feat(autocomplete): add md-autocomplete classes to overlay panel (#7176)

Transfers any classes added to `md-autocomplete` to the resulting panel, allowing for easier styling similarly to `md-menu`.

Fixes #4196.

src/lib/autocomplete/autocomplete.html

@@ -1,5 +1,5 @@
 <ng-template>
-  <div class="mat-autocomplete-panel" role="listbox" [id]="id" [ngClass]="_getClassList()" #panel>
+  <div class="mat-autocomplete-panel" role="listbox" [id]="id" [ngClass]="_classList" #panel>
     <ng-content></ng-content>
   </div>
 </ng-template>

src/lib/autocomplete/autocomplete.spec.ts

@@ -1521,6 +1521,25 @@ describe('MatAutocomplete', () => {
         expect(placeholder.classList).not.toContain('mat-form-field-empty');
       }));
 
+    it('should transfer the mat-autocomplete classes to the panel element', fakeAsync(() => {
+      const fixture = TestBed.createComponent(SimpleAutocomplete);
+      fixture.detectChanges();
+
+      fixture.componentInstance.trigger.openPanel();
+      tick();
+      fixture.detectChanges();
+
+      const autocomplete = fixture.debugElement.nativeElement.querySelector('mat-autocomplete');
+      const panel = overlayContainerElement.querySelector('.mat-autocomplete-panel')!;
+
+      expect(autocomplete.classList).not.toContain('class-one');
+      expect(autocomplete.classList).not.toContain('class-two');
+
+      expect(panel.classList).toContain('class-one');
+      expect(panel.classList).toContain('class-two');
+    }));
+
+
   });
 
   it('should have correct width when opened', () => {
@@ -1646,7 +1665,7 @@ describe('MatAutocomplete', () => {
       <input matInput placeholder="State" [matAutocomplete]="auto" [formControl]="stateCtrl">
     </mat-form-field>
 
-    <mat-autocomplete #auto="matAutocomplete" [displayWith]="displayFn">
+    <mat-autocomplete class="class-one class-two" #auto="matAutocomplete" [displayWith]="displayFn">
       <mat-option *ngFor="let state of filteredStates" [value]="state">
         <span> {{ state.code }}: {{ state.name }}  </span>
       </mat-option>

src/lib/autocomplete/autocomplete.ts

@@ -77,10 +77,23 @@ export class MatAutocomplete implements AfterContentInit {
   @Output() optionSelected: EventEmitter<MatAutocompleteSelectedEvent> =
       new EventEmitter<MatAutocompleteSelectedEvent>();
 
+  /**
+   * Takes classes set on the host md-autocomplete element and applies them to the panel
+   * inside the overlay container to allow for easy styling.
+   */
+  @Input('class')
+  set classList(classList: string) {
+    if (classList && classList.length) {
+      classList.split(' ').forEach(className => this._classList[className.trim()] = true);
+      this._elementRef.nativeElement.className = '';
+    }
+  }
+  _classList: {[key: string]: boolean} = {};
+
   /** Unique ID to be used by autocomplete trigger's "aria-owns" property. */
   id: string = `mat-autocomplete-${_uniqueAutocompleteIdCounter++}`;
 
-  constructor(private _changeDetectorRef: ChangeDetectorRef) { }
+  constructor(private _changeDetectorRef: ChangeDetectorRef, private _elementRef: ElementRef) { }
 
   ngAfterContentInit() {
     this._keyManager = new ActiveDescendantKeyManager<MatOption>(this.options).withWrap();
@@ -105,6 +118,8 @@ export class MatAutocomplete implements AfterContentInit {
   _setVisibility(): void {
     Promise.resolve().then(() => {
       this.showPanel = !!this.options.length;
+      this._classList['mat-autocomplete-visible'] = this.showPanel;
+      this._classList['mat-autocomplete-hidden'] = !this.showPanel;
       this._changeDetectorRef.markForCheck();
     });
   }
@@ -114,14 +129,5 @@ export class MatAutocomplete implements AfterContentInit {
     const event = new MatAutocompleteSelectedEvent(this, option);
     this.optionSelected.emit(event);
   }
-
-  /** Sets a class on the panel based on whether it is visible. */
-  _getClassList() {
-    return {
-      'mat-autocomplete-visible': this.showPanel,
-      'mat-autocomplete-hidden': !this.showPanel
-    };
-  }
-
 }