feat(effects): throw error when forRoot() is used more than once

modules/effects/spec/integration.spec.ts

@@ -1,4 +1,10 @@
+import { NgModuleFactoryLoader, NgModule } from '@angular/core';
 import { TestBed } from '@angular/core/testing';
+import {
+  RouterTestingModule,
+  SpyNgModuleFactoryLoader,
+} from '@angular/router/testing';
+import { Router } from '@angular/router';
 import { Store, Action } from '@ngrx/store';
 import {
   EffectsModule,
@@ -20,6 +26,7 @@ describe('NgRx Effects Integration spec', () => {
           RootEffectWithInitActionWithPayload,
         ]),
         EffectsModule.forFeature([FeatEffectWithInitAction]),
+        RouterTestingModule.withRoutes([]),
       ],
       providers: [
         {
@@ -73,6 +80,21 @@ describe('NgRx Effects Integration spec', () => {
     ]);
   });
 
+  it('throws if forRoot() is used more than once', (done: DoneFn) => {
+    let router: Router = TestBed.get(Router);
+    const loader: SpyNgModuleFactoryLoader = TestBed.get(NgModuleFactoryLoader);
+
+    loader.stubbedModules = { feature: FeatModuleWithForRoot };
+    router.resetConfig([{ path: 'feature-path', loadChildren: 'feature' }]);
+
+    router.navigateByUrl('/feature-path').catch((err: TypeError) => {
+      expect(err.message).toBe(
+        'EffectsModule.forRoot() called twice. Feature modules should use EffectsModule.forFeature() instead.'
+      );
+      done();
+    });
+  });
+
   class RootEffectWithInitAction implements OnInitEffects {
     ngrxOnInitEffects(): Action {
       return { type: '[RootEffectWithInitAction]: INIT' };
@@ -110,4 +132,9 @@ describe('NgRx Effects Integration spec', () => {
 
     constructor(private effectIdentifier: string) {}
   }
+
+  @NgModule({
+    imports: [EffectsModule.forRoot([])],
+  })
+  class FeatModuleWithForRoot {}
 });

modules/effects/src/effects_module.ts

@@ -1,7 +1,13 @@
-import { NgModule, ModuleWithProviders, Type } from '@angular/core';
+import {
+  NgModule,
+  ModuleWithProviders,
+  Type,
+  Optional,
+  SkipSelf,
+} from '@angular/core';
 import { EffectSources } from './effect_sources';
 import { Actions } from './actions';
-import { ROOT_EFFECTS, FEATURE_EFFECTS } from './tokens';
+import { ROOT_EFFECTS, FEATURE_EFFECTS, _ROOT_EFFECTS_GUARD } from './tokens';
 import { EffectsFeatureModule } from './effects_feature_module';
 import { EffectsRootModule } from './effects_root_module';
 import { EffectsRunner } from './effects_runner';
@@ -31,6 +37,11 @@ export class EffectsModule {
     return {
       ngModule: EffectsRootModule,
       providers: [
+        {
+          provide: _ROOT_EFFECTS_GUARD,
+          useFactory: _provideForRootGuard,
+          deps: [[EffectsRunner, new Optional(), new SkipSelf()]],
+        },
         EffectsRunner,
         EffectSources,
         Actions,
@@ -48,3 +59,12 @@ export class EffectsModule {
 export function createSourceInstances(...instances: any[]) {
   return instances;
 }
+
+export function _provideForRootGuard(runner: EffectsRunner): any {
+  if (runner) {
+    throw new TypeError(
+      `EffectsModule.forRoot() called twice. Feature modules should use EffectsModule.forFeature() instead.`
+    );
+  }
+  return 'guarded';
+}

modules/effects/src/effects_root_module.ts

@@ -7,7 +7,7 @@ import {
 } from '@ngrx/store';
 import { EffectsRunner } from './effects_runner';
 import { EffectSources } from './effect_sources';
-import { ROOT_EFFECTS } from './tokens';
+import { ROOT_EFFECTS, _ROOT_EFFECTS_GUARD } from './tokens';
 
 export const ROOT_EFFECTS_INIT = '@ngrx/effects/init';
 
@@ -19,7 +19,10 @@ export class EffectsRootModule {
     store: Store<any>,
     @Inject(ROOT_EFFECTS) rootEffects: any[],
     @Optional() storeRootModule: StoreRootModule,
-    @Optional() storeFeatureModule: StoreFeatureModule
+    @Optional() storeFeatureModule: StoreFeatureModule,
+    @Optional()
+    @Inject(_ROOT_EFFECTS_GUARD)
+    guard: any
   ) {
     runner.start();
 

modules/effects/src/tokens.ts

@@ -1,5 +1,8 @@
 import { InjectionToken, Type } from '@angular/core';
 
+export const _ROOT_EFFECTS_GUARD = new InjectionToken<void>(
+  '@ngrx/effects Internal Root Guard'
+);
 export const IMMEDIATE_EFFECTS = new InjectionToken<any[]>(
   'ngrx/effects: Immediate Effects'
 );