refactor(aria/listbox): avoid circular references at runtime

Reworks the Aria listbox to avoid a circular dependency between `Listbox` and `Option`.

Author: crisbeto

src/aria/listbox/index.ts

@@ -6,4 +6,5 @@
  * found in the LICENSE file at https://angular.dev/license
  */
 
-export {Listbox, Option} from './listbox';
+export {Listbox} from './listbox';
+export {Option} from './option';

src/aria/listbox/listbox.spec.ts

@@ -1,5 +1,6 @@
 import {Component, DebugElement, signal} from '@angular/core';
-import {Listbox, Option} from './listbox';
+import {Listbox} from './listbox';
+import {Option} from './option';
 import {ComponentFixture, TestBed} from '@angular/core/testing';
 import {By} from '@angular/platform-browser';
 import {Direction} from '@angular/cdk/bidi';

src/aria/listbox/listbox.ts

@@ -20,11 +20,13 @@ import {
   signal,
   untracked,
 } from '@angular/core';
-import {ComboboxListboxPattern, ListboxPattern, OptionPattern} from '@angular/aria/private';
+import {ComboboxListboxPattern, ListboxPattern} from '@angular/aria/private';
 import {Directionality} from '@angular/cdk/bidi';
 import {toSignal} from '@angular/core/rxjs-interop';
 import {_IdGenerator} from '@angular/cdk/a11y';
 import {ComboboxPopup} from '../combobox';
+import {Option} from './option';
+import {LISTBOX} from './tokens';
 
 /**
  * Represents a container used to display a list of items for a user to select from.
@@ -62,6 +64,7 @@ import {ComboboxPopup} from '../combobox';
     '(focusin)': '_onFocus()',
   },
   hostDirectives: [ComboboxPopup],
+  providers: [{provide: LISTBOX, useExisting: Listbox}],
 })
 export class Listbox<V> {
   /** A unique identifier for the listbox. */
@@ -82,13 +85,7 @@ export class Listbox<V> {
   private readonly _directionality = inject(Directionality);
 
   /** The Options nested inside of the Listbox. */
-  private readonly _options = contentChildren(
-    // We need a `forwardRef` here, because the option class is declared further down
-    // in the same file. When the reference is written to Angular's metadata this can
-    // cause an attempt to access the class before it's defined.
-    forwardRef(() => Option),
-    {descendants: true},
-  );
+  private readonly _options = contentChildren(Option, {descendants: true});
 
   /** A signal wrapper for directionality. */
   protected textDirection = toSignal(this._directionality.change, {
@@ -214,77 +211,3 @@ export class Listbox<V> {
     this._pattern.listBehavior.first();
   }
 }
-
-/**
- * A selectable option in an `ngListbox`.
- *
- * This directive should be applied to an element (e.g., `<li>`, `<div>`) within an
- * `ngListbox`. The `value` input is used to identify the option, and the `label` input provides
- * the accessible name for the option.
- *
- * ```html
- * <li ngOption value="item-id" label="Item Name">
- *   Item Name
- * </li>
- * ```
- *
- * @developerPreview 21.0
- */
-@Directive({
-  selector: '[ngOption]',
-  exportAs: 'ngOption',
-  host: {
-    'role': 'option',
-    '[attr.data-active]': 'active()',
-    '[attr.id]': '_pattern.id()',
-    '[attr.tabindex]': '_pattern.tabIndex()',
-    '[attr.aria-selected]': '_pattern.selected()',
-    '[attr.aria-disabled]': '_pattern.disabled()',
-  },
-})
-export class Option<V> {
-  /** A reference to the host element. */
-  private readonly _elementRef = inject(ElementRef);
-
-  /** A reference to the host element. */
-  readonly element = this._elementRef.nativeElement as HTMLElement;
-
-  /** Whether the option is currently active (focused). */
-  active = computed(() => this._pattern.active());
-
-  /** The parent Listbox. */
-  private readonly _listbox = inject(Listbox);
-
-  /** A unique identifier for the option. */
-  readonly id = input(inject(_IdGenerator).getId('ng-option-', true));
-
-  // TODO(wagnermaciel): See if we want to change how we handle this since textContent is not
-  // reactive. See https://github.com/angular/components/pull/30495#discussion_r1961260216.
-  /** The text used by the typeahead search. */
-  protected searchTerm = computed(() => this.label() ?? this.element.textContent);
-
-  /** The parent Listbox UIPattern. */
-  private readonly _listboxPattern = computed(() => this._listbox._pattern);
-
-  /** The value of the option. */
-  value = input.required<V>();
-
-  /** Whether an item is disabled. */
-  disabled = input(false, {transform: booleanAttribute});
-
-  /** The text used by the typeahead search. */
-  label = input<string>();
-
-  /** Whether the option is selected. */
-  readonly selected = computed(() => this._pattern.selected());
-
-  /** The Option UIPattern. */
-  readonly _pattern = new OptionPattern<V>({
-    ...this,
-    id: this.id,
-    value: this.value,
-    listbox: this._listboxPattern,
-    element: () => this.element,
-    searchTerm: () => this.searchTerm() ?? '',
-  });
-}

