fix(material/tabs): picking up mat-tab-label from child tabs

src/material-experimental/mdc-tabs/public-api.ts

@@ -28,5 +28,6 @@ export {
   MatTabsConfig,
   MAT_TABS_CONFIG,
   MAT_TAB_GROUP,
+  MAT_TAB,
   ScrollDirection,
 } from '@angular/material/tabs';

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

@@ -40,6 +40,7 @@ describe('MDC-based MatTabGroup', () => {
         NestedTabs,
         TabGroupWithIndirectDescendantTabs,
         TabGroupWithSpaceAbove,
+        NestedTabGroupWithLabel,
       ],
     });
 
@@ -673,6 +674,19 @@ describe('MDC-based MatTabGroup', () => {
 
       expect(fixture.nativeElement.textContent).toContain('pizza is active');
     }));
+
+    it('should not pick up mat-tab-label from a child tab', fakeAsync(() => {
+      const fixture = TestBed.createComponent(NestedTabGroupWithLabel);
+      fixture.detectChanges();
+      tick();
+      fixture.detectChanges();
+
+      const labels = fixture.nativeElement.querySelectorAll('.mdc-tab__text-label');
+      const contents = Array.from<HTMLElement>(labels).map(label => label.textContent?.trim());
+
+      expect(contents).toEqual(
+        ['Parent 1', 'Parent 2', 'Parent 3', 'Child 1', 'Child 2', 'Child 3']);
+    }));
   });
 
   describe('nested tabs', () => {
@@ -1166,3 +1180,25 @@ class TabGroupWithInkBarFitToContent {
 class TabGroupWithSpaceAbove {
   @ViewChild(MatTabGroup) tabGroup: MatTabGroup;
 }
+
+
+@Component({
+  template: `
+    <mat-tab-group>
+      <mat-tab label="Parent 1">
+        <mat-tab-group>
+          <mat-tab label="Child 1">Content 1</mat-tab>
+          <mat-tab>
+            <ng-template mat-tab-label>Child 2</ng-template>
+            Content 2
+          </mat-tab>
+          <mat-tab label="Child 3">Child 3</mat-tab>
+        </mat-tab-group>
+      </mat-tab>
+      <mat-tab label="Parent 2">Parent 2</mat-tab>
+      <mat-tab label="Parent 3">Parent 3</mat-tab>
+    </mat-tab-group>
+  `
+})
+class NestedTabGroupWithLabel {
+}

src/material-experimental/mdc-tabs/tab.ts

@@ -13,7 +13,7 @@ import {
   TemplateRef,
   ContentChild,
 } from '@angular/core';
-import {MatTab as BaseMatTab} from '@angular/material/tabs';
+import {MatTab as BaseMatTab, MAT_TAB} from '@angular/material/tabs';
 import {MatTabContent} from './tab-content';
 import {MatTabLabel} from './tab-label';
 
@@ -28,6 +28,7 @@ import {MatTabLabel} from './tab-label';
   changeDetection: ChangeDetectionStrategy.OnPush,
   encapsulation: ViewEncapsulation.None,
   exportAs: 'matTab',
+  providers: [{provide: MAT_TAB, useExisting: MatTab}]
 })
 export class MatTab extends BaseMatTab {
   /**

src/material/tabs/public-api.ts

@@ -19,7 +19,7 @@ export {
 export {MatTabHeader, _MatTabHeaderBase} from './tab-header';
 export {MatTabLabelWrapper} from './tab-label-wrapper';
 export {MatTab, MAT_TAB_GROUP} from './tab';
-export {MatTabLabel} from './tab-label';
+export {MatTabLabel, MAT_TAB} from './tab-label';
 export {MatTabNav, MatTabLink, _MatTabNavBase, _MatTabLinkBase} from './tab-nav-bar/index';
 export {MatTabContent} from './tab-content';
 export {ScrollDirection} from './paginated-tab-header';

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

@@ -40,6 +40,7 @@ describe('MatTabGroup', () => {
         NestedTabs,
         TabGroupWithIndirectDescendantTabs,
         TabGroupWithSpaceAbove,
+        NestedTabGroupWithLabel,
       ],
     });
 
@@ -673,6 +674,19 @@ describe('MatTabGroup', () => {
 
       expect(fixture.nativeElement.textContent).toContain('pizza is active');
     }));
+
+    it('should not pick up mat-tab-label from a child tab', fakeAsync(() => {
+      const fixture = TestBed.createComponent(NestedTabGroupWithLabel);
+      fixture.detectChanges();
+      tick();
+      fixture.detectChanges();
+
+      const labels = fixture.nativeElement.querySelectorAll('.mat-tab-label-content');
+      const contents = Array.from<HTMLElement>(labels).map(label => label.textContent?.trim());
+
+      expect(contents).toEqual(
+        ['Parent 1', 'Parent 2', 'Parent 3', 'Child 1', 'Child 2', 'Child 3']);
+    }));
   });
 
   describe('nested tabs', () => {
@@ -1099,3 +1113,25 @@ class TabGroupWithIndirectDescendantTabs {
 class TabGroupWithSpaceAbove {
   @ViewChild(MatTabGroup) tabGroup: MatTabGroup;
 }
+
+
+@Component({
+  template: `
+    <mat-tab-group>
+      <mat-tab label="Parent 1">
+        <mat-tab-group>
+          <mat-tab label="Child 1">Content 1</mat-tab>
+          <mat-tab>
+            <ng-template mat-tab-label>Child 2</ng-template>
+            Content 2
+          </mat-tab>
+          <mat-tab label="Child 3">Child 3</mat-tab>
+        </mat-tab-group>
+      </mat-tab>
+      <mat-tab label="Parent 2">Parent 2</mat-tab>
+      <mat-tab label="Parent 3">Parent 3</mat-tab>
+    </mat-tab-group>
+  `
+})
+class NestedTabGroupWithLabel {
+}

src/material/tabs/tab-label.ts

@@ -6,7 +6,14 @@
  * found in the LICENSE file at https://angular.io/license
  */
 
