fix(material/datepicker): add label to dialog overlay (#22625)

Fixes that the datepicker overlay element doesn't have a label which causes screen readers to read out "dialog". These changes point the overlay's `aria-labelledby` either to the label of the form field or the `aria-labelledby` of the input.

src/material/datepicker/date-range-input.spec.ts

@@ -199,6 +199,23 @@ describe('MatDateRangeInput', () => {
     expect(end.nativeElement.getAttribute('aria-labelledby')).toBeFalsy();
   });
 
+  it('should set aria-labelledby of the overlay to the form field label', fakeAsync(() => {
+    const fixture = createComponent(StandardRangePicker);
+    fixture.detectChanges();
+
+    const label: HTMLElement = fixture.nativeElement.querySelector('.mat-form-field-label');
+    expect(label).toBeTruthy();
+    expect(label.getAttribute('id')).toBeTruthy();
+
+    fixture.componentInstance.rangePicker.open();
+    fixture.detectChanges();
+    tick();
+
+    const popup = document.querySelector('.cdk-overlay-pane')!;
+    expect(popup).toBeTruthy();
+    expect(popup.getAttribute('aria-labelledby')).toBe(label.getAttribute('id'));
+  }));
+
   it('should float the form field label when either input is focused', () => {
     const fixture = createComponent(StandardRangePicker);
     fixture.detectChanges();

src/material/datepicker/date-range-input.ts

@@ -324,6 +324,11 @@ export class MatDateRangeInput<D> implements MatFormFieldControl<DateRange<D>>,
     return this._formField ? this._formField.getConnectedOverlayOrigin() : this._elementRef;
   }
 
+  /** Gets the ID of an element that should be used a description for the calendar overlay. */
+  getOverlayLabelId(): string | null {
+    return this._formField ? this._formField.getLabelId() : null;
+  }
+
   /** Gets the value that is used to mirror the state input. */
   _getInputMirrorValue() {
     return this._startInput ? this._startInput.getMirrorValue() : '';

src/material/datepicker/datepicker-base.ts

@@ -243,6 +243,7 @@ export interface MatDatepickerControl<D> {
   disabled: boolean;
   dateFilter: DateFilterFn<D>;
   getConnectedOverlayOrigin(): ElementRef;
+  getOverlayLabelId(): string | null;
   stateChanges: Observable<void>;
 }
 
@@ -615,6 +616,7 @@ export abstract class MatDatepickerBase<C extends MatDatepickerControl<D>, S,
     this._destroyOverlay();
 
     const isDialog = this.touchUi;
+    const labelId = this.datepickerInput.getOverlayLabelId();
     const portal = new ComponentPortal<MatDatepickerContent<S, D>>(MatDatepickerContent,
       this._viewContainerRef);
     const overlayRef = this._overlayRef = this._overlay.create(new OverlayConfig({
@@ -628,10 +630,15 @@ export abstract class MatDatepickerBase<C extends MatDatepickerControl<D>, S,
       scrollStrategy: isDialog ? this._overlay.scrollStrategies.block() : this._scrollStrategy(),
       panelClass: `mat-datepicker-${isDialog ? 'dialog' : 'popup'}`,
     }));
-    overlayRef.overlayElement.setAttribute('role', 'dialog');
+    const overlayElement = overlayRef.overlayElement;
+    overlayElement.setAttribute('role', 'dialog');
+
+    if (labelId) {
+      overlayElement.setAttribute('aria-labelledby', labelId);
+    }
 
     if (isDialog) {
-      overlayRef.overlayElement.setAttribute('aria-modal', 'true');
+      overlayElement.setAttribute('aria-modal', 'true');
     }
 
     this._getCloseStream(overlayRef).subscribe(event => {

src/material/datepicker/datepicker-input.ts

@@ -134,7 +134,7 @@ export class MatDatepickerInput<D> extends MatDatepickerInputBase<D | null, D>
       elementRef: ElementRef<HTMLInputElement>,
       @Optional() dateAdapter: DateAdapter<D>,
       @Optional() @Inject(MAT_DATE_FORMATS) dateFormats: MatDateFormats,
-      @Optional() @Inject(MAT_FORM_FIELD) private _formField: MatFormField) {
+      @Optional() @Inject(MAT_FORM_FIELD) private _formField?: MatFormField) {
     super(elementRef, dateAdapter, dateFormats);
     this._validator = Validators.compose(super._getValidators());
   }
@@ -147,6 +147,15 @@ export class MatDatepickerInput<D> extends MatDatepickerInputBase<D | null, D>
     return this._formField ? this._formField.getConnectedOverlayOrigin() : this._elementRef;
   }
 
