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@ContributesAndroidInjector doesn't work with gradle build system

See original GitHub issue

During :app:compileDebugJavaWithJavac task, following exception is thrown:

:app:compileDebugJavaWithJavac
/app/build/generated/source/apt/debug/pl/kibao/contributesandroidinjector/ContributesAndroidInjectorModule_ContributeMainActivityInjector.java:21: 
error: @dagger.android.ActivityKey methods should bind dagger.android.AndroidInjector.Factory<? extends android.app.Activity>, 
not dagger.android.AndroidInjector.Factory<? extends android.app.Activity>. 
See https://google.github.io/dagger/android
  abstract AndroidInjector.Factory<? extends Activity> bindAndroidInjectorFactory(
                                                       ^
1 error

Generated class:

package pl.kibao.contributesandroidinjector;

import android.app.Activity;
import dagger.Binds;
import dagger.Module;
import dagger.Subcomponent;
import dagger.android.ActivityKey;
import dagger.android.AndroidInjector;
import dagger.multibindings.IntoMap;

@Module(
  subcomponents =
      ContributesAndroidInjectorModule_ContributeMainActivityInjector.MainActivitySubcomponent.class
)
public abstract class ContributesAndroidInjectorModule_ContributeMainActivityInjector {
  private ContributesAndroidInjectorModule_ContributeMainActivityInjector() {}

  @Binds
  @IntoMap
  @ActivityKey(MainActivity.class)
  abstract AndroidInjector.Factory<? extends Activity> bindAndroidInjectorFactory(
      MainActivitySubcomponent.Builder builder);

  @Subcomponent(modules = MainModule.class)
  public interface MainActivitySubcomponent extends AndroidInjector<MainActivity> {
    @Subcomponent.Builder
    abstract class Builder extends AndroidInjector.Builder<MainActivity> {}
  }
}

I’ve created separate app with the same code, then replace @ContributesAndroidInjector with the generated class and that worked. That is why I think the problem is related to integration with gradle build system.

Example project: https://github.com/kibao/dagger-contributes-android-injector Travis build: https://travis-ci.org/kibao/dagger-contributes-android-injector/builds/223293977#L1756