src/aria/listbox/option.ts

@@ -0,0 +1,83 @@
+/**
+ * @license
+ * Copyright Google LLC All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.dev/license
+ */
+
+import {booleanAttribute, computed, Directive, ElementRef, inject, input} from '@angular/core';
+import {_IdGenerator} from '@angular/cdk/a11y';
+import {OptionPattern} from '../private';
+import {LISTBOX} from './tokens';
+
+/**
+ * A selectable option in an `ngListbox`.
+ *
+ * This directive should be applied to an element (e.g., `<li>`, `<div>`) within an
+ * `ngListbox`. The `value` input is used to identify the option, and the `label` input provides
+ * the accessible name for the option.
+ *
+ * ```html
+ * <li ngOption value="item-id" label="Item Name">
+ *   Item Name
+ * </li>
+ * ```
+ *
+ * @developerPreview 21.0
+ */
+@Directive({
+  selector: '[ngOption]',
+  exportAs: 'ngOption',
+  host: {
+    'role': 'option',
+    '[attr.data-active]': 'active()',
+    '[attr.id]': '_pattern.id()',
+    '[attr.tabindex]': '_pattern.tabIndex()',
+    '[attr.aria-selected]': '_pattern.selected()',
+    '[attr.aria-disabled]': '_pattern.disabled()',
+  },
+})
+export class Option<V> {
+  /** A reference to the host element. */
+  readonly element = inject(ElementRef).nativeElement as HTMLElement;
+
+  /** Whether the option is currently active (focused). */
+  active = computed(() => this._pattern.active());
+
+  /** The parent Listbox. */
+  private readonly _listbox = inject(LISTBOX);
+
+  /** A unique identifier for the option. */
+  readonly id = input(inject(_IdGenerator).getId('ng-option-', true));
+
+  // TODO(wagnermaciel): See if we want to change how we handle this since textContent is not
+  // reactive. See https://github.com/angular/components/pull/30495#discussion_r1961260216.
+  /** The text used by the typeahead search. */
+  protected searchTerm = computed(() => this.label() ?? this.element.textContent);
+
+  /** The parent Listbox UIPattern. */
+  private readonly _listboxPattern = computed(() => this._listbox._pattern);
+
+  /** The value of the option. */
+  value = input.required<V>();
+
+  /** Whether an item is disabled. */
+  disabled = input(false, {transform: booleanAttribute});
+
+  /** The text used by the typeahead search. */
+  label = input<string>();
+
+  /** Whether the option is selected. */
+  readonly selected = computed(() => this._pattern.selected());
+
+  /** The Option UIPattern. */
+  readonly _pattern = new OptionPattern<V>({
+    ...this,
+    id: this.id,
+    value: this.value,
+    listbox: this._listboxPattern,
+    element: () => this.element,
+    searchTerm: () => this.searchTerm() ?? '',
+  });
+}

src/aria/listbox/tokens.ts

@@ -0,0 +1,12 @@
+/**
+ * @license
+ * Copyright Google LLC All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.dev/license
+ */
+
+import {InjectionToken} from '@angular/core';
+import type {Listbox} from './listbox';
+
+export const LISTBOX = new InjectionToken<Listbox<any>>('LISTBOX');