feat(material/chip): Add focus indicator (#18019)

* Add focus indicators to mat-chip. Use a dynamically added element as the ripple target

* _document should be an optional param to avoid breaking change.

* Updated chips API golden.

Author: zelliott

src/material/chips/chip.ts

@@ -6,6 +6,7 @@
  * found in the LICENSE file at https://angular.io/license
  */
 
+import {DOCUMENT} from '@angular/common';
 import {FocusableOption} from '@angular/cdk/a11y';
 import {coerceBooleanProperty} from '@angular/cdk/coercion';
 import {BACKSPACE, DELETE, SPACE} from '@angular/cdk/keycodes';
@@ -100,7 +101,7 @@ export class MatChipTrailingIcon {}
   inputs: ['color', 'disabled', 'disableRipple'],
   exportAs: 'matChip',
   host: {
-    'class': 'mat-chip',
+    'class': 'mat-chip mat-focus-indicator',
     '[attr.tabindex]': 'disabled ? null : -1',
     'role': 'option',
     '[class.mat-chip-selected]': 'selected',
@@ -123,6 +124,13 @@ export class MatChip extends _MatChipMixinBase implements FocusableOption, OnDes
   /** Reference to the RippleRenderer for the chip. */
   private _chipRipple: RippleRenderer;
 
+  /**
+   * Reference to the element that acts as the chip's ripple target. This element is
+   * dynamically added as a child node of the chip. The chip itself cannot be used as the
+   * ripple target because it must be the host of the focus indicator.
+   */
+  private _chipRippleTarget: HTMLElement;
+
   /**
    * Ripple configuration for ripples that are launched on pointer down. The ripple config
    * is set to the global ripple options since we don't have any configurable options for
@@ -238,13 +246,22 @@ export class MatChip extends _MatChipMixinBase implements FocusableOption, OnDes
               // @breaking-change 8.0.0 `animationMode` parameter to become required.
               @Optional() @Inject(ANIMATION_MODULE_TYPE) animationMode?: string,
               // @breaking-change 9.0.0 `_changeDetectorRef` parameter to become required.
-              private _changeDetectorRef?: ChangeDetectorRef) {
+              private _changeDetectorRef?: ChangeDetectorRef,
+              // @breaking-change 11.0.0 `_document` parameter to become required.
+              @Optional() @Inject(DOCUMENT) _document?: any) {
     super(_elementRef);
 
     this._addHostClassName();
 
-    this._chipRipple = new RippleRenderer(this, _ngZone, _elementRef, platform);
+    // Dynamically create the ripple target, append it within the chip, and use it as the
+    // chip's ripple target. Adding the class '.mat-chip-ripple' ensures that it will have
+    // the proper styles.
+    this._chipRippleTarget = (_document || document).createElement('div');
+    this._chipRippleTarget.classList.add('mat-chip-ripple');
+    this._elementRef.nativeElement.appendChild(this._chipRippleTarget);
+    this._chipRipple = new RippleRenderer(this, _ngZone, this._chipRippleTarget, platform);
     this._chipRipple.setupTriggerEvents(_elementRef);
+
     this.rippleConfig = globalRippleOptions || {};
     this._animationsDisabled = animationMode === 'NoopAnimations';
   }

src/material/chips/chips.scss

@@ -27,7 +27,6 @@ $mat-chip-remove-size: 18px;
 
 .mat-chip {
   position: relative;
-  overflow: hidden;
   box-sizing: border-box;
   -webkit-tap-highlight-color: transparent;
 
@@ -171,6 +170,23 @@ $mat-chip-remove-size: 18px;
   }
 }
 
+// Styles for the chip's dynamically added ripple target.
+.mat-chip-ripple {
+  @include mat-fill;
+
+  // Disable pointer events for the ripple container and focus overlay because the container
+  // will overlay the user content and we don't want to disable mouse events on the user content.
+  // Pointer events can be safely disabled because the ripple trigger element is the host element.
+  pointer-events: none;
+
+  // Inherit the border radius from the parent so that ripples don't exceed the parent button
+  // boundaries.
+  border-radius: inherit;
+
+  // Ensures that the ripple effect doesn't overflow the ripple target.
+  overflow: hidden;
+}
+
 .mat-chip-list-wrapper {
   display: flex;
   flex-direction: row;

src/material/core/focus-indicator/_focus-indicator.scss

@@ -31,6 +31,7 @@
   .mat-focus-indicator.mat-button-base::before,
   .mat-focus-indicator.mat-button-base::before,
   .mat-focus-indicator.mat-card::before,
+  .mat-focus-indicator.mat-chip::before,
   .mat-focus-indicator.mat-sort-header-button::before {
     margin: $border-width * -2;
   }

tools/public_api_guard/material/chips.d.ts

@@ -25,7 +25,7 @@ export declare class MatChip extends _MatChipMixinBase implements FocusableOptio
     readonly selectionChange: EventEmitter<MatChipSelectionChange>;
     trailingIcon: MatChipTrailingIcon;
     value: any;
-    constructor(_elementRef: ElementRef<HTMLElement>, _ngZone: NgZone, platform: Platform, globalRippleOptions: RippleGlobalOptions | null, animationMode?: string, _changeDetectorRef?: ChangeDetectorRef | undefined);
+    constructor(_elementRef: ElementRef<HTMLElement>, _ngZone: NgZone, platform: Platform, globalRippleOptions: RippleGlobalOptions | null, animationMode?: string, _changeDetectorRef?: ChangeDetectorRef | undefined, _document?: any);
     _addHostClassName(): void;
     _blur(): void;
     _handleClick(event: Event): void;