialRevisions = [];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function initializeWorkspace(WorkspaceInterface $workspace) {
+    if ($parent_id = $workspace->parent->target_id) {
+      $indexed_rows = $this->database->select(static::TABLE);
+      $indexed_rows->addExpression(':new_id', 'workspace', [
+        ':new_id' => $workspace->id(),
+      ]);
+      $indexed_rows->fields(static::TABLE, [
+        'target_entity_type_id',
+        'target_entity_id',
+        'target_entity_revision_id',
+      ]);
+      $indexed_rows->condition('workspace', $parent_id);
+      $this->database->insert(static::TABLE)->from($indexed_rows)->execute();
+    }
+
+    $this->associatedRevisions = $this->associatedInitialRevisions = [];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function getSubscribedEvents(): array {
+    // Workspace association records cleanup should happen as late as possible.
+    $events[WorkspacePostPublishEvent::class][] = ['onPostPublish', -500];
+    return $events;
+  }
+
+  /**
+   * Triggers clean-up operations after a workspace is published.
+   *
+   * @param \Drupal\workspaces\Event\WorkspacePublishEvent $event
+   *   The workspace publish event.
+   */
+  public function onPostPublish(WorkspacePublishEvent $event): void {
+    $this->deleteAssociations($event->getWorkspace()->id());
+  }
+
+}

core/modules/workspaces/src/WorkspaceAssociationInterface.php

@@ -0,0 +1,168 @@
+<?php
+
+namespace Drupal\workspaces;
+
+use Drupal\Core\Entity\RevisionableInterface;
+
+/**
+ * Defines an interface for the workspace_association service.
+ *
+ * The canonical workspace association data is stored in a revision metadata
+ * field on each entity revision that is tracked by a workspace.
+ *
+ * For the purpose of optimizing workspace-specific queries, the default
+ * implementation of this interface defines a custom 'workspace_association'
+ * index table which stores only the latest revisions tracked by a workspace.
+ *
+ * @internal
+ */
+interface WorkspaceAssociationInterface {
+
+  /**
+   * Updates or creates the association for a given entity and a workspace.
+   *
+   * @param \Drupal\Core\Entity\RevisionableInterface $entity
+   *   The entity to update or create from.
+   * @param \Drupal\workspaces\WorkspaceInterface $workspace
+   *   The workspace in which the entity will be tracked.
+   */
+  public function trackEntity(RevisionableInterface $entity, WorkspaceInterface $workspace);
+
+  /**
+   * Responds to the creation of a new workspace entity.
+   *
+   * @param \Drupal\workspaces\WorkspaceInterface $workspace
+   *   The workspaces that was inserted.
+   */
+  public function workspaceInsert(WorkspaceInterface $workspace);
+
+  /**
+   * Retrieves the entities tracked by a given workspace.
+   *
+   * @param string $workspace_id
+   *   The ID of the workspace.
+   * @param string|null $entity_type_id
+   *   (optional) An entity type ID to filter the results by. Defaults to NULL.
+   * @param int[]|string[]|null $entity_ids
+   *   (optional) An array of entity IDs to filter the results by. Defaults to
+   *   NULL.
+   *
+   * @return array
+   *   Returns a multidimensional array where the first level keys are entity
+   *   type IDs and the values are an array of entity IDs keyed by revision IDs.
+   */
+  public function getTrackedEntities($workspace_id, $entity_type_id = NULL, $entity_ids = NULL);
+
+  /**
+   * Retrieves a paged list of entities tracked by a given workspace.
+   *
+   * @param string $workspace_id
+   *   The ID of the workspace.
+   * @param int|null $pager_id
+   *   (optional) A pager ID. Defaults to NULL.
+   * @param int|false $limit
+   *   (optional) An integer specifying the number of elements per page. If
+   *   passed a false value (FALSE, 0, NULL), the pager is disabled. Defaults to
+   *   50.
+   *
+   * @return array
+   *   Returns a multidimensional array where the first level keys are entity
+   *   type IDs and the values are an array of entity IDs keyed by revision IDs.
+   */
+  public function getTrackedEntitiesForListing($workspace_id, ?int $pager_id = NULL, int|false $limit = 50): array;
+
+  /**
+   * Retrieves all content revisions tracked by a given workspace.
+   *
+   * Since the 'workspace_association' index table only tracks the latest
+   * associated revisions, this method retrieves all the tracked revisions by
+   * querying the entity type's revision table directly.
+   *
+   * @param string $workspace_id
+   *   The ID of the workspace.
+   * @param string $entity_type_id
+   *   An entity type ID to find revisions for.
+   * @param int[]|string[]|null $entity_ids
+   *   (optional) An array of entity IDs to filter the results by. Defaults to
+   *   NULL.
+   *
+   * @return array
+   *   Returns an array where the values are an array of entity IDs keyed by
+   *   revision IDs.
+   */
+  public function getAssociatedRevisions($workspace_id, $entity_type_id, $entity_ids = NULL);
+
+  /**
+   * Retrieves all content revisions that were created in a given workspace.
+   *
+   * @param string $workspace_id
+   *   The ID of the workspace.
+   * @param string $entity_type_id
+   *   An entity type ID to find revisions for.
+   * @param int[]|string[] $entity_ids
+   *   (optional) An array of entity IDs to filter the results by. Defaults to
+   *   an empty array.
+   *
+   * @return array
+   *   Returns an array where the values are an array of entity IDs keyed by
+   *   revision IDs.
+   */
+  public function getAssociatedInitialRevisions(string $workspace_id, string $entity_type_id, array $entity_ids = []);
+
+  /**
+   * Gets a list of workspace IDs in which an entity is tracked.
+   *
+   * @param \Drupal\Core\Entity\RevisionableInterface $entity
+   *   An entity object.
+   * @param bool $latest_revision
+   *   (optional) Whether to return only the workspaces in which the latest
+   *   revision of the entity is tracked. Defaults to FALSE.
+   *
+   * @return string[]
+   *   An array of workspace IDs where the given entity is tracked, or an empty
+   *   array if it is not tracked anywhere.
+   */
+  public function getEntityTrackingWorkspaceIds(RevisionableInterface $entity, bool $latest_revision = FALSE);
+
+  /**
+   * Triggers clean-up operations after publishing a workspace.
+   *
+   * @param \Drupal\workspaces\WorkspaceInterface $workspace
+   *   A workspace entity.
+   *
+   * @deprecated in drupal:10.1.0 and is removed from drupal:11.0.0. Use the
+   *   \Drupal\workspaces\Event\WorkspacePostPublishEvent event instead.
+   *
+   * @see https://www.drupal.org/node/3242573
+   */
+  public function postPublish(WorkspaceInterface $workspace);
+
+  /**
+   * Deletes all the workspace association records for the given workspace.
+   *
+   * @param string|null $workspace_id
+   *   (optional) A workspace entity ID. Defaults to NULL.
+   * @param string|null $entity_type_id
+   *   (optional) The target entity type of the associations to delete. Defaults
+   *   to NULL.
+   * @param int[]|string[]|null $entity_ids
+   *   (optional) The target entity IDs of the associations to delete. Defaults
+   *   to NULL.
+   * @param int[]|string[]|null $revision_ids
+   *   (optional) The target entity revision IDs of the associations to delete.
+   *   Defaults to NULL.
+   *
+   * @throws \InvalidArgumentException
+   *   If neither $workspace_id nor $entity_type_id arguments were provided.
+   */
+  public function deleteAssociations($workspace_id = NULL, $entity_type_id = NULL, $entity_ids = NULL, $revision_ids = NULL);
+
+  /**
+   * Initializes a workspace with all the associations of its parent.
+   *
+   * @param \Drupal\workspaces\WorkspaceInterface $workspace
+   *   The workspace to be initialized.
+   */
+  public function initializeWorkspace(WorkspaceInterface $workspace);
+
+}

core/modules/workspaces/src/WorkspaceCacheContext.php

@@ -0,0 +1,57 @@
+<?php
+
+namespace Drupal\workspaces;
+
+use Drupal\Core\Cache\CacheableMetadata;
+use Drupal\Core\Cache\Context\CacheContextInterface;
+
+/**
+ * Defines the WorkspaceCacheContext service, for "per workspace" caching.
+ *
+ * Cache context ID: 'workspace'.
+ */
+class WorkspaceCacheContext implements CacheContextInterface {
+
+  /**
+   * The workspace manager.
+   *
+   * @var \Drupal\workspaces\WorkspaceManagerInterface
+   */
+  protected $workspaceManager;
+
+  /**
+   * Constructs a new WorkspaceCacheContext service.
+   *
+   * @param \Drupal\workspaces\WorkspaceManagerInterface $workspace_manager
+   *   The workspace manager.
+   */
+  public function __construct(WorkspaceManagerInterface $workspace_manager) {
+    $this->workspaceManager = $workspace_manager;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function getLabel() {
+    return t('Workspace');
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getContext() {
+    return $this->workspaceManager->hasActiveWorkspace() ? $this->workspaceManager->getActiveWorkspace()->id() : 'live';
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getCacheableMetadata($type = NULL) {
+    // The active workspace will always be stored in the user's session.
+    $cacheability = new CacheableMetadata();
+    $cacheability->addCacheContexts(['session']);
+
+    return $cacheability;
+  }
+
+}

core/modules/workspaces/src/WorkspaceConflictException.php

@@ -0,0 +1,10 @@
+<?php
+
+namespace Drupal\workspaces;
+
+/**
+ * An exception thrown when two workspaces are in a conflicting content state.
+ */
+class WorkspaceConflictException extends \RuntimeException {
+
+}

core/modules/workspaces/src/WorkspaceInformation.php

@@ -0,0 +1,121 @@
+<?php
+
+namespace Drupal\workspaces;
+
+use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Entity\EntityPublishedInterface;
+use Drupal\Core\Entity\EntityTypeInterface;
+use Drupal\Core\Entity\EntityTypeManagerInterface;
+use Drupal\workspaces\Entity\Handler\IgnoredWorkspaceHandler;
+
+/**
+ * General service for workspace support information.
+ */
+class WorkspaceInformation implements WorkspaceInformationInterface {
+
+  /**
+   * An array of workspace-support statuses, keyed by entity type ID.
+   *
+   * @var bool[]
+   */
+  protected array $supported = [];
+
+  /**
+   * An array of workspace-ignored statuses, keyed by entity type ID.
+   *
+   * @var bool[]
+   */
+  protected array $ignored = [];
+
+  public function __construct(
+    protected readonly EntityTypeManagerInterface $entityTypeManager,
+    protected readonly WorkspaceAssociationInterface $workspaceAssociation,
+  ) {}
+
+  /**
+   * {@inheritdoc}
+   */
+  public function isEntitySupported(EntityInterface $entity): bool {
+    $entity_type = $entity->getEntityType();
+
+    if (!$this->isEntityTypeSupported($entity_type)) {
+      return FALSE;
+    }
+
+    $handler = $this->entityTypeManager->getHandler($entity_type->id(), 'workspace');
+    return $handler->isEntitySupported($entity);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function isEntityTypeSupported(EntityTypeInterface $entity_type): bool {
+    if (!isset($this->supported[$entity_type->id()])) {
+      if ($entity_type->hasHandlerClass('workspace')) {
+        $supported = !is_a($entity_type->getHandlerClass('workspace'), IgnoredWorkspaceHandler::class, TRUE);
+      }
+      else {
+        // Fallback for cases when entity type info hasn't been altered yet, for
+        // example when the Workspaces module is being installed.
+        $supported = $entity_type->entityClassImplements(EntityPublishedInterface::class) && $entity_type->isRevisionable();
+      }
+
+      $this->supported[$entity_type->id()] = $supported;
+    }
+
+    return $this->supported[$entity_type->id()];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getSupportedEntityTypes(): array {
+    $entity_types = [];
+    foreach ($this->entityTypeManager->getDefinitions() as $entity_type_id => $entity_type) {
+      if ($this->isEntityTypeSupported($entity_type)) {
+        $entity_types[$entity_type_id] = $entity_type;
+      }
+    }
+    return $entity_types;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function isEntityIgnored(EntityInterface $entity): bool {
+    $entity_type = $entity->getEntityType();
+
+    if ($this->isEntityTypeIgnored($entity_type)) {
+      return TRUE;
+    }
+
+    if ($entity_type->hasHandlerClass('workspace')) {
+      $handler = $this->entityTypeManager->getHandler($entity_type->id(), 'workspace');
+      return !$handler->isEntitySupported($entity);
+    }
+
+    return FALSE;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function isEntityTypeIgnored(EntityTypeInterface $entity_type): bool {
+    if (!isset($this->ignored[$entity_type->id()])) {
+      $this->ignored[$entity_type->id()] = $entity_type->hasHandlerClass('workspace')
+        && is_a($entity_type->getHandlerClass('workspace'), IgnoredWorkspaceHandler::class, TRUE);
+    }
+
+    return $this->ignored[$entity_type->id()];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function isEntityDeletable(EntityInterface $entity, WorkspaceInterface $workspace): bool {
+    $initial_revisions = $this->workspaceAssociation->getAssociatedInitialRevisions($workspace->id(), $entity->getEntityTypeId());
+
+    return in_array($entity->id(), $initial_revisions, TRUE);
+  }
+
+}

core/modules/workspaces/src/WorkspaceInformationInterface.php

@@ -0,0 +1,86 @@
+<?php
+
+namespace Drupal\workspaces;
+
+use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Entity\EntityTypeInterface;
+
+/**
+ * Provides an interface for workspace-support information.
+ */
+interface WorkspaceInformationInterface {
+
+  /**
+   * Determines whether an entity can belong to a workspace.
+   *
+   * @param \Drupal\Core\Entity\EntityInterface $entity
+   *   The entity to check.
+   *
+   * @return bool
+   *   TRUE if the entity can belong to a workspace, FALSE otherwise.
+   */
+  public function isEntitySupported(EntityInterface $entity): bool;
+
+  /**
+   * Determines whether an entity type can belong to a workspace.
+   *
+   * @param \Drupal\Core\Entity\EntityTypeInterface $entity_type
+   *   The entity type to check.
+   *
+   * @return bool
+   *   TRUE if the entity type can belong to a workspace, FALSE otherwise.
+   */
+  public function isEntityTypeSupported(EntityTypeInterface $entity_type): bool;
+
+  /**
+   * Returns an array of entity types that can belong to workspaces.
+   *
+   * @return \Drupal\Core\Entity\EntityTypeInterface[]
+   *   An array of entity type definition objects.
+   */
+  public function getSupportedEntityTypes(): array;
+
+  /**
+   * Determines whether CRUD operations for an entity are allowed.
+   *
+   * CRUD operations for an ignored entity are allowed in a workspace, but their
+   * revisions are not tracked.
+   *
+   * @param \Drupal\Core\Entity\EntityInterface $entity
+   *   The entity to check.
+   *
+   * @return bool
+   *   TRUE if CRUD operations of an entity type can safely be done inside a
+   *   workspace, without impacting the Live site, FALSE otherwise.
+   */
+  public function isEntityIgnored(EntityInterface $entity): bool;
+
+  /**
+   * Determines whether CRUD operations for an entity type are allowed.
+   *
+   * CRUD operations for an ignored entity type are allowed in a workspace, but
+   * their revisions are not tracked.
+   *
+   * @param \Drupal\Core\Entity\EntityTypeInterface $entity_type
+   *   The entity type to check.
+   *
+   * @return bool
+   *   TRUE if CRUD operations of an entity type can safely be done inside a
+   *   workspace, without impacting the Live site, FALSE otherwise.
+   */
+  public function isEntityTypeIgnored(EntityTypeInterface $entity_type): bool;
+
+  /**
+   * Determines whether an entity can be deleted in the given workspace.
+   *
+   * @param \Drupal\Core\Entity\EntityInterface $entity
+   *   The entity object which needs to be checked.
+   * @param \Drupal\workspaces\WorkspaceInterface $workspace
+   *   The workspace in which the entity needs to be checked.
+   *
+   * @return bool
+   *   TRUE if the entity can be deleted, FALSE otherwise.
+   */
+  public function isEntityDeletable(EntityInterface $entity, WorkspaceInterface $workspace): bool;
+
+}

