fix(signals): correctly infer the type of methods with generics (#4249)

Author: markostanimirovic

modules/signals/spec/types/signal-store.types.spec.ts

@@ -623,6 +623,23 @@ describe('signalStore', () => {
     );
   });
 
+  it('correctly infers the type of methods with generics', () => {
+    const snippet = `
+      const Store = signalStore(
+        withMethods(() => ({
+          log<Str extends string>(str: Str) {
+            console.log(str);
+          },
+        }))
+      );
+
+      const store = inject(Store);
+    `;
+
+    expectSnippet(snippet + `store.log('ngrx');`).toSucceed();
+    expectSnippet(snippet + `store.log(10);`).toFail();
+  });
+
   describe('custom features', () => {
     const baseSnippet = `
       function withX() {

modules/signals/src/signal-store-models.ts

@@ -24,7 +24,7 @@ export type SignalStoreProps<FeatureResult extends SignalStoreFeatureResult> =
 
 export type SignalsDictionary = Record<string, Signal<unknown>>;
 
-export type MethodsDictionary = Record<string, (...args: any[]) => unknown>;
+export type MethodsDictionary = Record<string, Function>;
 
 export type SignalStoreHooks = {
   onInit?: () => void;