I’m trying to replace a little functionality with a fake one in dev, while every other environment must use the default one. For security reasons, I don’t want the call to the fake functionality even exist in production, so I’m using a macro. Here’s the barebones idea:

defmodule Myapp.MacroModule do

  defmacro build_impl(default) do
    if Mix.env() == :dev do
      quote do: Myapp.MacroModule.fake_impl()
    else
      quote do: unquote(default)
    end
  end

  def fake_impl() do
    :fake_value
  end

end

defmodule Myapp do
  require Myapp.MacroModule

  def hello(params) do
    result = Myapp.MacroModule.build_impl(Map.get(params, :key))
    IO.inspect(result)
    # do_something_else_with_result(result)
  end

  def hello2(param) do
    Myapp.MacroModule.build_impl(param)
    IO.inspect(param)
  end

end

In dev it uses fake_impl/0 and in other envs the default one passed to the macro and it works fine. The macro can be called with different implementations from different places.

The issue is that I of course get variable "params" is unused warning in dev since to my understanding the first line of hello/1 would turn out to be result = Myapp.MacroModule.fake_impl() and params is not used.

How could I go about suppressing the warning? Or should I approach the original issue some other way?

Thanks for any help!

EDIT: added hello2/1 function to demonstrate another default implementation