feat(radio): add required constraint validation

Fixes #4316

PiperOrigin-RevId: 585713253

labs/behaviors/validators/checkbox-validator.ts

@@ -13,12 +13,12 @@ export interface CheckboxState {
   /**
    * Whether the checkbox is checked.
    */
-  checked: boolean;
+  readonly checked: boolean;
 
   /**
    * Whether the checkbox is required.
    */
-  required: boolean;
+  readonly required: boolean;
 }
 
 /**

labs/behaviors/validators/radio-validator.ts

@@ -0,0 +1,90 @@
+/**
+ * @license
+ * Copyright 2023 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import {html, render} from 'lit';
+
+import {Validator} from './validator.js';
+
+/**
+ * Constraint validation properties for a radio.
+ */
+export interface RadioState {
+  /**
+   * Whether the radio is checked.
+   */
+  readonly checked: boolean;
+
+  /**
+   * Whether the radio is required.
+   */
+  readonly required: boolean;
+}
+
+/**
+ * Radio constraint validation properties for a single radio and its siblings.
+ */
+export type RadioGroupState = readonly [RadioState, ...RadioState[]];
+
+/**
+ * A validator that provides constraint validation that emulates
+ * `<input type="radio">` validation.
+ */
+export class RadioValidator extends Validator<RadioGroupState> {
+  private root?: HTMLElement;
+
+  protected override computeValidity(states: RadioGroupState) {
+    if (!this.root) {
+      // Lazily create the container element
+      this.root = document.createElement('div');
+    }
+
+    render(
+      states.map(
+        (state) =>
+          html`<input
+            type="radio"
+            name="group"
+            .checked=${state.checked}
+            ?required=${state.required} />`,
+      ),
+      this.root,
+    );
+
+    const control = this.root.firstElementChild as HTMLInputElement;
+    return {
+      validity: control.validity,
+      validationMessage: control.validationMessage,
+    };
+  }
+
+  protected override equals(
+    prevGroup: RadioGroupState,
+    nextGroup: RadioGroupState,
+  ) {
+    if (prevGroup.length !== nextGroup.length) {
+      return false;
+    }
+
+    for (let i = 0; i < prevGroup.length; i++) {
+      const prev = prevGroup[i];
+      const next = nextGroup[i];
+      if (prev.checked !== next.checked || prev.required !== next.required) {
+        return false;
+      }
+    }
+
+    return true;
+  }
+
+  protected override copy(states: RadioGroupState): RadioGroupState {
+    // Cast as unknown since typescript does not have enough information to
+    // infer that the array always has at least one element.
+    return states.map(({checked, required}) => ({
+      checked,
+      required,
+    })) as unknown as RadioGroupState;
+  }
+}

labs/behaviors/validators/radio-validator_test.ts

@@ -0,0 +1,77 @@
+/**
+ * @license
+ * Copyright 2023 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+// import 'jasmine'; (google3-only)
+
+import {RadioValidator} from './radio-validator.js';
+
+describe('RadioValidator', () => {
+  it('is invalid when required and no radios are checked', () => {
+    const states = [
+      {
+        required: true,
+        checked: false,
+      },
+      {
+        required: true,
+        checked: false,
+      },
+      {
+        required: true,
+        checked: false,
+      },
+    ] as const;
+
+    const validator = new RadioValidator(() => states);
+    const {validity, validationMessage} = validator.getValidity();
+    expect(validity.valueMissing).withContext('valueMissing').toBeTrue();
+    expect(validationMessage).withContext('validationMessage').not.toBe('');
+  });
+
+  it('is valid when required and any radio is checked', () => {
+    const states = [
+      {
+        required: true,
+        checked: false,
+      },
+      {
+        required: true,
+        checked: true,
+      },
+      {
+        required: true,
+        checked: false,
+      },
+    ] as const;
+
+    const validator = new RadioValidator(() => states);
+    const {validity, validationMessage} = validator.getValidity();
+    expect(validity.valueMissing).withContext('valueMissing').toBeFalse();
+    expect(validationMessage).withContext('validationMessage').toBe('');
+  });
+
+  it('is valid when not required', () => {
+    const states = [
+      {
+        required: false,
+        checked: false,
+      },
+      {
+        required: false,
+        checked: false,
+      },
+      {
+        required: false,
+        checked: false,
+      },
+    ] as const;
+
+    const validator = new RadioValidator(() => states);
+    const {validity, validationMessage} = validator.getValidity();
+    expect(validity.valueMissing).withContext('valueMissing').toBeFalse();
+    expect(validationMessage).withContext('validationMessage').toBe('');
+  });
+});

radio/internal/radio.ts

@@ -8,10 +8,15 @@ import '../../focus/md-focus-ring.js';
 import '../../ripple/ripple.js';
 
