chore(behaviors): add ElementInternals mixin

PiperOrigin-RevId: 576657058

button/internal/button.ts

@@ -14,7 +14,6 @@ import {literal, html as staticHtml} from 'lit/static-html.js';
 
 import {ARIAMixinStrict} from '../../internal/aria/aria.js';
 import {requestUpdateOnAriaChange} from '../../internal/aria/delegate.js';
-import {internals} from '../../internal/controller/element-internals.js';
 import {
   dispatchActivationClick,
   isActivationClick,
@@ -24,11 +23,18 @@ import {
   FormSubmitterType,
   setupFormSubmitter,
 } from '../../internal/controller/form-submitter.js';
+import {
+  internals,
+  mixinElementInternals,
+} from '../../labs/behaviors/element-internals.js';
+
+// Separate variable needed for closure.
+const buttonBaseClass = mixinElementInternals(LitElement);
 
 /**
  * A button component.
  */
-export abstract class Button extends LitElement implements FormSubmitter {
+export abstract class Button extends buttonBaseClass implements FormSubmitter {
   static {
     requestUpdateOnAriaChange(Button);
     setupFormSubmitter(Button);
@@ -95,10 +101,6 @@ export abstract class Button extends LitElement implements FormSubmitter {
   @queryAssignedElements({slot: 'icon', flatten: true})
   private readonly assignedIcons!: HTMLElement[];
 
-  /** @private */
-  [internals] = (this as HTMLElement) /* needed for closure */
-    .attachInternals();
-
   constructor() {
     super();
     if (!isServer) {

iconbutton/internal/icon-button.ts

@@ -14,18 +14,24 @@ import {literal, html as staticHtml} from 'lit/static-html.js';
 
 import {ARIAMixinStrict} from '../../internal/aria/aria.js';
 import {requestUpdateOnAriaChange} from '../../internal/aria/delegate.js';
-import {internals} from '../../internal/controller/element-internals.js';
 import {
   FormSubmitter,
   FormSubmitterType,
   setupFormSubmitter,
 } from '../../internal/controller/form-submitter.js';
 import {isRtl} from '../../internal/controller/is-rtl.js';
+import {
+  internals,
+  mixinElementInternals,
+} from '../../labs/behaviors/element-internals.js';
 
 type LinkTarget = '_blank' | '_parent' | '_self' | '_top';
 
+// Separate variable needed for closure.
+const iconButtonBaseClass = mixinElementInternals(LitElement);
+
 // tslint:disable-next-line:enforce-comments-on-exported-symbols
-export class IconButton extends LitElement implements FormSubmitter {
+export class IconButton extends iconButtonBaseClass implements FormSubmitter {
   static {
     requestUpdateOnAriaChange(IconButton);
     setupFormSubmitter(IconButton);
@@ -106,10 +112,6 @@ export class IconButton extends LitElement implements FormSubmitter {
 
   @state() private flipIcon = isRtl(this, this.flipIconInRtl);
 
-  /** @private */
-  [internals] = (this as HTMLElement) /* needed for closure */
-    .attachInternals();
-
   /**
    * Link buttons cannot be disabled.
    */

internal/controller/form-submitter.ts

@@ -6,7 +6,10 @@
 
 import {isServer, ReactiveElement} from 'lit';
 
-import {internals, WithInternals} from './element-internals.js';
+import {
+  internals,
+  WithElementInternals,
+} from '../../labs/behaviors/element-internals.js';
 
 /**
  * A string indicating the form submission behavior of the element.
@@ -23,7 +26,7 @@ export type FormSubmitterType = 'button' | 'submit' | 'reset';
  * An element that can submit or reset a `<form>`, similar to
  * `<button type="submit">`.
  */
-export interface FormSubmitter extends ReactiveElement, WithInternals {
+export interface FormSubmitter extends ReactiveElement, WithElementInternals {
   /**
    * A string indicating the form submission behavior of the element.
    *

internal/controller/form-submitter_test.ts

@@ -9,10 +9,9 @@
 import {html, LitElement} from 'lit';
 import {customElement, property} from 'lit/decorators.js';
 
