fix(material/radio): required attribute being set on buttons

fixes when `MatRadioGroup` is set to be required it was setting all of its `MatRadioButton`
to be required as-well which is confusing for assistive technologies, this commit ensures
we only set aria-required on group rather than all buttons unless button is being used
standalone of `MatRadioGroup`

fixes #30399

Author: naaajii

Diff for: src/material/radio/radio.html

@@ -8,7 +8,7 @@
            [disabled]="disabled && !disabledInteractive"
            [attr.name]="name"
            [attr.value]="value"
-           [required]="required"
+           [required]="getInputRequiredAttribute()"
            [attr.aria-label]="ariaLabel"
            [attr.aria-labelledby]="ariaLabelledby"
            [attr.aria-describedby]="ariaDescribedby"

Diff for: src/material/radio/radio.spec.ts

@@ -524,6 +524,33 @@ describe('MatRadio', () => {
       expect(groupInstance.selected).toBe(null);
       expect(groupInstance.value).toBe('fire');
     });
+
+    it('should set aria-required on radio group', () => {
+      fixture.changeDetectorRef.markForCheck();
+      fixture.detectChanges();
+
+      let group = fixture.debugElement.query(By.directive(MatRadioGroup)).nativeElement;
+
+      // by default it shouldn't be there
+      expect(group.getAttribute('aria-required')).toBe('false');
+
+      testComponent.isGroupRequired = true;
+      fixture.changeDetectorRef.markForCheck();
+      fixture.detectChanges();
+
+      group = fixture.debugElement.query(By.directive(MatRadioGroup)).nativeElement;
+      expect(group.getAttribute('aria-required')).toBe('true');
+    });
+
+    it('should set not set required attribute on matRadioButton when matRadioGroup is required', () => {
+      testComponent.isGroupRequired = true;
+      fixture.changeDetectorRef.markForCheck();
+      fixture.detectChanges();
+
+      for (const radio of radioDebugElements) {
+        expect(radio.nativeElement.hasAttribute('aria-required')).toBeFalse();
+      }
+    });
   });
 
   describe('group with ngModel', () => {

Diff for: src/material/radio/radio.ts

@@ -118,6 +118,7 @@ export function MAT_RADIO_DEFAULT_OPTIONS_FACTORY(): MatRadioDefaultOptions {
   host: {
     'role': 'radiogroup',
     'class': 'mat-mdc-radio-group',
+    '[attr.aria-required]': 'required',
   },
 })
 export class MatRadioGroup implements AfterContentInit, OnDestroy, ControlValueAccessor {
@@ -804,4 +805,13 @@ export class MatRadioButton implements OnInit, AfterViewInit, DoCheck, OnDestroy
       }
     }
   }
+
+  protected getInputRequiredAttribute(): boolean | null {
+    // we never want to set required attribute on input when we have MatRadioGroup as we will set
+    // aria-required directly on MatRadioGroup if its required as setting on all MatRadioButton for
+    // it's MatRadioGroup would be confusing for assistive technology.
+    if (this.radioGroup) return null;
+
+    return this.required;
+  }
 }

Diff for: src/material/radio/testing/radio-harness.spec.ts

@@ -145,7 +145,7 @@ describe('radio harness', () => {
   describe('MatRadioButtonHarness', () => {
     it('should load all radio-button harnesses', async () => {
       const radios = await loader.getAllHarnesses(MatRadioButtonHarness);
-      expect(radios.length).toBe(9);
+      expect(radios.length).toBe(10);
     });
 
     it('should load radio-button with exact label', async () => {
@@ -267,10 +267,25 @@ describe('radio harness', () => {
       expect(await radioButton.isChecked()).toBe(true);
     });
 
-    it('should get required state', async () => {
+    // radios with group should not contain required attribute as group itself is marked if its
+    // required or not, see #30399
+    it('should have falsy required state if used with MatRadioGroup', async () => {
+      const radioButton = await loader.getHarness(
+        MatRadioButtonHarness.with({selector: '#required-radio-inside-group'}),
+      );
+      expect(await radioButton.isRequired()).toBe(false);
+    });
+
+    it('should set required state of radio without group', async () => {
       const radioButton = await loader.getHarness(
         MatRadioButtonHarness.with({selector: '#required-radio'}),
       );
+      expect(await radioButton.isRequired()).toBe(false);
+
+      fixture.componentInstance.standaloneRequiredRadio = true;
+      fixture.changeDetectorRef.markForCheck();
+      fixture.detectChanges();
+
       expect(await radioButton.isRequired()).toBe(true);
     });
   });
@@ -302,11 +317,15 @@ describe('radio harness', () => {
 
 
     <mat-radio-group [id]="secondGroupId" [name]="secondGroupId + '-name'">
-      <mat-radio-button id="required-radio" required [value]="true">
+      <mat-radio-button id="required-radio-inside-group" required [value]="true">
         Accept terms of conditions
       </mat-radio-button>
     </mat-radio-group>
 
+    <mat-radio-button id="required-radio" [required]="standaloneRequiredRadio" [value]="true">
+      Accept terms of conditions
+    </mat-radio-button>
+
     <mat-radio-group [name]="thirdGroupName">
       <mat-radio-button [value]="true">First</mat-radio-button>
       <mat-radio-button [value]="false" [name]="thirdGroupButtonName"></mat-radio-button>
@@ -321,4 +340,5 @@ class MultipleRadioButtonsHarnessTest {
   secondGroupId = 'my-group-2';
   thirdGroupName: string = 'third-group-name';
   thirdGroupButtonName: string | undefined = undefined;
+  standaloneRequiredRadio = false;
 }

Diff for: tools/public_api_guard/material/radio.md

@@ -50,6 +50,8 @@ export class MatRadioButton implements OnInit, AfterViewInit, DoCheck, OnDestroy
     // (undocumented)
     protected _elementRef: ElementRef<any>;
     focus(options?: FocusOptions, origin?: FocusOrigin): void;
+    // (undocumented)
+    protected getInputRequiredAttribute(): boolean | null;
     id: string;
     _inputElement: ElementRef<HTMLInputElement>;
     get inputId(): string;