Misleading error caused by FactoryProvider(..., null)

[leonsenft]

When a FactoryProvider is configured with a null factory, the generated code behaves as though a ClassProvider was used instead.

Consider the following example.

const baseUrl = OpaqueToken<String>('baseUrl');

class Service {
  final String baseUrl;
  Service(@baseUrl this.baseUrl);
}

@Component(...)
class AppComponent implements OnInit {
  final Service service;
  AppComponent(this.service);

  @override
  void ngOnInit() {
    service.init();
  }
}

If we configured the following injector:

@GenerateInjector([
  FactoryProvider(Service, null),
])
final InjectorFactory injectorFactory => injectorFactory$Injector;

We see this error:

No provider found for OpaqueToken (Instance of 'OpaqueToken<String>') <String>('baseUrl'):
Service -> OpaqueToken (Instance of 'OpaqueToken<String>') <String>('baseUrl').

This error makes it appear as through a provider for Service was found. Furthermore, the fact that it knew to inject baseUrl implies that a ClassProvider(Service) was provided. I have a suspicious that when the factory of FactoryProvider is null, the compiler treats this condition as though the provider is a ClassProvider.

It's probably beneficial that we throw a build error if a FactoryProvider explicitly provides null, since this would never be desired.