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

Resolves the long-standing issue where the required asterisk wasn't being shown in the form field label when using the `required` validator from Forms.

Fixes #2574.

Author: crisbeto

src/material-experimental/mdc-input/input.spec.ts

@@ -327,6 +327,16 @@ describe('MatMdcInput without forms', () => {
     expect(label.nativeElement.classList).toContain('mdc-floating-label--required');
   }));
 
+  it('should show the required star when using a FormControl', fakeAsync(() => {
+    const fixture = createComponent(MatInputWithRequiredFormControl);
+    fixture.detectChanges();
+
+    const label = fixture.debugElement.query(By.css('label'))!;
+    expect(label).not.toBeNull();
+    expect(label.nativeElement.textContent).toBe('Hello');
+    expect(label.nativeElement.classList).toContain('mdc-floating-label--required');
+  }));
+
   it('should not hide the required star if input is disabled', () => {
     const fixture = createComponent(MatInputLabelRequiredTestComponent);
 
@@ -1058,7 +1068,7 @@ describe('MatMdcInput with forms', () => {
 
       expect(testComponent.formControl.invalid)
         .withContext('Expected form control to be invalid').toBe(true);
-      expect(inputEl.value).toBeFalsy();
+      expect(inputEl.value).toBe('incorrect');
       expect(inputEl.getAttribute('aria-invalid'))
         .withContext('Expected aria-invalid to be set to "true"').toBe('true');
 
@@ -1548,7 +1558,10 @@ class MatInputMissingMatInputTestController {}
 })
 class MatInputWithFormErrorMessages {
   @ViewChild('form') form: NgForm;
-  formControl = new FormControl('', [Validators.required, Validators.pattern(/valid value/)]);
+  formControl = new FormControl('incorrect', [
+    Validators.required,
+    Validators.pattern(/valid value/)
+  ]);
   renderError = true;
 }
 
@@ -1591,7 +1604,7 @@ class MatInputWithCustomErrorStateMatcher {
 class MatInputWithFormGroupErrorMessages {
   @ViewChild(FormGroupDirective) formGroupDirective: FormGroupDirective;
   formGroup = new FormGroup({
-    name: new FormControl('', [Validators.required, Validators.pattern(/valid value/)])
+    name: new FormControl('incorrect', [Validators.required, Validators.pattern(/valid value/)])
   });
 }
 
@@ -1790,3 +1803,15 @@ class MatInputWithColor {
   `
 })
 class MatInputInsideOutsideFormField {}
+
+
+@Component({
+  template: `
+    <mat-form-field>
+      <mat-label>Hello</mat-label>
+      <input matInput [formControl]="formControl">
+    </mat-form-field>`
+})
+class MatInputWithRequiredFormControl {
+  formControl = new FormControl('', [Validators.required]);
+}

src/material/input/input.spec.ts

@@ -410,6 +410,15 @@ describe('MatInput without forms', () => {
     expect(labelEl.nativeElement.textContent).toBe('hello *');
   }));
 
+  it('should show the required star when using a FormControl', fakeAsync(() => {
+    const fixture = createComponent(MatInputWithRequiredFormControl);
+    fixture.detectChanges();
+
+    const labelEl = fixture.debugElement.query(By.css('label'))!;
+    expect(labelEl).not.toBeNull();
+    expect(labelEl.nativeElement.textContent).toBe('Hello *');
+  }));
+
   it('should hide the required star if input is disabled', () => {
     const fixture = createComponent(MatInputPlaceholderRequiredTestComponent);
 
@@ -1203,7 +1212,7 @@ describe('MatInput with forms', () => {
 
       expect(testComponent.formControl.invalid)
         .withContext('Expected form control to be invalid').toBe(true);
-      expect(inputEl.value).toBeFalsy();
+      expect(inputEl.value).toBe('incorrect');
       expect(inputEl.getAttribute('aria-invalid'))
         .withContext('Expected aria-invalid to be set to "true".').toBe('true');
 
@@ -2018,7 +2027,10 @@ class MatInputMissingMatInputTestController {}
 })
 class MatInputWithFormErrorMessages {
   @ViewChild('form') form: NgForm;
-  formControl = new FormControl('', [Validators.required, Validators.pattern(/valid value/)]);
+  formControl = new FormControl('incorrect', [
+    Validators.required,
+    Validators.pattern(/valid value/)
+  ]);
   renderError = true;
 }
 
@@ -2061,7 +2073,7 @@ class MatInputWithCustomErrorStateMatcher {
 class MatInputWithFormGroupErrorMessages {
   @ViewChild(FormGroupDirective) formGroupDirective: FormGroupDirective;
   formGroup = new FormGroup({
-    name: new FormControl('', [Validators.required, Validators.pattern(/valid value/)])
+    name: new FormControl('incorrect', [Validators.required, Validators.pattern(/valid value/)])
   });
 }
 
@@ -2360,3 +2372,14 @@ class MatInputWithAnotherNgIf {
 class MatInputWithColor {
   color: ThemePalette;
 }
+
+
+@Component({
+  template: `
+    <mat-form-field>
+      <input matInput placeholder="Hello" [formControl]="formControl">
+    </mat-form-field>`
+})
+class MatInputWithRequiredFormControl {
+  formControl = new FormControl('', [Validators.required]);
+}

src/material/input/input.ts

@@ -23,7 +23,7 @@ import {
   Optional,
   Self,
 } from '@angular/core';
-import {FormGroupDirective, NgControl, NgForm} from '@angular/forms';
+import {FormGroupDirective, NgControl, NgForm, Validators} from '@angular/forms';
 import {
   CanUpdateErrorState,
   ErrorStateMatcher,
@@ -174,9 +174,11 @@ export class MatInput extends _MatInputBase implements MatFormFieldControl<any>,
    * @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); }
-  protected _required = false;
+  protected _required: boolean | undefined;
 
   /** Input type of the element. */
   @Input()