+import {mixinElementInternals} from '../../labs/behaviors/element-internals.js';
 import {Environment} from '../../testing/environment.js';
 import {Harness} from '../../testing/harness.js';
-
-import {internals} from './element-internals.js';
 import {FormSubmitterType, setupFormSubmitter} from './form-submitter.js';
 
 declare global {
@@ -22,7 +21,7 @@ declare global {
 }
 
 @customElement('test-form-submitter-button')
-class FormSubmitterButton extends LitElement {
+class FormSubmitterButton extends mixinElementInternals(LitElement) {
   static {
     setupFormSubmitter(FormSubmitterButton);
   }
@@ -32,8 +31,6 @@ class FormSubmitterButton extends LitElement {
   type: FormSubmitterType = 'submit';
   @property({reflect: true}) name = '';
   value = '';
-
-  [internals] = this.attachInternals();
 }
 
 describe('setupFormSubmitter()', () => {

labs/behaviors/element-internals.ts

@@ -0,0 +1,62 @@
+/**
+ * @license
+ * Copyright 2023 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import {LitElement} from 'lit';
+
+import {MixinBase, MixinReturn} from './mixin.js';
+
+/**
+ * A unique symbol used for protected access to an instance's
+ * `ElementInternals`.
+ *
+ * @example
+ * ```ts
+ * class MyElement extends mixinElementInternals(LitElement) {
+ *   constructor() {
+ *     super();
+ *     this[internals].role = 'button';
+ *   }
+ * }
+ * ```
+ */
+export const internals = Symbol('internals');
+
+/**
+ * An instance with an `internals` symbol property for the component's
+ * `ElementInternals`.
+ *
+ * Use this when protected access is needed for an instance's `ElementInternals`
+ * from other files. A unique symbol is used to access the internals.
+ */
+export interface WithElementInternals {
+  /**
+   * An instance's `ElementInternals`.
+   */
+  [internals]: ElementInternals;
+}
+
+/**
+ * Mixes in an attached `ElementInternals` instance.
+ *
+ * This mixin is only needed when other shared code needs access to a
+ * component's `ElementInternals`, such as form-associated mixins.
+ *
+ * @param base The class to mix functionality into.
+ * @return The provided class with `WithElementInternals` mixed in.
+ */
+export function mixinElementInternals<T extends MixinBase<LitElement>>(
+  base: T,
+): MixinReturn<T, WithElementInternals> {
+  abstract class WithElementInternalsElement
+    extends base
+    implements WithElementInternals
+  {
+    // Cast needed for closure
+    [internals] = (this as HTMLElement).attachInternals();
+  }
+
+  return WithElementInternalsElement;
+}

labs/behaviors/element-internals_test.ts

@@ -0,0 +1,37 @@
+/**
+ * @license
+ * Copyright 2023 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+// import 'jasmine'; (google3-only)
+
+import {html, LitElement} from 'lit';
+import {customElement} from 'lit/decorators.js';
+
+import {Environment} from '../../testing/environment.js';
+
+import {internals, mixinElementInternals} from './element-internals.js';
+
+describe('mixinElementInternals()', () => {
+  @customElement('test-element-internals')
+  class TestElementInternals extends mixinElementInternals(LitElement) {}
+
+  const env = new Environment();
+
+  async function setupTest() {
+    const root = env.render(
+      html`<test-element-internals></test-element-internals>`,
+    );
+    const element = root.querySelector(
+      'test-element-internals',
+    ) as TestElementInternals;
+    await env.waitForStability();
+    return element;
+  }
+
+  it('should provide an `ElementInternals` instance', async () => {
+    const element = await setupTest();
+    expect(element[internals]).toBeInstanceOf(ElementInternals);
+  });
+});