fix(expansion): unable to toggle disabled panel via methods (#18181)

In our expansion panel readme we state that a disabled panel can still be toggled and this is partially true, because it works only for toggling through the `expanded` property, but not via the `open`, `close` and `toggle` methods since they're inherited from the CDK `AccordionItem`. These changes override the methods so that we can allow them to work on disabled panels. We can't make this change safely for the CDK accordion item, because it doesn't have a panel header which means that we have to assume that all calls to the methods are user-generated.

Fixes #18171.

(cherry picked from commit 3a6c16f)

src/material/expansion/expansion-panel-header.ts

@@ -148,7 +148,9 @@ export class MatExpansionPanelHeader implements OnDestroy, FocusableOption {
 
   /** Toggles the expanded state of the panel. */
   _toggle(): void {
-    this.panel.toggle();
+    if (!this.disabled) {
+      this.panel.toggle();
+    }
   }
 
   /** Gets whether the panel is expanded. */

src/material/expansion/expansion-panel.ts

@@ -192,6 +192,21 @@ export class MatExpansionPanel extends CdkAccordionItem implements AfterContentI
     return this.expanded ? 'expanded' : 'collapsed';
   }
 
+  /** Toggles the expanded state of the expansion panel. */
+  toggle(): void {
+    this.expanded = !this.expanded;
+  }
+
+  /** Sets the expanded state of the expansion panel to false. */
+  close(): void {
+    this.expanded = false;
+  }
+
+  /** Sets the expanded state of the expansion panel to true. */
+  open(): void {
+    this.expanded = true;
+  }
+
   ngAfterContentInit() {
     if (this._lazyContent) {
       // Render the content as soon as the panel becomes open.

src/material/expansion/expansion.spec.ts

@@ -403,6 +403,52 @@ describe('MatExpansionPanel', () => {
       expect(header.classList).toContain('mat-expanded');
     });
 
+    it('should be able to toggle a disabled expansion panel programmatically via the ' +
+      'open/close methods', () => {
+        const panelInstance = fixture.componentInstance.panel;
+
+        expect(panelInstance.expanded).toBe(false);
+        expect(header.classList).not.toContain('mat-expanded');
+
+        fixture.componentInstance.disabled = true;
+        fixture.detectChanges();
+
+        panelInstance.open();
+        fixture.detectChanges();
+
+        expect(panelInstance.expanded).toBe(true);
+        expect(header.classList).toContain('mat-expanded');
+
+        panelInstance.close();
+        fixture.detectChanges();
+
+        expect(panelInstance.expanded).toBe(false);
+        expect(header.classList).not.toContain('mat-expanded');
+      });
+
+    it('should be able to toggle a disabled expansion panel programmatically via the ' +
+      'toggle method', () => {
+        const panelInstance = fixture.componentInstance.panel;
+
+        expect(panelInstance.expanded).toBe(false);
+        expect(header.classList).not.toContain('mat-expanded');
+
+        fixture.componentInstance.disabled = true;
+        fixture.detectChanges();
+
+        panelInstance.toggle();
+        fixture.detectChanges();
+
+        expect(panelInstance.expanded).toBe(true);
+        expect(header.classList).toContain('mat-expanded');
+
+        panelInstance.toggle();
+        fixture.detectChanges();
+
+        expect(panelInstance.expanded).toBe(false);
+        expect(header.classList).not.toContain('mat-expanded');
+      });
+
   });
 });
 

tools/public_api_guard/material/expansion.d.ts

@@ -58,9 +58,12 @@ export declare class MatExpansionPanel extends CdkAccordionItem implements After
     _containsFocus(): boolean;
     _getExpandedState(): MatExpansionPanelState;
     _hasSpacing(): boolean;
+    close(): void;
     ngAfterContentInit(): void;
     ngOnChanges(changes: SimpleChanges): void;
     ngOnDestroy(): void;
+    open(): void;
+    toggle(): void;
     static ngAcceptInputType_disabled: BooleanInput;
     static ngAcceptInputType_expanded: BooleanInput;
     static ngAcceptInputType_hideToggle: BooleanInput;