fix(forms): Support readonly arrays in signal forms

This would allow using `readonly Array<...>` in types

(cherry picked from commit 282220d)

Author: kirjs

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

@@ -182,7 +182,7 @@ export interface FieldState<TValue, TKey extends string | number = string | numb
 }
 
 // @public
-export type FieldTree<TModel, TKey extends string | number = string | number> = (() => [TModel] extends [AbstractControl] ? CompatFieldState<TModel, TKey> : FieldState<TModel, TKey>) & ([TModel] extends [AbstractControl] ? object : [TModel] extends [Array<infer U>] ? ReadonlyArrayLike<MaybeFieldTree<U, number>> : TModel extends Record<string, any> ? Subfields<TModel> : object);
+export type FieldTree<TModel, TKey extends string | number = string | number> = (() => [TModel] extends [AbstractControl] ? CompatFieldState<TModel, TKey> : FieldState<TModel, TKey>) & ([TModel] extends [AbstractControl] ? object : [TModel] extends [ReadonlyArray<infer U>] ? ReadonlyArrayLike<MaybeFieldTree<U, number>> : TModel extends Record<string, any> ? Subfields<TModel> : object);
 
 // @public
 export type FieldValidator<TValue, TPathKind extends PathKind = PathKind.Root> = LogicFn<TValue, ValidationResult<ValidationError.WithoutField>, TPathKind>;
@@ -513,7 +513,7 @@ export namespace SchemaPathRules {
 }
 
 // @public
-export type SchemaPathTree<TModel, TPathKind extends PathKind = PathKind.Root> = ([TModel] extends [AbstractControl] ? CompatSchemaPath<TModel, TPathKind> : SchemaPath<TModel, SchemaPathRules.Supported, TPathKind>) & (TModel extends AbstractControl ? unknown : TModel extends Array<any> ? unknown : TModel extends Record<string, any> ? {
+export type SchemaPathTree<TModel, TPathKind extends PathKind = PathKind.Root> = ([TModel] extends [AbstractControl] ? CompatSchemaPath<TModel, TPathKind> : SchemaPath<TModel, SchemaPathRules.Supported, TPathKind>) & (TModel extends AbstractControl ? unknown : TModel extends ReadonlyArray<any> ? unknown : TModel extends Record<string, any> ? {
     [K in keyof TModel]: MaybeSchemaPathTree<TModel[K], PathKind.Child>;
 } : unknown);
 

packages/forms/signals/src/api/types.ts

@@ -9,8 +9,7 @@
 import {Signal, ɵFieldState} from '@angular/core';
 import {AbstractControl} from '@angular/forms';
 import type {Field} from './field_directive';
-import type {MetadataKey} from './rules/metadata';
-import type {ValidationError} from './rules/validation/validation_errors';
+import type {ValidationError, MetadataKey} from './rules';
 
 /**
  * Symbol used to retain generic type information when it would otherwise be lost.
@@ -169,7 +168,7 @@ export type FieldTree<TModel, TKey extends string | number = string | number> =
     // Children:
     ([TModel] extends [AbstractControl]
       ? object
-      : [TModel] extends [Array<infer U>]
+      : [TModel] extends [ReadonlyArray<infer U>]
         ? ReadonlyArrayLike<MaybeFieldTree<U, number>>
         : TModel extends Record<string, any>
           ? Subfields<TModel>
@@ -408,7 +407,7 @@ export type SchemaPathTree<TModel, TPathKind extends PathKind = PathKind.Root> =
     (TModel extends AbstractControl
       ? unknown
       : // Array paths have no subpaths
-        TModel extends Array<any>
+        TModel extends ReadonlyArray<any>
         ? unknown
         : // Object subfields
           TModel extends Record<string, any>

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

@@ -7,7 +7,7 @@
  */
 
 import {signal, WritableSignal} from '@angular/core';
-import {form, required, schema, SchemaFn} from '../../public_api';
+import {FieldTree, form, required, schema, SchemaFn} from '../../public_api';
 
 interface Order {
   id: string;
@@ -87,5 +87,30 @@ function typeVerificationOnlyDoNotRunMe() {
       type RecursiveType = (number | RecursiveType)[];
       form(signal<RecursiveType>([5]));
     });
+
+    it('should allow ReadonlyArray in model and be iterable', () => {
+      interface Order {
+        readonly products: readonly string[];
+      }
+      const order: WritableSignal<Order> = null!;
+      const f = form(order);
+      // Iterating over products should yield FieldTree<string> items, not [string, FieldTree] entries
+      for (const product of f.products) {
+        const p: FieldTree<string> = product;
+        p().value();
+      }
+    });
+
+    it('should allow Array in model and be iterable', () => {
+      interface Order {
+        products: string[];
+      }
+      const order: WritableSignal<Order> = null!;
+      const f = form(order);
+      for (const product of f.products) {
+        const p: FieldTree<string> = product;
+        p().value();
+      }
+    });
   });
 }