feat(cdk/a11y): allow safe HTML to be passed to live announcer

Adds support for passing safe HTML into the `LiveAnnouncer`. This can be necessary when announcing content in a different language from the rest of the page.

Fixes #31835.

Author: crisbeto

goldens/cdk/a11y/index.api.md

@@ -18,6 +18,7 @@ import { OnChanges } from '@angular/core';
 import { OnDestroy } from '@angular/core';
 import { Provider } from '@angular/core';
 import { QueryList } from '@angular/core';
+import { SafeHtml } from '@angular/platform-browser';
 import { Signal } from '@angular/core';
 import { SimpleChanges } from '@angular/core';
 import { Subject } from 'rxjs';
@@ -404,10 +405,10 @@ export const LIVE_ANNOUNCER_ELEMENT_TOKEN: InjectionToken<HTMLElement | null>;
 // @public (undocumented)
 export class LiveAnnouncer implements OnDestroy {
     constructor(...args: unknown[]);
-    announce(message: string): Promise<void>;
-    announce(message: string, politeness?: AriaLivePoliteness): Promise<void>;
-    announce(message: string, duration?: number): Promise<void>;
-    announce(message: string, politeness?: AriaLivePoliteness, duration?: number): Promise<void>;
+    announce(message: LiveAnnouncerMessage): Promise<void>;
+    announce(message: LiveAnnouncerMessage, politeness?: AriaLivePoliteness): Promise<void>;
+    announce(message: LiveAnnouncerMessage, duration?: number): Promise<void>;
+    announce(message: LiveAnnouncerMessage, politeness?: AriaLivePoliteness, duration?: number): Promise<void>;
     clear(): void;
     // (undocumented)
     ngOnDestroy(): void;
@@ -423,6 +424,9 @@ export interface LiveAnnouncerDefaultOptions {
     politeness?: AriaLivePoliteness;
 }
 
+// @public
+export type LiveAnnouncerMessage = string | SafeHtml;
+
 // @public @deprecated
 export const MESSAGES_CONTAINER_ID = "cdk-describedby-message-container";
 

src/cdk/a11y/BUILD.bazel

@@ -18,6 +18,7 @@ ng_project(
     deps = [
         "//:node_modules/@angular/common",
         "//:node_modules/@angular/core",
+        "//:node_modules/@angular/platform-browser",
         "//:node_modules/rxjs",
         "//src:dev_mode_types",
         "//src/cdk/coercion",

src/cdk/a11y/live-announcer/live-announcer.spec.ts

@@ -2,9 +2,9 @@ import {MutationObserverFactory} from '../../observers';
 import {ComponentPortal} from '../../portal';
 import {Component, inject, Injector} from '@angular/core';
 import {ComponentFixture, TestBed, fakeAsync, flush, tick} from '@angular/core/testing';
-import {By} from '@angular/platform-browser';
+import {By, DomSanitizer} from '@angular/platform-browser';
 import {A11yModule} from '../index';
-import {LiveAnnouncer} from './live-announcer';
+import {LiveAnnouncer, LiveAnnouncerMessage} from './live-announcer';
 import {
   AriaLivePoliteness,
   LIVE_ANNOUNCER_DEFAULT_OPTIONS,
@@ -202,6 +202,19 @@ describe('LiveAnnouncer', () => {
       tick(100);
       expect(modal.getAttribute('aria-owns')).toBe(`foo bar ${ariaLiveElement.id}`);
     }));
+
+    it('should be able to announce safe HTML', fakeAsync(() => {
+      const sanitizer = TestBed.inject(DomSanitizer);
+      const message = sanitizer.bypassSecurityTrustHtml(
+        '<span class="message" lang="fr">Bonjour</span>',
+      );
+      fixture.componentInstance.announce(message);
+
+      // This flushes our 100ms timeout for the screenreaders.
+      tick(100);
+
+      expect(ariaLiveElement.querySelector('.message')?.textContent).toBe('Bonjour');
+    }));
   });
 
   describe('with a custom element', () => {
@@ -378,13 +391,13 @@ function getLiveElement(): Element {
 }
 
 @Component({
-  template: `<button (click)="announceText('Test')">Announce</button>`,
+  template: `<button (click)="announce('Test')">Announce</button>`,
   imports: [A11yModule],
 })
 class TestApp {
   live = inject(LiveAnnouncer);
 
