fix(material/form-field): move error aria-live to parent container

Author: andrewseguin

src/material/form-field/directives/error.ts

@@ -6,14 +6,7 @@
  * found in the LICENSE file at https://angular.dev/license
  */
 
-import {
-  Directive,
-  ElementRef,
-  InjectionToken,
-  Input,
-  HostAttributeToken,
-  inject,
-} from '@angular/core';
+import {Directive, InjectionToken, Input, inject} from '@angular/core';
 import {_IdGenerator} from '@angular/cdk/a11y';
 
 /**
@@ -28,7 +21,6 @@ export const MAT_ERROR = new InjectionToken<MatError>('MatError');
   selector: 'mat-error, [matError]',
   host: {
     'class': 'mat-mdc-form-field-error mat-mdc-form-field-bottom-align',
-    'aria-atomic': 'true',
     '[id]': 'id',
   },
   providers: [{provide: MAT_ERROR, useExisting: MatError}],
@@ -38,14 +30,5 @@ export class MatError {
 
   constructor(...args: unknown[]);
 
-  constructor() {
-    const ariaLive = inject(new HostAttributeToken('aria-live'), {optional: true});
-
-    // If no aria-live value is set add 'polite' as a default. This is preferred over setting
-    // role='alert' so that screen readers do not interrupt the current task to read this aloud.
-    if (!ariaLive) {
-      const elementRef = inject(ElementRef);
-      elementRef.nativeElement.setAttribute('aria-live', 'polite');
-    }
-  }
+  constructor() {}
 }

src/material/form-field/form-field.html

@@ -99,25 +99,27 @@
   class="mat-mdc-form-field-subscript-wrapper mat-mdc-form-field-bottom-align"
   [class.mat-mdc-form-field-subscript-dynamic-size]="subscriptSizing === 'dynamic'"
 >
-  @switch (_getDisplayedMessages()) {
-    @case ('error') {
+  @let subscriptMessageType = _getSubscriptMessageType();
+
+  <div aria-atomic="true" aria-live="polite">
+    @if (subscriptMessageType == 'error') {
       <div
         class="mat-mdc-form-field-error-wrapper"
         [@transitionMessages]="_subscriptAnimationState"
       >
         <ng-content select="mat-error, [matError]"></ng-content>
       </div>
     }
+  </div>
 
-    @case ('hint') {
-      <div class="mat-mdc-form-field-hint-wrapper" [@transitionMessages]="_subscriptAnimationState">
-        @if (hintLabel) {
-          <mat-hint [id]="_hintLabelId">{{hintLabel}}</mat-hint>
-        }
-        <ng-content select="mat-hint:not([align='end'])"></ng-content>
-        <div class="mat-mdc-form-field-hint-spacer"></div>
-        <ng-content select="mat-hint[align='end']"></ng-content>
-      </div>
-    }
+  @if (subscriptMessageType == 'hint') {
+    <div class="mat-mdc-form-field-hint-wrapper" [@transitionMessages]="_subscriptAnimationState">
+      @if (hintLabel) {
+        <mat-hint [id]="_hintLabelId">{{hintLabel}}</mat-hint>
+      }
+      <ng-content select="mat-hint:not([align='end'])"></ng-content>
+      <div class="mat-mdc-form-field-hint-spacer"></div>
+      <ng-content select="mat-hint[align='end']"></ng-content>
+    </div>
   }
 </div>

src/material/form-field/form-field.ts

@@ -592,8 +592,8 @@ export class MatFormField
     return control && control[prop];
   }
 
-  /** Determines whether to display hints or errors. */
-  _getDisplayedMessages(): 'error' | 'hint' {
+  /** Gets the type of subscript message to render (error or hint). */
+  _getSubscriptMessageType(): 'error' | 'hint' {
     return this._errorChildren && this._errorChildren.length > 0 && this._control.errorState
       ? 'error'
       : 'hint';
@@ -661,7 +661,7 @@ export class MatFormField
         ids.push(...this._control.userAriaDescribedBy.split(' '));
       }
 
-      if (this._getDisplayedMessages() === 'hint') {
+      if (this._getSubscriptMessageType() === 'hint') {
         const startHint = this._hintChildren
           ? this._hintChildren.find(hint => hint.align === 'start')
           : null;

src/material/input/input.spec.ts

@@ -1238,11 +1238,13 @@ describe('MatMdcInput with forms', () => {
         .toBe(1);
     }));
 
-    it('should set the proper aria-live attribute on the error messages', fakeAsync(() => {
+    it('should be in a parent element with the an aria-live attribute to announce the error', fakeAsync(() => {
       testComponent.formControl.markAsTouched();
       fixture.detectChanges();
 
-      expect(containerEl.querySelector('mat-error')!.getAttribute('aria-live')).toBe('polite');
+      expect(
+        containerEl.querySelector('[aria-live]:has(mat-error)')!.getAttribute('aria-live'),
+      ).toBe('polite');
     }));
 
     it('sets the aria-describedby to reference errors when in error state', fakeAsync(() => {