core/modules/workspaces/src/WorkspaceInterface.php

@@ -0,0 +1,45 @@
+<?php
+
+namespace Drupal\workspaces;
+
+use Drupal\Core\Entity\ContentEntityInterface;
+use Drupal\Core\Entity\EntityChangedInterface;
+use Drupal\user\EntityOwnerInterface;
+
+/**
+ * Defines an interface for the workspace entity type.
+ */
+interface WorkspaceInterface extends ContentEntityInterface, EntityChangedInterface, EntityOwnerInterface {
+
+  /**
+   * Publishes the contents of this workspace to the default (Live) workspace.
+   */
+  public function publish();
+
+  /**
+   * Gets the workspace creation timestamp.
+   *
+   * @return int
+   *   Creation timestamp of the workspace.
+   */
+  public function getCreatedTime();
+
+  /**
+   * Sets the workspace creation timestamp.
+   *
+   * @param int $timestamp
+   *   The workspace creation timestamp.
+   *
+   * @return $this
+   */
+  public function setCreatedTime($timestamp);
+
+  /**
+   * Determines whether the workspace has a parent.
+   *
+   * @return bool
+   *   TRUE if the workspace has a parent, FALSE otherwise.
+   */
+  public function hasParent();
+
+}

core/modules/workspaces/src/WorkspaceListBuilder.php

@@ -0,0 +1,402 @@
+<?php
+
+namespace Drupal\workspaces;
+
+use Drupal\Component\Serialization\Json;
+use Drupal\Core\Ajax\AjaxHelperTrait;
+use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Entity\EntityListBuilder;
+use Drupal\Core\Entity\EntityStorageInterface;
+use Drupal\Core\Entity\EntityTypeInterface;
+use Drupal\Core\Render\RendererInterface;
+use Drupal\Core\Url;
+use Drupal\user\UserInterface;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Defines a class to build a listing of workspace entities.
+ *
+ * @see \Drupal\workspaces\Entity\Workspace
+ */
+class WorkspaceListBuilder extends EntityListBuilder {
+
+  use AjaxHelperTrait;
+
+  /**
+   * The workspace manager service.
+   *
+   * @var \Drupal\workspaces\WorkspaceManagerInterface
+   */
+  protected $workspaceManager;
+
+  /**
+   * The workspace repository service.
+   *
+   * @var \Drupal\workspaces\WorkspaceRepositoryInterface
+   */
+  protected $workspaceRepository;
+
+  /**
+   * The renderer service.
+   *
+   * @var \Drupal\Core\Render\RendererInterface
+   */
+  protected $renderer;
+
+  /**
+   * Constructs a new EntityListBuilder object.
+   *
+   * @param \Drupal\Core\Entity\EntityTypeInterface $entity_type
+   *   The entity type definition.
+   * @param \Drupal\Core\Entity\EntityStorageInterface $storage
+   *   The entity storage class.
+   * @param \Drupal\workspaces\WorkspaceManagerInterface $workspace_manager
+   *   The workspace manager service.
+   * @param \Drupal\workspaces\WorkspaceRepositoryInterface $workspace_repository
+   *   The workspace repository service.
+   * @param \Drupal\Core\Render\RendererInterface $renderer
+   *   The renderer service.
+   */
+  public function __construct(EntityTypeInterface $entity_type, EntityStorageInterface $storage, WorkspaceManagerInterface $workspace_manager, WorkspaceRepositoryInterface $workspace_repository, RendererInterface $renderer) {
+    parent::__construct($entity_type, $storage);
+    $this->workspaceManager = $workspace_manager;
+    $this->workspaceRepository = $workspace_repository;
+    $this->renderer = $renderer;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function createInstance(ContainerInterface $container, EntityTypeInterface $entity_type) {
+    return new static(
+      $entity_type,
+      $container->get('entity_type.manager')->getStorage($entity_type->id()),
+      $container->get('workspaces.manager'),
+      $container->get('workspaces.repository'),
+      $container->get('renderer')
+    );
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function load() {
+    // Get all the workspace entities and sort them in tree order.
+    $workspace_tree = $this->workspaceRepository->loadTree();
+    $entities = array_replace($workspace_tree, $this->storage->loadMultiple());
+    foreach ($entities as $id => $entity) {
+      $entity->_depth = $workspace_tree[$id]['depth'];
+    }
+
+    return $entities;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function buildHeader() {
+    $header['label'] = $this->t('Workspace');
+    $header['uid'] = $this->t('Owner');
+
+    return $header + parent::buildHeader();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function buildRow(EntityInterface $entity) {
+    /** @var \Drupal\workspaces\WorkspaceInterface $entity */
+    if (isset($entity->_depth) && $entity->_depth > 0) {
+      $indentation = [
+        '#theme' => 'indentation',
+        '#size' => $entity->_depth,
+      ];
+    }
+
+    $row['data'] = [
+      'label' => [
+        'data' => [
+          '#prefix' => isset($indentation) ? $this->renderer->render($indentation) : '',
+          '#type' => 'link',
+          '#title' => $entity->label(),
+          '#url' => $entity->toUrl(),
+        ],
+      ],
+      'owner' => (($owner = $entity->getOwner()) && $owner instanceof UserInterface)
+        ? $owner->getDisplayName()
+        : $this->t('N/A'),
+    ];
+    $row['data'] = $row['data'] + parent::buildRow($entity);
+
+    $active_workspace = $this->workspaceManager->getActiveWorkspace();
+    if ($active_workspace && $entity->id() === $active_workspace->id()) {
+      $row['class'] = ['active-workspace', 'active-workspace--not-default'];
+    }
+    return $row;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getDefaultOperations(EntityInterface $entity) {
+    /** @var \Drupal\workspaces\WorkspaceInterface $entity */
+    $operations = parent::getDefaultOperations($entity);
+    if (isset($operations['edit'])) {
+      $operations['edit']['query']['destination'] = $entity->toUrl('collection')->toString();
+    }
+
+    $active_workspace = $this->workspaceManager->getActiveWorkspace();
+    if (!$active_workspace || $entity->id() != $active_workspace->id()) {
+      $operations['activate'] = [
+        'title' => $this->t('Switch to @workspace', ['@workspace' => $entity->label()]),
+        // Use a weight lower than the one of the 'Edit' operation because we
+        // want the 'Activate' operation to be the primary operation.
+        'weight' => 0,
+        'url' => $entity->toUrl('activate-form', ['query' => ['destination' => $entity->toUrl('collection')->toString()]]),
+      ];
+    }
+
+    if (!$entity->hasParent()) {
+      $operations['publish'] = [
+        'title' => $this->t('Publish content'),
+        // The 'Publish' operation should be the default one for the currently
+        // active workspace.
+        'weight' => ($active_workspace && $entity->id() == $active_workspace->id()) ? 0 : 20,
+        'url' => Url::fromRoute('entity.workspace.publish_form',
+          ['workspace' => $entity->id()],
+          ['query' => ['destination' => $entity->toUrl('collection')->toString()]]
+        ),
+      ];
+    }
+    else {
+      /** @var \Drupal\workspaces\WorkspaceInterface $parent */
+      $parent = $entity->parent->entity;
+      $operations['merge'] = [
+        'title' => $this->t('Merge into @target_label', [
+          '@target_label' => $parent->label(),
+        ]),
+        'weight' => 5,
+        'url' => Url::fromRoute('entity.workspace.merge_form',
+          [
+            'source_workspace' => $entity->id(),
+            'target_workspace' => $parent->id(),
+          ],
+          [
+            'query' => ['destination' => $entity->toUrl('collection')->toString()],
+          ]
+        ),
+      ];
+    }
+
+    $operations['manage'] = [
+      'title' => $this->t('Manage'),
+      'weight' => 5,
+      'url' => $entity->toUrl(),
+    ];
+
+    return $operations;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function render() {
+    $build = parent::render();
+    if ($this->isAjax()) {
+      $this->offCanvasRender($build);
+    }
+    else {
+      // Add a row for switching to Live.
+      $has_active_workspace = $this->workspaceManager->hasActiveWorkspace();
+      $row_live = [
+        'data' => [
+          'label' => [
+            'data' => [
+              '#markup' => $this->t('Live'),
+            ],
+          ],
+          'owner' => '',
+          'operations' => [
+            'data' => [
+              '#type' => 'operations',
+              '#links' => [
+                'activate' => [
+                  'title' => 'Switch to Live',
+                  'weight' => 0,
+                  'url' => Url::fromRoute('workspaces.switch_to_live', [], ['query' => $this->getDestinationArray()]),
+                ],
+              ],
+              '#access' => $has_active_workspace,
+            ],
+          ],
+        ],
+      ];
+
+      if (!$has_active_workspace) {
+        $row_live['class'] = ['active-workspace', 'active-workspace--default'];
+      }
+      array_unshift($build['table']['#rows'], $row_live);
+
+      $build['#attached'] = [
+        'library' => ['workspaces/drupal.workspaces.overview'],
+      ];
+    }
+    return $build;
+  }
+
+  /**
+   * Renders the off canvas elements.
+   *
+   * @param array $build
+   *   A render array.
+   */
+  protected function offCanvasRender(array &$build) {
+    $active_workspace = $this->workspaceManager->getActiveWorkspace();
+    if ($active_workspace) {
+      $active_workspace_classes = [
+        'active-workspace--not-default',
+        'active-workspace--' . $active_workspace->id(),
+      ];
+    }
+    else {
+      $active_workspace_classes = [
+        'active-workspace--default',
+      ];
+    }
+
+    $build['active_workspace'] = [
+      '#type' => 'container',
+      '#weight' => -20,
+      '#attributes' => [
+        'class' => array_merge(['active-workspace'], $active_workspace_classes),
+      ],
+      'title' => [
+        '#type' => 'html_tag',
+        '#tag' => 'div',
+        '#value' => $this->t('Current workspace:'),
+        '#attributes' => ['class' => 'active-workspace__title'],
+      ],
+      'label' => [
+        '#type' => 'container',
+        '#attributes' => ['class' => 'active-workspace__label'],
+        'value' => [
+          '#type' => 'html_tag',
+          '#tag' => 'span',
+          '#value' => $active_workspace ? $active_workspace->label() : $this->t('Live'),
+        ],
+      ],
+    ];
+    if ($active_workspace) {
+      $build['active_workspace']['label']['manage'] = [
+        '#type' => 'link',
+        '#title' => $this->t('Manage workspace'),
+        '#url' => $active_workspace->toUrl('canonical'),
+        '#attributes' => [
+          'class' => ['active-workspace__manage'],
+        ],
+      ];
+      $build['active_workspace']['actions'] = [
+        '#type' => 'container',
+        '#weight' => 20,
+        '#attributes' => [
+          'class' => ['active-workspace__actions'],
+        ],
+      ];
+      if (!$active_workspace->hasParent()) {
+        $build['active_workspace']['actions']['publish'] = [
+          '#type' => 'link',
+          '#title' => $this->t('Publish content'),
+          '#url' => Url::fromRoute('entity.workspace.publish_form',
+            ['workspace' => $active_workspace->id()],
+            ['query' => ['destination' => $active_workspace->toUrl('collection')->toString()]]
+          ),
+          '#attributes' => [
+            'class' => ['button', 'button--primary', 'active-workspace__button'],
+          ],
+        ];
+      }
+      else {
+        $build['active_workspace']['actions']['merge'] = [
+          '#type' => 'link',
+          '#title' => $this->t('Merge content'),
+          '#url' => Url::fromRoute('entity.workspace.merge_form',
+            [
+              'source_workspace' => $active_workspace->id(),
+              'target_workspace' => $active_workspace->parent->target_id,
+            ],
+            [
+              'query' => ['destination' => $active_workspace->toUrl('collection')->toString()],
+            ]
+          ),
+          '#attributes' => [
+            'class' => ['button', 'button--primary', 'active-workspace__button'],
+          ],
+        ];
+      }
+    }
+
+    $items = [];
+    $rows = array_slice($build['table']['#rows'], 0, 5, TRUE);
+    foreach ($rows as $id => $row) {
+      if (!$active_workspace || $active_workspace->id() !== $id) {
+        $url = Url::fromRoute('entity.workspace.activate_form', ['workspace' => $id], ['query' => $this->getDestinationArray()]);
+        $items[] = [
+          '#type' => 'link',
+          '#title' => ltrim($row['data']['label']['data']['#title']),
+          '#url' => $url,
+          '#attributes' => [
+            'class' => ['use-ajax', 'workspaces__item', 'workspaces__item--not-default'],
+            'data-dialog-type' => 'modal',
+            'data-dialog-options' => Json::encode([
+              'width' => 500,
+            ]),
+          ],
+        ];
+      }
+    }
+
+    // Add an item for switching to Live.
+    if ($active_workspace) {
+      $items[] = [
+        '#type' => 'link',
+        '#title' => $this->t('Live'),
+        '#url' => Url::fromRoute('workspaces.switch_to_live', [], ['query' => $this->getDestinationArray()]),
+        '#attributes' => [
+          'class' => ['use-ajax', 'workspaces__item', 'workspaces__item--default'],
+          'data-dialog-type' => 'modal',
+          'data-dialog-options' => Json::encode([
+            'width' => 500,
+          ]),
+        ],
+      ];
+    }
+
+    $build['workspaces_list'] = [
+      '#type' => 'container',
+      '#attributes' => [
+        'class' => 'workspaces',
+      ],
+    ];
+    $build['workspaces_list']['workspaces'] = [
+      '#theme' => 'item_list',
+      '#title' => $this->t('Other workspaces:'),
+      '#items' => $items,
+      '#wrapper_attributes' => ['class' => ['workspaces__list']],
+      '#cache' => [
+        'contexts' => $this->entityType->getListCacheContexts(),
+        'tags' => $this->entityType->getListCacheTags(),
+      ],
+    ];
+    $build['workspaces_list']['all_workspaces'] = [
+      '#type' => 'link',
+      '#title' => $this->t('View all workspaces'),
+      '#url' => Url::fromRoute('entity.workspace.collection'),
+      '#attributes' => [
+        'class' => ['all-workspaces'],
+      ],
+    ];
+    unset($build['table']);
+    unset($build['pager']);
+  }
+
+}

