[Proposal] Explicit indication of the execution mode in %Macro.Env{}

[Ivan Rublev]

Hi folks,
After delivering the library generating code from type specs, I realised that I'm missing the explicit indication of whether the function/macro is executed within the mix compile task, the mix test task, or interactively (iex / live book) during the compile-time.

Here is the code to illustrate the use case:
defmacro __using__(opts) do
  ...
   cond do
      in_mix_compile? ->
        # plan the code generation when mix compile finishes to resolve type dependencies between BEAM files.
      in_mix_test? ->
        # raise an error and suggest compiling the module as an .ex file for the test environment.
      true ->
        # we're in iex / live book, generate code immediately because type dependencies are resolved during the sequential definition of the modules.
   end
end

Currently, I use the following hacks to get to know the execution mode:
def in_mix_compile?(module_env) do        
  tracers = Map.get(module_env || %{}, :tracers, [])        
  Enum.member?(tracers, Mix.Compilers.ApplicationTracer)
end
 
def in_mix_test?(_module_env) do
  not is_nil(GenServer.whereis(ExUnit.Server))          
end

Is it an absurd idea to add the explicit field indicating execution mode like the following?:
%Module.Env{
   execution_mode: :compile | :test | :interactive
}

that can be returned by __CALLER__ in a macro or by __EVN__ in a function.

Warm regards,
Ivan.

[José Valim]

Can you please explain why you need to know the execution mode.

The fact a library can compile different code depending if it is compile, test, or something else is not something we should encourage.

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[José Valim]

Oh, doh! It is there in your comments. :) Who reads code comments anyway? :D

You want Code.can_await_module_compilation?, available since v1.11. mix test, livebook, iex, are all the same (and all return false).

[Ivan Rublev]

Ha-ha, turns out sometimes comments have value :D
Thanks for pointing to the correct function. It's much less hacky.