fix(menu): reintroduce panel position classes (#11612)

Reintroduces adding CSS classes to the `mat-menu` based on its position. This is useful to some consumers which may want to style the panel based on how it's being displayed.

Fixes #11597.

Author: crisbeto

src/lib/menu/menu-directive.ts

@@ -28,6 +28,7 @@ import {
   QueryList,
   ViewChild,
   ViewEncapsulation,
+  OnInit,
 } from '@angular/core';
 import {merge, Observable, Subject, Subscription} from 'rxjs';
 import {startWith, switchMap, take} from 'rxjs/operators';
@@ -97,7 +98,7 @@ const MAT_MENU_BASE_ELEVATION = 2;
     {provide: MAT_MENU_PANEL, useExisting: MatMenu}
   ]
 })
-export class MatMenu implements AfterContentInit, MatMenuPanel<MatMenuItem>, OnDestroy {
+export class MatMenu implements AfterContentInit, MatMenuPanel<MatMenuItem>, OnInit, OnDestroy {
   private _keyManager: FocusKeyManager<MatMenuItem>;
   private _xPosition: MenuPositionX = this._defaultOptions.xPosition;
   private _yPosition: MenuPositionY = this._defaultOptions.yPosition;
@@ -141,6 +142,7 @@ export class MatMenu implements AfterContentInit, MatMenuPanel<MatMenuItem>, OnD
       throwMatMenuInvalidPositionX();
     }
     this._xPosition = value;
+    this.setPositionClasses();
   }
 
   /** Position of the menu in the Y axis. */
@@ -151,6 +153,7 @@ export class MatMenu implements AfterContentInit, MatMenuPanel<MatMenuItem>, OnD
       throwMatMenuInvalidPositionY();
     }
     this._yPosition = value;
+    this.setPositionClasses();
   }
 
   /** @docs-private */
@@ -230,6 +233,10 @@ export class MatMenu implements AfterContentInit, MatMenuPanel<MatMenuItem>, OnD
     private _ngZone: NgZone,
     @Inject(MAT_MENU_DEFAULT_OPTIONS) private _defaultOptions: MatMenuDefaultOptions) { }
 
+  ngOnInit() {
+    this.setPositionClasses();
+  }
+
   ngAfterContentInit() {
     this._keyManager = new FocusKeyManager<MatMenuItem>(this._items).withWrap().withTypeAhead();
     this._tabSubscription = this._keyManager.tabOut.subscribe(() => this.closed.emit('tab'));
@@ -347,6 +354,21 @@ export class MatMenu implements AfterContentInit, MatMenuPanel<MatMenuItem>, OnD
     }
   }
 
+  /**
+   * Adds classes to the menu panel based on its position. Can be used by
+   * consumers to add specific styling based on the position.
+   * @param posX Position of the menu along the x axis.
+   * @param posY Position of the menu along the y axis.
+   * @docs-private
+   */
+  setPositionClasses(posX: MenuPositionX = this.xPosition, posY: MenuPositionY = this.yPosition) {
+    const classes = this._classList;
+    classes['mat-menu-before'] = posX === 'before';
+    classes['mat-menu-after'] = posX === 'after';
+    classes['mat-menu-above'] = posY === 'above';
+    classes['mat-menu-below'] = posY === 'below';
+  }
+
   /** Starts the enter animation. */
   _startAnimation() {
     // @deletion-target 7.0.0 Combine with _resetAnimation.

src/lib/menu/menu.spec.ts

@@ -50,7 +50,8 @@ describe('MatMenu', () => {
   let overlayContainerElement: HTMLElement;
   let focusMonitor: FocusMonitor;
 
-  function createComponent<T>(component: Type<T>, providers: Provider[] = [],
+  function createComponent<T>(component: Type<T>,
+                              providers: Provider[] = [],
                               declarations: any[] = []): ComponentFixture<T> {
     TestBed.configureTestingModule({
       imports: [MatMenuModule, NoopAnimationsModule],
@@ -491,6 +492,68 @@ describe('MatMenu', () => {
     }));
   });
 
+  describe('positions', () => {
+    let fixture: ComponentFixture<PositionedMenu>;
+    let panel: HTMLElement;
+
+    beforeEach(() => {
+      fixture = createComponent(PositionedMenu);
+      fixture.detectChanges();
+
+      const trigger = fixture.componentInstance.triggerEl.nativeElement;
+
+      // Push trigger to the bottom edge of viewport,so it has space to open "above"
+      trigger.style.position = 'fixed';
+      trigger.style.top = '600px';
+
+      // Push trigger to the right, so it has space to open "before"
+      trigger.style.left = '100px';
+
+      fixture.componentInstance.trigger.openMenu();
+      fixture.detectChanges();
+      panel = overlayContainerElement.querySelector('.mat-menu-panel') as HTMLElement;
+    });
+
+    it('should append mat-menu-before if the x position is changed', () => {
+      expect(panel.classList).toContain('mat-menu-before');
+      expect(panel.classList).not.toContain('mat-menu-after');
+
+      fixture.componentInstance.xPosition = 'after';
+      fixture.detectChanges();
+
+      expect(panel.classList).toContain('mat-menu-after');
+      expect(panel.classList).not.toContain('mat-menu-before');
+    });
+
+    it('should append mat-menu-above if the y position is changed', () => {
+      expect(panel.classList).toContain('mat-menu-above');
+      expect(panel.classList).not.toContain('mat-menu-below');
+
+      fixture.componentInstance.yPosition = 'below';
+      fixture.detectChanges();
+
+      expect(panel.classList).toContain('mat-menu-below');
+      expect(panel.classList).not.toContain('mat-menu-above');
+    });
+
+    it('should default to the "below" and "after" positions', () => {
+      overlayContainer.ngOnDestroy();
+      fixture.destroy();
+      TestBed.resetTestingModule();
+
+      const newFixture = createComponent(SimpleMenu, [], [FakeIcon]);
+
+      newFixture.detectChanges();
+      newFixture.componentInstance.trigger.openMenu();
+      newFixture.detectChanges();
+      panel = overlayContainerElement.querySelector('.mat-menu-panel') as HTMLElement;
+
+      expect(panel.classList).toContain('mat-menu-below');
+      expect(panel.classList).toContain('mat-menu-after');
+    });
+
+  });
+
   describe('fallback positions', () => {
 
     it('should fall back to "before" mode if "after" mode would not fit on screen', () => {
@@ -696,6 +759,14 @@ describe('MatMenu', () => {
             .toBe(Math.floor(subject.triggerRect.top),
                 `Expected menu to open in "above" position if "below" position wouldn't fit.`);
       });
+
+      it('repositions the origin to be below, so the menu opens from the trigger', () => {
+        subject.openMenu();
+        subject.fixture.detectChanges();
+
+        expect(subject.menuPanel!.classList).toContain('mat-menu-below');
+        expect(subject.menuPanel!.classList).not.toContain('mat-menu-above');
+      });
     });
   });