core/modules/workspaces/src/WorkspaceManager.php

@@ -0,0 +1,393 @@
+<?php
+
+namespace Drupal\workspaces;
+
+use Drupal\Core\Cache\MemoryCache\MemoryCacheInterface;
+use Drupal\Core\DependencyInjection\ClassResolverInterface;
+use Drupal\Core\Entity\EntityTypeInterface;
+use Drupal\Core\Entity\EntityTypeManagerInterface;
+use Drupal\Core\Session\AccountProxyInterface;
+use Drupal\Core\Site\Settings;
+use Drupal\Core\State\StateInterface;
+use Drupal\Core\StringTranslation\StringTranslationTrait;
+use Psr\Log\LoggerInterface;
+use Symfony\Component\HttpFoundation\RequestStack;
+
+/**
+ * Provides the workspace manager.
+ */
+class WorkspaceManager implements WorkspaceManagerInterface {
+
+  use StringTranslationTrait;
+
+  /**
+   * The request stack.
+   *
+   * @var \Symfony\Component\HttpFoundation\RequestStack
+   */
+  protected $requestStack;
+
+  /**
+   * The entity type manager.
+   *
+   * @var \Drupal\Core\Entity\EntityTypeManagerInterface
+   */
+  protected $entityTypeManager;
+
+  /**
+   * The entity memory cache service.
+   *
+   * @var \Drupal\Core\Cache\MemoryCache\MemoryCacheInterface
+   */
+  protected $entityMemoryCache;
+
+  /**
+   * The current user.
+   *
+   * @var \Drupal\Core\Session\AccountProxyInterface
+   */
+  protected $currentUser;
+
+  /**
+   * The state service.
+   *
+   * @var \Drupal\Core\State\StateInterface
+   */
+  protected $state;
+
+  /**
+   * A logger instance.
+   *
+   * @var \Psr\Log\LoggerInterface
+   */
+  protected $logger;
+
+  /**
+   * The class resolver.
+   *
+   * @var \Drupal\Core\DependencyInjection\ClassResolverInterface
+   */
+  protected $classResolver;
+
+  /**
+   * The workspace association service.
+   *
+   * @var \Drupal\workspaces\WorkspaceAssociationInterface
+   */
+  protected $workspaceAssociation;
+
+  /**
+   * The workspace information service.
+   *
+   * @var \Drupal\workspaces\WorkspaceInformationInterface
+   */
+  protected WorkspaceInformationInterface $workspaceInfo;
+
+  /**
+   * The workspace negotiator service IDs.
+   *
+   * @var array
+   */
+  protected $negotiatorIds;
+
+  /**
+   * The current active workspace or FALSE if there is no active workspace.
+   *
+   * @var \Drupal\workspaces\WorkspaceInterface|false
+   */
+  protected $activeWorkspace;
+
+  /**
+   * Constructs a new WorkspaceManager.
+   *
+   * @param \Symfony\Component\HttpFoundation\RequestStack $request_stack
+   *   The request stack.
+   * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
+   *   The entity type manager.
+   * @param \Drupal\Core\Cache\MemoryCache\MemoryCacheInterface $entity_memory_cache
+   *   The entity memory cache service.
+   * @param \Drupal\Core\Session\AccountProxyInterface $current_user
+   *   The current user.
+   * @param \Drupal\Core\State\StateInterface $state
+   *   The state service.
+   * @param \Psr\Log\LoggerInterface $logger
+   *   A logger instance.
+   * @param \Drupal\Core\DependencyInjection\ClassResolverInterface $class_resolver
+   *   The class resolver.
+   * @param \Drupal\workspaces\WorkspaceAssociationInterface $workspace_association
+   *   The workspace association service.
+   * @param \Drupal\workspaces\WorkspaceInformationInterface|null $workspace_information
+   *   The workspace information service.
+   * @param array|null $negotiator_ids
+   *   The workspace negotiator service IDs.
+   */
+  public function __construct(RequestStack $request_stack, EntityTypeManagerInterface $entity_type_manager, MemoryCacheInterface $entity_memory_cache, AccountProxyInterface $current_user, StateInterface $state, LoggerInterface $logger, ClassResolverInterface $class_resolver, WorkspaceAssociationInterface $workspace_association, protected ?WorkspaceInformationInterface $workspace_information = NULL, ?array $negotiator_ids = NULL) {
+    $this->requestStack = $request_stack;
+    $this->entityTypeManager = $entity_type_manager;
+    $this->entityMemoryCache = $entity_memory_cache;
+    $this->currentUser = $current_user;
+    $this->state = $state;
+    $this->logger = $logger;
+    $this->classResolver = $class_resolver;
+    $this->workspaceAssociation = $workspace_association;
+
+    if (!$workspace_information instanceof WorkspaceInformationInterface) {
+      @trigger_error('Calling ' . __METHOD__ . '() without the $workspace_information argument is deprecated in drupal:10.3.0 and will be required in drupal:11.0.0. See https://www.drupal.org/node/3324297', E_USER_DEPRECATED);
+      $this->workspaceInfo = \Drupal::service('workspaces.information');
+
+      // The negotiator IDs are always the last constructor argument.
+      $this->negotiatorIds = $workspace_information;
+    }
+    else {
+      $this->workspaceInfo = $workspace_information;
+      $this->negotiatorIds = $negotiator_ids;
+    }
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function isEntityTypeSupported(EntityTypeInterface $entity_type) {
+    @trigger_error(__METHOD__ . '() is deprecated in drupal:10.3.0 and is removed from drupal:11.0.0. Use \Drupal\workspaces\WorkspaceInformation::isEntityTypeSupported instead. See https://www.drupal.org/node/3324297', E_USER_DEPRECATED);
+    return $this->workspaceInfo->isEntityTypeSupported($entity_type);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getSupportedEntityTypes() {
+    @trigger_error(__METHOD__ . '() is deprecated in drupal:10.3.0 and is removed from drupal:11.0.0. Use \Drupal\workspaces\WorkspaceInformation::getSupportedEntityTypes instead. See https://www.drupal.org/node/3324297', E_USER_DEPRECATED);
+    return $this->workspaceInfo->getSupportedEntityTypes();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function hasActiveWorkspace() {
+    return $this->getActiveWorkspace() !== FALSE;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getActiveWorkspace() {
+    if (!isset($this->activeWorkspace)) {
+      $request = $this->requestStack->getCurrentRequest();
+
+      foreach ($this->negotiatorIds as $negotiator_id) {
+        /** @var \Drupal\workspaces\Negotiator\WorkspaceIdNegotiatorInterface $negotiator */
+        $negotiator = $this->classResolver->getInstanceFromDefinition($negotiator_id);
+
+        if ($negotiator->applies($request)) {
+          if ($workspace_id = $negotiator->getActiveWorkspaceId($request)) {
+            /** @var \Drupal\workspaces\WorkspaceInterface $negotiated_workspace */
+            $negotiated_workspace = $this->entityTypeManager
+              ->getStorage('workspace')
+              ->load($workspace_id);
+          }
+
+          // By default, 'view' access is checked when a workspace is activated,
+          // but it should also be checked when retrieving the currently active
+          // workspace.
+          if (isset($negotiated_workspace) && $negotiated_workspace->access('view')) {
+            // Notify the negotiator that its workspace has been selected.
+            $negotiator->setActiveWorkspace($negotiated_workspace);
+
+            $active_workspace = $negotiated_workspace;
+            break;
+          }
+        }
+      }
+
+      // If no negotiator was able to provide a valid workspace, default to the
+      // live version of the site.
+      $this->activeWorkspace = $active_workspace ?? FALSE;
+    }
+
+    return $this->activeWorkspace;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function setActiveWorkspace(WorkspaceInterface $workspace) {
+    $this->doSwitchWorkspace($workspace);
+
+    // Set the workspace on the proper negotiator.
+    $request = $this->requestStack->getCurrentRequest();
+    foreach ($this->negotiatorIds as $negotiator_id) {
+      $negotiator = $this->classResolver->getInstanceFromDefinition($negotiator_id);
+      if ($negotiator->applies($request)) {
+        $negotiator->setActiveWorkspace($workspace);
+        break;
+      }
+    }
+
+    return $this;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function switchToLive() {
+    $this->doSwitchWorkspace(NULL);
+
+    // Unset the active workspace on all negotiators.
+    foreach ($this->negotiatorIds as $negotiator_id) {
+      $negotiator = $this->classResolver->getInstanceFromDefinition($negotiator_id);
+      $negotiator->unsetActiveWorkspace();
+    }
+
+    return $this;
+  }
+
+  /**
+   * Switches the current workspace.
+   *
+   * @param \Drupal\workspaces\WorkspaceInterface|null $workspace
+   *   The workspace to set as active or NULL to switch out of the currently
+   *   active workspace.
+   *
+   * @throws \Drupal\workspaces\WorkspaceAccessException
+   *   Thrown when the current user doesn't have access to view the workspace.
+   */
+  protected function doSwitchWorkspace($workspace) {
+    // If the current user doesn't have access to view the workspace, they
+    // shouldn't be allowed to switch to it, except in CLI processes.
+    if ($workspace && PHP_SAPI !== 'cli' && !$workspace->access('view')) {
+      $this->logger->error('Denied access to view workspace %workspace_label for user %uid', [
+        '%workspace_label' => $workspace->label(),
+        '%uid' => $this->currentUser->id(),
+      ]);
+      throw new WorkspaceAccessException('The user does not have permission to view that workspace.');
+    }
+
+    $this->activeWorkspace = $workspace ?: FALSE;
+
+    // Clear the static entity cache for the supported entity types.
+    $cache_tags_to_invalidate = array_map(function ($entity_type_id) {
+      return 'entity.memory_cache:' . $entity_type_id;
+    }, array_keys($this->workspaceInfo->getSupportedEntityTypes()));
+    $this->entityMemoryCache->invalidateTags($cache_tags_to_invalidate);
+
+    // Clear the static cache for path aliases. We can't inject the path alias
+    // manager service because it would create a circular dependency.
+    if (\Drupal::hasService('path_alias.manager')) {
+      \Drupal::service('path_alias.manager')->cacheClear();
+    }
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function executeInWorkspace($workspace_id, callable $function) {
+    /** @var \Drupal\workspaces\WorkspaceInterface $workspace */
+    $workspace = $this->entityTypeManager->getStorage('workspace')->load($workspace_id);
+
+    if (!$workspace) {
+      throw new \InvalidArgumentException('The ' . $workspace_id . ' workspace does not exist.');
+    }
+
+    $previous_active_workspace = $this->getActiveWorkspace();
+    $this->doSwitchWorkspace($workspace);
+    $result = $function();
+    $this->doSwitchWorkspace($previous_active_workspace);
+
+    return $result;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function executeOutsideWorkspace(callable $function) {
+    $previous_active_workspace = $this->getActiveWorkspace();
+    $this->doSwitchWorkspace(NULL);
+    $result = $function();
+    $this->doSwitchWorkspace($previous_active_workspace);
+
+    return $result;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function shouldAlterOperations(EntityTypeInterface $entity_type) {
+    @trigger_error(__METHOD__ . '() is deprecated in drupal:10.3.0 and is removed from drupal:11.0.0. There is no replacement. See https://www.drupal.org/node/3324297', E_USER_DEPRECATED);
+    return $this->workspaceInfo->isEntityTypeSupported($entity_type) && $this->hasActiveWorkspace();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function purgeDeletedWorkspacesBatch() {
+    $deleted_workspace_ids = $this->state->get('workspace.deleted', []);
+
+    // Bail out early if there are no workspaces to purge.
+    if (empty($deleted_workspace_ids)) {
+      return;
+    }
+
+    $batch_size = Settings::get('entity_update_batch_size', 50);
+
+    // Get the first deleted workspace from the list and delete the revisions
+    // associated with it, along with the workspace association records.
+    $workspace_id = reset($deleted_workspace_ids);
+
+    $all_associated_revisions = [];
+    foreach (array_keys($this->workspaceInfo->getSupportedEntityTypes()) as $entity_type_id) {
+      $all_associated_revisions[$entity_type_id] = $this->workspaceAssociation->getAssociatedRevisions($workspace_id, $entity_type_id);
+    }
+    $all_associated_revisions = array_filter($all_associated_revisions);
+
+    $count = 1;
+    foreach ($all_associated_revisions as $entity_type_id => $associated_revisions) {
+      /** @var \Drupal\Core\Entity\RevisionableStorageInterface $associated_entity_storage */
+      $associated_entity_storage = $this->entityTypeManager->getStorage($entity_type_id);
+
+      // Sort the associated revisions in reverse ID order, so we can delete the
+      // most recent revisions first.
+      krsort($associated_revisions);
+
+      // Get a list of default revisions tracked by the given workspace, because
+      // they need to be handled differently than pending revisions.
+      $initial_revision_ids = $this->workspaceAssociation->getAssociatedInitialRevisions($workspace_id, $entity_type_id);
+
+      foreach (array_keys($associated_revisions) as $revision_id) {
+        if ($count > $batch_size) {
+          continue 2;
+        }
+
+        // If the workspace is tracking the entity's default revision (i.e. the
+        // entity was created inside that workspace), we need to delete the
+        // whole entity after all of its pending revisions are gone.
+        if (isset($initial_revision_ids[$revision_id])) {
+          $associated_entity_storage->delete([$associated_entity_storage->load($initial_revision_ids[$revision_id])]);
+        }
+        else {
+          // Delete the associated entity revision.
+          $associated_entity_storage->deleteRevision($revision_id);
+        }
+        $count++;
+      }
+    }
+
+    // The purging operation above might have taken a long time, so we need to
+    // request a fresh list of tracked entities. If it is empty, we can go ahead
+    // and remove the deleted workspace ID entry from state.
+    $has_associated_revisions = FALSE;
+    foreach (array_keys($this->workspaceInfo->getSupportedEntityTypes()) as $entity_type_id) {
+      if (!empty($this->workspaceAssociation->getAssociatedRevisions($workspace_id, $entity_type_id))) {
+        $has_associated_revisions = TRUE;
+        break;
+      }
+    }
+    if (!$has_associated_revisions) {
+      unset($deleted_workspace_ids[$workspace_id]);
+      $this->state->set('workspace.deleted', $deleted_workspace_ids);
+
+      // Delete any possible leftover association entries.
+      $this->workspaceAssociation->deleteAssociations($workspace_id);
+    }
+  }
+
+}

core/modules/workspaces/src/WorkspaceManagerInterface.php

@@ -0,0 +1,123 @@
+<?php
+
+namespace Drupal\workspaces;
+
+use Drupal\Core\Entity\EntityTypeInterface;
+
+/**
+ * Provides an interface for managing Workspaces.
+ */
+interface WorkspaceManagerInterface {
+
+  /**
+   * Returns whether an entity type can belong to a workspace or not.
+   *
+   * @param \Drupal\Core\Entity\EntityTypeInterface $entity_type
+   *   The entity type to check.
+   *
+   * @return bool
+   *   TRUE if the entity type can belong to a workspace, FALSE otherwise.
+   *
+   * @deprecated in drupal:10.3.0 and is removed from drupal:11.0.0. Use
+   *   \Drupal\workspaces\WorkspaceInformation::isEntityTypeSupported instead.
+   *
+   * @see https://www.drupal.org/node/3324297
+   */
+  public function isEntityTypeSupported(EntityTypeInterface $entity_type);
+
+  /**
+   * Returns an array of entity types that can belong to workspaces.
+   *
+   * @return \Drupal\Core\Entity\EntityTypeInterface[]
+   *   The entity types what can belong to workspaces.
+   *
+   * @deprecated in drupal:10.3.0 and is removed from drupal:11.0.0. Use
+   *   \Drupal\workspaces\WorkspaceInformation::getSupportedEntityTypes instead.
+   *
+   * @see https://www.drupal.org/node/3324297
+   */
+  public function getSupportedEntityTypes();
+
+  /**
+   * Determines whether a workspace is active in the current request.
+   *
+   * @return bool
+   *   TRUE if a workspace is active, FALSE otherwise.
+   */
+  public function hasActiveWorkspace();
+
+  /**
+   * Gets the active workspace.
+   *
+   * @return \Drupal\workspaces\WorkspaceInterface
+   *   The active workspace entity object.
+   */
+  public function getActiveWorkspace();
+
+  /**
+   * Sets the active workspace via the workspace negotiators.
+   *
+   * @param \Drupal\workspaces\WorkspaceInterface $workspace
+   *   The workspace to set as active.
+   *
+   * @return $this
+   *
+   * @throws \Drupal\workspaces\WorkspaceAccessException
+   *   Thrown when the current user doesn't have access to view the workspace.
+   */
+  public function setActiveWorkspace(WorkspaceInterface $workspace);
+
+  /**
+   * Unsets the active workspace via the workspace negotiators.
+   *
+   * @return $this
+   */
+  public function switchToLive();
+
+  /**
+   * Executes the given callback function in the context of a workspace.
+   *
+   * @param string $workspace_id
+   *   The ID of a workspace.
+   * @param callable $function
+   *   The callback to be executed.
+   *
+   * @return mixed
+   *   The callable's return value.
+   */
+  public function executeInWorkspace($workspace_id, callable $function);
+
+  /**
+   * Executes the given callback function without any workspace context.
+   *
+   * @param callable $function
+   *   The callback to be executed.
+   *
+   * @return mixed
+   *   The callable's return value.
+   */
+  public function executeOutsideWorkspace(callable $function);
+
+  /**
+   * Determines whether runtime entity operations should be altered.
+   *
+   * @param \Drupal\Core\Entity\EntityTypeInterface $entity_type
+   *   The entity type to check.
+   *
+   * @return bool
+   *   TRUE if the entity operations or queries should be altered in the current
+   *   request, FALSE otherwise.
+   *
+   * @deprecated in drupal:10.3.0 and is removed from drupal:11.0.0. There is no
+   *   replacement.
+   *
+   * @see https://www.drupal.org/node/3324297
+   */
+  public function shouldAlterOperations(EntityTypeInterface $entity_type);
+
+  /**
+   * Deletes the revisions associated with deleted workspaces.
+   */
+  public function purgeDeletedWorkspacesBatch();
+
+}

