fix(material/autocomplete): avoid assigning invalid aria-labelledby values

src/material-experimental/mdc-autocomplete/autocomplete.spec.ts

@@ -1513,6 +1513,18 @@ describe('MDC-based MatAutocomplete', () => {
       expect(panel.hasAttribute('aria-label')).toBe(false);
     });
 
+    it('should trim aria-labelledby if the input does not have a label', () => {
+      fixture.componentInstance.hasLabel = false;
+      fixture.detectChanges();
+      fixture.componentInstance.ariaLabelledby = 'myLabelId';
+      fixture.componentInstance.trigger.openPanel();
+      fixture.detectChanges();
+
+      const panel =
+        fixture.debugElement.query(By.css('.mat-mdc-autocomplete-panel'))!.nativeElement;
+      expect(panel.getAttribute('aria-labelledby')).toBe(`myLabelId`);
+    });
+
     it('should clear aria-labelledby from the panel if an aria-label is set', () => {
       fixture.componentInstance.ariaLabel = 'My label';
       fixture.componentInstance.trigger.openPanel();
@@ -1524,6 +1536,17 @@ describe('MDC-based MatAutocomplete', () => {
       expect(panel.hasAttribute('aria-labelledby')).toBe(false);
     });
 
+    it('should clear aria-labelledby if the form field does not have a label', () => {
+      fixture.componentInstance.hasLabel = false;
+      fixture.detectChanges();
+      fixture.componentInstance.trigger.openPanel();
+      fixture.detectChanges();
+
+      const panel =
+        fixture.debugElement.query(By.css('.mat-mdc-autocomplete-panel'))!.nativeElement;
+      expect(panel.hasAttribute('aria-labelledby')).toBe(false);
+    });
+
     it('should support setting a custom aria-label', () => {
       fixture.componentInstance.ariaLabel = 'Custom Label';
       fixture.componentInstance.trigger.openPanel();
@@ -2762,7 +2785,7 @@ describe('MDC-based MatAutocomplete', () => {
 
 const SIMPLE_AUTOCOMPLETE_TEMPLATE = `
   <mat-form-field [floatLabel]="floatLabel" [style.width.px]="width">
-    <mat-label>State</mat-label>
+    <mat-label *ngIf="hasLabel">State</mat-label>
     <input
       matInput
       placeholder="State"
@@ -2795,6 +2818,7 @@ class SimpleAutocomplete implements OnDestroy {
   width: number;
   disableRipple = false;
   autocompleteDisabled = false;
+  hasLabel = true;
   ariaLabel: string;
   ariaLabelledby: string;
   panelClass = 'class-one class-two';

src/material/autocomplete/autocomplete-trigger.ts

@@ -574,7 +574,7 @@ export abstract class _MatAutocompleteTriggerBase implements ControlValueAccesso
     if (!overlayRef) {
       this._portal = new TemplatePortal(this.autocomplete.template,
         this._viewContainerRef,
-        {id: this._formField?._labelId});
+        {id: this._formField?.getLabelId()});
       overlayRef = this._overlay.create(this._getOverlayConfig());
       this._overlayRef = overlayRef;
 

src/material/autocomplete/autocomplete.spec.ts

@@ -1500,6 +1500,17 @@ describe('MatAutocomplete', () => {
       expect(panel.hasAttribute('aria-label')).toBe(false);
     });
 
+    it('should trim aria-labelledby if the input does not have a label', () => {
+      fixture.componentInstance.hasLabel = false;
+      fixture.detectChanges();
+      fixture.componentInstance.ariaLabelledby = 'myLabelId';
+      fixture.componentInstance.trigger.openPanel();
+      fixture.detectChanges();
+
+      const panel = fixture.debugElement.query(By.css('.mat-autocomplete-panel'))!.nativeElement;
+      expect(panel.getAttribute('aria-labelledby')).toBe(`myLabelId`);
+    });
+
     it('should clear aria-labelledby from the panel if an aria-label is set', () => {
       fixture.componentInstance.ariaLabel = 'My label';
       fixture.componentInstance.trigger.openPanel();
@@ -1510,6 +1521,16 @@ describe('MatAutocomplete', () => {
       expect(panel.hasAttribute('aria-labelledby')).toBe(false);
     });
 
+    it('should clear aria-labelledby if the form field does not have a label', () => {
+      fixture.componentInstance.hasLabel = false;
+      fixture.detectChanges();
+      fixture.componentInstance.trigger.openPanel();
+      fixture.detectChanges();
+
+      const panel = fixture.debugElement.query(By.css('.mat-autocomplete-panel'))!.nativeElement;
+      expect(panel.hasAttribute('aria-labelledby')).toBe(false);
+    });
+
     it('should support setting a custom aria-label', () => {
       fixture.componentInstance.ariaLabel = 'Custom Label';
       fixture.componentInstance.trigger.openPanel();
@@ -2760,9 +2781,9 @@ describe('MatAutocomplete', () => {
 
 const SIMPLE_AUTOCOMPLETE_TEMPLATE = `
   <mat-form-field [floatLabel]="floatLabel" [style.width.px]="width">
+    <mat-label *ngIf="hasLabel">State</mat-label>
     <input
       matInput
-      placeholder="State"
       [matAutocomplete]="auto"
       [matAutocompletePosition]="position"
       [matAutocompleteDisabled]="autocompleteDisabled"
@@ -2792,6 +2813,7 @@ class SimpleAutocomplete implements OnDestroy {
   width: number;
   disableRipple = false;
   autocompleteDisabled = false;
+  hasLabel = true;
   ariaLabel: string;
   ariaLabelledby: string;
   panelClass = 'class-one class-two';

src/material/autocomplete/autocomplete.ts

@@ -258,12 +258,13 @@ export abstract class _MatAutocompleteBase extends _MatAutocompleteMixinBase imp
   }
 
   /** Gets the aria-labelledby for the autocomplete panel. */
-  _getPanelAriaLabelledby(labelId: string): string | null {
+  _getPanelAriaLabelledby(labelId: string | null): string | null {
     if (this.ariaLabel) {
       return null;
     }
 
-    return this.ariaLabelledby ? labelId + ' ' + this.ariaLabelledby : labelId;
+    const labelExpression = labelId ? labelId + ' ' : '';
+    return this.ariaLabelledby ? labelExpression + this.ariaLabelledby : labelId;
   }
 
 

tools/public_api_guard/material/autocomplete.d.ts

@@ -27,7 +27,7 @@ export declare abstract class _MatAutocompleteBase extends _MatAutocompleteMixin
     template: TemplateRef<any>;
     constructor(_changeDetectorRef: ChangeDetectorRef, _elementRef: ElementRef<HTMLElement>, defaults: MatAutocompleteDefaultOptions, platform?: Platform);
     _emitSelectEvent(option: _MatOptionBase): void;
-    _getPanelAriaLabelledby(labelId: string): string | null;
+    _getPanelAriaLabelledby(labelId: string | null): string | null;
     _getScrollTop(): number;
     _setScrollTop(scrollTop: number): void;
     _setVisibility(): void;