Hey 
We just tried to upgrade Elixir from 1.11.3 to 1.12.0, while sticking to OTP 23.2.3 for now.
We got some warnings for our behaviours:
@behaviour MyApp.Some.Behaviour does not exist (in module MyApp.Some.Module.UsingBehaviour) & warning: got "MyApp.Some.Behaviour" for function some_function/1 but this behaviour does not specify such callback. There are no known callbacks, please specify the proper @behaviour and make sure it defines callbacks
Some time ago, we saw similar errors when defining mocks for behaviours. There we used Code.ensure_compiled(MyApp.Some.Behaviour) for the “missing” behaviour. But as it is now complaining about the use of behaviours in several modules, putting a Code.ensure_compiled/1 at the top doesn’t feel right.
Does anyone have an idea where this might be coming from?