core/modules/workspaces/src/WorkspaceMerger.php

@@ -0,0 +1,210 @@
+<?php
+
+namespace Drupal\workspaces;
+
+use Drupal\Core\Database\Connection;
+use Drupal\Core\Entity\EntityTypeManagerInterface;
+use Drupal\Core\Utility\Error;
+use Psr\Log\LoggerInterface;
+
+/**
+ * Default implementation of the workspace merger.
+ *
+ * @internal
+ */
+class WorkspaceMerger implements WorkspaceMergerInterface {
+
+  /**
+   * The source workspace entity.
+   *
+   * @var \Drupal\workspaces\WorkspaceInterface
+   */
+  protected $sourceWorkspace;
+
+  /**
+   * The target workspace entity.
+   *
+   * @var \Drupal\workspaces\WorkspaceInterface
+   */
+  protected $targetWorkspace;
+
+  /**
+   * The entity type manager.
+   *
+   * @var \Drupal\Core\Entity\EntityTypeManagerInterface
+   */
+  protected $entityTypeManager;
+
+  /**
+   * The database connection.
+   *
+   * @var \Drupal\Core\Database\Connection
+   */
+  protected $database;
+
+  /**
+   * The workspace association service.
+   *
+   * @var \Drupal\workspaces\WorkspaceAssociationInterface
+   */
+  protected $workspaceAssociation;
+
+  /**
+   * Constructs a new WorkspaceMerger.
+   *
+   * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
+   *   The entity type manager.
+   * @param \Drupal\Core\Database\Connection $database
+   *   Database connection.
+   * @param \Drupal\workspaces\WorkspaceAssociationInterface $workspace_association
+   *   The workspace association service.
+   * @param \Drupal\workspaces\WorkspaceInterface $source
+   *   The source workspace.
+   * @param \Drupal\workspaces\WorkspaceInterface $target
+   *   The target workspace.
+   * @param \Psr\Log\LoggerInterface|null $logger
+   *   The logger.
+   */
+  public function __construct(EntityTypeManagerInterface $entity_type_manager, Connection $database, WorkspaceAssociationInterface $workspace_association, WorkspaceInterface $source, WorkspaceInterface $target, protected ?LoggerInterface $logger = NULL) {
+    $this->entityTypeManager = $entity_type_manager;
+    $this->database = $database;
+    $this->workspaceAssociation = $workspace_association;
+    $this->sourceWorkspace = $source;
+    $this->targetWorkspace = $target;
+    if ($this->logger === NULL) {
+      @trigger_error('Calling ' . __METHOD__ . '() without the $logger argument is deprecated in drupal:10.1.0 and it will be required in drupal:11.0.0. See https://www.drupal.org/node/2932520', E_USER_DEPRECATED);
+      $this->logger = \Drupal::service('logger.channel.workspaces');
+    }
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function merge() {
+    if (!$this->sourceWorkspace->hasParent() || $this->sourceWorkspace->parent->target_id != $this->targetWorkspace->id()) {
+      throw new \InvalidArgumentException('The contents of a workspace can only be merged into its parent workspace.');
+    }
+
+    if ($this->checkConflictsOnTarget()) {
+      throw new WorkspaceConflictException();
+    }
+
+    try {
+      $transaction = $this->database->startTransaction();
+      foreach ($this->getDifferringRevisionIdsOnSource() as $entity_type_id => $revision_difference) {
+        $entity_type = $this->entityTypeManager->getDefinition($entity_type_id);
+        $revisions_on_source = $this->entityTypeManager->getStorage($entity_type_id)
+          ->loadMultipleRevisions(array_keys($revision_difference));
+
+        /** @var \Drupal\Core\Entity\ContentEntityInterface $revision */
+        foreach ($revisions_on_source as $revision) {
+          // Track all the differing revisions from the source workspace in
+          // the context of the target workspace. This will automatically
+          // update all the descendants of the target workspace as well.
+          $this->workspaceAssociation->trackEntity($revision, $this->targetWorkspace);
+
+          // Set the workspace in which the revision was merged.
+          $field_name = $entity_type->getRevisionMetadataKey('workspace');
+          $revision->{$field_name}->target_id = $this->targetWorkspace->id();
+          $revision->setSyncing(TRUE);
+          $revision->save();
+        }
+      }
+    }
+    catch (\Exception $e) {
+      if (isset($transaction)) {
+        $transaction->rollBack();
+      }
+      Error::logException($this->logger, $e);
+      throw $e;
+    }
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getSourceLabel() {
+    return $this->sourceWorkspace->label();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getTargetLabel() {
+    return $this->targetWorkspace->label();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function checkConflictsOnTarget() {
+    // Nothing to do for now, we can not get to a conflicting state because an
+    // entity which is being edited in a workspace can not be edited in any
+    // other workspace.
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getDifferringRevisionIdsOnTarget() {
+    $target_revision_difference = [];
+
+    $tracked_entities_on_source = $this->workspaceAssociation->getTrackedEntities($this->sourceWorkspace->id());
+    $tracked_entities_on_target = $this->workspaceAssociation->getTrackedEntities($this->targetWorkspace->id());
+    foreach ($tracked_entities_on_target as $entity_type_id => $tracked_revisions) {
+      // Now we compare the revision IDs which are tracked by the target
+      // workspace to those that are tracked by the source workspace, and the
+      // difference between these two arrays gives us all the entities which
+      // have a different revision ID on the target.
+      if (!isset($tracked_entities_on_source[$entity_type_id])) {
+        $target_revision_difference[$entity_type_id] = $tracked_revisions;
+      }
+      elseif ($revision_difference = array_diff_key($tracked_revisions, $tracked_entities_on_source[$entity_type_id])) {
+        $target_revision_difference[$entity_type_id] = $revision_difference;
+      }
+    }
+
+    return $target_revision_difference;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getDifferringRevisionIdsOnSource() {
+    $source_revision_difference = [];
+
+    $tracked_entities_on_source = $this->workspaceAssociation->getTrackedEntities($this->sourceWorkspace->id());
+    $tracked_entities_on_target = $this->workspaceAssociation->getTrackedEntities($this->targetWorkspace->id());
+    foreach ($tracked_entities_on_source as $entity_type_id => $tracked_revisions) {
+      // Now we compare the revision IDs which are tracked by the source
+      // workspace to those that are tracked by the target workspace, and the
+      // difference between these two arrays gives us all the entities which
+      // have a different revision ID on the source.
+      if (!isset($tracked_entities_on_target[$entity_type_id])) {
+        $source_revision_difference[$entity_type_id] = $tracked_revisions;
+      }
+      elseif ($revision_difference = array_diff_key($tracked_revisions, $tracked_entities_on_target[$entity_type_id])) {
+        $source_revision_difference[$entity_type_id] = $revision_difference;
+      }
+    }
+
+    return $source_revision_difference;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getNumberOfChangesOnTarget() {
+    $total_changes = $this->getDifferringRevisionIdsOnTarget();
+    return count($total_changes, COUNT_RECURSIVE) - count($total_changes);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getNumberOfChangesOnSource() {
+    $total_changes = $this->getDifferringRevisionIdsOnSource();
+    return count($total_changes, COUNT_RECURSIVE) - count($total_changes);
+  }
+
+}

core/modules/workspaces/src/WorkspaceMergerInterface.php

@@ -0,0 +1,17 @@
+<?php
+
+namespace Drupal\workspaces;
+
+/**
+ * Defines an interface for the workspace merger.
+ *
+ * @internal
+ */
+interface WorkspaceMergerInterface extends WorkspaceOperationInterface {
+
+  /**
+   * Merges the contents of the source workspace into the target workspace.
+   */
+  public function merge();
+
+}

core/modules/workspaces/src/WorkspaceOperationFactory.php

@@ -0,0 +1,143 @@
+<?php
+
+namespace Drupal\workspaces;
+
+use Drupal\Core\Cache\CacheTagsInvalidatorInterface;
+use Drupal\Core\Database\Connection;
+use Drupal\Core\DependencyInjection\DeprecatedServicePropertyTrait;
+use Drupal\Core\Entity\EntityTypeManagerInterface;
+use Psr\Log\LoggerInterface;
+use Symfony\Contracts\EventDispatcher\EventDispatcherInterface;
+
+/**
+ * Defines a factory class for workspace operations.
+ *
+ * @see \Drupal\workspaces\WorkspaceOperationInterface
+ * @see \Drupal\workspaces\WorkspacePublisherInterface
+ *
+ * @internal
+ */
+class WorkspaceOperationFactory {
+
+  use DeprecatedServicePropertyTrait;
+
+  /**
+   * Defines deprecated injected properties.
+   *
+   * @var array
+   */
+  protected array $deprecatedProperties = [
+    'cacheTagInvalidator' => 'cache_tags.invalidator',
+  ];
+
+  /**
+   * The entity type manager.
+   *
+   * @var \Drupal\Core\Entity\EntityTypeManagerInterface
+   */
+  protected $entityTypeManager;
+
+  /**
+   * The database connection.
+   *
+   * @var \Drupal\Core\Database\Connection
+   */
+  protected $database;
+
+  /**
+   * The workspace manager.
+   *
+   * @var \Drupal\workspaces\WorkspaceManagerInterface
+   */
+  protected $workspaceManager;
+
+  /**
+   * The workspace association service.
+   *
+   * @var \Drupal\workspaces\WorkspaceAssociationInterface
+   */
+  protected $workspaceAssociation;
+
+  /**
+   * An event dispatcher instance to use for configuration events.
+   *
+   * @var \Symfony\Contracts\EventDispatcher\EventDispatcherInterface
+   */
+  protected $eventDispatcher;
+
+  /**
+   * The logger service.
+   *
+   * @var \Psr\Log\LoggerInterface
+   */
+  protected $logger;
+
+  /**
+   * Constructs a new WorkspaceOperationFactory.
+   *
+   * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
+   *   The entity type manager.
+   * @param \Drupal\Core\Database\Connection $database
+   *   Database connection.
+   * @param \Drupal\workspaces\WorkspaceManagerInterface $workspace_manager
+   *   The workspace manager service.
+   * @param \Drupal\workspaces\WorkspaceAssociationInterface $workspace_association
+   *   The workspace association service.
+   * @param \Symfony\Contracts\EventDispatcher\EventDispatcherInterface|\Drupal\Core\Cache\CacheTagsInvalidatorInterface $event_dispatcher
+   *   The event dispatcher.
+   * @param \Psr\Log\LoggerInterface|null $logger
+   *   The logger.
+   */
+  public function __construct(EntityTypeManagerInterface $entity_type_manager, Connection $database, WorkspaceManagerInterface $workspace_manager, WorkspaceAssociationInterface $workspace_association, EventDispatcherInterface|CacheTagsInvalidatorInterface $event_dispatcher, LoggerInterface|EventDispatcherInterface|null $logger = NULL) {
+    $this->entityTypeManager = $entity_type_manager;
+    $this->database = $database;
+    $this->workspaceManager = $workspace_manager;
+    $this->workspaceAssociation = $workspace_association;
+
+    if ($event_dispatcher instanceof CacheTagsInvalidatorInterface) {
+      $event_dispatcher = \Drupal::service('event_dispatcher');
+      @trigger_error('Calling ' . __METHOD__ . '() with the $cache_tags_invalidator argument is deprecated in drupal:10.3.0 and is removed from drupal:11.0.0. See https://www.drupal.org/node/3440755', E_USER_DEPRECATED);
+    }
+    elseif (!$event_dispatcher instanceof EventDispatcherInterface) {
+      $event_dispatcher = \Drupal::service('event_dispatcher');
+      @trigger_error('Calling ' . __METHOD__ . '() without the $event_dispatcher argument is deprecated in drupal:10.1.0 and it will be required in drupal:11.0.0. See https://www.drupal.org/node/3242573', E_USER_DEPRECATED);
+    }
+    $this->eventDispatcher = $event_dispatcher;
+
+    $logger = func_get_arg(5);
+    if (!$logger instanceof LoggerInterface) {
+      $logger = \Drupal::service('logger.channel.workspaces');
+      @trigger_error('Calling ' . __METHOD__ . '() without the $logger argument is deprecated in drupal:10.1.0 and it will be required in drupal:11.0.0. See https://www.drupal.org/node/2932520', E_USER_DEPRECATED);
+    }
+    $this->logger = $logger;
+  }
+
+  /**
+   * Gets the workspace publisher.
+   *
+   * @param \Drupal\workspaces\WorkspaceInterface $source
+   *   A workspace entity.
+   *
+   * @return \Drupal\workspaces\WorkspacePublisherInterface
+   *   A workspace publisher object.
+   */
+  public function getPublisher(WorkspaceInterface $source) {
+    return new WorkspacePublisher($this->entityTypeManager, $this->database, $this->workspaceManager, $this->workspaceAssociation, $this->eventDispatcher, $source, $this->logger);
+  }
+
+  /**
+   * Gets the workspace merger.
+   *
+   * @param \Drupal\workspaces\WorkspaceInterface $source
+   *   The source workspace entity.
+   * @param \Drupal\workspaces\WorkspaceInterface $target
+   *   The target workspace entity.
+   *
+   * @return \Drupal\workspaces\WorkspaceMergerInterface
+   *   A workspace merger object.
+   */
+  public function getMerger(WorkspaceInterface $source, WorkspaceInterface $target) {
+    return new WorkspaceMerger($this->entityTypeManager, $this->database, $this->workspaceAssociation, $source, $target, $this->logger);
+  }
+
+}

core/modules/workspaces/src/WorkspaceOperationInterface.php

@@ -0,0 +1,82 @@
+<?php
+
+namespace Drupal\workspaces;
+
+/**
+ * Defines an interface for workspace operations.
+ *
+ * Example operations are publishing, merging and syncing with a remote
+ * workspace.
+ *
+ * @internal
+ */
+interface WorkspaceOperationInterface {
+
+  /**
+   * Returns the human-readable label of the source.
+   *
+   * @return string
+   *   The source label.
+   */
+  public function getSourceLabel();
+
+  /**
+   * Returns the human-readable label of the target.
+   *
+   * @return string
+   *   The target label.
+   */
+  public function getTargetLabel();
+
+  /**
+   * Checks if there are any conflicts between the source and the target.
+   *
+   * @return array
+   *   Returns an array consisting of the number of conflicts between the source
+   *   and the target, keyed by the conflict type constant.
+   */
+  public function checkConflictsOnTarget();
+
+  /**
+   * Gets the revision identifiers for items which have changed on the target.
+   *
+   * @return array
+   *   A multidimensional array of revision identifiers, keyed by entity type
+   *   IDs.
+   */
+  public function getDifferringRevisionIdsOnTarget();
+
+  /**
+   * Gets the revision identifiers for items which have changed on the source.
+   *
+   * @return array
+   *   A multidimensional array of revision identifiers, keyed by entity type
+   *   IDs.
+   */
+  public function getDifferringRevisionIdsOnSource();
+
+  /**
+   * Gets the total number of items which have changed on the target.
+   *
+   * This returns the aggregated changes count across all entity types.
+   * For example, if two nodes and one taxonomy term have changed on the target,
+   * the return value is 3.
+   *
+   * @return int
+   *   The number of differing revisions.
+   */
+  public function getNumberOfChangesOnTarget();
+
+  /**
+   * Gets the total number of items which have changed on the source.
+   *
+   * This returns the aggregated changes count across all entity types.
+   * For example, if two nodes and one taxonomy term have changed on the source,
+   * the return value is 3.
+   *
+   * @return int
+   *   The number of differing revisions.
+   */
+  public function getNumberOfChangesOnSource();
+
+}

core/modules/workspaces/src/WorkspacePublishException.php

@@ -0,0 +1,9 @@
+<?php
+
+namespace Drupal\workspaces;
+
+/**
+ * An exception thrown when a workspace can not be published.
+ */
+class WorkspacePublishException extends WorkspaceAccessException {
+}

