Function calls are not supported in decorators but 'LoggerModule' was called.

Type of Issue

[x] Bug Report
[ ] Feature Request

Description

I wrote an angular logger library with ng-packagr to use this in different angular applications. The library doesn’t do much more than printing something to the console in the constructor of the service. Everything works fine without --prod, so without AOT compile, in the angular application.

Besides I tried different ng-versions (5.x.x, 6.x.x & 7.x.x). But in all cases everytime (with AOT) the same error when I call LoggerModule.forRoot() in the app.module of the application:

ERROR in Error during template compile of 'AppModule' 
Function calls are not supported in decorators but 'LoggerModule' was called.

I read many articles about this topic, tried different angularCompilerOptions in tsconfig. Any further ideas out there? The module works fine without AOT (but this is no option for us)…

How To Reproduce

Write a library like the usage example of: https://www.npmjs.com/package/ng-packagr

Use this library in a new angular application which is generated by the angular cli by calling LoggerModule.forRoot() in the app.module.ts.

NgModule of the library:

@NgModule({
  declarations: [],
  imports: [],
  providers: []
})
export class LoggerModule {

  static forRoot(): ModuleWithProviders {
    return {
        ngModule: LoggerModule,
        providers: [LoggerService]
    }
  }
}

NgModule of the application:

@NgModule({
  declarations: [
    AppComponent
  ],
  imports: [
    BrowserModule,
    AppRoutingModule,
    LoggerModule.forRoot()
  ],
  providers: [],
  bootstrap: [AppComponent],
  entryComponents: [AppComponent]
})
export class AppModule {
}

Try ng build --prod…

Expected Behaviour

The build of the ng-app works with and without --prod flag / aot compiler.

Version Information

$ node_modules/.bin/ng-packagr --version
ng-packagr: ^4.3.1
@angular/*: ^6.1.0
typescript: ~2.9.2

[TimMeissner]

export loggerModule = LoggerModule.forRoot();

add loggerModule to imports, should work

[christophercr]

I finally found the root cause of the issue: calling throw (or any function) inside the forRoot() breaks the metadata.json generated by ngc.

So, previously I had this:

// inside the NgxFormErrorsModule class

public static forRoot(formErrorsConfig: NgxFormErrorsConfig): ModuleWithProviders {
	if (!formErrorsConfig || !formErrorsConfig.formErrorComponent) {
		throw new Error("NgxFormErrorsModule: a config object should be provided containing the error message component to be used");
	}
	return {
		ngModule: NgxFormErrorsModule,
		providers: [NgxFormErrorsMessageService, { provide: NGX_FORM_ERRORS_CONFIG, useValue: formErrorsConfig }]
	};
}

So, refactoring the method as follows solved the issue:

public static forRoot(formErrorsConfig: NgxFormErrorsConfig): ModuleWithProviders {
	return {
		ngModule: NgxFormErrorsModule,
		providers: [NgxFormErrorsMessageService, { provide: NGX_FORM_ERRORS_CONFIG, useValue: formErrorsConfig }]
	};
}

// now the check is done in the constructor
public constructor(@Optional() @Inject(NGX_FORM_ERRORS_CONFIG) formErrorsConfig: NgxFormErrorsConfig) {
	if (!formErrorsConfig || !formErrorsConfig.formErrorComponent) {
		throw new Error("NgxFormErrorsModule: a config object containing the Error component to be used should be provided via the forRoot() method."
		);
	}
}