feat(effects): allow usage of empty forRoot array multiple times (#2774)

Author: alex-okrushko

modules/effects/spec/integration.spec.ts

@@ -20,7 +20,7 @@ import { mapTo, exhaustMap, tap } from 'rxjs/operators';
 import { Observable } from 'rxjs';
 
 describe('NgRx Effects Integration spec', () => {
-  it('throws if forRoot() is used more than once', (done: any) => {
+  it('throws if forRoot() with Effects is used more than once', (done: any) => {
     TestBed.configureTestingModule({
       imports: [
         StoreModule.forRoot({}),
@@ -45,6 +45,30 @@ describe('NgRx Effects Integration spec', () => {
     });
   });
 
+  it('does not throw if forRoot() is used more than once with empty effects', (done: any) => {
+    TestBed.configureTestingModule({
+      imports: [
+        StoreModule.forRoot({}),
+        EffectsModule.forRoot([]),
+        RouterTestingModule.withRoutes([]),
+      ],
+    });
+
+    let router: Router = TestBed.inject(Router);
+    const loader: SpyNgModuleFactoryLoader = TestBed.inject(
+      NgModuleFactoryLoader
+    ) as SpyNgModuleFactoryLoader;
+
+    //                       empty forRoot([]) 👇
+    loader.stubbedModules = { feature: FeatModuleWithEmptyForRoot };
+    router.resetConfig([{ path: 'feature-path', loadChildren: 'feature' }]);
+
+    router.navigateByUrl('/feature-path').then(() => {
+      // success
+      done();
+    });
+  });
+
   describe('actions', () => {
     const createDispatchedReducer = (dispatchedActions: string[] = []) => (
       state = {},
@@ -386,11 +410,19 @@ describe('NgRx Effects Integration spec', () => {
     }
   }
 
+  @Injectable()
+  class SomeEffect {}
+
   @NgModule({
-    imports: [EffectsModule.forRoot()],
+    imports: [EffectsModule.forRoot([SomeEffect])],
   })
   class FeatModuleWithForRoot {}
 
+  @NgModule({
+    imports: [EffectsModule.forRoot([])],
+  })
+  class FeatModuleWithEmptyForRoot {}
+
   @NgModule({
     imports: [
       EffectsModule.forFeature([FeatEffectFromLazyLoadedModuleWithInitAction]),

modules/effects/src/effects_module.ts

@@ -3,6 +3,7 @@ import {
   ModuleWithProviders,
   NgModule,
   Optional,
+  Self,
   SkipSelf,
   Type,
 } from '@angular/core';
@@ -57,11 +58,6 @@ export class EffectsModule {
     return {
       ngModule: EffectsRootModule,
       providers: [
-        {
-          provide: _ROOT_EFFECTS_GUARD,
-          useFactory: _provideForRootGuard,
-          deps: [[EffectsRunner, new Optional(), new SkipSelf()]],
-        },
         {
           provide: EFFECTS_ERROR_HANDLER,
           useValue: defaultEffectsErrorHandler,
@@ -74,6 +70,14 @@ export class EffectsModule {
           provide: _ROOT_EFFECTS,
           useValue: [rootEffects],
         },
+        {
+          provide: _ROOT_EFFECTS_GUARD,
+          useFactory: _provideForRootGuard,
+          deps: [
+            [EffectsRunner, new Optional(), new SkipSelf()],
+            [_ROOT_EFFECTS, new Self()],
+          ],
+        },
         {
           provide: USER_PROVIDED_EFFECTS,
           multi: true,
@@ -114,8 +118,13 @@ export function createEffectInstances(
   return effects.map((effect) => injector.get(effect));
 }
 
-export function _provideForRootGuard(runner: EffectsRunner): any {
-  if (runner) {
+export function _provideForRootGuard(
+  runner: EffectsRunner,
+  rootEffects: any[][]
+): any {
+  // check whether any effects are actually passed
+  const hasEffects = !(rootEffects.length === 1 && rootEffects[0].length === 0);
+  if (hasEffects && runner) {
     throw new TypeError(
       `EffectsModule.forRoot() called twice. Feature modules should use EffectsModule.forFeature() instead.`
     );