fix(datepicker-toggle): forward tabindex to underlying button

Forwards the tabindex of a `mat-button-toggle` to its underlying `button` and clears it from the host element.

Fixes #12456.

Author: crisbeto

src/lib/datepicker/datepicker-toggle.html

@@ -3,6 +3,7 @@
   type="button"
   aria-haspopup="true"
   [attr.aria-label]="_intl.openCalendarLabel"
+  [attr.tabindex]="tabIndex"
   [disabled]="disabled"
   (click)="_open($event)">
 

src/lib/datepicker/datepicker-toggle.ts

@@ -9,6 +9,7 @@
 import {coerceBooleanProperty} from '@angular/cdk/coercion';
 import {
   AfterContentInit,
+  Attribute,
   ChangeDetectionStrategy,
   ChangeDetectorRef,
   Component,
@@ -39,6 +40,8 @@ export class MatDatepickerToggleIcon {}
   styleUrls: ['datepicker-toggle.css'],
   host: {
     'class': 'mat-datepicker-toggle',
+    // Clear out the native tabindex here since we forward it to the underlying button
+    '[attr.tabindex]': 'null',
     '[class.mat-datepicker-toggle-active]': 'datepicker && datepicker.opened',
     '[class.mat-accent]': 'datepicker && datepicker.color === "accent"',
     '[class.mat-warn]': 'datepicker && datepicker.color === "warn"',
@@ -53,6 +56,9 @@ export class MatDatepickerToggle<D> implements AfterContentInit, OnChanges, OnDe
   /** Datepicker instance that the button will toggle. */
   @Input('for') datepicker: MatDatepicker<D>;
 
+  /** Tabindex for the toggle. */
+  @Input() tabIndex: number | null;
+
   /** Whether the toggle button is disabled. */
   @Input()
   get disabled(): boolean {
@@ -66,7 +72,12 @@ export class MatDatepickerToggle<D> implements AfterContentInit, OnChanges, OnDe
   /** Custom icon set by the consumer. */
   @ContentChild(MatDatepickerToggleIcon) _customIcon: MatDatepickerToggleIcon;
 
-  constructor(public _intl: MatDatepickerIntl, private _changeDetectorRef: ChangeDetectorRef) {}
+  constructor(
+    public _intl: MatDatepickerIntl,
+    private _changeDetectorRef: ChangeDetectorRef,
+    @Attribute('tabindex') defaultTabIndex: string) {
+    this.tabIndex = Number(defaultTabIndex) || null;
+  }
 
   ngOnChanges(changes: SimpleChanges) {
     if (changes.datepicker) {

src/lib/datepicker/datepicker.spec.ts

@@ -935,6 +935,26 @@ describe('MatDatepicker', () => {
       }));
     });
 
+    describe('datepicker with tabindex on mat-datepicker-toggle', () => {
+      it('should forward the tabindex to the underlying button', () => {
+        const fixture = createComponent(DatepickerWithTabindexOnToggle, [MatNativeDateModule]);
+        fixture.detectChanges();
+
+        const button = fixture.nativeElement.querySelector('.mat-datepicker-toggle button');
+
+        expect(button.getAttribute('tabindex')).toBe('7');
+      });
+
+      it('should clear the tabindex from the mat-datepicker-toggle host', () => {
+        const fixture = createComponent(DatepickerWithTabindexOnToggle, [MatNativeDateModule]);
+        fixture.detectChanges();
+
+        const host = fixture.nativeElement.querySelector('.mat-datepicker-toggle');
+
+        expect(host.hasAttribute('tabindex')).toBe(false);
+      });
+    });
+
     describe('datepicker inside mat-form-field', () => {
       let fixture: ComponentFixture<FormFieldDatepicker>;
       let testComponent: FormFieldDatepicker;
@@ -1787,3 +1807,15 @@ class DatepickerWithCustomHeader {
   `,
 })
 class CustomHeaderForDatepicker {}
+
+
+@Component({
+  template: `
+    <input [matDatepicker]="d">
+    <mat-datepicker-toggle tabIndex="7" [for]="d">
+      <div class="custom-icon" matDatepickerToggleIcon></div>
+    </mat-datepicker-toggle>
+    <mat-datepicker #d></mat-datepicker>
+  `,
+})
+class DatepickerWithTabindexOnToggle {}