Optional callbacks emitting compilation warnings on Elixir v1.18

[ulissesalmeida]

Elixir and Erlang/OTP versions

Erlang/OTP 27 [erts-15.2] [source] [64-bit] [smp:10:10] [ds:10:10:10] [async-threads:1] [jit]

Elixir 1.18.1 (compiled with Erlang/OTP 27)

Operating system

MacOs

Current behavior

If I did wrote a code like this:

if function_exported?(module, :my_fun, 0) do
  module.my_fun()
else
  :error
end

In Elixir v1.18 emits a compilation warning like this:

      warning: MyModule.my_fun/0 is undefined or private
      │
 56 │       module.my_fun()
      │                     ~
      │

Expected behavior

The MyModule.my_fun/0 indeed doesn't exist because it's an optional callback, so the function_exported?/3 would never return true, so the that line would never be called. I would say the warning shouldn't be triggered.

Is the warning expected anyway? Is there other ways to write a similar code without triggering the warning?

Thank you.

[josevalim]

This only happens for now because you are probably explicitly setting the module somewhere, right? Something like:

module = MyModule

Or:

module = if condition?, do: MyModule, else: OtherModule

Right?

So in those cases, you can add:

@compile {:no_warn_undefined, {MyModule, :my_fun, 0}}

In the future, you will be able to annotate that something is a behaviour and if a function is optional or not, so the experience is streamlined. :)

[ulissesalmeida]

@josevalim thank you! ❤️

[josevalim]

Alright, I will go ahead and close this then, as dealing with this is part of #13881. Thanks!