feat(forms): add debounce option to validateAsync and validateHttp

This adds support for a `debounce` option to the `validateAsync` and `validateHttp` functions.
This allows developers to debounce the triggering of async validators to improve performance.

A `DebounceTimer` type was also added to `@angular/core` to represent the wait condition parameters uniformly.

goldens/public-api/core/index.api.md

@@ -499,7 +499,7 @@ export const CSP_NONCE: InjectionToken<string | null>;
 export const CUSTOM_ELEMENTS_SCHEMA: SchemaMetadata;
 
 // @public
-export function debounced<T>(source: () => T, wait: NoInfer<number | ((value: T, lastValue: ResourceSnapshot<T>) => Promise<void> | void)>, options?: NoInfer<DebouncedOptions<T>>): Resource<T>;
+export function debounced<T>(source: () => T, wait: NoInfer<DebounceTimer<T>>, options?: NoInfer<DebouncedOptions<T>>): Resource<T>;
 
 // @public
 export interface DebouncedOptions<T> {
@@ -507,6 +507,9 @@ export interface DebouncedOptions<T> {
     injector?: Injector;
 }
 
+// @public
+export type DebounceTimer<T> = number | ((value: T, lastValue: ResourceSnapshot<T>) => Promise<void> | void);
+
 // @public (undocumented)
 export class DebugElement extends DebugNode {
     constructor(nativeNode: Element);

goldens/public-api/forms/signals/index.api.md

@@ -6,6 +6,7 @@
 
 import { AbstractControl } from '@angular/forms';
 import { ControlValueAccessor } from '@angular/forms';
+import { DebounceTimer } from '@angular/core';
 import { FormControlStatus } from '@angular/forms';
 import { HttpResourceOptions } from '@angular/common/http';
 import { HttpResourceRequest } from '@angular/common/http';
@@ -47,6 +48,7 @@ export type AsyncValidationResult<E extends ValidationError = ValidationError> =
 
 // @public
 export interface AsyncValidatorOptions<TValue, TParams, TResult, TPathKind extends PathKind = PathKind.Root> {
+    readonly debounce?: DebounceTimer<TParams | undefined>;
     readonly factory: (params: Signal<TParams | undefined>) => ResourceRef<TResult | undefined>;
     readonly onError: (error: unknown, ctx: FieldContext<TValue, TPathKind>) => TreeValidationResult;
     readonly onSuccess: MapToErrorsFn<TValue, TResult, TPathKind>;
@@ -260,6 +262,7 @@ export function hidden<TValue, TPathKind extends PathKind = PathKind.Root>(path:
 
 // @public
 export interface HttpValidatorOptions<TValue, TResult, TPathKind extends PathKind = PathKind.Root> {
+    readonly debounce?: DebounceTimer<string | HttpResourceRequest | undefined>;
     readonly onError: (error: unknown, ctx: FieldContext<TValue, TPathKind>) => TreeValidationResult;
     readonly onSuccess: MapToErrorsFn<TValue, TResult, TPathKind>;
     readonly options?: HttpResourceOptions<TResult, unknown>;

packages/core/src/resource/api.ts

@@ -305,3 +305,11 @@ export interface DebouncedOptions<T> {
   /** The equality function to use for comparing values. */
   equal?: ValueEqualityFn<T>;
 }
+
+/**
+ * Represents the wait condition for item debouncing.
+ * Can be a number of milliseconds or a function that returns a Promise.
+ */
+export type DebounceTimer<T> =
+  | number
+  | ((value: T, lastValue: ResourceSnapshot<T>) => Promise<void> | void);

packages/core/src/resource/debounce.ts

@@ -12,7 +12,7 @@ import {effect} from '../render3/reactivity/effect';
 import {linkedSignal} from '../render3/reactivity/linked_signal';
 import {signal} from '../render3/reactivity/signal';
 import {untracked} from '../render3/reactivity/untracked';
-import {Resource, ResourceSnapshot, type DebouncedOptions} from './api';
+import {Resource, ResourceSnapshot, type DebounceTimer, type DebouncedOptions} from './api';
 import {resourceFromSnapshots} from './from_snapshots';
 import {
   invalidResourceCreationInParams,
@@ -33,7 +33,7 @@ import {
  */
 export function debounced<T>(
   source: () => T,
-  wait: NoInfer<number | ((value: T, lastValue: ResourceSnapshot<T>) => Promise<void> | void)>,
+  wait: NoInfer<DebounceTimer<T>>,
   options?: NoInfer<DebouncedOptions<T>>,
 ): Resource<T> {
   if (isInParamsFunction()) {

packages/forms/signals/src/api/rules/validation/validate_async.ts

@@ -6,7 +6,7 @@
  * found in the LICENSE file at https://angular.dev/license
  */
 