 import {html, isServer, LitElement} from 'lit';
-import {property} from 'lit/decorators.js';
+import {property, query} from 'lit/decorators.js';
 import {classMap} from 'lit/directives/class-map.js';
 
 import {isActivationClick} from '../../internal/controller/events.js';
+import {
+  createValidator,
+  getValidityAnchor,
+  mixinConstraintValidation,
+} from '../../labs/behaviors/constraint-validation.js';
 import {
   internals,
   mixinElementInternals,
@@ -22,15 +27,16 @@ import {
   getFormValue,
   mixinFormAssociated,
 } from '../../labs/behaviors/form-associated.js';
+import {RadioValidator} from '../../labs/behaviors/validators/radio-validator.js';
 
 import {SingleSelectionController} from './single-selection-controller.js';
 
 const CHECKED = Symbol('checked');
 let maskId = 0;
 
 // Separate variable needed for closure.
-const radioBaseClass = mixinFormAssociated(
-  mixinElementInternals(mixinFocusable(LitElement)),
+const radioBaseClass = mixinConstraintValidation(
+  mixinFormAssociated(mixinElementInternals(mixinFocusable(LitElement))),
 );
 
 /**
@@ -66,11 +72,17 @@ export class Radio extends radioBaseClass {
 
   [CHECKED] = false;
 
+  /**
+   * Whether or not the radio is disabled.
+   */
+  @property({type: Boolean}) required = false;
+
   /**
    * The element value to use in form submission when checked.
    */
   @property() value = 'on';
 
+  @query('.container') private readonly container!: HTMLElement;
   private readonly selectionController = new SingleSelectionController(this);
 
   constructor() {
@@ -175,4 +187,20 @@ export class Radio extends radioBaseClass {
   override formStateRestoreCallback(state: string) {
     this.checked = state === 'true';
   }
+
+  [createValidator]() {
+    return new RadioValidator(() => {
+      if (!this.selectionController) {
+        // Validation runs on superclass construction, so selection controller
+        // might not actually be ready until this class constructs.
+        return [this];
+      }
+
+      return this.selectionController.controls as [Radio, ...Radio[]];
+    });
+  }
+
+  [getValidityAnchor]() {
+    return this.container;
+  }
 }

radio/internal/single-selection-controller.ts

@@ -51,6 +51,23 @@ export interface SingleSelectionElement extends HTMLElement {
  * }
  */
 export class SingleSelectionController implements ReactiveController {
+  /**
+   * All single selection elements in the host element's root with the same
+   * `name` attribute, including the host element.
+   */
+  get controls(): [SingleSelectionElement, ...SingleSelectionElement[]] {
+    const name = this.host.getAttribute('name');
+    if (!name || !this.root) {
+      return [this.host];
+    }
+
+    // Cast as unknown since there is not enough information for typescript to
+    // know that there is always at least one element (the host).
+    return Array.from(
+      this.root.querySelectorAll<SingleSelectionElement>(`[name="${name}"]`),
+    ) as unknown as [SingleSelectionElement, ...SingleSelectionElement[]];
+  }
+
   private focused = false;
   private root: ParentNode | null = null;
 
@@ -104,7 +121,7 @@ export class SingleSelectionController implements ReactiveController {
   };
 
   private uncheckSiblings() {
-    for (const sibling of this.getNamedSiblings()) {
+    for (const sibling of this.controls) {
       if (sibling !== this.host) {
         sibling.checked = false;
       }
@@ -117,7 +134,7 @@ export class SingleSelectionController implements ReactiveController {
   private updateTabIndices() {
     // There are three tabindex states for a group of elements:
     // 1. If any are checked, that element is focusable.
-    const siblings = this.getNamedSiblings();
+    const siblings = this.controls;
     const checkedSibling = siblings.find((sibling) => sibling.checked);
     // 2. If an element is focused, the others are no longer focusable.
     if (checkedSibling || this.focused) {
@@ -138,21 +155,6 @@ export class SingleSelectionController implements ReactiveController {
     }
   }
 
-  /**
-   * Retrieves all siblings in the host element's root with the same `name`
-   * attribute.
-   */
-  private getNamedSiblings() {
-    const name = this.host.getAttribute('name');
-    if (!name || !this.root) {
-      return [];
-    }
-
-    return Array.from(
-      this.root.querySelectorAll<SingleSelectionElement>(`[name="${name}"]`),
-    );
-  }
-
   /**
    * Handles arrow key events from the host. Using the arrow keys will
    * select and check the next or previous sibling with the host's
@@ -169,7 +171,7 @@ export class SingleSelectionController implements ReactiveController {
     }
 
     // Don't try to select another sibling if there aren't any.
-    const siblings = this.getNamedSiblings();
+    const siblings = this.controls;
     if (!siblings.length) {
       return;
     }