+  /** Gets the ID of an element that should be used a description for the calendar overlay. */
+  getOverlayLabelId(): string | null {
+    if (this._formField) {
+      return this._formField.getLabelId();
+    }
+
+    return this._elementRef.nativeElement.getAttribute('aria-labelledby');
+  }
+
   /** Returns the palette used by the input's form field, if any. */
   getThemePalette(): ThemePalette {
     return this._formField ? this._formField.color : undefined;

src/material/datepicker/datepicker.spec.ts

@@ -249,6 +249,22 @@ describe('MatDatepicker', () => {
         expect(popup.getAttribute('role')).toBe('dialog');
       }));
 
+      it('should set aria-labelledby to the one from the input, if not placed inside ' +
+        'a mat-form-field', fakeAsync(() => {
+          expect(fixture.nativeElement.querySelector('mat-form-field')).toBeFalsy();
+
+          const input: HTMLInputElement = fixture.nativeElement.querySelector('input');
+          input.setAttribute('aria-labelledby', 'test-label');
+
+          testComponent.datepicker.open();
+          fixture.detectChanges();
+          flush();
+
+          const popup = document.querySelector('.cdk-overlay-pane')!;
+          expect(popup).toBeTruthy();
+          expect(popup.getAttribute('aria-labelledby')).toBe('test-label');
+        }));
+
       it('close should close dialog', fakeAsync(() => {
         testComponent.touch = true;
         fixture.detectChanges();
@@ -1357,6 +1373,21 @@ describe('MatDatepicker', () => {
         expect(contentEl.classList).toContain('mat-accent');
         expect(contentEl.classList).not.toContain('mat-warn');
       }));
+
+      it('should set aria-labelledby of the overlay to the form field label', fakeAsync(() => {
+        const label: HTMLElement = fixture.nativeElement.querySelector('.mat-form-field-label');
+
+        expect(label).toBeTruthy();
+        expect(label.getAttribute('id')).toBeTruthy();
+
+        testComponent.datepicker.open();
+        fixture.detectChanges();
+        flush();
+
+        const popup = document.querySelector('.cdk-overlay-pane')!;
+        expect(popup).toBeTruthy();
+        expect(popup.getAttribute('aria-labelledby')).toBe(label.getAttribute('id'));
+      }));
     });
 
     describe('datepicker with min and max dates and validation', () => {
@@ -2385,6 +2416,7 @@ class DatepickerWithCustomIcon {}
 @Component({
   template: `
       <mat-form-field>
+        <mat-label>Pick a date</mat-label>
         <input matInput [matDatepicker]="d">
         <mat-datepicker #d></mat-datepicker>
       </mat-form-field>

tools/public_api_guard/material/datepicker.d.ts

@@ -246,7 +246,7 @@ export declare class MatDatepickerInput<D> extends MatDatepickerInputBase<D | nu
     set max(value: D | null);
     get min(): D | null;
     set min(value: D | null);
-    constructor(elementRef: ElementRef<HTMLInputElement>, dateAdapter: DateAdapter<D>, dateFormats: MatDateFormats, _formField: MatFormField);
+    constructor(elementRef: ElementRef<HTMLInputElement>, dateAdapter: DateAdapter<D>, dateFormats: MatDateFormats, _formField?: MatFormField | undefined);
     protected _assignValueToModel(value: D | null): void;
     protected _getDateFilter(): DateFilterFn<D | null>;
     _getMaxDate(): D | null;
@@ -255,6 +255,7 @@ export declare class MatDatepickerInput<D> extends MatDatepickerInputBase<D | nu
     protected _openPopup(): void;
     protected _shouldHandleChangeEvent(event: DateSelectionModelChange<D>): boolean;
     getConnectedOverlayOrigin(): ElementRef;
+    getOverlayLabelId(): string | null;
     getStartValue(): D | null;
     getThemePalette(): ThemePalette;
     ngOnDestroy(): void;
@@ -360,6 +361,7 @@ export declare class MatDateRangeInput<D> implements MatFormFieldControl<DateRan
     _shouldHideSeparator(): boolean | "" | null;
     _updateFocus(origin: FocusOrigin): void;
     getConnectedOverlayOrigin(): ElementRef;
+    getOverlayLabelId(): string | null;
     getStartValue(): D | null;
     getThemePalette(): ThemePalette;
     ngAfterContentInit(): void;