fix(material/tabs): enable hydration (#28366)

Adds a workaround that allows us to enable hydration in the tab group component.

src/material/tabs/tab-group.html

@@ -51,6 +51,16 @@
   }
 </mat-tab-header>
 
+<!--
+  We need to project the content somewhere to avoid hydration errors. Some observations:
+  1. This is only necessary on the server.
+  2. We get a hydration error if there aren't any nodes after the `ng-content`.
+  3. We get a hydration error if `ng-content` is wrapped in another element.
+-->
+@if (_isServer) {
+  <ng-content/>
+}
+
 <div
   class="mat-mdc-tab-body-wrapper"
   [class._mat-animation-noopable]="_animationMode === 'NoopAnimations'"

src/material/tabs/tab-group.ts

@@ -24,6 +24,7 @@ import {
   ViewChild,
   ViewEncapsulation,
   booleanAttribute,
+  inject,
   numberAttribute,
 } from '@angular/core';
 import {ANIMATION_MODULE_TYPE} from '@angular/platform-browser/animations';
@@ -38,6 +39,7 @@ import {MatTabBody} from './tab-body';
 import {CdkPortalOutlet} from '@angular/cdk/portal';
 import {NgClass} from '@angular/common';
 import {MatTabLabelWrapper} from './tab-label-wrapper';
+import {Platform} from '@angular/cdk/platform';
 
 /** Used to generate unique ID's for each tab component */
 let nextId = 0;
@@ -75,7 +77,6 @@ const ENABLE_BACKGROUND_INPUT = true;
     },
   ],
   host: {
-    'ngSkipHydration': '',
     'class': 'mat-mdc-tab-group',
     '[class]': '"mat-" + (color || "primary")',
     '[class.mat-mdc-tab-group-dynamic-height]': 'dynamicHeight',
@@ -248,6 +249,9 @@ export class MatTabGroup implements AfterContentInit, AfterContentChecked, OnDes
 
   private _groupId: number;
 
+  /** Whether the tab group is rendered on the server. */
+  protected _isServer: boolean = !inject(Platform).isBrowser;
+
   constructor(
     readonly _elementRef: ElementRef,
     private _changeDetectorRef: ChangeDetectorRef,

src/material/tabs/tab.ts

@@ -47,6 +47,11 @@ export const MAT_TAB_GROUP = new InjectionToken<any>('MAT_TAB_GROUP');
   exportAs: 'matTab',
   providers: [{provide: MAT_TAB, useExisting: MatTab}],
   standalone: true,
+  host: {
+    // This element will be rendered on the server in order to support hydration.
+    // Hide it so it doesn't cause a layout shift when it's removed on the client.
+    'hidden': '',
+  },
 })
 export class MatTab implements OnInit, OnChanges, OnDestroy {
   /** whether the tab is disabled. */

src/universal-app/kitchen-sink/kitchen-sink.html

@@ -307,13 +307,37 @@ <h2>Tabs</h2>
 -->
 <mat-tab-group [selectedIndex]="1">
   <mat-tab label="Overview">
-    The overview
+    <h3>The overview</h3>
+    <p>Lorem ipsum dolor sit amet consectetur adipisicing elit. Doloremque assumenda doloribus,
+      rerum temporibus fugit aliquid adipisci aliquam eaque sint voluptas dolore cumque voluptatibus
+      quam quod. Quasi adipisci officia similique in?</p>
+    <p>Deleniti neque placeat magnam, voluptatibus eligendi illo consectetur dolore minima dolorem
+      nemo suscipit dolorum accusantium? Numquam officia culpa itaque qui repudiandae nulla,
+      laboriosam nihil molestiae ad aut perferendis alias amet.</p>
+    <p>Officia esse temporibus consequatur ipsa! Veritatis alias facere amet reiciendis sint
+      impedit atque iste doloremque dolor? Ullam, aspernatur? Alias, fuga! At dolorum odio
+      molestiae laudantium nihil alias inventore veritatis voluptatum.</p>
+    <button mat-raised-button color="primary">See the overview</button>
   </mat-tab>
   <mat-tab>
-    <ng-template mat-tab-label>
-      API docs
-    </ng-template>
-    The API docs
+    <ng-template mat-tab-label>API docs</ng-template>
+    <h3>The API docs</h3>
+    <p>Lorem ipsum dolor sit amet consectetur adipisicing elit. Dolorum facere quasi natus rerum
+      quae, nisi, quis, voluptate assumenda necessitatibus labore illo. Illum ipsum consequatur,
+      excepturi aspernatur odio veritatis sint perferendis!</p>
+    <p>Dicta ex laborum repudiandae nesciunt. Ea asperiores quo totam velit! Aliquid cum laudantium
+      officiis molestias, excepturi odio, autem magni dignissimos perspiciatis, amet qui! Dolorem
+      molestiae similique necessitatibus cupiditate ipsa aspernatur?</p>
+    <button mat-raised-button color="accent">See the API docs</button>
+  </mat-tab>
+
+  <mat-tab>
+    <ng-template mat-tab-label>Examples</ng-template>
+    <h3>The examples</h3>
+    <p>Lorem ipsum dolor sit amet consectetur adipisicing elit. Modi animi saepe, optio sequi
+      accusantium, eos perspiciatis reprehenderit, nobis exercitationem sunt ducimus molestiae
+      laborum inventore itaque incidunt. Neque dolorum adipisci quidem.</p>
+    <button mat-raised-button color="warn">See the examples</button>
   </mat-tab>
 </mat-tab-group>
 