core/modules/workspaces/src/WorkspacePublisher.php

@@ -0,0 +1,240 @@
+<?php
+
+namespace Drupal\workspaces;
+
+use Drupal\Core\Database\Connection;
+use Drupal\Core\Entity\EntityTypeManagerInterface;
+use Drupal\Core\StringTranslation\StringTranslationTrait;
+use Drupal\Core\Utility\Error;
+use Drupal\workspaces\Event\WorkspacePostPublishEvent;
+use Drupal\workspaces\Event\WorkspacePrePublishEvent;
+use Psr\Log\LoggerInterface;
+
+/**
+ * Default implementation of the workspace publisher.
+ *
+ * @internal
+ */
+class WorkspacePublisher implements WorkspacePublisherInterface {
+
+  use StringTranslationTrait;
+
+  /**
+   * The source workspace entity.
+   *
+   * @var \Drupal\workspaces\WorkspaceInterface
+   */
+  protected $sourceWorkspace;
+
+  /**
+   * The entity type manager.
+   *
+   * @var \Drupal\Core\Entity\EntityTypeManagerInterface
+   */
+  protected $entityTypeManager;
+
+  /**
+   * The database connection.
+   *
+   * @var \Drupal\Core\Database\Connection
+   */
+  protected $database;
+
+  /**
+   * The workspace manager.
+   *
+   * @var \Drupal\workspaces\WorkspaceManagerInterface
+   */
+  protected $workspaceManager;
+
+  /**
+   * The workspace association service.
+   *
+   * @var \Drupal\workspaces\WorkspaceAssociationInterface
+   */
+  protected $workspaceAssociation;
+
+  /**
+   * The event dispatcher.
+   *
+   * @var \Symfony\Contracts\EventDispatcher\EventDispatcherInterface
+   */
+  protected $eventDispatcher;
+
+  /**
+   * Constructs a new WorkspacePublisher.
+   *
+   * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
+   *   The entity type manager.
+   * @param \Drupal\Core\Database\Connection $database
+   *   Database connection.
+   * @param \Drupal\workspaces\WorkspaceManagerInterface $workspace_manager
+   *   The workspace manager.
+   * @param \Drupal\workspaces\WorkspaceAssociationInterface $workspace_association
+   *   The workspace association service.
+   * @param \Symfony\Contracts\EventDispatcher\EventDispatcherInterface $event_dispatcher
+   *   The event dispatcher.
+   * @param \Drupal\workspaces\WorkspaceInterface $source
+   *   The source workspace entity.
+   * @param \Psr\Log\LoggerInterface|null $logger
+   *   The logger.
+   */
+  public function __construct(EntityTypeManagerInterface $entity_type_manager, Connection $database, WorkspaceManagerInterface $workspace_manager, WorkspaceAssociationInterface $workspace_association, $event_dispatcher, ?WorkspaceInterface $source = NULL, protected ?LoggerInterface $logger = NULL) {
+    $this->entityTypeManager = $entity_type_manager;
+    $this->database = $database;
+    $this->workspaceManager = $workspace_manager;
+    $this->workspaceAssociation = $workspace_association;
+    if ($event_dispatcher instanceof WorkspaceInterface) {
+      @trigger_error('Calling WorkspacePublisher::__construct() without the $event_dispatcher argument is deprecated in drupal:10.1.0 and will be required in drupal:11.0.0. See https://www.drupal.org/node/3242573', E_USER_DEPRECATED);
+      $source = $event_dispatcher;
+      $event_dispatcher = \Drupal::service('event_dispatcher');
+    }
+    $this->eventDispatcher = $event_dispatcher;
+    $this->sourceWorkspace = $source;
+    if ($this->logger === NULL) {
+      @trigger_error('Calling ' . __METHOD__ . '() without the $logger argument is deprecated in drupal:10.1.0 and it will be required in drupal:11.0.0. See https://www.drupal.org/node/2932520', E_USER_DEPRECATED);
+      $this->logger = \Drupal::service('logger.channel.workspaces');
+    }
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function publish() {
+    if ($this->sourceWorkspace->hasParent()) {
+      throw new WorkspacePublishException('Only top-level workspaces can be published.');
+    }
+
+    if ($this->checkConflictsOnTarget()) {
+      throw new WorkspaceConflictException();
+    }
+
+    $tracked_entities = $this->workspaceAssociation->getTrackedEntities($this->sourceWorkspace->id());
+    $event = new WorkspacePrePublishEvent($this->sourceWorkspace, $tracked_entities);
+    $this->eventDispatcher->dispatch($event);
+
+    if ($event->isPublishingStopped()) {
+      throw new WorkspacePublishException((string) $event->getPublishingStoppedReason());
+    }
+
+    try {
+      $transaction = $this->database->startTransaction();
+      // @todo Handle the publishing of a workspace with a batch operation in
+      //   https://www.drupal.org/node/2958752.
+      $this->workspaceManager->executeOutsideWorkspace(function () use ($tracked_entities) {
+        foreach ($tracked_entities as $entity_type_id => $revision_difference) {
+          $entity_revisions = $this->entityTypeManager->getStorage($entity_type_id)
+            ->loadMultipleRevisions(array_keys($revision_difference));
+          $default_revisions = $this->entityTypeManager->getStorage($entity_type_id)
+            ->loadMultiple(array_values($revision_difference));
+
+          /** @var \Drupal\Core\Entity\ContentEntityInterface $entity */
+          foreach ($entity_revisions as $entity) {
+            // When pushing workspace-specific revisions to the default
+            // workspace (Live), we simply need to mark them as default
+            // revisions.
+            $entity->setSyncing(TRUE);
+            $entity->isDefaultRevision(TRUE);
+
+            // The default revision is not workspace-specific anymore.
+            $field_name = $entity->getEntityType()->getRevisionMetadataKey('workspace');
+            $entity->{$field_name}->target_id = NULL;
+
+            $entity->original = $default_revisions[$entity->id()];
+            $entity->save();
+          }
+        }
+      });
+    }
+    catch (\Exception $e) {
+      if (isset($transaction)) {
+        $transaction->rollBack();
+      }
+      Error::logException($this->logger, $e);
+      throw $e;
+    }
+
+    $event = new WorkspacePostPublishEvent($this->sourceWorkspace, $tracked_entities);
+    $this->eventDispatcher->dispatch($event);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getSourceLabel() {
+    return $this->sourceWorkspace->label();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getTargetLabel() {
+    return $this->t('Live');
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function checkConflictsOnTarget() {
+    // Nothing to do for now, we can not get to a conflicting state because an
+    // entity which is being edited in a workspace can not be edited in any
+    // other workspace.
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getDifferringRevisionIdsOnTarget() {
+    $target_revision_difference = [];
+
+    $tracked_entities = $this->workspaceAssociation->getTrackedEntities($this->sourceWorkspace->id());
+    foreach ($tracked_entities as $entity_type_id => $tracked_revisions) {
+      $entity_type = $this->entityTypeManager->getDefinition($entity_type_id);
+
+      // Get the latest revision IDs for all the entities that are tracked by
+      // the source workspace.
+      $query = $this->entityTypeManager
+        ->getStorage($entity_type_id)
+        ->getQuery()
+        ->accessCheck(FALSE)
+        ->condition($entity_type->getKey('id'), $tracked_revisions, 'IN')
+        ->latestRevision();
+      $result = $query->execute();
+
+      // Now we compare the revision IDs which are tracked by the source
+      // workspace to the latest revision IDs of those entities and the
+      // difference between these two arrays gives us all the entities which
+      // have been modified on the target.
+      if ($revision_difference = array_diff_key($result, $tracked_revisions)) {
+        $target_revision_difference[$entity_type_id] = $revision_difference;
+      }
+    }
+
+    return $target_revision_difference;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getDifferringRevisionIdsOnSource() {
+    // Get the Workspace association revisions which haven't been pushed yet.
+    return $this->workspaceAssociation->getTrackedEntities($this->sourceWorkspace->id());
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getNumberOfChangesOnTarget() {
+    $total_changes = $this->getDifferringRevisionIdsOnTarget();
+    return count($total_changes, COUNT_RECURSIVE) - count($total_changes);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getNumberOfChangesOnSource() {
+    $total_changes = $this->getDifferringRevisionIdsOnSource();
+    return count($total_changes, COUNT_RECURSIVE) - count($total_changes);
+  }
+
+}

core/modules/workspaces/src/WorkspacePublisherInterface.php

@@ -0,0 +1,17 @@
+<?php
+
+namespace Drupal\workspaces;
+
+/**
+ * Defines an interface for the workspace publisher.
+ *
+ * @internal
+ */
+interface WorkspacePublisherInterface extends WorkspaceOperationInterface {
+
+  /**
+   * Publishes the contents of a workspace to the default (Live) workspace.
+   */
+  public function publish();
+
+}

core/modules/workspaces/src/WorkspaceRepository.php

@@ -0,0 +1,154 @@
+<?php
+
+namespace Drupal\workspaces;
+
+use Drupal\Component\Assertion\Inspector;
+use Drupal\Component\Graph\Graph;
+use Drupal\Core\Cache\Cache;
+use Drupal\Core\Cache\CacheBackendInterface;
+use Drupal\Core\Entity\EntityTypeManagerInterface;
+
+/**
+ * Provides the default workspace tree lookup operations.
+ */
+class WorkspaceRepository implements WorkspaceRepositoryInterface {
+
+  /**
+   * The entity type manager service.
+   *
+   * @var \Drupal\Core\Entity\EntityTypeManagerInterface
+   */
+  protected $entityTypeManager;
+
+  /**
+   * The cache backend used to store the workspace tree.
+   *
+   * @var \Drupal\Core\Cache\CacheBackendInterface
+   */
+  protected $cache;
+
+  /**
+   * An array of tree items, keyed by workspace IDs and sorted in tree order.
+   *
+   * @var array|null
+   */
+  protected $tree;
+
+  /**
+   * Constructs a new WorkspaceRepository instance.
+   *
+   * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
+   *   The entity type manager service.
+   * @param \Drupal\Core\Cache\CacheBackendInterface $cache_backend
+   *   The cache backend.
+   */
+  public function __construct(EntityTypeManagerInterface $entity_type_manager, CacheBackendInterface $cache_backend) {
+    $this->entityTypeManager = $entity_type_manager;
+    $this->cache = $cache_backend;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function loadTree() {
+    if (!isset($this->tree)) {
+      $cache = $this->cache->get('workspace_tree');
+      if ($cache) {
+        $this->tree = $cache->data;
+        return $this->tree;
+      }
+
+      /** @var \Drupal\workspaces\WorkspaceInterface[] $workspaces */
+      $workspaces = $this->entityTypeManager->getStorage('workspace')->loadMultiple();
+
+      // First, sort everything alphabetically.
+      uasort($workspaces, function (WorkspaceInterface $a, WorkspaceInterface $b) {
+        assert(Inspector::assertStringable($a->label()) && Inspector::assertStringable($b->label()), 'Workspace labels are expected to be a string.');
+        return strnatcasecmp($a->label(), $b->label());
+      });
+
+      $tree_children = [];
+      foreach ($workspaces as $workspace_id => $workspace) {
+        $tree_children[$workspace->parent->target_id][] = $workspace_id;
+      }
+
+      // Keeps track of the parents we have to process, the last entry is used
+      // for the next processing step. Top-level (root) workspace use NULL as
+      // the parent, so we need to initialize the list with that value.
+      $process_parents[] = NULL;
+
+      // Loops over the parent entities and adds its children to the tree array.
+      // Uses a loop instead of a recursion, because it's more efficient.
+      $tree = [];
+      while (count($process_parents)) {
+        $parent = array_pop($process_parents);
+
+        if (!empty($tree_children[$parent])) {
+          $child_id = current($tree_children[$parent]);
+          do {
+            if (empty($child_id)) {
+              break;
+            }
+            $tree[$child_id] = $workspaces[$child_id];
+
+            if (!empty($tree_children[$child_id])) {
+              // We have to continue with this parent later.
+              $process_parents[] = $parent;
+              // Use the current entity as parent for the next iteration.
+              $process_parents[] = $child_id;
+
+              // Move pointer so that we get the correct entity the next time.
+              next($tree_children[$parent]);
+              break;
+            }
+          } while ($child_id = next($tree_children[$parent]));
+        }
+      }
+
+      // Generate a graph object in order to populate the `_depth`, `_ancestors`
+      // and '_descendants' properties for all the entities.
+      $graph = [];
+      foreach ($workspaces as $workspace_id => $workspace) {
+        $graph[$workspace_id]['edges'] = [];
+        if (!$workspace->parent->isEmpty()) {
+          $graph[$workspace_id]['edges'][$workspace->parent->target_id] = TRUE;
+        }
+      }
+      $graph = (new Graph($graph))->searchAndSort();
+
+      $this->tree = [];
+      foreach (array_keys($tree) as $workspace_id) {
+        $this->tree[$workspace_id] = [
+          'depth' => count($graph[$workspace_id]['paths']),
+          'ancestors' => array_keys($graph[$workspace_id]['paths']),
+          'descendants' => isset($graph[$workspace_id]['reverse_paths']) ? array_keys($graph[$workspace_id]['reverse_paths']) : [],
+        ];
+      }
+
+      // Use the 'workspace_list' entity type cache tag because it will be
+      // invalidated automatically when a workspace is added, updated or
+      // deleted.
+      $this->cache->set('workspace_tree', $this->tree, Cache::PERMANENT, $this->entityTypeManager->getDefinition('workspace')->getListCacheTags());
+    }
+
+    return $this->tree;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getDescendantsAndSelf($workspace_id) {
+    return array_merge([$workspace_id], $this->loadTree()[$workspace_id]['descendants']);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function resetCache() {
+    $this->cache->invalidate('workspace_tree');
+    $this->tree = NULL;
+
+    return $this;
+  }
+
+}

core/modules/workspaces/src/WorkspaceRepositoryInterface.php

@@ -0,0 +1,40 @@
+<?php
+
+namespace Drupal\workspaces;
+
+/**
+ * Provides an interface for workspace tree lookup operations.
+ */
+interface WorkspaceRepositoryInterface {
+
+  /**
+   * Returns an array of workspaces tree item properties, sorted in tree order.
+   *
+   * @return array
+   *   An array of workspace tree item properties, keyed by the workspace IDs.
+   *   The tree item properties are:
+   *   - depth: The depth of the workspace in the tree;
+   *   - ancestors: The ancestor IDs of the workspace;
+   *   - descendants: The descendant IDs of the workspace.
+   */
+  public function loadTree();
+
+  /**
+   * Returns the descendant IDs of the passed-in workspace, including itself.
+   *
+   * @param string $workspace_id
+   *   A workspace ID.
+   *
+   * @return string[]
+   *   An array of descendant workspace IDs, including the passed-in one.
+   */
+  public function getDescendantsAndSelf($workspace_id);
+
+  /**
+   * Resets the cached workspace tree.
+   *
+   * @return $this
+   */
+  public function resetCache();
+
+}

core/modules/workspaces/src/WorkspaceViewBuilder.php

@@ -0,0 +1,183 @@
+<?php
+
+namespace Drupal\workspaces;
+
+use Drupal\Core\Entity\EntityChangedInterface;
+use Drupal\Core\Entity\EntityListBuilder;
+use Drupal\Core\Entity\EntityTypeInterface;
+use Drupal\Core\Entity\EntityViewBuilder;
+use Drupal\user\EntityOwnerInterface;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Provides a Workspace view builder.
+ */
+class WorkspaceViewBuilder extends EntityViewBuilder {
+
+  /**
+   * The entity type manager.
+   *
+   * @var \Drupal\Core\Entity\EntityTypeManagerInterface
+   */
+  protected $entityTypeManager;
+
+  /**
+   * The workspace association service.
+   *
+   * @var \Drupal\workspaces\WorkspaceAssociationInterface
+   */
+  protected $workspaceAssociation;
+
+  /**
+   * The date formatter service.
+   *
+   * @var \Drupal\Core\Datetime\DateFormatterInterface
+   */
+  protected $dateFormatter;
+
+  /**
+   * The entity bundle information service.
+   *
+   * @var \Drupal\Core\Entity\EntityTypeBundleInfoInterface
+   */
+  protected $bundleInfo;
+
+  /**
+   * The number of entities to display on the workspace manage page.
+   */
+  protected int|false $limit = 50;
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function createInstance(ContainerInterface $container, EntityTypeInterface $entity_type) {
+    $instance = parent::createInstance($container, $entity_type);
+    $instance->entityTypeManager = $container->get('entity_type.manager');
+    $instance->workspaceAssociation = $container->get('workspaces.association');
+    $instance->dateFormatter = $container->get('date.formatter');
+    $instance->bundleInfo = $container->get('entity_type.bundle.info');
+    return $instance;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function buildComponents(array &$build, array $entities, array $displays, $view_mode) {
+    parent::buildComponents($build, $entities, $displays, $view_mode);
+    $bundle_info = $this->bundleInfo->getAllBundleInfo();
+
+    $header = [
+      'title' => $this->t('Title'),
+      'type' => $this->t('Type'),
+      'changed' => $this->t('Last changed'),
+      'owner' => $this->t('Author'),
+      'operations' => $this->t('Operations'),
+    ];
+    foreach ($entities as $build_id => $entity) {
+      // Display the number of entities changed in the workspace regardless of
+      // how many of them are listed on each page.
+      $changes_count = [];
+      $all_tracked_entities = $this->workspaceAssociation->getTrackedEntities($entity->id());
+      foreach ($all_tracked_entities as $entity_type_id => $tracked_entity_ids) {
+        $changes_count[$entity_type_id] = $this->entityTypeManager->getDefinition($entity_type_id)->getCountLabel(count($tracked_entity_ids));
+      }
+
+      $build[$build_id]['changes']['overview'] = [
+        '#type' => 'item',
+        '#title' => $this->t('Workspace changes'),
+      ];
+
+      $build[$build_id]['changes']['list'] = [
+        '#type' => 'table',
+        '#header' => $header,
+        '#empty' => $this->t('This workspace has no changes.'),
+      ];
+
+      $paged_tracked_entities = $this->workspaceAssociation->getTrackedEntitiesForListing($entity->id(), $build_id, $this->limit);
+      foreach ($paged_tracked_entities as $entity_type_id => $tracked_entities) {
+        $entity_type = $this->entityTypeManager->getDefinition($entity_type_id);
+        if ($this->entityTypeManager->hasHandler($entity_type_id, 'list_builder')) {
+          $list_builder = $this->entityTypeManager->getListBuilder($entity_type_id);
+        }
+        else {
+          $list_builder = $this->entityTypeManager->createHandlerInstance(EntityListBuilder::class, $entity_type);
+        }
+
+        $revisions = $this->entityTypeManager->getStorage($entity_type_id)->loadMultipleRevisions(array_keys($tracked_entities));
+
+        // Load all users at once.
+        $user_ids = [];
+        foreach ($revisions as $revision) {
+          if ($revision instanceof EntityOwnerInterface) {
+            $user_ids[$revision->getOwnerId()] = $revision->getOwnerId();
+          }
+        }
+
+        if ($user_ids = array_filter($user_ids)) {
+          $revision_owners = $this->entityTypeManager->getStorage('user')->loadMultiple($user_ids);
+        }
+
+        foreach ($revisions as $revision) {
+          if ($revision->getEntityType()->hasLinkTemplate('canonical')) {
+            $title = [
+              '#type' => 'link',
+              '#title' => $revision->label(),
+              '#url' => $revision->toUrl(),
+            ];
+          }
+          else {
+            $title = ['#markup' => $revision->label()];
+          }
+
+          if (count($bundle_info[$entity_type_id]) > 1) {
+            $type = [
+              '#markup' => $this->t('@entity_type_label: @entity_bundle_label', [
+                '@entity_type_label' => $entity_type->getLabel(),
+                '@entity_bundle_label' => $bundle_info[$entity_type_id][$revision->bundle()]['label'],
+              ]),
+            ];
+          }
+          else {
+            $type = ['#markup' => $bundle_info[$entity_type_id][$revision->bundle()]['label']];
+          }
+
+          $changed = $revision instanceof EntityChangedInterface
+            ? $this->dateFormatter->format($revision->getChangedTime())
+            : '';
+
+          if ($revision instanceof EntityOwnerInterface && isset($revision_owners[$revision->getOwnerId()])) {
+            $author = [
+              '#theme' => 'username',
+              '#account' => $revision_owners[$revision->getOwnerId()],
+            ];
+          }
+          else {
+            $author = ['#markup' => ''];
+          }
+
+          $build[$build_id]['changes']['list'][$entity_type_id . ':' . $revision->id()] = [
+            '#entity' => $revision,
+            'title' => $title,
+            'type' => $type,
+            'changed' => ['#markup' => $changed],
+            'owner' => $author,
+            'operations' => [
+              '#type' => 'operations',
+              '#links' => $list_builder->getOperations($revision),
+            ],
+          ];
+        }
+      }
+
+      if ($changes_count) {
+        $build[$build_id]['changes']['overview']['#markup'] = implode(', ', $changes_count);
+      }
+
+      $build[$build_id]['pager'] = [
+        '#type' => 'pager',
+        '#element' => $build_id,
+      ];
+    }
+  }
+
+}

