fix(signals): make patchState work with TS 5.4 (#4294)

modules/signals/spec/types/patch-state.types.spec.ts

@@ -0,0 +1,72 @@
+import { expecter } from 'ts-snippet';
+import { compilerOptions } from './helpers';
+
+describe('patchState', () => {
+  const expectSnippet = expecter(
+    (code) => `
+        import {
+          PartialStateUpdater,
+          patchState,
+          signalState,
+        } from '@ngrx/signals';
+
+        const state = signalState({ count: 1, foo: 'bar' });
+
+        function increment(): PartialStateUpdater<{ count: number }> {
+          return ({ count }) => ({ count: count + 1 });
+        }
+
+        function addNumber(num: number): PartialStateUpdater<{
+          numbers: number[];
+        }> {
+          return ({ numbers }) => ({ numbers: [...numbers, num] });
+        }
+
+        ${code}
+      `,
+    compilerOptions()
+  );
+
+  it('infers the state type from StateSignal', () => {
+    expectSnippet('patchState(state, increment())').toSucceed();
+    expectSnippet("patchState(state, { foo: 'baz' })").toSucceed();
+    expectSnippet("patchState(state, { foo: 'baz' }, increment())").toSucceed();
+    expectSnippet("patchState(state, increment(), { foo: 'baz' })").toSucceed();
+  });
+
+  it('fails with wrong partial state object', () => {
+    expectSnippet('patchState(state, { x: 1 })').toFail(
+      /'x' does not exist in type 'Partial<{ count: number; foo: string; }>/
+    );
+    expectSnippet("patchState(state, { foo: 'baz' }, { x: 1 })").toFail(
+      /'x' does not exist in type 'Partial<{ count: number; foo: string; }>/
+    );
+    expectSnippet('patchState(state, { x: 1 }, { count: 0 })').toFail(
+      /'x' does not exist in type 'Partial<{ count: number; foo: string; }>/
+    );
+    expectSnippet('patchState(state, increment(), { x: 1 })').toFail(
+      /'x' does not exist in type 'Partial<{ count: number; foo: string; }>/
+    );
+    expectSnippet('patchState(state, { x: 1 }, increment())').toFail(
+      /'x' does not exist in type 'Partial<{ count: number; foo: string; }>/
+    );
+  });
+
+  it('fails with wrong partial state updater', () => {
+    expectSnippet('patchState(state, addNumber(10))').toFail(
+      /Property 'numbers' is missing in type '{ count: number; foo: string; }'/
+    );
+    expectSnippet('patchState(state, { count: 10 }, addNumber(10))').toFail(
+      /Property 'numbers' is missing in type '{ count: number; foo: string; }'/
+    );
+    expectSnippet('patchState(state, addNumber(10), { count: 10 })').toFail(
+      /Property 'numbers' is missing in type '{ count: number; foo: string; }'/
+    );
+    expectSnippet('patchState(state, increment(), addNumber(10))').toFail(
+      /Property 'numbers' is missing in type '{ count: number; foo: string; }'/
+    );
+    expectSnippet('patchState(state, addNumber(10), increment())').toFail(
+      /Property 'numbers' is missing in type '{ count: number; foo: string; }'/
+    );
+  });
+});

modules/signals/src/patch-state.ts

@@ -1,12 +1,15 @@
 import { STATE_SIGNAL, StateSignal } from './state-signal';
+import { Prettify } from './ts-helpers';
 
 export type PartialStateUpdater<State extends object> = (
   state: State
 ) => Partial<State>;
 
 export function patchState<State extends object>(
   stateSignal: StateSignal<State>,
-  ...updaters: Array<Partial<State & {}> | PartialStateUpdater<State & {}>>
+  ...updaters: Array<
+    Partial<Prettify<State>> | PartialStateUpdater<Prettify<State>>
+  >
 ): void {
   stateSignal[STATE_SIGNAL].update((currentState) =>
     updaters.reduce(