-  announceText(message: string) {
+  announce(message: LiveAnnouncerMessage) {
     this.live.announce(message);
   }
 }

src/cdk/a11y/live-announcer/live-announcer.ts

@@ -17,18 +17,23 @@ import {
   OnDestroy,
   inject,
   DOCUMENT,
+  SecurityContext,
 } from '@angular/core';
+import {DomSanitizer, SafeHtml} from '@angular/platform-browser';
 import {Subscription} from 'rxjs';
 import {
   AriaLivePoliteness,
   LiveAnnouncerDefaultOptions,
   LIVE_ANNOUNCER_ELEMENT_TOKEN,
   LIVE_ANNOUNCER_DEFAULT_OPTIONS,
 } from './live-announcer-tokens';
-import {_CdkPrivateStyleLoader, _VisuallyHiddenLoader} from '../../private';
+import {_CdkPrivateStyleLoader, _VisuallyHiddenLoader, trustedHTMLFromString} from '../../private';
 
 let uniqueIds = 0;
 
+/** Possible types for a message that can be announced by the `LiveAnnouncer`. */
+export type LiveAnnouncerMessage = string | SafeHtml;
+
 @Injectable({providedIn: 'root'})
 export class LiveAnnouncer implements OnDestroy {
   private _ngZone = inject(NgZone);
@@ -38,6 +43,7 @@ export class LiveAnnouncer implements OnDestroy {
 
   private _liveElement: HTMLElement;
   private _document = inject(DOCUMENT);
+  private _sanitizer = inject(DomSanitizer);
   private _previousTimeout: ReturnType<typeof setTimeout>;
   private _currentPromise: Promise<void> | undefined;
   private _currentResolve: (() => void) | undefined;
@@ -54,15 +60,15 @@ export class LiveAnnouncer implements OnDestroy {
    * @param message Message to be announced to the screen reader.
    * @returns Promise that will be resolved when the message is added to the DOM.
    */
-  announce(message: string): Promise<void>;
+  announce(message: LiveAnnouncerMessage): Promise<void>;
 
   /**
    * Announces a message to screen readers.
    * @param message Message to be announced to the screen reader.
    * @param politeness The politeness of the announcer element.
    * @returns Promise that will be resolved when the message is added to the DOM.
    */
-  announce(message: string, politeness?: AriaLivePoliteness): Promise<void>;
+  announce(message: LiveAnnouncerMessage, politeness?: AriaLivePoliteness): Promise<void>;
 
   /**
    * Announces a message to screen readers.
@@ -72,7 +78,7 @@ export class LiveAnnouncer implements OnDestroy {
    *   100ms after `announce` has been called.
    * @returns Promise that will be resolved when the message is added to the DOM.
    */
-  announce(message: string, duration?: number): Promise<void>;
+  announce(message: LiveAnnouncerMessage, duration?: number): Promise<void>;
 
   /**
    * Announces a message to screen readers.
@@ -83,9 +89,13 @@ export class LiveAnnouncer implements OnDestroy {
    *   100ms after `announce` has been called.
    * @returns Promise that will be resolved when the message is added to the DOM.
    */
-  announce(message: string, politeness?: AriaLivePoliteness, duration?: number): Promise<void>;
+  announce(
+    message: LiveAnnouncerMessage,
+    politeness?: AriaLivePoliteness,
+    duration?: number,
+  ): Promise<void>;
 
-  announce(message: string, ...args: any[]): Promise<void> {
+  announce(message: LiveAnnouncerMessage, ...args: any[]): Promise<void> {
     const defaultOptions = this._defaultOptions;
     let politeness: AriaLivePoliteness | undefined;
     let duration: number | undefined;
@@ -127,7 +137,22 @@ export class LiveAnnouncer implements OnDestroy {
 
       clearTimeout(this._previousTimeout);
       this._previousTimeout = setTimeout(() => {
-        this._liveElement.textContent = message;
+        if (!message || typeof message === 'string') {
+          this._liveElement.textContent = message;
+        } else {
+          const cleanMessage = this._sanitizer.sanitize(SecurityContext.HTML, message);
+
+          if (cleanMessage === null && (typeof ngDevMode === 'undefined' || ngDevMode)) {
+            throw new Error(
+              `The message provided to LiveAnnouncer was not trusted as safe HTML by ` +
+                `Angular's DomSanitizer. Attempted message was "${message}".`,
+            );
+          }
+
+          this._liveElement.innerHTML = trustedHTMLFromString(
+            cleanMessage || '',
+          ) as unknown as string;
+        }
 
         if (typeof duration === 'number') {
           this._previousTimeout = setTimeout(() => this.clear(), duration);