fix(signals): do not create nested signals for STATE_SIGNAL property (#4062)

Author: markostanimirovic

modules/signals/spec/signal-state.spec.ts

@@ -59,6 +59,15 @@ describe('signalState', () => {
     expect((state.user.firstName as any).y).toBe(undefined);
   });
 
+  it('does not modify STATE_SIGNAL', () => {
+    const state = signalState(initialState);
+
+    expect((state[STATE_SIGNAL] as any).user).toBe(undefined);
+    expect((state[STATE_SIGNAL] as any).foo).toBe(undefined);
+    expect((state[STATE_SIGNAL] as any).numbers).toBe(undefined);
+    expect((state[STATE_SIGNAL] as any).ngrx).toBe(undefined);
+  });
+
   it(
     'emits new values only for affected signals',
     testEffects((tick) => {

modules/signals/src/deep-signal.ts

@@ -1,4 +1,4 @@
-import { isSignal, Signal, untracked } from '@angular/core';
+import { Signal, untracked } from '@angular/core';
 import { selectSignal } from './select-signal';
 
 export type DeepSignal<T> = Signal<T> &
@@ -14,11 +14,15 @@ export function toDeepSignal<T>(signal: Signal<T>): DeepSignal<T> {
 
   return new Proxy(signal, {
     get(target: any, prop) {
-      if (prop in value && !target[prop]) {
+      if (!(prop in value)) {
+        return target[prop];
+      }
+
+      if (!target[prop]) {
         target[prop] = selectSignal(() => target()[prop]);
       }
 
-      return isSignal(target[prop]) ? toDeepSignal(target[prop]) : target[prop];
+      return toDeepSignal(target[prop]);
     },
   });
 }