feat: prevent core modules from getting loaded multiple times (#1196)

This change should prevent `NativeScriptModule` and `NativeScriptAnimationsModule` from getting loaded in multiple `NgModules` across an Angular NativeScript app.

When the core modules are imported multiple times, this change will cause Errors to be thrown with the following message:

 * For NativeScriptModule:
 > NativeScriptModule has already been loaded. Import NativeScriptModule in the AppModule only.

 * For NativeScriptAnimationsModule:
> NativeScriptAnimationsModule has already been loaded. Import NativeScriptAnimationsModule in the AppModule only.

BREAKING CHANGES:


Importing `NativeScriptModule` and `NativeScriptAnimationsModule` in multiple ngModules is no longer allowed.

To migrate:
 * in `AppModule`:
   * import `NativeScriptModule`
   * import`NativeScriptAnimationsModule` - only if you are planning to use Angular Animations
 * in the remaining modules:
   * remove `NativeScriptModule` imports and replace with `NativeScriptCommonModule` import
   * remove `NativeScriptAnimationsModule` imports

## Example
    
Before:
app.module.ts:
```
import { NativeScriptModule } from 'nativescript-angular/nativescript.module';
import { NativeScriptAnimationsModule } from 'nativescript-angular/animations';
...
@NgModule({
  imports: [
    NativeScriptModule,
    NativeScriptAnimationsModule
  ],
...
})
```

another.module.ts:
```
import { NativeScriptModule } from 'nativescript-angular/nativescript.module';
import { NativeScriptAnimationsModule } from 'nativescript-angular/animations';
...
@NgModule({
  imports: [
    NativeScriptModule,
    NativeScriptAnimationsModule
  ],
...
})
```
   
    
After:
app.module.ts:
```
import { NativeScriptModule } from 'nativescript-angular/nativescript.module';
import { NativeScriptAnimationsModule } from 'nativescript-angular/animations';
...
@NgModule({
  imports: [
    NativeScriptModule,
    NativeScriptAnimationsModule
  ],
...
})
```

another.module.ts:
```
import { NativeScriptCommonModule } from 'nativescript-angular/common';
...
@NgModule({
  imports: [
    NativeScriptCommonModule
  ],
...
})
```

Author: sebawita

Diff for: e2e/router/app/lazy/lazy.module.ts

@@ -1,7 +1,7 @@
 import { NgModule, NO_ERRORS_SCHEMA } from "@angular/core";
 import { Route } from "@angular/router";
 
-import { NativeScriptModule } from "nativescript-angular/nativescript.module";
+import { NativeScriptCommonModule } from "nativescript-angular/common";
 import { NativeScriptRouterModule } from "nativescript-angular/router";
 
 import { LazyComponent } from "./lazy.component";
@@ -26,7 +26,7 @@ const routes: Route[] = [
 @NgModule({
     schemas: [NO_ERRORS_SCHEMA],
     imports: [
-        NativeScriptModule,
+        NativeScriptCommonModule,
         NativeScriptRouterModule,
         NativeScriptRouterModule.forChild(routes)
     ],

Diff for: nativescript-angular/animations/animations.module.ts

@@ -1,4 +1,4 @@
-import { NgModule, Injectable, NgZone, Provider, RendererFactory2 } from "@angular/core";
+import { NgModule, Injectable, NgZone, Provider, RendererFactory2, Optional, SkipSelf } from "@angular/core";
 
 import { AnimationBuilder } from "@angular/animations";
 
@@ -17,6 +17,7 @@ import {
 import { NativeScriptModule } from "../nativescript.module";
 import { NativeScriptRendererFactory } from "../renderer";
 import { NativeScriptAnimationDriver } from "./animation-driver";
+import { throwIfAlreadyLoaded } from "../common/utils";
 
 @Injectable()
 export class InjectableAnimationEngine extends AnimationEngine {
@@ -55,4 +56,8 @@ export const NATIVESCRIPT_ANIMATIONS_PROVIDERS: Provider[] = [
     providers: NATIVESCRIPT_ANIMATIONS_PROVIDERS,
 })
 export class NativeScriptAnimationsModule {
+    constructor(@Optional() @SkipSelf() parentModule: NativeScriptAnimationsModule) {
+        // Prevents NativeScriptAnimationsModule from getting imported multiple times
+        throwIfAlreadyLoaded(parentModule, "NativeScriptAnimationsModule");
+    }
 }

Diff for: nativescript-angular/common/utils.ts

@@ -0,0 +1,8 @@
+export function throwIfAlreadyLoaded(
+    parentModule: any,
+    moduleName: string,
+) {
+    if ( parentModule ) {
+        throw new Error(`${moduleName} has already been loaded. Import ${moduleName} in the AppModule only.`);
+    }
+}

Diff for: nativescript-angular/nativescript.module.ts

@@ -14,11 +14,14 @@ import {
     NgModule,
     RendererFactory2,
     SystemJsNgModuleLoader,
+    Optional,
+    SkipSelf,
 } from "@angular/core";
 
 import { NativeScriptCommonModule } from "./common";
 import { NativeScriptRendererFactory } from "./renderer";
 import { DetachedLoader } from "./common/detached-loader";
+import { throwIfAlreadyLoaded } from "./common/utils";
 
 export function errorHandlerFactory() {
     return new ErrorHandler();
@@ -49,4 +52,8 @@ export function errorHandlerFactory() {
     schemas: [NO_ERRORS_SCHEMA]
 })
 export class NativeScriptModule {
+    constructor(@Optional() @SkipSelf() parentModule: NativeScriptModule) {
+        // Prevents NativeScriptModule from getting imported multiple times
+        throwIfAlreadyLoaded(parentModule, "NativeScriptModule");
+    }
 }

Diff for: tests/app/lazy-loaded.module.ts

@@ -1,5 +1,5 @@
 import { Component, NgModule } from "@angular/core";
-import { NativeScriptModule } from "nativescript-angular/nativescript.module";
+import { NativeScriptCommonModule } from "nativescript-angular/common";
 import { NativeScriptRouterModule } from "nativescript-angular/router";
 import { ModalDialogParams } from "nativescript-angular/directives/dialogs";
 import { Page } from "ui/page";
@@ -31,7 +31,7 @@ export class ModalLazyComponent {
     ],
     entryComponents: [ModalLazyComponent], // when lazily loaded and opened via modal on demand
     imports: [
-        NativeScriptModule,
+        NativeScriptCommonModule,
         NativeScriptRouterModule,
         NativeScriptRouterModule.forChild(routes)
     ],