fix(cdk/a11y): complete input modality streams on destroy

src/cdk/a11y/input-modality/input-modality-detector.spec.ts

@@ -194,4 +194,20 @@ describe('InputModalityDetector', () => {
     dispatchMouseEvent(document, 'mousedown');
     expect(detector.mostRecentModality).toBe('mouse');
   }));
+
+  it('should complete the various observables on destroy', () => {
+    setupTest();
+
+    const modalityDetectedSpy = jasmine.createSpy('modalityDetected complete spy');
+    const modalityChangedSpy = jasmine.createSpy('modalityChanged complete spy');
+
+    detector.modalityDetected.subscribe({complete: modalityDetectedSpy});
+    detector.modalityChanged.subscribe({complete: modalityChangedSpy});
+
+    detector.ngOnDestroy();
+
+    expect(modalityDetectedSpy).toHaveBeenCalled();
+    expect(modalityChangedSpy).toHaveBeenCalled();
+  });
+
 });

src/cdk/a11y/input-modality/input-modality-detector.ts

@@ -87,7 +87,7 @@ const modalityEventListenerOptions = normalizePassiveListenerOptions({
  * update the input modality to keyboard, but in general this service's behavior is largely
  * undefined.
  */
-@Injectable({ providedIn: 'root' })
+@Injectable({providedIn: 'root'})
 export class InputModalityDetector implements OnDestroy {
   /** Emits whenever an input modality is detected. */
   readonly modalityDetected: Observable<InputModality>;
@@ -185,21 +185,22 @@ export class InputModalityDetector implements OnDestroy {
 
     // If we're not in a browser, this service should do nothing, as there's no relevant input
     // modality to detect.
-    if (!_platform.isBrowser) { return; }
-
-    // Add the event listeners used to detect the user's input modality.
-    ngZone.runOutsideAngular(() => {
-      document.addEventListener('keydown', this._onKeydown, modalityEventListenerOptions);
-      document.addEventListener('mousedown', this._onMousedown, modalityEventListenerOptions);
-      document.addEventListener('touchstart', this._onTouchstart, modalityEventListenerOptions);
-    });
+    if (_platform.isBrowser) {
+      ngZone.runOutsideAngular(() => {
+        document.addEventListener('keydown', this._onKeydown, modalityEventListenerOptions);
+        document.addEventListener('mousedown', this._onMousedown, modalityEventListenerOptions);
+        document.addEventListener('touchstart', this._onTouchstart, modalityEventListenerOptions);
+      });
+    }
   }
 
   ngOnDestroy() {
-    if (!this._platform.isBrowser) { return; }
+    this._modality.complete();
 
-    document.removeEventListener('keydown', this._onKeydown, modalityEventListenerOptions);
-    document.removeEventListener('mousedown', this._onMousedown, modalityEventListenerOptions);
-    document.removeEventListener('touchstart', this._onTouchstart, modalityEventListenerOptions);
+    if (this._platform.isBrowser) {
+      document.removeEventListener('keydown', this._onKeydown, modalityEventListenerOptions);
+      document.removeEventListener('mousedown', this._onMousedown, modalityEventListenerOptions);
+      document.removeEventListener('touchstart', this._onTouchstart, modalityEventListenerOptions);
+    }
   }
 }