fix(a11y): focus monitor incorrectly detecting fake mousedown from screen reader

src/cdk/a11y/focus-monitor/focus-monitor.spec.ts

@@ -4,6 +4,8 @@ import {
   dispatchKeyboardEvent,
   dispatchMouseEvent,
   patchElementFocus,
+  createMouseEvent,
+  dispatchEvent,
 } from '@angular/cdk/testing/private';
 import {Component, NgZone} from '@angular/core';
 import {ComponentFixture, fakeAsync, flush, inject, TestBed, tick} from '@angular/core/testing';
@@ -112,6 +114,26 @@ describe('FocusMonitor', () => {
     expect(changeHandler).toHaveBeenCalledWith('program');
   }));
 
+  it('should detect fake mousedown from a screen reader', fakeAsync(() => {
+    // Simulate focus via a fake mousedown from a screen reader.
+    dispatchMouseEvent(buttonElement, 'mousedown');
+    const event = createMouseEvent('mousedown');
+    Object.defineProperty(event, 'buttons', {get: () => 0});
+    dispatchEvent(buttonElement, event);
+
+    buttonElement.focus();
+    fixture.detectChanges();
+    flush();
+
+    expect(buttonElement.classList.length)
+        .toBe(2, 'button should have exactly 2 focus classes');
+    expect(buttonElement.classList.contains('cdk-focused'))
+        .toBe(true, 'button should have cdk-focused class');
+    expect(buttonElement.classList.contains('cdk-keyboard-focused'))
+        .toBe(true, 'button should have cdk-keyboard-focused class');
+    expect(changeHandler).toHaveBeenCalledWith('keyboard');
+  }));
+
   it('focusVia keyboard should simulate keyboard focus', fakeAsync(() => {
     focusMonitor.focusVia(buttonElement, 'keyboard');
     flush();

src/cdk/a11y/focus-monitor/focus-monitor.ts

@@ -21,6 +21,7 @@ import {
 import {Observable, of as observableOf, Subject, Subscription} from 'rxjs';
 import {coerceElement} from '@angular/cdk/coercion';
 import {DOCUMENT} from '@angular/common';
+import {isFakeMousedownFromScreenReader} from '../fake-mousedown';
 
 
 // This is the value used by AngularJS Material. Through trial and error (on iPhone 6S) they found
@@ -99,11 +100,14 @@ export class FocusMonitor implements OnDestroy {
    * Event listener for `mousedown` events on the document.
    * Needs to be an arrow function in order to preserve the context when it gets bound.
    */
-  private _documentMousedownListener = () => {
+  private _documentMousedownListener = (event: MouseEvent) => {
     // On mousedown record the origin only if there is not touch
     // target, since a mousedown can happen as a result of a touch event.
     if (!this._lastTouchTarget) {
-      this._setOriginForCurrentEventQueue('mouse');
+      // In some cases screen readers fire fake `mousedown` events instead of `keydown`.
+      // Resolve the focus source to `keyboard` if we detect one of them.
+      const source = isFakeMousedownFromScreenReader(event) ? 'keyboard' : 'mouse';
+      this._setOriginForCurrentEventQueue(source);
     }
   }