fix(snack-bar): snack bar not animating in if no positions are passed in

Adds some better handling for the case where no positions are passed into a snack bar. Currently the snack bar attempts to animate in to an invalid animation state.

Fixes #11197.

Author: crisbeto

src/lib/snack-bar/snack-bar-container.ts

@@ -30,6 +30,14 @@ import {take} from 'rxjs/operators';
 import {matSnackBarAnimations} from './snack-bar-animations';
 import {MatSnackBarConfig} from './snack-bar-config';
 
+/**
+ * Default positions to be used as fallbacks if necessary.
+ * @docs-private
+ */
+const {
+  horizontalPosition: defaultHorizontalPosition,
+  verticalPosition: defaultVerticalPosition
+} = new MatSnackBarConfig();
 
 /**
  * Internal component that wraps user-provided snack bar content.
@@ -113,14 +121,14 @@ export class MatSnackBarContainer extends BasePortalOutlet implements OnDestroy
   /** Begin animation of snack bar entrance into view. */
   enter(): void {
     if (!this._destroyed) {
-      this._animationState = `visible-${this.snackBarConfig.verticalPosition}`;
+      this._animationState = `visible-${this._getVerticalPosition()}`;
       this._changeDetectorRef.detectChanges();
     }
   }
 
   /** Begin animation of the snack bar exiting from view. */
   exit(): Observable<void> {
-    this._animationState = `hidden-${this.snackBarConfig.verticalPosition}`;
+    this._animationState = `hidden-${this._getVerticalPosition()}`;
     return this._onExit;
   }
 
@@ -155,11 +163,11 @@ export class MatSnackBarContainer extends BasePortalOutlet implements OnDestroy
       }
     }
 
-    if (this.snackBarConfig.horizontalPosition === 'center') {
+    if ((this.snackBarConfig.horizontalPosition || defaultHorizontalPosition) === 'center') {
       element.classList.add('mat-snack-bar-center');
     }
 
-    if (this.snackBarConfig.verticalPosition === 'top') {
+    if (this._getVerticalPosition() === 'top') {
       element.classList.add('mat-snack-bar-top');
     }
   }
@@ -170,4 +178,8 @@ export class MatSnackBarContainer extends BasePortalOutlet implements OnDestroy
       throw Error('Attempting to attach snack bar content after content is already attached');
     }
   }
+
+  private _getVerticalPosition() {
+    return this.snackBarConfig.verticalPosition || defaultVerticalPosition;
+  }
 }

src/lib/snack-bar/snack-bar.spec.ts

@@ -422,6 +422,31 @@ describe('MatSnackBar', () => {
         .toContain('custom-class', 'Expected class applied through the defaults to be applied.');
   }));
 
+  it('should position the snack bar correctly if no default position is defined', fakeAsync(() => {
+    overlayContainer.ngOnDestroy();
+    viewContainerFixture.destroy();
+
+    TestBed
+      .resetTestingModule()
+      .overrideProvider(MAT_SNACK_BAR_DEFAULT_OPTIONS, {
+        deps: [],
+        useFactory: () => ({politeness: 'polite'})
+      })
+      .configureTestingModule({imports: [MatSnackBarModule, NoopAnimationsModule]})
+      .compileComponents();
+
+    inject([MatSnackBar, OverlayContainer], (sb: MatSnackBar, oc: OverlayContainer) => {
+      snackBar = sb;
+      overlayContainer = oc;
+      overlayContainerElement = oc.getContainerElement();
+    })();
+
+    const snackBarRef = snackBar.open(simpleMessage);
+    flush();
+
+    expect(snackBarRef.containerInstance._animationState).toBe('visible-bottom');
+  }));
+
   describe('with custom component', () => {
     it('should open a custom component', () => {
       const snackBarRef = snackBar.openFromComponent(BurritosNotification);