tools/public_api_guard/material/tabs.md

@@ -281,6 +281,7 @@ export class MatTabGroup implements AfterContentInit, AfterContentChecked, OnDes
     _getTabLabelId(i: number): string;
     _handleClick(tab: MatTab, tabHeader: MatTabGroupBaseHeader, index: number): void;
     headerPosition: MatTabHeaderPosition;
+    protected _isServer: boolean;
     // (undocumented)
     static ngAcceptInputType_contentTabIndex: unknown;
     // (undocumented)
@@ -319,7 +320,7 @@ export class MatTabGroup implements AfterContentInit, AfterContentChecked, OnDes
     _tabs: QueryList<MatTab>;
     updatePagination(): void;
     // (undocumented)
-    static ɵcmp: i0.ɵɵComponentDeclaration<MatTabGroup, "mat-tab-group", ["matTabGroup"], { "color": { "alias": "color"; "required": false; }; "fitInkBarToContent": { "alias": "fitInkBarToContent"; "required": false; }; "stretchTabs": { "alias": "mat-stretch-tabs"; "required": false; }; "dynamicHeight": { "alias": "dynamicHeight"; "required": false; }; "selectedIndex": { "alias": "selectedIndex"; "required": false; }; "headerPosition": { "alias": "headerPosition"; "required": false; }; "animationDuration": { "alias": "animationDuration"; "required": false; }; "contentTabIndex": { "alias": "contentTabIndex"; "required": false; }; "disablePagination": { "alias": "disablePagination"; "required": false; }; "disableRipple": { "alias": "disableRipple"; "required": false; }; "preserveContent": { "alias": "preserveContent"; "required": false; }; "backgroundColor": { "alias": "backgroundColor"; "required": false; }; }, { "selectedIndexChange": "selectedIndexChange"; "focusChange": "focusChange"; "animationDone": "animationDone"; "selectedTabChange": "selectedTabChange"; }, ["_allTabs"], never, true, never>;
+    static ɵcmp: i0.ɵɵComponentDeclaration<MatTabGroup, "mat-tab-group", ["matTabGroup"], { "color": { "alias": "color"; "required": false; }; "fitInkBarToContent": { "alias": "fitInkBarToContent"; "required": false; }; "stretchTabs": { "alias": "mat-stretch-tabs"; "required": false; }; "dynamicHeight": { "alias": "dynamicHeight"; "required": false; }; "selectedIndex": { "alias": "selectedIndex"; "required": false; }; "headerPosition": { "alias": "headerPosition"; "required": false; }; "animationDuration": { "alias": "animationDuration"; "required": false; }; "contentTabIndex": { "alias": "contentTabIndex"; "required": false; }; "disablePagination": { "alias": "disablePagination"; "required": false; }; "disableRipple": { "alias": "disableRipple"; "required": false; }; "preserveContent": { "alias": "preserveContent"; "required": false; }; "backgroundColor": { "alias": "backgroundColor"; "required": false; }; }, { "selectedIndexChange": "selectedIndexChange"; "focusChange": "focusChange"; "animationDone": "animationDone"; "selectedTabChange": "selectedTabChange"; }, ["_allTabs"], ["*"], true, never>;
     // (undocumented)
     static ɵfac: i0.ɵɵFactoryDeclaration<MatTabGroup, [null, null, { optional: true; }, { optional: true; }]>;
 }