fix(datepicker): not resetting when detached externally

src/lib/datepicker/datepicker.spec.ts

@@ -1,5 +1,5 @@
 import {ENTER, ESCAPE, RIGHT_ARROW} from '@angular/cdk/keycodes';
-import {OverlayContainer} from '@angular/cdk/overlay';
+import {OverlayContainer, Overlay, ScrollDispatcher} from '@angular/cdk/overlay';
 import {
   createKeyboardEvent,
   dispatchEvent,
@@ -27,7 +27,8 @@ import {MatInputModule} from '../input/index';
 import {MatDatepicker} from './datepicker';
 import {MatDatepickerInput} from './datepicker-input';
 import {MatDatepickerToggle} from './datepicker-toggle';
-import {MatDatepickerIntl, MatDatepickerModule} from './index';
+import {MatDatepickerIntl, MatDatepickerModule, MAT_DATEPICKER_SCROLL_STRATEGY} from './index';
+import {Subject} from 'rxjs/Subject';
 
 describe('MatDatepicker', () => {
   const SUPPORTS_INTL = typeof Intl != 'undefined';
@@ -342,17 +343,55 @@ describe('MatDatepicker', () => {
         testComponent.datepicker.open();
         fixture.detectChanges();
 
-        spyOn(testComponent.datepicker, 'close').and.callThrough();
-
+        const spy = jasmine.createSpy('close event spy');
+        const subscription = testComponent.datepicker.closedStream.subscribe(spy);
         const backdrop = document.querySelector('.cdk-overlay-backdrop')! as HTMLElement;
 
         backdrop.click();
         fixture.detectChanges();
         flush();
 
-        expect(testComponent.datepicker.close).toHaveBeenCalledTimes(1);
+        expect(spy).toHaveBeenCalledTimes(1);
         expect(testComponent.datepicker.opened).toBe(false);
+        subscription.unsubscribe();
       }));
+
+      it('should reset the datepicker when it is closed externally',
+        fakeAsync(inject([OverlayContainer], (oldOverlayContainer: OverlayContainer) => {
+
+          // Destroy the old container manually since resetting the testing module won't do it.
+          oldOverlayContainer.ngOnDestroy();
+          TestBed.resetTestingModule();
+
+          const scrolledSubject = new Subject();
+
+          // Stub out a `CloseScrollStrategy` so we can trigger a detachment via the `OverlayRef`.
+          fixture = createComponent(StandardDatepicker, [MatNativeDateModule], [
+            {
+              provide: ScrollDispatcher,
+              useValue: {scrolled: () => scrolledSubject}
+            },
+            {
+              provide: MAT_DATEPICKER_SCROLL_STRATEGY,
+              deps: [Overlay],
+              useFactory: (overlay: Overlay) => () => overlay.scrollStrategies.close()
+            }
+          ]);
+
+          fixture.detectChanges();
+          testComponent = fixture.componentInstance;
+
+          testComponent.datepicker.open();
+          fixture.detectChanges();
+
+          expect(testComponent.datepicker.opened).toBe(true);
+
+          scrolledSubject.next();
+          flush();
+          fixture.detectChanges();
+
+          expect(testComponent.datepicker.opened).toBe(false);
+        })));
     });
 
     describe('datepicker with too many inputs', () => {

src/lib/datepicker/datepicker.ts

@@ -41,6 +41,7 @@ import {MatDialog, MatDialogRef} from '@angular/material/dialog';
 import {DOCUMENT} from '@angular/common';
 import {Subject} from 'rxjs/Subject';
 import {Subscription} from 'rxjs/Subscription';
+import {merge} from 'rxjs/observable/merge';
 import {MatCalendar} from './calendar';
 import {createMissingDateImplError} from './datepicker-errors';
 import {MatDatepickerInput} from './datepicker-input';
@@ -312,9 +313,13 @@ export class MatDatepicker<D> implements OnDestroy {
     }
 
     const completeClose = () => {
-      this._opened = false;
-      this.closedStream.emit();
-      this._focusedElementBeforeOpen = null;
+      // The `_opened` could've been reset already if
+      // we got two events in quick succession.
+      if (this._opened) {
+        this._opened = false;
+        this.closedStream.emit();
+        this._focusedElementBeforeOpen = null;
+      }
     };
 
     if (this._focusedElementBeforeOpen &&
@@ -376,7 +381,9 @@ export class MatDatepicker<D> implements OnDestroy {
     });
 
     this._popupRef = this._overlay.create(overlayConfig);
-    this._popupRef.backdropClick().subscribe(() => this.close());
+
+    merge(this._popupRef.backdropClick(), this._popupRef.detachments())
+      .subscribe(() => this.close());
   }
 
   /** Create the popup PositionStrategy. */