ExUnit: Unused alias warning with behaviour and nested modules

[novaugust]

Elixir and Erlang/OTP versions

Erlang/OTP 27 [erts-15.2.2] [source] [64-bit] [smp:16:16] [ds:16:16:10] [async-threads:1]

Elixir 1.18.2 (compiled with Erlang/OTP 27)

Operating system

macos

Current behavior

this this minimal repro emits an unused alias warning for alias A.B.C

defmodule A.B.C do
  @callback foo() :: :ok
end

defmodule A do
  use ExUnit.Case
  alias A.B.C

  test "with submodule" do
    defmodule B do
      @behaviour C
      @impl C
      def foo, do: :ok
    end

    assert true
  end
end

    warning: unused alias C
    │
  7 │   alias A.B.C
    │   ~
    │
    └─ test/foo_test.exs:7:3

Expected behavior

no warning.
obviously, there are trivial fixes the user can take to fix this situation, like

1. define the submodules outside of the test macro
2. move the alias into the submodule itself

but i thought it might be worth shining a light on for you. no worries if it's a wontfix =)
found via styler user issue

[josevalim]

The contents of a defmodule are only executed when the code runs, in this case, the test. So it is a won't fix because the alias has indeed not been used by the time the file has done compiling. It is an expected false warning. You can pass alias A.B.C, warn: false instead. Thanks for the report!

[novaugust]

thanks for the learnings =)