fix(material/core): mat-option sets aria-selected="false"

For mat-option, set `aria-selected="false"` on deselected options.
Confirms with [WAI ARIA Listbox authoring practices
guide](https://www.w3.org/WAI/ARIA/apg/patterns/listbox/), which says to
always include aria-selected attribute on listbox options that can be
selected. Fix issue where VoiceOver reads every option as "selected"
(21491).

Fix #21491

Author: zarend

src/material/core/option/option.ts

@@ -204,16 +204,6 @@ export class _MatOptionBase<T = any> implements FocusableOption, AfterViewChecke
     }
   }
 
-  /**
-   * Gets the `aria-selected` value for the option. We explicitly omit the `aria-selected`
-   * attribute from single-selection, unselected options. Including the `aria-selected="false"`
-   * attributes adds a significant amount of noise to screen-reader users without providing useful
-   * information.
-   */
-  _getAriaSelected(): boolean | null {
-    return this.selected || (this.multiple ? false : null);
-  }
-
   /** Returns the correct tabindex for the option depending on disabled state. */
   _getTabIndex(): string {
     return this.disabled ? '-1' : '0';
@@ -267,7 +257,16 @@ export class _MatOptionBase<T = any> implements FocusableOption, AfterViewChecke
     '[class.mat-mdc-option-active]': 'active',
     '[class.mdc-list-item--disabled]': 'disabled',
     '[id]': 'id',
-    '[attr.aria-selected]': '_getAriaSelected()',
+    // Set aria-selected to false for non-selected items and true for selected items. Conform to
+    // [WAI ARIA Listbox authoring practices guide](
+    //  https://www.w3.org/WAI/ARIA/apg/patterns/listbox/), "If any options are selected, each
+    // selected option has either aria-selected or aria-checked  set to true. All options that are
+    // selectable but not selected have either aria-selected or aria-checked set to false." Align
+    // aria-selected implementation of Chips and List components.
+    //
+    // Set `aria-selected="false"` on not-selected listbox options to fix VoiceOver announcing
+    // every option as "selected" (#21491).
+    '[attr.aria-selected]': 'selected',
     '[attr.aria-disabled]': 'disabled.toString()',
     '(click)': '_selectViaInteraction()',
     '(keydown)': '_handleKeydown($event)',

src/material/select/select.spec.ts

@@ -1184,9 +1184,10 @@ describe('MDC-based MatSelect', () => {
         }));
 
         it('should set aria-selected on each option for single select', fakeAsync(() => {
-          expect(options.every(option => !option.hasAttribute('aria-selected')))
+          expect(options.every(option => option.getAttribute('aria-selected') === 'false'))
             .withContext(
-              'Expected all unselected single-select options not to have ' + 'aria-selected set.',
+              'Expected all unselected single-select options not to have ' +
+                'aria-selected="false".',
             )
             .toBe(true);
 
@@ -1203,9 +1204,10 @@ describe('MDC-based MatSelect', () => {
             )
             .toEqual('true');
           options.splice(1, 1);
-          expect(options.every(option => !option.hasAttribute('aria-selected')))
+          expect(options.every(option => option.getAttribute('aria-selected') === 'false'))
             .withContext(
-              'Expected all unselected single-select options not to have ' + 'aria-selected set.',
+              'Expected all unselected single-select options not to have ' +
+                'aria-selected="false".',
             )
             .toBe(true);
         }));