fix(radio): add support for tabindex on radio-buttons (#9467)

Fixes #9427

src/lib/radio/radio.html

@@ -18,6 +18,7 @@
          [id]="inputId"
          [checked]="checked"
          [disabled]="disabled"
+         [tabIndex]="tabIndex"
          [attr.name]="name"
          [required]="required"
          [attr.aria-label]="ariaLabel"

src/lib/radio/radio.spec.ts

@@ -657,12 +657,26 @@ describe('MatRadio', () => {
       let inputEl = fixture.debugElement.query(By.css('.mat-radio-input')).nativeElement;
 
       radioButtonEl.focus();
-      // Focus events don't always fire in tests, so we needc to fake it.
+      // Focus events don't always fire in tests, so we need to fake it.
       dispatchFakeEvent(radioButtonEl, 'focus');
       fixture.detectChanges();
 
       expect(document.activeElement).toBe(inputEl);
     });
+
+    it('should allow specifying an explicit tabindex for a single radio-button', () => {
+      const radioButtonInput = fixture.debugElement
+        .query(By.css('.mat-radio-button input')).nativeElement as HTMLInputElement;
+
+      expect(radioButtonInput.tabIndex)
+        .toBe(0, 'Expected the tabindex to be set to "0" by default.');
+
+      fixture.componentInstance.tabIndex = 4;
+      fixture.detectChanges();
+
+      expect(radioButtonInput.tabIndex)
+        .toBe(4, 'Expected the tabindex to be set to "4".');
+    });
   });
 
   describe('group interspersed with other tags', () => {
@@ -777,9 +791,11 @@ class RadioGroupWithFormControl {
 }
 
 @Component({
-  template: `<mat-radio-button tabindex="-1"></mat-radio-button>`
+  template: `<mat-radio-button [tabIndex]="tabIndex"></mat-radio-button>`
 })
-class FocusableRadioButton {}
+class FocusableRadioButton {
+  tabIndex: number;
+}
 
 @Component({
   template: `

src/lib/radio/radio.ts

@@ -34,10 +34,12 @@ import {
   CanColor,
   CanDisable,
   CanDisableRipple,
+  HasTabIndex,
   MatRipple,
   mixinColor,
   mixinDisabled,
   mixinDisableRipple,
+  mixinTabIndex,
   RippleConfig,
   RippleRef,
 } from '@angular/material/core';
@@ -313,12 +315,17 @@ export class MatRadioGroup extends _MatRadioGroupMixinBase
 // Boilerplate for applying mixins to MatRadioButton.
 /** @docs-private */
 export class MatRadioButtonBase {
+  // Since the disabled property is manually defined for the MatRadioButton and isn't set up in
+  // the mixin base class. To be able to use the tabindex mixin, a disabled property must be
+  // defined to properly work.
+  disabled: boolean;
+
   constructor(public _elementRef: ElementRef) {}
 }
 // As per Material design specifications the selection control radio should use the accent color
 // palette by default. https://material.io/guidelines/components/selection-controls.html
 export const _MatRadioButtonMixinBase =
-    mixinColor(mixinDisableRipple(MatRadioButtonBase), 'accent');
+    mixinColor(mixinDisableRipple(mixinTabIndex(MatRadioButtonBase)), 'accent');
 
 /**
  * A Material design radio-button. Typically placed inside of `<mat-radio-group>` elements.
@@ -328,7 +335,7 @@ export const _MatRadioButtonMixinBase =
   selector: 'mat-radio-button',
   templateUrl: 'radio.html',
   styleUrls: ['radio.css'],
-  inputs: ['color', 'disableRipple'],
+  inputs: ['color', 'disableRipple', 'tabIndex'],
   encapsulation: ViewEncapsulation.None,
   preserveWhitespaces: false,
   exportAs: 'matRadioButton',
@@ -345,7 +352,7 @@ export const _MatRadioButtonMixinBase =
   changeDetection: ChangeDetectionStrategy.OnPush,
 })
 export class MatRadioButton extends _MatRadioButtonMixinBase
-    implements OnInit, AfterViewInit, OnDestroy, CanColor, CanDisableRipple {
+    implements OnInit, AfterViewInit, OnDestroy, CanColor, CanDisableRipple, HasTabIndex {
 
   private _uniqueId: string = `mat-radio-${++nextUniqueId}`;