fix(material/chips): don't remove aria-selected from deselected options

src/material/chips/chip-listbox.spec.ts

@@ -513,19 +513,19 @@ describe('MDC-based MatChipListbox', () => {
           '.mdc-evolution-chip__action--primary',
         );
 
-        expect(getAriaSelected()).toEqual([null, null, null]);
+        expect(getAriaSelected()).toEqual(['false', 'false', 'false']);
 
         primaryActions[1].click();
         fixture.detectChanges();
-        expect(getAriaSelected()).toEqual([null, 'true', null]);
+        expect(getAriaSelected()).toEqual(['false', 'true', 'false']);
 
         primaryActions[2].click();
         fixture.detectChanges();
-        expect(getAriaSelected()).toEqual([null, null, 'true']);
+        expect(getAriaSelected()).toEqual(['false', 'false', 'true']);
 
         primaryActions[0].click();
         fixture.detectChanges();
-        expect(getAriaSelected()).toEqual(['true', null, null]);
+        expect(getAriaSelected()).toEqual(['true', 'false', 'false']);
       }));
 
       it('should set `aria-selected` based on the selection state in multi-selection mode', fakeAsync(() => {
@@ -548,23 +548,23 @@ describe('MDC-based MatChipListbox', () => {
           '.mdc-evolution-chip__action--primary',
         );
 
-        expect(getAriaSelected()).toEqual([null, null, null]);
+        expect(getAriaSelected()).toEqual(['false', 'false', 'false']);
 
         primaryActions[1].click();
         fixture.detectChanges();
-        expect(getAriaSelected()).toEqual([null, 'true', null]);
+        expect(getAriaSelected()).toEqual(['false', 'true', 'false']);
 
         primaryActions[2].click();
         fixture.detectChanges();
-        expect(getAriaSelected()).toEqual([null, 'true', 'true']);
+        expect(getAriaSelected()).toEqual(['false', 'true', 'true']);
 
         primaryActions[0].click();
         fixture.detectChanges();
         expect(getAriaSelected()).toEqual(['true', 'true', 'true']);
 
         primaryActions[1].click();
         fixture.detectChanges();
-        expect(getAriaSelected()).toEqual(['true', null, 'true']);
+        expect(getAriaSelected()).toEqual(['true', 'false', 'true']);
       }));
     });
 

src/material/chips/chip-option.spec.ts

@@ -233,7 +233,7 @@ describe('MDC-based Option Chips', () => {
         });
 
         it('should have correct aria-selected in single selection mode', () => {
-          expect(primaryAction.hasAttribute('aria-selected')).toBe(false);
+          expect(primaryAction.getAttribute('aria-selected')).toBe('false');
 
           testComponent.selected = true;
           fixture.detectChanges();

src/material/chips/chip-option.ts

@@ -106,13 +106,21 @@ export class MatChipOption extends MatChip implements OnInit {
   }
   private _selected = false;
 
-  /** The ARIA selected applied to the chip. */
+  /**
+   * The ARIA selected applied to the chip. Conforms to WAI ARIA best practices for listbox
+   * interaction patterns.
+   *
+   * From [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."
+   *
+   * Set `aria-selected="false"` on not-selected listbox options that are selectable to fix
+   * VoiceOver reading every option as "selected" (#25736).
+   */
   get ariaSelected(): string | null {
-    // Remove the `aria-selected` when the chip is deselected in single-selection mode, because
-    // it adds noise to NVDA users where "not selected" will be read out for each chip.
-    return this.selectable && (this._chipListMultiple || this.selected)
-      ? this.selected.toString()
-      : null;
+    return this.selectable ? this.selected.toString() : null;
   }
 
   /** The unstyled chip selector for this component. */