Multibinding doesn't work with Component Dependencies

Dagger docs states:

A binding in a subcomponent can depend on a multibound set or map from its parent, just as it can depend on any other binding from its parent. But a subcomponent can add elements to multibound sets or maps that are bound in its parent as well, by simply including the appropriate @Provides methods in its modules.

However, the same is not true when using component dependencies. If one has many small components that shares dependencies using “component dependencies” - a “child” component that has a dependency to another component might not be able to contribute to its Graph.

For example, consider the following classes:

@Component
interface CommonComponent {
    fun factoryBindings(): Map<String, Factory>
}

@Component(
    modules = [FeatureModule::class]
    dependencies = [CommonComponent::class]
)
interface FeatureComponent

@Module
interface FeatureModule {
    // Contributes to factories map.
    @[Binds IntoMap FactoryKey("featureFactory")]
    fun featureFactory(impl: FeatureFactory): CustomFactory
}

class CompositeCustomFactory @Inject constructor(
   val factoriesMap: Map<String, Factory>
)

In this if I use FeatureComponent to inject the CompositeCustomFactory, I would only receive the ones contributed inside CommonComponent - ignoring the ones inside FeatureComponent (e.g., FeatureFactory).

Note that using a subcomponent setup, it’d work as expected.

Is this a design decision and/or limitation of Dagger, a bug when dealing with component dependencies or am I doing something wrong?

Obs: #1186 is related but the use cases are slightly different so I opened this PR.

[bcorso]

Hi Marcello, no need to provide an example. I think @Chang-Eric is right that the reason you don’t get a conflict is because the FactoryComponent is installing into the map with type Map<String, CustomFactory>.

However, I think the suggestion in https://github.com/google/dagger/issues/2027#issuecomment-670589644 still applies, just make sure your map types are the same.

[marcellogalhardo]

Hey @bcorso,

The workaround from https://github.com/google/dagger/issues/1112#issuecomment-474985867 is working as expected and it is enough for my use case and therefore, I will close this issue.

Thanks a lot for yours and @Chang-Eric help! ✌️