fix(material/chips): show required asterisk when using required validator

Similar to angular#23362. Fixes that the required asterisk wasn't being shown when a chip list is required.

Author: crisbeto

src/material-experimental/mdc-chips/chip-grid.spec.ts

@@ -732,7 +732,7 @@ describe('MDC-based MatChipGrid', () => {
         .withContext(`Expected placeholder not to have an asterisk, as control was not required.`)
         .toBeNull();
 
-      fixture.componentInstance.isRequired = true;
+      fixture.componentInstance.chipGrid.required = true;
       fixture.detectChanges();
 
       requiredMarker = fixture.debugElement.query(By.css('.mdc-floating-label--required'))!;
@@ -741,6 +741,15 @@ describe('MDC-based MatChipGrid', () => {
         .toBeNull();
     });
 
+    it('should mark the component as required if the control has a required validator', () => {
+      fixture.destroy();
+      fixture = TestBed.createComponent(InputChipGrid);
+      fixture.componentInstance.control = new FormControl(undefined, [Validators.required]);
+      fixture.detectChanges();
+
+      expect(fixture.nativeElement.querySelector('.mdc-floating-label--required')).toBeTruthy();
+    });
+
     it('should blur the form field when the active chip is blurred', fakeAsync(() => {
       const formField: HTMLElement = fixture.nativeElement.querySelector('.mat-mdc-form-field');
 
@@ -1077,8 +1086,7 @@ class FormFieldChipGrid {
   template: `
     <mat-form-field>
       <mat-label>New food...</mat-label>
-      <mat-chip-grid #chipGrid
-                    placeholder="Food" [formControl]="control" [required]="isRequired">
+      <mat-chip-grid #chipGrid placeholder="Food" [formControl]="control">
         <mat-chip-row *ngFor="let food of foods" [value]="food.value" (removed)="remove(food)">
           {{ food.viewValue }}
         </mat-chip-row>
@@ -1106,7 +1114,6 @@ class InputChipGrid {
 
   separatorKeyCodes = [ENTER, SPACE];
   addOnBlur: boolean = true;
-  isRequired: boolean;
 
   add(event: MatChipInputEvent): void {
     const value = (event.value || '').trim();

src/material-experimental/mdc-chips/chip-grid.ts

@@ -27,7 +27,13 @@ import {
   Self,
   ViewEncapsulation
 } from '@angular/core';
-import {ControlValueAccessor, FormGroupDirective, NgControl, NgForm} from '@angular/forms';
+import {
+  ControlValueAccessor,
+  FormGroupDirective,
+  NgControl,
+  NgForm,
+  Validators,
+} from '@angular/forms';
 import {
   CanUpdateErrorState,
   CanUpdateErrorStateCtor,
@@ -186,12 +192,14 @@ export class MatChipGrid extends _MatChipGridMixinBase implements AfterContentIn
    * @docs-private
    */
   @Input()
-  get required(): boolean { return this._required; }
+  get required(): boolean {
+    return this._required ?? this.ngControl?.control?.hasValidator(Validators.required) ?? false;
+  }
   set required(value: boolean) {
     this._required = coerceBooleanProperty(value);
     this.stateChanges.next();
   }
-  protected _required: boolean = false;
+  protected _required: boolean | undefined;
 
   /**
    * Implemented as part of MatFormFieldControl.

src/material/chips/chip-list.spec.ts

@@ -857,7 +857,7 @@ describe('MatChipList', () => {
           .withContext(`Expected placeholder not to have an asterisk, as control was not required.`)
           .toBeNull();
 
-        fixture.componentInstance.isRequired = true;
+        fixture.componentInstance.chipList.required = true;
         fixture.detectChanges();
 
         requiredMarker = fixture.debugElement.query(By.css('.mat-form-field-required-marker'))!;
@@ -866,6 +866,13 @@ describe('MatChipList', () => {
           .not.toBeNull();
       });
 
+      it('should mark the component as required if the control has a required validator', () => {
+        fixture.componentInstance.control = new FormControl(undefined, [Validators.required]);
+        fixture.detectChanges();
+
+        expect(fixture.nativeElement.querySelector('.mat-form-field-required-marker')).toBeTruthy();
+      });
+
       it('should be able to programmatically select a falsy option', () => {
         fixture.destroy();
         TestBed.resetTestingModule();
@@ -1487,7 +1494,7 @@ class FormFieldChipList {
   selector: 'basic-chip-list',
   template: `
     <mat-form-field>
-      <mat-chip-list placeholder="Food" [formControl]="control" [required]="isRequired"
+      <mat-chip-list placeholder="Food" [formControl]="control"
         [tabIndex]="tabIndexOverride" [selectable]="selectable">
         <mat-chip *ngFor="let food of foods" [value]="food.value" [disabled]="food.disabled">
           {{ food.viewValue }}
@@ -1508,7 +1515,6 @@ class BasicChipList {
     {value: 'sushi-7', viewValue: 'Sushi'},
   ];
   control = new FormControl();
-  isRequired: boolean;
   tabIndexOverride: number;
   selectable: boolean;
 

src/material/chips/chip-list.ts

@@ -28,7 +28,13 @@ import {
   Self,
   ViewEncapsulation,
 } from '@angular/core';
-import {ControlValueAccessor, FormGroupDirective, NgControl, NgForm} from '@angular/forms';
+import {
+  ControlValueAccessor,
+  FormGroupDirective,
+  NgControl,
+  NgForm,
+  Validators,
+} from '@angular/forms';
 import {
   CanUpdateErrorState,
   ErrorStateMatcher,
@@ -213,12 +219,14 @@ export class MatChipList extends _MatChipListBase implements MatFormFieldControl
    * @docs-private
    */
   @Input()
-  get required(): boolean { return this._required; }
+  get required(): boolean {
+    return this._required ?? this.ngControl?.control?.hasValidator(Validators.required) ?? false;
+  }
   set required(value: boolean) {
     this._required = coerceBooleanProperty(value);
     this.stateChanges.next();
   }
-  protected _required: boolean = false;
+  protected _required: boolean | undefined;
 
   /**
    * Implemented as part of MatFormFieldControl.

tools/public_api_guard/material/chips.md

@@ -259,7 +259,7 @@ export class MatChipList extends _MatChipListBase implements MatFormFieldControl
     get required(): boolean;
     set required(value: boolean);
     // (undocumented)
-    protected _required: boolean;
+    protected _required: boolean | undefined;
     get role(): string | null;
     get selectable(): boolean;
     set selectable(value: boolean);