fix(material/tabs): allow ID to be set on tab (#30768)

Fixes a long-standing issue where users weren't able to assign an ID to a tab.

Fixes #4136.

(cherry picked from commit 387313f)

Author: crisbeto

goldens/material/tabs/index.api.md

@@ -152,6 +152,7 @@ export class MatTab implements OnInit, OnChanges, OnDestroy {
     _closestTabGroup: any;
     get content(): TemplatePortal | null;
     disabled: boolean;
+    id: string | null;
     _implicitContent: TemplateRef<any>;
     isActive: boolean;
     labelClass: string | string[];
@@ -170,7 +171,7 @@ export class MatTab implements OnInit, OnChanges, OnDestroy {
     set templateLabel(value: MatTabLabel);
     textLabel: string;
     // (undocumented)
-    static ɵcmp: i0.ɵɵComponentDeclaration<MatTab, "mat-tab", ["matTab"], { "disabled": { "alias": "disabled"; "required": false; }; "textLabel": { "alias": "label"; "required": false; }; "ariaLabel": { "alias": "aria-label"; "required": false; }; "ariaLabelledby": { "alias": "aria-labelledby"; "required": false; }; "labelClass": { "alias": "labelClass"; "required": false; }; "bodyClass": { "alias": "bodyClass"; "required": false; }; }, {}, ["templateLabel", "_explicitContent"], ["*"], true, never>;
+    static ɵcmp: i0.ɵɵComponentDeclaration<MatTab, "mat-tab", ["matTab"], { "disabled": { "alias": "disabled"; "required": false; }; "textLabel": { "alias": "label"; "required": false; }; "ariaLabel": { "alias": "aria-label"; "required": false; }; "ariaLabelledby": { "alias": "aria-labelledby"; "required": false; }; "labelClass": { "alias": "labelClass"; "required": false; }; "bodyClass": { "alias": "bodyClass"; "required": false; }; "id": { "alias": "id"; "required": false; }; }, {}, ["templateLabel", "_explicitContent"], ["*"], true, never>;
     // (undocumented)
     static ɵfac: i0.ɵɵFactoryDeclaration<MatTab, never>;
 }
@@ -267,9 +268,9 @@ export class MatTabGroup implements AfterViewInit, AfterContentInit, AfterConten
     // (undocumented)
     _focusChanged(index: number): void;
     focusTab(index: number): void;
-    _getTabContentId(i: number): string;
+    _getTabContentId(index: number): string;
     _getTabIndex(index: number): number;
-    _getTabLabelId(i: number): string;
+    _getTabLabelId(tab: MatTab, index: number): string;
     _handleClick(tab: MatTab, tabHeader: MatTabGroupBaseHeader, index: number): void;
     headerPosition: MatTabHeaderPosition;
     protected _isServer: boolean;

src/material/tabs/tab-group.html

@@ -7,26 +7,26 @@
                 (indexFocused)="_focusChanged($event)"
                 (selectFocusedIndex)="selectedIndex = $event">
 
-  @for (tab of _tabs; track tab; let i = $index) {
+  @for (tab of _tabs; track tab) {
     <div class="mdc-tab mat-mdc-tab mat-focus-indicator"
         #tabNode
         role="tab"
         matTabLabelWrapper
         cdkMonitorElementFocus
-        [id]="_getTabLabelId(i)"
-        [attr.tabIndex]="_getTabIndex(i)"
-        [attr.aria-posinset]="i + 1"
+        [id]="_getTabLabelId(tab, $index)"
+        [attr.tabIndex]="_getTabIndex($index)"
+        [attr.aria-posinset]="$index + 1"
         [attr.aria-setsize]="_tabs.length"
-        [attr.aria-controls]="_getTabContentId(i)"
-        [attr.aria-selected]="selectedIndex === i"
+        [attr.aria-controls]="_getTabContentId($index)"
+        [attr.aria-selected]="selectedIndex === $index"
         [attr.aria-label]="tab.ariaLabel || null"
         [attr.aria-labelledby]="(!tab.ariaLabel && tab.ariaLabelledby) ? tab.ariaLabelledby : null"
-        [class.mdc-tab--active]="selectedIndex === i"
+        [class.mdc-tab--active]="selectedIndex === $index"
         [class]="tab.labelClass"
         [disabled]="tab.disabled"
         [fitInkBarToContent]="fitInkBarToContent"
-        (click)="_handleClick(tab, tabHeader, i)"
-        (cdkFocusChange)="_tabFocusChanged($event, i)">
+        (click)="_handleClick(tab, tabHeader, $index)"
+        (cdkFocusChange)="_tabFocusChanged($event, $index)">
       <span class="mdc-tab__ripple"></span>
 