-import {ResourceRef, Signal} from '@angular/core';
+import {DebounceTimer, ResourceRef, ResourceSnapshot, Signal, debounced} from '@angular/core';
 import {FieldNode} from '../../../field/node';
 import {addDefaultField} from '../../../field/validation';
 import {FieldPathNode} from '../../../schema/path_node';
@@ -67,6 +67,12 @@ export interface AsyncValidatorOptions<
    */
   readonly params: (ctx: FieldContext<TValue, TPathKind>) => TParams;
 
+  /**
+   * Duration in milliseconds to wait before triggering the async operation, or a function that
+   * returns a promise that resolves when the update should proceed.
+   */
+  readonly debounce?: DebounceTimer<TParams | undefined>;
+
   /**
    * A function that receives the resource params and returns a resource of the given params.
    * The given params should be used as is to create the resource.
@@ -118,7 +124,13 @@ export function validateAsync<TValue, TParams, TResult, TPathKind extends PathKi
   const pathNode = FieldPathNode.unwrapFieldPath(path);
 
   const RESOURCE = createManagedMetadataKey<ReturnType<typeof opts.factory>, TParams | undefined>(
-    (_state, params) => opts.factory(params),
+    (_state, params) => {
+      if (opts.debounce !== undefined) {
+        const debouncedResource = debounced(() => params(), opts.debounce);
+        return opts.factory(debouncedResource.value);
+      }
+      return opts.factory(params);
+    },
   );
   RESOURCE[IS_ASYNC_VALIDATION_RESOURCE] = true;
 

packages/forms/signals/src/api/rules/validation/validate_http.ts

@@ -7,7 +7,7 @@
  */
 
 import {httpResource, HttpResourceOptions, HttpResourceRequest} from '@angular/common/http';
-import {Signal} from '@angular/core';
+import {DebounceTimer, ResourceSnapshot, Signal} from '@angular/core';
 import {
   FieldContext,
   SchemaPath,
@@ -62,6 +62,12 @@ export interface HttpValidatorOptions<TValue, TResult, TPathKind extends PathKin
    * The options to use when creating the httpResource.
    */
   readonly options?: HttpResourceOptions<TResult, unknown>;
+
+  /**
+   * Duration in milliseconds to wait before triggering the async operation, or a function that
+   * returns a promise that resolves when the update should proceed.
+   */
+  readonly debounce?: DebounceTimer<string | HttpResourceRequest | undefined>;
 }
 
 /**
@@ -83,7 +89,10 @@ export function validateHttp<TValue, TResult = unknown, TPathKind extends PathKi
   opts: HttpValidatorOptions<TValue, TResult, TPathKind>,
 ) {
   validateAsync(path, {
-    params: opts.request,
+    params: opts.request as (
+      ctx: FieldContext<TValue, TPathKind>,
+    ) => string | HttpResourceRequest | undefined,
+    debounce: opts.debounce,
     factory: (request: Signal<any>) => httpResource(request, opts.options),
     onSuccess: opts.onSuccess,
     onError: opts.onError,

packages/forms/signals/test/node/resource.spec.ts

@@ -16,7 +16,7 @@ import {
   type Signal,
 } from '@angular/core';
 import {TestBed} from '@angular/core/testing';
-import {isNode} from '@angular/private/testing';
+import {isNode, timeout, useAutoTick} from '@angular/private/testing';
 
 import {
   applyEach,
@@ -43,6 +43,8 @@ interface Address {
 }
 
 describe('resources', () => {
+  useAutoTick();
+
   let appRef: ApplicationRef;
   let backend: HttpTestingController;
   let injector: Injector;
@@ -404,6 +406,41 @@ describe('resources', () => {
     expect(f().metadata(RES)).toBe(undefined);
   });
 
+  it('should support debounce in validateHttp', async () => {
+    const usernameForm = form(
+      signal('unique-user'),
+      (p) => {
+        validateHttp(p, {
+          request: ({value}) => `/api/check?username=${value()}`,
+          debounce: 50, // Short debounce
+          onSuccess: (available: boolean) => (available ? undefined : {kind: 'username-taken'}),
+          onError: () => null,
+        });
+      },
+      {injector},
+    );
+
+    TestBed.tick();
+    const req1 = backend.expectOne('/api/check?username=unique-user');
+    req1.flush(true);
+    await appRef.whenStable();
+    expect(usernameForm().valid()).toBe(true);
+    usernameForm().value.set('taken-user');
+    TestBed.tick();
+
+    // Should not have triggered a new request yet
+    backend.expectNone('/api/check?username=taken-user');
+
+    // Wait for debounce
+    await timeout(80);
+    TestBed.tick();
+    const req2 = backend.expectOne('/api/check?username=taken-user');
+    req2.flush(false);
+    await appRef.whenStable();
+
+    expect(usernameForm().valid()).toBe(false);
+  });
+
   describe('reloadValidation', () => {
     it('should trigger a reload of async http validation', async () => {
       const usernameForm = form(