fix(autocomplete): not updating origin if it changes after init (#14677)

* Fixes changes to the `matAutocompleteOrigin` input being ignored if they happen after the overlay has been initialized.
* Fixes the `MatAutocompleteOrigin` class not being exported as a part of the public API.

src/lib/autocomplete/autocomplete-trigger.ts

@@ -569,13 +569,16 @@ export class MatAutocompleteTrigger implements ControlValueAccessor, OnDestroy {
       throw getMatAutocompleteMissingPanelError();
     }
 
-    if (!this._overlayRef) {
+    let overlayRef = this._overlayRef;
+
+    if (!overlayRef) {
       this._portal = new TemplatePortal(this.autocomplete.template, this._viewContainerRef);
-      this._overlayRef = this._overlay.create(this._getOverlayConfig());
+      overlayRef = this._overlay.create(this._getOverlayConfig());
+      this._overlayRef = overlayRef;
 
       // Use the `keydownEvents` in order to take advantage of
       // the overlay event targeting provided by the CDK overlay.
-      this._overlayRef.keydownEvents().subscribe(event => {
+      overlayRef.keydownEvents().subscribe(event => {
         // Close when pressing ESCAPE or ALT + UP_ARROW, based on the a11y guidelines.
         // See: https://www.w3.org/TR/wai-aria-practices-1.1/#textbox-keyboard-interaction
         if (event.keyCode === ESCAPE || (event.keyCode === UP_ARROW && event.altKey)) {
@@ -586,18 +589,21 @@ export class MatAutocompleteTrigger implements ControlValueAccessor, OnDestroy {
 
       if (this._viewportRuler) {
         this._viewportSubscription = this._viewportRuler.change().subscribe(() => {
-          if (this.panelOpen && this._overlayRef) {
-            this._overlayRef.updateSize({width: this._getPanelWidth()});
+          if (this.panelOpen && overlayRef) {
+            overlayRef.updateSize({width: this._getPanelWidth()});
           }
         });
       }
     } else {
-      // Update the panel width and direction, in case anything has changed.
-      this._overlayRef.updateSize({width: this._getPanelWidth()});
+      const position = overlayRef.getConfig().positionStrategy as FlexibleConnectedPositionStrategy;
+
+      // Update the trigger, panel width and direction, in case anything has changed.
+      position.setOrigin(this._getConnectedElement());
+      overlayRef.updateSize({width: this._getPanelWidth()});
     }
 
-    if (this._overlayRef && !this._overlayRef.hasAttached()) {
-      this._overlayRef.attach(this._portal);
+    if (overlayRef && !overlayRef.hasAttached()) {
+      overlayRef.attach(this._portal);
       this._closingActionsSubscription = this._subscribeToClosingActions();
     }
 

src/lib/autocomplete/autocomplete.spec.ts

@@ -47,6 +47,7 @@ import {
   MatAutocompleteModule,
   MatAutocompleteSelectedEvent,
   MatAutocompleteTrigger,
+  MatAutocompleteOrigin,
 } from './index';
 
 
@@ -2218,6 +2219,34 @@ describe('MatAutocomplete', () => {
     const fixture = createComponent(AutocompleteWithDifferentOrigin);
 
     fixture.detectChanges();
+    fixture.componentInstance.connectedTo = fixture.componentInstance.alternateOrigin;
+    fixture.detectChanges();
+    fixture.componentInstance.trigger.openPanel();
+    fixture.detectChanges();
+    zone.simulateZoneExit();
+
+    const overlayRect =
+        overlayContainerElement.querySelector('.cdk-overlay-pane')!.getBoundingClientRect();
+    const originRect = fixture.nativeElement.querySelector('.origin').getBoundingClientRect();
+
+    expect(Math.floor(overlayRect.top)).toBe(Math.floor(originRect.bottom),
+        'Expected autocomplete panel to align with the bottom of the new origin.');
+  });
+
+  it('should be able to change the origin after the panel has been opened', () => {
+    const fixture = createComponent(AutocompleteWithDifferentOrigin);
+
+    fixture.detectChanges();
+    fixture.componentInstance.trigger.openPanel();
+    fixture.detectChanges();
+    zone.simulateZoneExit();
+
+    fixture.componentInstance.trigger.closePanel();
+    fixture.detectChanges();
+
+    fixture.componentInstance.connectedTo = fixture.componentInstance.alternateOrigin;
+    fixture.detectChanges();
+
     fixture.componentInstance.trigger.openPanel();
     fixture.detectChanges();
     zone.simulateZoneExit();
@@ -2603,7 +2632,7 @@ class AutocompleteWithNumberInputAndNgModel {
         <input
           matInput
           [matAutocomplete]="auto"
-          [matAutocompleteConnectedTo]="origin"
+          [matAutocompleteConnectedTo]="connectedTo"
           [(ngModel)]="selectedValue">
       </mat-form-field>
     </div>
@@ -2623,8 +2652,10 @@ class AutocompleteWithNumberInputAndNgModel {
 })
 class AutocompleteWithDifferentOrigin {
   @ViewChild(MatAutocompleteTrigger) trigger: MatAutocompleteTrigger;
+  @ViewChild(MatAutocompleteOrigin) alternateOrigin: MatAutocompleteOrigin;
   selectedValue: string;
   values = ['one', 'two', 'three'];
+  connectedTo?: MatAutocompleteOrigin;
 }
 
 @Component({

src/lib/autocomplete/public-api.ts

@@ -9,4 +9,4 @@
 export * from './autocomplete';
 export * from './autocomplete-module';
 export * from './autocomplete-trigger';
-
+export * from './autocomplete-origin';