fix(forms): align FormField CVA selection priority with standard forms

Prioritize custom ControlValueAccessor instances over default or built-in accessors when applying the [formField] directive. This is achieved by directly consuming selectValueAccessor from @angular/forms, ensuring absolute alignment with the precedence rules used across standard Angular form directives.

packages/forms/signals/src/directive/form_field.ts

@@ -30,6 +30,7 @@ import {
   NG_VALUE_ACCESSOR,
   NgControl,
   ɵFORM_FIELD_PARSE_ERRORS as FORM_FIELD_PARSE_ERRORS,
+  ɵselectValueAccessor as selectValueAccessor,
 } from '@angular/forms';
 import {type ValidationError} from '../api/rules';
 import type {Field, FieldState} from '../api/types';
@@ -193,7 +194,18 @@ export class FormField<T> {
    * @internal
    */
   get controlValueAccessor(): ControlValueAccessor | undefined {
-    return this.controlValueAccessors?.[0] ?? this.interopNgControl?.valueAccessor ?? undefined;
+    if (!this.controlValueAccessors || this.controlValueAccessors.length === 0) {
+      return this.interopNgControl?.valueAccessor ?? undefined;
+    }
+
+    // Rely on the exact logic in `@angular/forms` to pick the accessors with correct priority,
+    // passing our fake `InteropNgControl` to fulfill its first parameter requirement.
+    return (
+      selectValueAccessor(
+        this.interopNgControl as unknown as NgControl,
+        this.controlValueAccessors,
+      ) ?? undefined
+    );
   }
 
   /**

packages/forms/signals/test/web/interop.spec.ts

@@ -18,7 +18,13 @@ import {
   viewChild,
 } from '@angular/core';
 import {TestBed} from '@angular/core/testing';
-import {ControlValueAccessor, NG_VALUE_ACCESSOR, NgControl} from '@angular/forms';
+import {
+  ControlValueAccessor,
+  DefaultValueAccessor,
+  NG_VALUE_ACCESSOR,
+  NgControl,
+  ReactiveFormsModule,
+} from '@angular/forms';
 import {
   debounce,
   disabled,
@@ -373,6 +379,25 @@ describe('ControlValueAccessor', () => {
     expect(() => fixture.componentInstance.disabled.set(true)).not.toThrowError(/NG0600/);
   });
 
+  it('should pick custom CVA over default CVA when both are present', () => {
+    @Component({
+      selector: 'app-root',
+      // Import ReactiveFormsModule to provide the non-standalone DefaultValueAccessor directive.
+      // The selector for DefaultValueAccessor matches `[ngDefaultControl]`.
+      imports: [FormField, CustomControl, ReactiveFormsModule],
+      template: `<custom-control [formField]="f" ngDefaultControl />`,
+    })
+    class App {
+      f = form<string>(signal(''));
+    }
+
+    const fixture = act(() => TestBed.createComponent(App));
+    const customControlInstance = fixture.debugElement.children[0].injector.get(CustomControl);
+
+    act(() => fixture.componentInstance.f().value.set('updated'));
+    expect(customControlInstance.writeCount).toBe(2); // 1 initial + 1 update
+  });
+
   describe('properties', () => {
     describe('disabled', () => {
       it('should bind to directive input', () => {

packages/forms/src/directives/shared.ts

@@ -393,7 +393,7 @@ export function syncPendingControls(
 // TODO: vsavkin remove it once https://github.com/angular/angular/issues/3011 is implemented
 export function selectValueAccessor(
   dir: NgControl,
-  valueAccessors: ControlValueAccessor[] | null | undefined,
+  valueAccessors: readonly ControlValueAccessor[] | null | undefined,
 ): ControlValueAccessor | null {
   if (!valueAccessors) return null;
 

packages/forms/src/forms.ts

@@ -48,7 +48,11 @@ export {
   SelectMultipleControlValueAccessor,
   ɵNgSelectMultipleOption,
 } from './directives/select_multiple_control_value_accessor';
-export {SetDisabledStateOption, ɵFORM_FIELD_PARSE_ERRORS} from './directives/shared';
+export {
+  selectValueAccessor as ɵselectValueAccessor,
+  SetDisabledStateOption,
+  ɵFORM_FIELD_PARSE_ERRORS,
+} from './directives/shared';
 export {
   AsyncValidator,
   AsyncValidatorFn,