fix(progress-spinner): clear aria-valuenow in indeterminate mode (#15052)

Clears the `aria-valuenow` attribute when the progress spinner is in indeterminate mode, [based on the a11y spec](https://www.w3.org/TR/wai-aria-1.1/#progressbar).

Fixes #15018.

Author: crisbeto

src/lib/progress-spinner/progress-spinner.spec.ts

@@ -296,6 +296,31 @@ describe('MatProgressSpinner', () => {
     expect(progressElement.componentInstance.strokeWidth).toBe(7);
   });
 
+  it('should set `aria-valuenow` to the current value in determinate mode', () => {
+    const fixture = TestBed.createComponent(ProgressSpinnerWithValueAndBoundMode);
+    const progressElement = fixture.debugElement.query(By.css('mat-progress-spinner'));
+    fixture.componentInstance.mode = 'determinate';
+    fixture.componentInstance.value = 37;
+    fixture.detectChanges();
+
+    expect(progressElement.nativeElement.getAttribute('aria-valuenow')).toBe('37');
+  });
+
+  it('should clear `aria-valuenow` in indeterminate mode', () => {
+    const fixture = TestBed.createComponent(ProgressSpinnerWithValueAndBoundMode);
+    const progressElement = fixture.debugElement.query(By.css('mat-progress-spinner'));
+    fixture.componentInstance.mode = 'determinate';
+    fixture.componentInstance.value = 89;
+    fixture.detectChanges();
+
+    expect(progressElement.nativeElement.hasAttribute('aria-valuenow')).toBe(true);
+
+    fixture.componentInstance.mode = 'indeterminate';
+    fixture.detectChanges();
+
+    expect(progressElement.nativeElement.hasAttribute('aria-valuenow')).toBe(false);
+  });
+
 });
 
 

src/lib/progress-spinner/progress-spinner.ts

@@ -114,7 +114,7 @@ const INDETERMINATE_ANIMATION_TEMPLATE = `
     '[style.height.px]': 'diameter',
     '[attr.aria-valuemin]': 'mode === "determinate" ? 0 : null',
     '[attr.aria-valuemax]': 'mode === "determinate" ? 100 : null',
-    '[attr.aria-valuenow]': 'value',
+    '[attr.aria-valuenow]': 'mode === "determinate" ? value : null',
     '[attr.mode]': 'mode',
   },
   inputs: ['color'],