core/modules/workspaces/src/WorkspacesAliasManager.php

@@ -0,0 +1,59 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\workspaces;
+
+use Drupal\path_alias\AliasManagerInterface;
+
+/**
+ * Decorates the path_alias.manager service for workspace-specific caching.
+ *
+ * @internal
+ */
+class WorkspacesAliasManager implements AliasManagerInterface {
+
+  public function __construct(
+    protected readonly AliasManagerInterface $inner,
+    protected readonly WorkspaceManagerInterface $workspaceManager,
+  ) {}
+
+  /**
+   * {@inheritdoc}
+   */
+  public function setCacheKey($key): void {
+    if ($this->workspaceManager->hasActiveWorkspace()) {
+      $key = $this->workspaceManager->getActiveWorkspace()->id() . ':' . $key;
+    }
+    $this->inner->setCacheKey($key);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function writeCache(): void {
+    $this->inner->writeCache();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getPathByAlias($alias, $langcode = NULL): string {
+    return $this->inner->getPathByAlias($alias, $langcode);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getAliasByPath($path, $langcode = NULL): string {
+    return $this->inner->getAliasByPath($path, $langcode);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function cacheClear($source = NULL): void {
+    $this->inner->cacheClear($source);
+  }
+
+}

core/modules/workspaces/src/WorkspacesAliasRepository.php

@@ -0,0 +1,52 @@
+<?php
+
+namespace Drupal\workspaces;
+
+use Drupal\path_alias\AliasRepository;
+
+/**
+ * Provides workspace-specific path alias lookup queries.
+ */
+class WorkspacesAliasRepository extends AliasRepository {
+
+  /**
+   * The workspace manager.
+   *
+   * @var \Drupal\workspaces\WorkspaceManagerInterface
+   */
+  protected $workspaceManager;
+
+  /**
+   * Sets the workspace manager.
+   *
+   * @param \Drupal\workspaces\WorkspaceManagerInterface $workspace_manager
+   *   The workspace manager service.
+   *
+   * @return $this
+   */
+  public function setWorkspacesManager(WorkspaceManagerInterface $workspace_manager) {
+    $this->workspaceManager = $workspace_manager;
+    return $this;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function getBaseQuery() {
+    // Don't alter any queries if we're not in a workspace context.
+    if (!$this->workspaceManager->hasActiveWorkspace()) {
+      return parent::getBaseQuery();
+    }
+
+    $active_workspace = $this->workspaceManager->getActiveWorkspace();
+
+    $query = $this->connection->select('path_alias', 'base_table_2');
+    $wa_join = $query->leftJoin('workspace_association', NULL, "[%alias].[target_entity_type_id] = 'path_alias' AND [%alias].[target_entity_id] = [base_table_2].[id] AND [%alias].[workspace] = :active_workspace_id", [
+      ':active_workspace_id' => $active_workspace->id(),
+    ]);
+    $query->innerJoin('path_alias_revision', 'base_table', "[%alias].[revision_id] = COALESCE([$wa_join].[target_entity_revision_id], [base_table_2].[revision_id])");
+
+    return $query;
+  }
+
+}

core/modules/workspaces/src/WorkspacesLazyBuilders.php

@@ -0,0 +1,87 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\workspaces;
+
+use Drupal\Component\Serialization\Json;
+use Drupal\Core\Render\ElementInfoManagerInterface;
+use Drupal\Core\Security\TrustedCallbackInterface;
+use Drupal\Core\StringTranslation\StringTranslationTrait;
+use Drupal\Core\Url;
+
+/**
+ * Defines a service for workspaces #lazy_builder callbacks.
+ *
+ * @internal
+ */
+final class WorkspacesLazyBuilders implements TrustedCallbackInterface {
+
+  use StringTranslationTrait;
+
+  public function __construct(
+    protected readonly WorkspaceManagerInterface $workspaceManager,
+    protected readonly ElementInfoManagerInterface $elementInfo,
+  ) {}
+
+  /**
+   * Lazy builder callback for rendering the workspace toolbar tab.
+   *
+   * @return array
+   *   A render array.
+   */
+  public function renderToolbarTab(): array {
+    $active_workspace = $this->workspaceManager->getActiveWorkspace();
+
+    $build = [
+      '#type' => 'link',
+      '#title' => $active_workspace ? $active_workspace->label() : $this->t('Live'),
+      '#url' => Url::fromRoute('entity.workspace.collection', [], ['query' => \Drupal::destination()->getAsArray()]),
+      '#attributes' => [
+        'title' => t('Switch workspace'),
+        'class' => [
+          'toolbar-item',
+          'toolbar-icon',
+          'toolbar-icon-workspace',
+          'use-ajax',
+        ],
+        'data-dialog-type' => 'dialog',
+        'data-dialog-renderer' => 'off_canvas_top',
+        'data-dialog-options' => Json::encode([
+          'height' => 161,
+          'classes' => [
+            'ui-dialog' => 'workspaces-dialog',
+          ],
+        ]),
+      ],
+      '#attached' => [
+        'library' => ['workspaces/drupal.workspaces.toolbar'],
+      ],
+      '#cache' => [
+        'max-age' => 0,
+      ],
+    ];
+
+    // The renderer has already added element defaults by the time the lazy
+    // builder is run.
+    // @see https://www.drupal.org/project/drupal/issues/2609250
+    $build += $this->elementInfo->getInfo('link');
+    return $build;
+  }
+
+  /**
+   * Render callback for the workspace toolbar tab.
+   */
+  public static function removeTabAttributes(array $element): array {
+    unset($element['tab']['#attributes']);
+    return $element;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function trustedCallbacks(): array {
+    return ['removeTabAttributes', 'renderToolbarTab'];
+  }
+
+}

core/modules/workspaces/src/WorkspacesMenuTreeStorage.php

@@ -0,0 +1,96 @@
+<?php
+
+namespace Drupal\workspaces;
+
+use Drupal\Core\Cache\CacheBackendInterface;
+use Drupal\Core\Cache\CacheTagsInvalidatorInterface;
+use Drupal\Core\Database\Connection;
+use Drupal\Core\Entity\EntityTypeManagerInterface;
+use Drupal\Core\Menu\MenuTreeParameters;
+use Drupal\Core\Menu\MenuTreeStorage as CoreMenuTreeStorage;
+
+/**
+ * Overrides the default menu storage to provide workspace-specific menu links.
+ *
+ * @internal
+ */
+class WorkspacesMenuTreeStorage extends CoreMenuTreeStorage {
+
+  /**
+   * WorkspacesMenuTreeStorage constructor.
+   *
+   * @param \Drupal\workspaces\WorkspaceManagerInterface $workspaceManager
+   *   The workspace manager service.
+   * @param \Drupal\workspaces\WorkspaceAssociationInterface $workspaceAssociation
+   *   The workspace association service.
+   * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entityTypeManager
+   *   The entity type manager.
+   * @param \Drupal\Core\Database\Connection $connection
+   *   A Database connection to use for reading and writing configuration data.
+   * @param \Drupal\Core\Cache\CacheBackendInterface $menu_cache_backend
+   *   Cache backend instance for the extracted tree data.
+   * @param \Drupal\Core\Cache\CacheTagsInvalidatorInterface $cache_tags_invalidator
+   *   The cache tags invalidator.
+   * @param string $table
+   *   A database table name to store configuration data in.
+   * @param array $options
+   *   (optional) Any additional database connection options to use in queries.
+   */
+  public function __construct(
+    protected readonly WorkspaceManagerInterface $workspaceManager,
+    protected readonly WorkspaceAssociationInterface $workspaceAssociation,
+    protected readonly EntityTypeManagerInterface $entityTypeManager,
+    Connection $connection,
+    CacheBackendInterface $menu_cache_backend,
+    CacheTagsInvalidatorInterface $cache_tags_invalidator,
+    string $table,
+    array $options = [],
+  ) {
+    parent::__construct($connection, $menu_cache_backend, $cache_tags_invalidator, $table, $options);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function loadTreeData($menu_name, MenuTreeParameters $parameters) {
+    // Add the active workspace as a menu tree condition parameter in order to
+    // include it in the cache ID.
+    if ($active_workspace = $this->workspaceManager->getActiveWorkspace()) {
+      $parameters->conditions['workspace'] = $active_workspace->id();
+    }
+    return parent::loadTreeData($menu_name, $parameters);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function loadLinks($menu_name, MenuTreeParameters $parameters) {
+    $links = parent::loadLinks($menu_name, $parameters);
+
+    // Replace the menu link plugin definitions with workspace-specific ones.
+    if ($active_workspace = $this->workspaceManager->getActiveWorkspace()) {
+      $tracked_revisions = $this->workspaceAssociation->getTrackedEntities($active_workspace->id());
+      if (isset($tracked_revisions['menu_link_content'])) {
+        /** @var \Drupal\menu_link_content\MenuLinkContentInterface[] $workspace_revisions */
+        $workspace_revisions = $this->entityTypeManager->getStorage('menu_link_content')->loadMultipleRevisions(array_keys($tracked_revisions['menu_link_content']));
+        foreach ($workspace_revisions as $workspace_revision) {
+          if (isset($links[$workspace_revision->getPluginId()])) {
+            $pending_plugin_definition = $workspace_revision->getPluginDefinition();
+            $links[$workspace_revision->getPluginId()] = [
+              'title' => serialize($pending_plugin_definition['title']),
+              'description' => serialize($pending_plugin_definition['description']),
+              'enabled' => (string) $pending_plugin_definition['enabled'],
+              'url' => $pending_plugin_definition['url'],
+              'route_name' => $pending_plugin_definition['route_name'],
+              'route_parameters' => serialize($pending_plugin_definition['route_parameters']),
+              'options' => serialize($pending_plugin_definition['options']),
+            ] + $links[$workspace_revision->getPluginId()];
+          }
+        }
+      }
+    }
+
+    return $links;
+  }
+
+}

core/modules/workspaces/src/WorkspacesServiceProvider.php

@@ -0,0 +1,54 @@
+<?php
+
+namespace Drupal\workspaces;
+
+use Drupal\Core\DependencyInjection\ContainerBuilder;
+use Drupal\Core\DependencyInjection\ServiceProviderBase;
+use Drupal\Core\Update\UpdateKernel;
+use Symfony\Component\DependencyInjection\Reference;
+
+/**
+ * Defines a service provider for the Workspaces module.
+ */
+class WorkspacesServiceProvider extends ServiceProviderBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function alter(ContainerBuilder $container) {
+    // Add the 'workspace' cache context as required.
+    $renderer_config = $container->getParameter('renderer.config');
+    $renderer_config['required_cache_contexts'][] = 'workspace';
+    $container->setParameter('renderer.config', $renderer_config);
+
+    // Decorate the 'path_alias.manager' service.
+    if ($container->hasDefinition('path_alias.manager')) {
+      $container->register('workspaces.path_alias.manager', WorkspacesAliasManager::class)
+        ->setPublic(FALSE)
+        ->setDecoratedService('path_alias.manager', NULL, 50)
+        ->addArgument(new Reference('workspaces.path_alias.manager.inner'))
+        ->addArgument(new Reference('workspaces.manager'));
+    }
+
+    // Replace the class of the 'path_alias.repository' service.
+    if ($container->hasDefinition('path_alias.repository')) {
+      $definition = $container->getDefinition('path_alias.repository');
+      if (!$definition->isDeprecated()) {
+        $definition
+          ->setClass(WorkspacesAliasRepository::class)
+          ->addMethodCall('setWorkspacesManager', [new Reference('workspaces.manager')]);
+      }
+    }
+
+    // Ensure that there's no active workspace while running database updates by
+    // removing the relevant tag from all workspace negotiator services.
+    if ($container->get('kernel') instanceof UpdateKernel) {
+      foreach ($container->getDefinitions() as $definition) {
+        if ($definition->hasTag('workspace_negotiator')) {
+          $definition->clearTag('workspace_negotiator');
+        }
+      }
+    }
+  }
+
+}

core/modules/workspaces/tests/modules/workspace_access_test/workspace_access_test.info.yml

@@ -0,0 +1,12 @@
+name: 'Workspace Access Test'
+type: module
+description: 'Provides supporting code for testing access for workspaces.'
+package: Testing
+# version: VERSION
+dependencies:
+  - drupal:workspaces
+
+# Information added by Drupal.org packaging script on 2024-07-04
+version: '10.3.1'
+project: 'drupal'
+datestamp: 1720094222

core/modules/workspaces/tests/modules/workspace_access_test/workspace_access_test.module

@@ -0,0 +1,17 @@
+<?php
+
+/**
+ * @file
+ * Provides supporting code for testing access for workspaces.
+ */
+
+use Drupal\Core\Access\AccessResult;
+use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Session\AccountInterface;
+
+/**
+ * Implements hook_ENTITY_TYPE_access() for the 'workspace' entity type.
+ */
+function workspace_access_test_workspace_access(EntityInterface $entity, $operation, AccountInterface $account) {
+  return \Drupal::state()->get("workspace_access_test.result.$operation", AccessResult::neutral());
+}

core/modules/workspaces/tests/modules/workspace_update_test/src/Negotiator/TestWorkspaceNegotiator.php

@@ -0,0 +1,51 @@
+<?php
+
+namespace Drupal\workspace_update_test\Negotiator;
+
+use Drupal\workspaces\Entity\Workspace;
+use Drupal\workspaces\Negotiator\WorkspaceIdNegotiatorInterface;
+use Drupal\workspaces\Negotiator\WorkspaceNegotiatorInterface;
+use Drupal\workspaces\WorkspaceInterface;
+use Symfony\Component\HttpFoundation\Request;
+
+/**
+ * Defines a workspace negotiator used for testing.
+ */
+class TestWorkspaceNegotiator implements WorkspaceNegotiatorInterface, WorkspaceIdNegotiatorInterface {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function applies(Request $request) {
+    return TRUE;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getActiveWorkspaceId(Request $request): ?string {
+    return 'test';
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getActiveWorkspace(Request $request) {
+    return Workspace::load($this->getActiveWorkspaceId($request));
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function setActiveWorkspace(WorkspaceInterface $workspace) {
+    // Nothing to do here.
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function unsetActiveWorkspace() {
+    // Nothing to do here.
+  }
+
+}

core/modules/workspaces/tests/modules/workspace_update_test/workspace_update_test.info.yml

@@ -0,0 +1,12 @@
+name: 'Workspace Update Test'
+type: module
+description: 'Provides supporting code for testing workspaces during database updates.'
+package: Testing
+# version: VERSION
+dependencies:
+  - drupal:workspaces
+
+# Information added by Drupal.org packaging script on 2024-07-04
+version: '10.3.1'
+project: 'drupal'
+datestamp: 1720094222

core/modules/workspaces/tests/modules/workspace_update_test/workspace_update_test.post_update.php

