Component gets other component injected even if it is not a child of it.

[rkj]

I have two components:

@Component(selector: 'outer-component')
class OuterComponent {
}

@Component(
    selector: 'inner-component',
    publishAs: 'ctrl')
class InnerComponent {
  OuterComponent outerComponent;
  InnerComponent(this.outerComponent);
}

When the InnerComponent is created I expect it to get 'null' value if OuterComponent is not present as its parent, but it's not the case.

Here's a failing test:

group('Nested', () {
  setUp(() {
    setUpInjector();
    module((Module module) {
      module
          ..bind(OuterComponent)
          ..bind(InnerComponent)
          ;
    });
  });

  test('should not get outer component', inject((TestBed testBed) {
    setupHtml(testBed, '''<inner-component></inner-component>''');
    var html = testBed.rootElement.children.first;
    InnerComponent component = ngProbe(html).directives[0];
    expect(component.outerComponent, null);
  }));
});

[rkj]

This can be overcome by using: .bind(OuterComponent, toValue: null)

[rkirov]

Yeah, that doesn't sound very intuitive. The application injector is creating the Outer component, but that job should be left only to the directive injectors.

In fact I would argue that instead of passing in null, we should throw, i.e. all injector dependencies are hard, not optional.

A dirty way to achieve that would be to add NgElement as a constructor dependency, which can only be resolved by the directive injector.

[BlackHC]

I tried to point out the same issue a couple of days ago (less clear than you did though). I agree that it is really confusing. Registering directives in the injector is wrong because we don't want a default instance of components to be created. Hard injector dependencies would also be better imo. Otherwise, you might get hard-to-debug NPEs now and then.

[mhevery]

Agreed, very confusing, will be addressed in the upcoming compiler rewrite.