       <!-- Needs to be a separate element, because we can't put
@@ -71,7 +71,7 @@
     <mat-tab-body role="tabpanel"
                  [id]="_getTabContentId($index)"
                  [attr.tabindex]="(contentTabIndex != null && selectedIndex === $index) ? contentTabIndex : null"
-                 [attr.aria-labelledby]="_getTabLabelId($index)"
+                 [attr.aria-labelledby]="_getTabLabelId(tab, $index)"
                  [attr.aria-hidden]="selectedIndex !== $index"
                  [class]="tab.bodyClass"
                  [content]="tab.content!"

src/material/tabs/tab-group.spec.ts

@@ -442,6 +442,45 @@ describe('MatTabGroup', () => {
       fixture.detectChanges();
       expect(tabList.hasAttribute('aria-labelledby')).toBe(false);
     }));
+
+    it('should set IDs on individual tabs and use them to label the tab bodies', () => {
+      fixture.detectChanges();
+      const tabs = Array.from<HTMLElement>(fixture.nativeElement.querySelectorAll('.mat-mdc-tab'));
+      const bodies = Array.from<HTMLElement>(
+        fixture.nativeElement.querySelectorAll('mat-tab-body'),
+      );
+
+      expect(tabs.length).toBe(3);
+      expect(bodies.length).toBe(3);
+      expect(tabs.every(tab => !!tab.getAttribute('id')))
+        .withContext('All tabs should have IDs')
+        .toBe(true);
+      expect(
+        bodies.every((body, index) => {
+          const attr = body.getAttribute('aria-labelledby');
+          return !!attr && tabs[index].getAttribute('id') === attr;
+        }),
+      )
+        .withContext('All tab bodies should be labelled')
+        .toBe(true);
+    });
+
+    it('should be able to set a custom ID for a tab', () => {
+      fixture.detectChanges();
+      const tab = fixture.nativeElement.querySelectorAll('.mat-mdc-tab')[1] as HTMLElement;
+      const body = fixture.nativeElement.querySelectorAll('mat-tab-body')[1] as HTMLElement;
+
+      expect(tab.getAttribute('id')).toBeTruthy();
+      expect(tab.getAttribute('id')).not.toBe('foo');
+      expect(body.getAttribute('aria-labelledby')).toBeTruthy();
+      expect(body.getAttribute('aria-labelledby')).toBe(tab.getAttribute('id'));
+
+      fixture.componentInstance.secondTabId = 'foo';
+      fixture.changeDetectorRef.markForCheck();
+      fixture.detectChanges();
+      expect(tab.getAttribute('id')).toBe('foo');
+      expect(body.getAttribute('aria-labelledby')).toBe('foo');
+    });
   });
 
   describe('aria labelling', () => {
@@ -1236,7 +1275,7 @@ describe('MatTabGroup labels aligned with a config', () => {
         <ng-template mat-tab-label>Tab One</ng-template>
         Tab one content
       </mat-tab>
-      <mat-tab>
+      <mat-tab [id]="secondTabId">
         <ng-template mat-tab-label>Tab Two</ng-template>
         <span>Tab </span><span>two</span><span>content</span>
       </mat-tab>
@@ -1259,6 +1298,7 @@ class SimpleTabsTestApp {
   headerPosition: MatTabHeaderPosition = 'above';
   ariaLabel: string;
   ariaLabelledby: string;
+  secondTabId: string | null = null;
   handleFocus(event: any) {
     this.focusEvent = event;
   }

src/material/tabs/tab-group.ts

@@ -498,13 +498,13 @@ export class MatTabGroup
   }
 
   /** Returns a unique id for each tab label element */
-  _getTabLabelId(i: number): string {
-    return `${this._groupId}-label-${i}`;
+  _getTabLabelId(tab: MatTab, index: number): string {
+    return tab.id || `${this._groupId}-label-${index}`;
   }
 
   /** Returns a unique id for each tab content element */
-  _getTabContentId(i: number): string {
-    return `${this._groupId}-content-${i}`;
+  _getTabContentId(index: number): string {
+    return `${this._groupId}-content-${index}`;
   }
 
   /**

src/material/tabs/tab.ts

@@ -51,6 +51,9 @@ export const MAT_TAB_GROUP = new InjectionToken<any>('MAT_TAB_GROUP');
     // 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': '',
+
+    // Clear any custom IDs from the tab since they'll be forwarded to the actual tab.
+    '[attr.id]': 'null',
   },
 })
 export class MatTab implements OnInit, OnChanges, OnDestroy {
@@ -99,6 +102,12 @@ export class MatTab implements OnInit, OnChanges, OnDestroy {
   /** Classes to be passed to the tab mat-tab-body container. */
   @Input() bodyClass: string | string[];
 
+  /**
+   * Custom ID for the tab, overriding the auto-generated one by Material.
+   * Note that when using this input, it's your responsibility to ensure that the ID is unique.
+   */
+  @Input() id: string | null = null;
+
   /** Portal that will be the hosted content of the tab */
   private _contentPortal: TemplatePortal | null = null;