Dagger should error out when components have injection methods for interfaces

interface MyInterface {
}

@Component
interface MyComponent {
  void inject(MyInterface foo);
}

Dagger builds just fine and doesn’t complain. The inject method is implemented as a no-op.

We made that mistake and this wasn’t detected until we tried to build our release. Seems like it’d be nice it Dagger told us we made a mistake 😃 .

[gk5885]

So, that’s actually a question about any type without members to inject and whether or not that should be an error.

First, we try to avoid spooky action at a distance. Say you have A extends B extends C. If C has an @Injected field and that’s the only field that is injected, it would be potentially surprising and hard to manage if a change to a field on C suddenly breaks components that request members injection on A. The distance between the code that changes and the error is too great. Totally fine for a warning though, IMO.

Second, intentional no-ops can be nice. If you have a whole class of types (Say, Activity subclasses) that get a members injection method apiece, it might be more manageable to have each get injected even if some of them don’t have injectable members.

Third, I think it can be annoying to be building out a new structure and get errors like the one you’re proposing when you’re just not done assembling all of the parts. It can be a little frustrating to have to inject a placeholder something just to make sure that the component builds while you’re trying to get everything set up.

Finally, I think it’s in the spirit of the JLS to only error on “dead code” when it is unreachable. I.e. why we have errors for private members that can’t be injected, but why we don’t fail builds for private methods that aren’t called.

So, those are all of my reasons for not wanting to make it a mandatory error, but:

• +1 to a warning
• +1 to static analysis that you can opt into for your project if you want

[pyricau]

Sorry, I don’t think I follow. What’s the issue with having an error for any no-op injection method on components, how would that be a pain in development?