-import {Directive, InjectionToken} from '@angular/core';
+import {
+  Directive,
+  Inject,
+  InjectionToken,
+  Optional,
+  TemplateRef,
+  ViewContainerRef,
+} from '@angular/core';
 import {CdkPortal} from '@angular/cdk/portal';
 
 /**
@@ -16,9 +23,22 @@ import {CdkPortal} from '@angular/cdk/portal';
  */
 export const MAT_TAB_LABEL = new InjectionToken<MatTabLabel>('MatTabLabel');
 
+/**
+ * Used to provide a tab label to a tab without causing a circular dependency.
+ * @docs-private
+ */
+ export const MAT_TAB = new InjectionToken<any>('MAT_TAB');
+
 /** Used to flag tab labels for use with the portal directive */
 @Directive({
   selector: '[mat-tab-label], [matTabLabel]',
   providers: [{provide: MAT_TAB_LABEL, useExisting: MatTabLabel}],
 })
-export class MatTabLabel extends CdkPortal {}
+export class MatTabLabel extends CdkPortal {
+  constructor(
+    templateRef: TemplateRef<any>,
+    viewContainerRef: ViewContainerRef,
+    @Inject(MAT_TAB) @Optional() public _closestTab: any) {
+    super(templateRef, viewContainerRef);
+  }
+}

src/material/tabs/tab.ts

@@ -28,7 +28,7 @@ import {
 import {CanDisable, mixinDisabled} from '@angular/material/core';
 import {Subject} from 'rxjs';
 import {MAT_TAB_CONTENT} from './tab-content';
-import {MAT_TAB_LABEL, MatTabLabel} from './tab-label';
+import {MAT_TAB_LABEL, MatTabLabel, MAT_TAB} from './tab-label';
 
 
 // Boilerplate for applying mixins to MatTab.
@@ -49,6 +49,7 @@ export const MAT_TAB_GROUP = new InjectionToken<any>('MAT_TAB_GROUP');
   changeDetection: ChangeDetectionStrategy.Default,
   encapsulation: ViewEncapsulation.None,
   exportAs: 'matTab',
+  providers: [{provide: MAT_TAB, useExisting: MatTab}]
 })
 export class MatTab extends _MatTabBase implements OnInit, CanDisable, OnChanges, OnDestroy {
   /** Content for the tab label given by `<ng-template mat-tab-label>`. */
@@ -133,12 +134,12 @@ export class MatTab extends _MatTabBase implements OnInit, CanDisable, OnChanges
    * TS 4.0 doesn't allow properties to override accessors or vice-versa.
    * @docs-private
    */
-  protected _setTemplateLabelInput(value: MatTabLabel) {
-    // Only update the templateLabel via query if there is actually
-    // a MatTabLabel found. This works around an issue where a user may have
-    // manually set `templateLabel` during creation mode, which would then get clobbered
-    // by `undefined` when this query resolves.
-    if (value) {
+  protected _setTemplateLabelInput(value: MatTabLabel|undefined) {
+    // Only update the label if the query managed to find one. This works around an issue where a
+    // user may have manually set `templateLabel` during creation mode, which would then get
+    // clobbered by `undefined` when the query resolves. Also note that we check that the closest
+    // tab matches the current one so that we don't pick up labels from nested tabs.
+    if (value && value._closestTab === this) {
       this._templateLabel = value;
     }
   }

tools/public_api_guard/material/tabs.md

@@ -58,6 +58,9 @@ export const _MAT_INK_BAR_POSITIONER: InjectionToken<_MatInkBarPositioner>;
 // @public
 function _MAT_INK_BAR_POSITIONER_FACTORY(): _MatInkBarPositioner;
 
+// @public
+export const MAT_TAB: InjectionToken<any>;
+
 // @public
 const MAT_TAB_CONTENT: InjectionToken<MatTabContent>;
 
@@ -114,7 +117,7 @@ export class MatTab extends _MatTabBase implements OnInit, CanDisable, OnChanges
     ngOnInit(): void;
     origin: number | null;
     position: number | null;
-    protected _setTemplateLabelInput(value: MatTabLabel): void;
+    protected _setTemplateLabelInput(value: MatTabLabel | undefined): void;
     readonly _stateChanges: Subject<void>;
     get templateLabel(): MatTabLabel;
     set templateLabel(value: MatTabLabel);
@@ -316,10 +319,13 @@ export type MatTabHeaderPosition = 'above' | 'below';
 
 // @public
 export class MatTabLabel extends CdkPortal {
+    constructor(templateRef: TemplateRef<any>, viewContainerRef: ViewContainerRef, _closestTab: any);
+    // (undocumented)
+    _closestTab: any;
     // (undocumented)
     static ɵdir: i0.ɵɵDirectiveDeclaration<MatTabLabel, "[mat-tab-label], [matTabLabel]", never, {}, {}, never>;
     // (undocumented)
-    static ɵfac: i0.ɵɵFactoryDeclaration<MatTabLabel, never>;
+    static ɵfac: i0.ɵɵFactoryDeclaration<MatTabLabel, [null, null, { optional: true; }]>;
 }
 
 // @public