@@ -0,0 +1,13 @@
+<?php
+
+/**
+ * @file
+ * Post update functions for the Workspace Update Test module.
+ */
+
+/**
+ * Checks the active workspace during database updates.
+ */
+function workspace_update_test_post_update_check_active_workspace() {
+  \Drupal::state()->set('workspace_update_test.has_active_workspace', \Drupal::service('workspaces.manager')->hasActiveWorkspace());
+}

core/modules/workspaces/tests/modules/workspace_update_test/workspace_update_test.services.yml

@@ -0,0 +1,5 @@
+services:
+  workspace_update_test.negotiator.test:
+    class: Drupal\workspace_update_test\Negotiator\TestWorkspaceNegotiator
+    tags:
+      - { name: workspace_negotiator, priority: 0 }

core/modules/workspaces/tests/modules/workspaces_test/src/EntityTestRevPubWorkspaceHandler.php

@@ -0,0 +1,20 @@
+<?php
+
+namespace Drupal\workspaces_test;
+
+use Drupal\Core\Entity\EntityInterface;
+use Drupal\workspaces\Entity\Handler\DefaultWorkspaceHandler;
+
+/**
+ * Provides a custom workspace handler for testing purposes.
+ */
+class EntityTestRevPubWorkspaceHandler extends DefaultWorkspaceHandler {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function isEntitySupported(EntityInterface $entity): bool {
+    return $entity->bundle() !== 'ignored_bundle';
+  }
+
+}

core/modules/workspaces/tests/modules/workspaces_test/workspaces_test.info.yml

@@ -0,0 +1,12 @@
+name: 'Workspace Test'
+type: module
+description: 'Provides supporting code for testing workspaces.'
+package: Testing
+# version: VERSION
+dependencies:
+  - drupal:workspaces
+
+# Information added by Drupal.org packaging script on 2024-07-04
+version: '10.3.1'
+project: 'drupal'
+datestamp: 1720094222

core/modules/workspaces/tests/modules/workspaces_test/workspaces_test.module

@@ -0,0 +1,19 @@
+<?php
+
+/**
+ * @file
+ * Provides supporting code for testing workspaces.
+ */
+
+/**
+ * Implements hook_entity_type_alter().
+ */
+function workspaces_test_entity_type_alter(array &$entity_types) {
+  $state = \Drupal::state();
+
+  // Allow all entity types to have their definition changed dynamically for
+  // testing purposes.
+  foreach ($entity_types as $entity_type_id => $entity_type) {
+    $entity_types[$entity_type_id] = $state->get("$entity_type_id.entity_type", $entity_types[$entity_type_id]);
+  }
+}

core/modules/workspaces/tests/src/Functional/GenericTest.php

@@ -0,0 +1,25 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\workspaces\Functional;
+
+use Drupal\Tests\system\Functional\Module\GenericModuleTestBase;
+
+/**
+ * Generic module test for workspaces.
+ *
+ * @group workspaces
+ */
+class GenericTest extends GenericModuleTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function preUninstallSteps(): void {
+    $storage = \Drupal::entityTypeManager()->getStorage('workspace');
+    $workspaces = $storage->loadMultiple();
+    $storage->delete($workspaces);
+  }
+
+}

core/modules/workspaces/tests/src/Functional/PathWorkspacesTest.php

@@ -0,0 +1,345 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\workspaces\Functional;
+
+use Drupal\Tests\BrowserTestBase;
+use Drupal\Tests\content_translation\Traits\ContentTranslationTestTrait;
+use Drupal\Tests\WaitTerminateTestTrait;
+use Drupal\workspaces\Entity\Workspace;
+
+/**
+ * Tests path aliases with workspaces.
+ *
+ * @group path
+ * @group workspaces
+ */
+class PathWorkspacesTest extends BrowserTestBase {
+
+  use ContentTranslationTestTrait;
+  use WorkspaceTestUtilities;
+  use WaitTerminateTestTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = [
+    'block',
+    'content_translation',
+    'node',
+    'path',
+    'workspaces',
+  ];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    static::createLanguageFromLangcode('ro');
+    $this->rebuildContainer();
+
+    // Create a content type.
+    $this->drupalCreateContentType([
+      'name' => 'article',
+      'type' => 'article',
+    ]);
+
+    $permissions = [
+      'administer languages',
+      'administer nodes',
+      'administer url aliases',
+      'administer workspaces',
+      'create article content',
+      'create content translations',
+      'edit any article content',
+      'translate any entity',
+    ];
+    $this->drupalLogin($this->drupalCreateUser($permissions));
+
+    // Enable URL language detection and selection.
+    $edit = ['language_interface[enabled][language-url]' => 1];
+    $this->drupalGet('admin/config/regional/language/detection');
+    $this->submitForm($edit, 'Save settings');
+
+    // Enable translation for article node.
+    static::enableContentTranslation('node', 'article');
+
+    $this->setupWorkspaceSwitcherBlock();
+
+    // The \Drupal\path_alias\AliasWhitelist service performs cache clears after
+    // Drupal has flushed the response to the client. We use
+    // WaitTerminateTestTrait to wait for Drupal to do this before continuing.
+    $this->setWaitForTerminate();
+  }
+
+  /**
+   * Tests path aliases with workspaces.
+   */
+  public function testPathAliases(): void {
+    // Create a published node in Live, without an alias.
+    $node = $this->drupalCreateNode([
+      'type' => 'article',
+      'status' => TRUE,
+    ]);
+
+    // Switch to Stage and create an alias for the node.
+    $stage = Workspace::load('stage');
+    $this->switchToWorkspace($stage);
+
+    $edit = [
+      'path[0][alias]' => '/' . $this->randomMachineName(),
+    ];
+    $this->drupalGet('node/' . $node->id() . '/edit');
+    $this->submitForm($edit, 'Save');
+
+    // Check that the node can be accessed in Stage with the given alias.
+    $path = $edit['path[0][alias]'];
+    $this->assertAccessiblePaths([$path]);
+
+    // Check that the 'preload-paths' cache includes the active workspace ID in
+    // the cache key.
+    $this->assertNotEmpty(\Drupal::cache('data')->get('preload-paths:stage:/node/1'));
+    $this->assertFalse(\Drupal::cache('data')->get('preload-paths:/node/1'));
+
+    // Check that the alias can not be accessed in Live.
+    $this->switchToLive();
+    $this->assertNotAccessiblePaths([$path]);
+    $this->assertFalse(\Drupal::cache('data')->get('preload-paths:/node/1'));
+
+    // Publish the workspace and check that the alias can be accessed in Live.
+    $stage->publish();
+    $this->assertAccessiblePaths([$path]);
+    $this->assertNotEmpty(\Drupal::cache('data')->get('preload-paths:/node/1'));
+  }
+
+  /**
+   * Tests path aliases with workspaces and user switching.
+   */
+  public function testPathAliasesUserSwitch(): void {
+    // Create a published node in Live, without an alias.
+    $node = $this->drupalCreateNode([
+      'type' => 'article',
+      'status' => TRUE,
+    ]);
+
+    // Switch to Stage and create an alias for the node.
+    $stage = Workspace::load('stage');
+    $this->switchToWorkspace($stage);
+
+    $edit = [
+      'path[0][alias]' => '/' . $this->randomMachineName(),
+    ];
+    $this->drupalGet('node/' . $node->id() . '/edit');
+    $this->submitForm($edit, 'Save');
+
+    // Check that the node can be accessed in Stage with the given alias.
+    $path = $edit['path[0][alias]'];
+    $this->assertAccessiblePaths([$path]);
+
+    // Check that the 'preload-paths' cache includes the active workspace ID in
+    // the cache key.
+    $this->assertNotEmpty(\Drupal::cache('data')->get('preload-paths:stage:/node/1'));
+    $this->assertFalse(\Drupal::cache('data')->get('preload-paths:/node/1'));
+
+    // Check that the alias can not be accessed in Live, by logging out without
+    // an explicit switch.
+    $this->drupalLogout();
+    $this->assertNotAccessiblePaths([$path]);
+    $this->assertFalse(\Drupal::cache('data')->get('preload-paths:/node/1'));
+
+    // Publish the workspace and check that the alias can be accessed in Live.
+    $this->drupalLogin($this->rootUser);
+    $stage->publish();
+
+    $this->drupalLogout();
+    $this->assertAccessiblePaths([$path]);
+    $this->assertNotEmpty(\Drupal::cache('data')->get('preload-paths:/node/1'));
+  }
+
+  /**
+   * Tests path aliases with workspaces for translatable nodes.
+   */
+  public function testPathAliasesWithTranslation(): void {
+    $stage = Workspace::load('stage');
+
+    // Create one node with a random alias.
+    $default_node = $this->drupalCreateNode([
+      'type' => 'article',
+      'langcode' => 'en',
+      'status' => TRUE,
+      'path' => '/' . $this->randomMachineName(),
+    ]);
+
+    // Add published translation with another alias.
+    $this->drupalGet('node/' . $default_node->id());
+    $this->drupalGet('node/' . $default_node->id() . '/translations');
+    $this->clickLink('Add');
+    $edit_translation = [
+      'body[0][value]' => $this->randomMachineName(),
+      'status[value]' => TRUE,
+      'path[0][alias]' => '/' . $this->randomMachineName(),
+    ];
+    $this->submitForm($edit_translation, 'Save (this translation)');
+    // Confirm that the alias works.
+    $this->drupalGet('ro' . $edit_translation['path[0][alias]']);
+    $this->assertSession()->pageTextContains($edit_translation['body[0][value]']);
+
+    $default_path = $default_node->path->alias;
+    $translation_path = 'ro' . $edit_translation['path[0][alias]'];
+
+    $this->assertAccessiblePaths([$default_path, $translation_path]);
+
+    $this->switchToWorkspace($stage);
+
+    $this->assertAccessiblePaths([$default_path, $translation_path]);
+
+    // Create a workspace-specific revision for the translation with a new path
+    // alias.
+    $edit_new_translation_draft_with_alias = [
+      'path[0][alias]' => '/' . $this->randomMachineName(),
+    ];
+    $this->drupalGet('ro/node/' . $default_node->id() . '/edit');
+    $this->submitForm($edit_new_translation_draft_with_alias, 'Save (this translation)');
+    $stage_translation_path = 'ro' . $edit_new_translation_draft_with_alias['path[0][alias]'];
+
+    // The new alias of the translation should be available in Stage, but not
+    // available in Live.
+    $this->assertAccessiblePaths([$default_path, $stage_translation_path]);
+
+    // Check that the previous (Live) path alias no longer works.
+    $this->assertNotAccessiblePaths([$translation_path]);
+
+    // Switch out of Stage and check that the initial path aliases still work.
+    $this->switchToLive();
+    $this->assertAccessiblePaths([$default_path, $translation_path]);
+    $this->assertNotAccessiblePaths([$stage_translation_path]);
+
+    // Switch back to Stage.
+    $this->switchToWorkspace($stage);
+
+    // Create new workspace-specific revision for translation without changing
+    // the path alias.
+    $edit_new_translation_draft = [
+      'body[0][value]' => $this->randomMachineName(),
+    ];
+    $this->drupalGet('ro/node/' . $default_node->id() . '/edit');
+    $this->submitForm($edit_new_translation_draft, 'Save (this translation)');
+    // Confirm that the new draft revision was created.
+    $this->assertSession()->pageTextContains($edit_new_translation_draft['body[0][value]']);
+
+    // Switch out of Stage and check that the initial path aliases still work.
+    $this->switchToLive();
+    $this->assertAccessiblePaths([$default_path, $translation_path]);
+    $this->assertNotAccessiblePaths([$stage_translation_path]);
+
+    // Switch back to Stage.
+    $this->switchToWorkspace($stage);
+    $this->assertAccessiblePaths([$default_path, $stage_translation_path]);
+    $this->assertNotAccessiblePaths([$translation_path]);
+
+    // Create a new workspace-specific revision for translation with path alias
+    // from the original language's default revision.
+    $edit_new_translation_draft_with_defaults_alias = [
+      'path[0][alias]' => $default_node->path->alias,
+    ];
+    $this->drupalGet('ro/node/' . $default_node->id() . '/edit');
+    $this->submitForm($edit_new_translation_draft_with_defaults_alias, 'Save (this translation)');
+
+    // Switch out of Stage and check that the initial path aliases still work.
+    $this->switchToLive();
+    $this->assertAccessiblePaths([$default_path, $translation_path]);
+    $this->assertNotAccessiblePaths([$stage_translation_path]);
+
+    // Check that only one path alias (the original one) is available in Stage.
+    $this->switchToWorkspace($stage);
+    $this->assertAccessiblePaths([$default_path]);
+    $this->assertNotAccessiblePaths([$translation_path, $stage_translation_path]);
+
+    // Create new workspace-specific revision for translation with a deleted
+    // (empty) path alias.
+    $edit_new_translation_draft_empty_alias = [
+      'body[0][value]' => $this->randomMachineName(),
+      'path[0][alias]' => '',
+    ];
+    $this->drupalGet('ro/node/' . $default_node->id() . '/edit');
+    $this->submitForm($edit_new_translation_draft_empty_alias, 'Save (this translation)');
+
+    // Check that only one path alias (the original one) is available now.
+    $this->switchToLive();
+    $this->assertAccessiblePaths([$default_path, $translation_path]);
+    $this->assertNotAccessiblePaths([$stage_translation_path]);
+
+    $this->switchToWorkspace($stage);
+    $this->assertAccessiblePaths([$default_path]);
+    $this->assertNotAccessiblePaths([$translation_path, $stage_translation_path]);
+
+    // Create a new workspace-specific revision for the translation with a new
+    // path alias.
+    $edit_new_translation = [
+      'body[0][value]' => $this->randomMachineName(),
+      'path[0][alias]' => '/' . $this->randomMachineName(),
+    ];
+    $this->drupalGet('ro/node/' . $default_node->id() . '/edit');
+    $this->submitForm($edit_new_translation, 'Save (this translation)');
+
+    // Confirm that the new revision was created.
+    $this->assertSession()->pageTextContains($edit_new_translation['body[0][value]']);
+    $this->assertSession()->addressEquals('ro' . $edit_new_translation['path[0][alias]']);
+
+    // Check that only the new path alias of the translation can be accessed.
+    $new_stage_translation_path = 'ro' . $edit_new_translation['path[0][alias]'];
+    $this->assertAccessiblePaths([$default_path, $new_stage_translation_path]);
+    $this->assertNotAccessiblePaths([$stage_translation_path]);
+
+    // Switch out of Stage and check that none of the workspace-specific path
+    // aliases can be accessed.
+    $this->switchToLive();
+    $this->assertAccessiblePaths([$default_path, $translation_path]);
+    $this->assertNotAccessiblePaths([$stage_translation_path, $new_stage_translation_path]);
+
+    // Publish Stage and check that its path alias for the translation can be
+    // accessed.
+    $stage->publish();
+    $this->assertAccessiblePaths([$default_path, $new_stage_translation_path]);
+    $this->assertNotAccessiblePaths([$stage_translation_path]);
+  }
+
+  /**
+   * Helper callback to verify paths are responding with status 200.
+   *
+   * @param string[] $paths
+   *   An array of paths to check for.
+   *
+   * @internal
+   */
+  protected function assertAccessiblePaths(array $paths): void {
+    foreach ($paths as $path) {
+      $this->drupalGet($path);
+      $this->assertSession()->statusCodeEquals(200);
+    }
+  }
+
+  /**
+   * Helper callback to verify paths are responding with status 404.
+   *
+   * @param string[] $paths
+   *   An array of paths to check for.
+   *
+   * @internal
+   */
+  protected function assertNotAccessiblePaths(array $paths): void {
+    foreach ($paths as $path) {
+      $this->drupalGet($path);
+      $this->assertSession()->statusCodeEquals(404);
+    }
+  }
+
+}

core/modules/workspaces/tests/src/Functional/Rest/WorkspaceJsonAnonTest.php

@@ -0,0 +1,33 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\workspaces\Functional\Rest;
+
+use Drupal\Tests\rest\Functional\AnonResourceTestTrait;
+
+/**
+ * Test workspace entities for unauthenticated JSON requests.
+ *
+ * @group workspaces
+ */
+class WorkspaceJsonAnonTest extends WorkspaceResourceTestBase {
+
+  use AnonResourceTestTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $format = 'json';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $mimeType = 'application/json';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+}

