fix(signals): add current state as second argument of case reducer (#4800)

Author: markostanimirovic

modules/signals/events/spec/with-reducer.spec.ts

@@ -78,6 +78,27 @@ describe('withReducer', () => {
     expect(getState(store)).toEqual({ count: 2, count2: 11 });
   });
 
+  it('has access to the current state', () => {
+    const incrementBy = event('incrementBy', type<number>());
+
+    const CounterStore = signalStore(
+      { providedIn: 'root' },
+      withState({ count: 10, count2: 0 }),
+      withReducer(
+        on(incrementBy, ({ payload }, state) => ({
+          count: state.count + payload,
+        }))
+      )
+    );
+
+    const store = TestBed.inject(CounterStore);
+    const dispatcher = TestBed.inject(Dispatcher);
+
+    dispatcher.dispatch(incrementBy(20));
+
+    expect(getState(store)).toEqual({ count: 30, count2: 0 });
+  });
+
   it('allows listening to multiple events', () => {
     const set = event('set', type<number>());
     const set_ = event('set_', type<number>());

modules/signals/events/src/case-reducer.ts

@@ -13,7 +13,8 @@ type CaseReducer<
   State extends object,
   EventCreators extends EventCreator<string, any>[]
 > = (
-  event: { [K in keyof EventCreators]: ReturnType<EventCreators[K]> }[number]
+  event: { [K in keyof EventCreators]: ReturnType<EventCreators[K]> }[number],
+  state: State
 ) =>
   | Partial<State>
   | PartialStateUpdater<State>

modules/signals/events/src/with-reducer.ts

@@ -1,8 +1,9 @@
-import { inject } from '@angular/core';
+import { inject, untracked } from '@angular/core';
 import { takeUntilDestroyed } from '@angular/core/rxjs-interop';
 import { merge, tap } from 'rxjs';
 import {
   EmptyFeatureResult,
+  getState,
   patchState,
   SignalStoreFeature,
   signalStoreFeature,
@@ -48,7 +49,8 @@ export function withReducer<State extends object>(
         const updates = caseReducers.map((caseReducer) =>
           events.on(...caseReducer.events).pipe(
             tap((event) => {
-              const result = caseReducer.reducer(event);
+              const state = untracked(() => getState(store));
+              const result = caseReducer.reducer(event, state);
               const updaters = Array.isArray(result) ? result : [result];
 
               patchState(store, ...updaters);