core/modules/workspaces/tests/src/Functional/Rest/WorkspaceJsonBasicAuthTest.php

@@ -0,0 +1,43 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\workspaces\Functional\Rest;
+
+use Drupal\Tests\rest\Functional\BasicAuthResourceTestTrait;
+
+/**
+ * Test workspace entities for JSON requests via basic auth.
+ *
+ * @group workspaces
+ */
+class WorkspaceJsonBasicAuthTest extends WorkspaceResourceTestBase {
+
+  use BasicAuthResourceTestTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['basic_auth'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $format = 'json';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $mimeType = 'application/json';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $auth = 'basic_auth';
+
+}

core/modules/workspaces/tests/src/Functional/Rest/WorkspaceJsonCookieTest.php

@@ -0,0 +1,38 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\workspaces\Functional\Rest;
+
+use Drupal\Tests\rest\Functional\CookieResourceTestTrait;
+
+/**
+ * Test workspace entities for JSON requests with cookie authentication.
+ *
+ * @group workspaces
+ */
+class WorkspaceJsonCookieTest extends WorkspaceResourceTestBase {
+
+  use CookieResourceTestTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $format = 'json';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $mimeType = 'application/json';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $auth = 'cookie';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+}

core/modules/workspaces/tests/src/Functional/Rest/WorkspaceResourceTestBase.php

@@ -0,0 +1,205 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\workspaces\Functional\Rest;
+
+use Drupal\Tests\rest\Functional\EntityResource\EntityResourceTestBase;
+use Drupal\user\Entity\User;
+use Drupal\workspaces\Entity\Workspace;
+
+/**
+ * Base class for workspace EntityResource tests.
+ */
+abstract class WorkspaceResourceTestBase extends EntityResourceTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['workspaces'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $entityTypeId = 'workspace';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $patchProtectedFieldNames = [
+    'changed' => NULL,
+  ];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $uniqueFieldNames = [
+    'id',
+  ];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $firstCreatedEntityId = 'running_on_faith';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $secondCreatedEntityId = 'running_on_faith_2';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUpAuthorization($method) {
+    switch ($method) {
+      case 'GET':
+        $this->grantPermissionsToTestedRole(['view any workspace']);
+        break;
+
+      case 'POST':
+        $this->grantPermissionsToTestedRole(['create workspace']);
+        break;
+
+      case 'PATCH':
+        $this->grantPermissionsToTestedRole(['edit any workspace']);
+        break;
+
+      case 'DELETE':
+        $this->grantPermissionsToTestedRole(['delete any workspace']);
+        break;
+    }
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function createEntity() {
+    $workspace = Workspace::create([
+      'id' => 'layla',
+      'label' => 'Layla',
+    ]);
+    $workspace->save();
+    return $workspace;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function createAnotherEntity() {
+    $workspace = $this->entity->createDuplicate();
+    $workspace->id = 'layla_dupe';
+    $workspace->label = 'Layla_dupe';
+    $workspace->save();
+    return $workspace;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function getExpectedNormalizedEntity() {
+    $author = User::load($this->entity->getOwnerId());
+    return [
+      'created' => [
+        [
+          'value' => (new \DateTime())->setTimestamp((int) $this->entity->getCreatedTime())->setTimezone(new \DateTimeZone('UTC'))->format(\DateTime::RFC3339),
+          'format' => \DateTime::RFC3339,
+        ],
+      ],
+      'changed' => [
+        [
+          'value' => (new \DateTime())->setTimestamp($this->entity->getChangedTime())->setTimezone(new \DateTimeZone('UTC'))->format(\DateTime::RFC3339),
+          'format' => \DateTime::RFC3339,
+        ],
+      ],
+      'id' => [
+        [
+          'value' => 'layla',
+        ],
+      ],
+      'label' => [
+        [
+          'value' => 'Layla',
+        ],
+      ],
+      'revision_id' => [
+        [
+          'value' => 2,
+        ],
+      ],
+      'parent' => [],
+      'uid' => [
+        [
+          'target_id' => (int) $author->id(),
+          'target_type' => 'user',
+          'target_uuid' => $author->uuid(),
+          'url' => base_path() . 'user/' . $author->id(),
+        ],
+      ],
+      'uuid' => [
+        [
+          'value' => $this->entity->uuid(),
+        ],
+      ],
+    ];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function getNormalizedPostEntity() {
+    return [
+      'id' => [
+        [
+          'value' => static::$firstCreatedEntityId,
+        ],
+      ],
+      'label' => [
+        [
+          'value' => 'Running on faith',
+        ],
+      ],
+    ];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function getNormalizedPatchEntity() {
+    return array_diff_key($this->getNormalizedPostEntity(), ['id' => TRUE]);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function getExpectedUnauthorizedAccessMessage($method) {
+    switch ($method) {
+      case 'GET':
+        return "The 'view any workspace' permission is required.";
+
+      case 'POST':
+        return "The following permissions are required: 'administer workspaces' OR 'create workspace'.";
+
+      case 'PATCH':
+        return "The 'edit any workspace' permission is required.";
+
+      case 'DELETE':
+        return "The 'delete any workspace' permission is required.";
+
+    }
+    return parent::getExpectedUnauthorizedAccessMessage($method);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function getModifiedEntityForPostTesting() {
+    $modified = parent::getModifiedEntityForPostTesting();
+    // Even though the field type of the workspace ID is 'string', it acts as a
+    // machine name through a custom constraint, so we need to ensure that we
+    // generate a proper random value for it.
+    // @see \Drupal\workspaces\Entity\Workspace::baseFieldDefinitions()
+    $modified['id'] = [$this->randomMachineName()];
+    return $modified;
+  }
+
+}

core/modules/workspaces/tests/src/Functional/Rest/WorkspaceXmlAnonTest.php

@@ -0,0 +1,43 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\workspaces\Functional\Rest;
+
+use Drupal\Tests\rest\Functional\AnonResourceTestTrait;
+use Drupal\Tests\rest\Functional\EntityResource\XmlEntityNormalizationQuirksTrait;
+
+/**
+ * Test workspace entities for unauthenticated XML requests.
+ *
+ * @group workspaces
+ */
+class WorkspaceXmlAnonTest extends WorkspaceResourceTestBase {
+
+  use AnonResourceTestTrait;
+  use XmlEntityNormalizationQuirksTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $format = 'xml';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $mimeType = 'text/xml; charset=UTF-8';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * {@inheritdoc}
+   */
+  public function testPatchPath(): void {
+    // Deserialization of the XML format is not supported.
+    $this->markTestSkipped();
+  }
+
+}

core/modules/workspaces/tests/src/Functional/Rest/WorkspaceXmlBasicAuthTest.php

@@ -0,0 +1,53 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\workspaces\Functional\Rest;
+
+use Drupal\Tests\rest\Functional\BasicAuthResourceTestTrait;
+use Drupal\Tests\rest\Functional\EntityResource\XmlEntityNormalizationQuirksTrait;
+
+/**
+ * Test workspace entities for XML requests with cookie authentication.
+ *
+ * @group workspaces
+ */
+class WorkspaceXmlBasicAuthTest extends WorkspaceResourceTestBase {
+
+  use BasicAuthResourceTestTrait;
+  use XmlEntityNormalizationQuirksTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['basic_auth'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $format = 'xml';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $mimeType = 'text/xml; charset=UTF-8';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $auth = 'basic_auth';
+
+  /**
+   * {@inheritdoc}
+   */
+  public function testPatchPath(): void {
+    // Deserialization of the XML format is not supported.
+    $this->markTestSkipped();
+  }
+
+}

core/modules/workspaces/tests/src/Functional/Rest/WorkspaceXmlCookieTest.php

@@ -0,0 +1,48 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\workspaces\Functional\Rest;
+
+use Drupal\Tests\rest\Functional\CookieResourceTestTrait;
+use Drupal\Tests\rest\Functional\EntityResource\XmlEntityNormalizationQuirksTrait;
+
+/**
+ * Test workspace entities for XML requests.
+ *
+ * @group workspaces
+ */
+class WorkspaceXmlCookieTest extends WorkspaceResourceTestBase {
+
+  use CookieResourceTestTrait;
+  use XmlEntityNormalizationQuirksTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $format = 'xml';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $mimeType = 'text/xml; charset=UTF-8';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $auth = 'cookie';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * {@inheritdoc}
+   */
+  public function testPatchPath(): void {
+    // Deserialization of the XML format is not supported.
+    $this->markTestSkipped();
+  }
+
+}

core/modules/workspaces/tests/src/Functional/UpdateSystem/ActiveWorkspaceUpdateTest.php

@@ -0,0 +1,77 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\workspaces\Functional\UpdateSystem;
+
+use Drupal\Tests\BrowserTestBase;
+use Drupal\Tests\UpdatePathTestTrait;
+use Drupal\Tests\user\Traits\UserCreationTrait;
+use Drupal\workspaces\Entity\Workspace;
+
+/**
+ * Tests that there is no active workspace during database updates.
+ *
+ * @group workspaces
+ * @group Update
+ */
+class ActiveWorkspaceUpdateTest extends BrowserTestBase {
+
+  use UpdatePathTestTrait;
+  use UserCreationTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['workspaces'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    $this->setUpCurrentUser([], ['view any workspace']);
+    $this->container->get('module_installer')->install(['workspace_update_test']);
+    $this->rebuildContainer();
+
+    // Ensure the workspace_update_test_post_update_check_active_workspace()
+    // update runs.
+    $existing_updates = \Drupal::keyValue('post_update')->get('existing_updates', []);
+    $index = array_search('workspace_update_test_post_update_check_active_workspace', $existing_updates);
+    unset($existing_updates[$index]);
+    \Drupal::keyValue('post_update')->set('existing_updates', $existing_updates);
+
+    // Create a valid workspace that can be used for testing.
+    Workspace::create(['id' => 'test', 'label' => 'Test'])->save();
+  }
+
+  /**
+   * Tests that there is no active workspace during database updates.
+   */
+  public function testActiveWorkspaceDuringUpdate(): void {
+    /** @var \Drupal\workspaces\WorkspaceManagerInterface $workspace_manager */
+    $workspace_manager = \Drupal::service('workspaces.manager');
+
+    // Check that we have an active workspace before running the updates.
+    $this->assertTrue($workspace_manager->hasActiveWorkspace());
+    $this->assertEquals('test', $workspace_manager->getActiveWorkspace()->id());
+
+    $this->runUpdates();
+
+    // Check that we didn't have an active workspace while running the updates.
+    // @see workspace_update_test_post_update_check_active_workspace()
+    $this->assertFalse(\Drupal::state()->get('workspace_update_test.has_active_workspace'));
+
+    // Check that we have an active workspace after running the updates.
+    $workspace_manager = \Drupal::service('workspaces.manager');
+    $this->assertTrue($workspace_manager->hasActiveWorkspace());
+    $this->assertEquals('test', $workspace_manager->getActiveWorkspace()->id());
+  }
+
+}

core/modules/workspaces/tests/src/Functional/WorkspaceBypassTest.php

@@ -0,0 +1,73 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\workspaces\Functional;
+
+use Drupal\Tests\BrowserTestBase;
+use Drupal\Tests\node\Traits\ContentTypeCreationTrait;
+
+// cspell:ignore ditka
+
+/**
+ * Tests access bypass permission controls on workspaces.
+ *
+ * @group workspaces
+ */
+class WorkspaceBypassTest extends BrowserTestBase {
+
+  use WorkspaceTestUtilities;
+  use ContentTypeCreationTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['node', 'user', 'block', 'workspaces'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * Verifies that a user can edit anything in a workspace they own.
+   */
+  public function testBypassOwnWorkspace(): void {
+    $permissions = [
+      'create workspace',
+      'edit own workspace',
+      'view own workspace',
+      'bypass entity access own workspace',
+    ];
+
+    $this->createContentType(['type' => 'test', 'label' => 'Test']);
+    $this->setupWorkspaceSwitcherBlock();
+
+    $coach = $this->drupalCreateUser(array_merge($permissions, ['create test content']));
+
+    // Login as a limited-access user and create a workspace.
+    $this->drupalLogin($coach);
+    $bears = $this->createAndActivateWorkspaceThroughUi('Bears', 'bears');
+
+    // Now create a node in the Bears workspace, as the owner of that workspace.
+    $coach_bears_node = $this->createNodeThroughUi('Ditka Bears node', 'test');
+    $coach_bears_node_id = $coach_bears_node->id();
+
+    // Editing both nodes should be possible.
+    $this->drupalGet('/node/' . $coach_bears_node_id . '/edit');
+    $this->assertSession()->statusCodeEquals(200);
+
+    // Create a new user that should be able to edit anything in the Bears
+    // workspace.
+    $this->switchToLive();
+    $lombardi = $this->drupalCreateUser(array_merge($permissions, ['view any workspace']));
+    $this->drupalLogin($lombardi);
+    $this->switchToWorkspace($bears);
+
+    // Editor 2 has the bypass permission but does not own the workspace and so,
+    // should not be able to create and edit any node.
+    $this->drupalGet('/node/' . $coach_bears_node_id . '/edit');
+    $this->assertSession()->statusCodeEquals(403);
+  }
+
+}

core/modules/workspaces/tests/src/Functional/WorkspaceCacheContextTest.php

@@ -0,0 +1,95 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\workspaces\Functional;
+
+use Drupal\Core\Cache\CacheableMetadata;
+use Drupal\Tests\BrowserTestBase;
+use Drupal\Tests\system\Functional\Cache\AssertPageCacheContextsAndTagsTrait;
+use Drupal\workspaces\Entity\Workspace;
+use Drupal\workspaces\WorkspaceCacheContext;
+
+/**
+ * Tests the workspace cache context.
+ *
+ * @group workspaces
+ * @group Cache
+ */
+class WorkspaceCacheContextTest extends BrowserTestBase {
+
+  use AssertPageCacheContextsAndTagsTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['block', 'node', 'workspaces'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * Tests the 'workspace' cache context.
+   */
+  public function testWorkspaceCacheContext(): void {
+    $renderer = \Drupal::service('renderer');
+    $cache_contexts_manager = \Drupal::service("cache_contexts_manager");
+    /** @var \Drupal\Core\Cache\VariationCacheFactoryInterface $variation_cache_factory */
+    $variation_cache_factory = $this->container->get('variation_cache_factory');
+
+    // Check that the 'workspace' cache context is present when the module is
+    // installed.
+    $this->drupalGet('<front>');
+    $this->assertCacheContext('workspace');
+
+    $cache_context = new WorkspaceCacheContext(\Drupal::service('workspaces.manager'));
+    $this->assertSame('live', $cache_context->getContext());
+
+    // Create a node and check that its render array contains the proper cache
+    // context.
+    $this->drupalCreateContentType(['type' => 'page']);
+    $node = $this->createNode();
+
+    // Get a fully built entity view render array.
+    $build = \Drupal::entityTypeManager()->getViewBuilder('node')->view($node, 'full');
+
+    // Render it so the default cache contexts are applied.
+    $renderer->renderRoot($build);
+    $this->assertContains('workspace', $build['#cache']['contexts']);
+
+    $context_tokens = $cache_contexts_manager->convertTokensToKeys($build['#cache']['contexts'])->getKeys();
+    $this->assertContains('[workspace]=live', $context_tokens);
+
+    // Test that a cache entry is created.
+    $cache_bin = $variation_cache_factory->get($build['#cache']['bin']);
+    $this->assertInstanceOf(\stdClass::class, $cache_bin->get($build['#cache']['keys'], CacheableMetadata::createFromRenderArray($build)));
+
+    // Switch to the 'stage' workspace and check that the correct workspace
+    // cache context is used.
+    $test_user = $this->drupalCreateUser(['view any workspace']);
+    $this->drupalLogin($test_user);
+
+    $stage = Workspace::load('stage');
+    $workspace_manager = \Drupal::service('workspaces.manager');
+    $workspace_manager->setActiveWorkspace($stage);
+
+    $cache_context = new WorkspaceCacheContext($workspace_manager);
+    $this->assertSame('stage', $cache_context->getContext());
+
+    $build = \Drupal::entityTypeManager()->getViewBuilder('node')->view($node, 'full');
+
+    // Render it so the default cache contexts are applied.
+    $renderer->renderRoot($build);
+    $this->assertContains('workspace', $build['#cache']['contexts']);
+
+    $context_tokens = $cache_contexts_manager->convertTokensToKeys($build['#cache']['contexts'])->getKeys();
+    $this->assertContains('[workspace]=stage', $context_tokens);
+
+    // Test that a cache entry is created.
+    $cache_bin = $variation_cache_factory->get($build['#cache']['bin']);
+    $this->assertInstanceOf(\stdClass::class, $cache_bin->get($build['#cache']['keys'], CacheableMetadata::createFromRenderArray($build)));
+  }
+
+}