Is it possible to detect if code is executing at compile time?

The problem is that it is pretty hard to differentiate between “compile time” and “run time” as “compile time” is “run time with saving created modules to .beam files”.

You can check __CALLER__.function to detect whether macro was called within function body or outside of it.

compiling? = is_list(Process.get(:elixir_module_binaries))
But as @hauleth pointed out, difference between runtime and compile time is ephemeral. Compilation can happen in runtime, and anything can be called during compilation

Yes, sorry, I did not make this clear in my question. I’m interested to know if the code is being called during compilation, not necessarily at some mythical ‘compile time’.

Given that, I think your suggestion should work! Thank you.

That distinction doesn’t change anything he said though, you can still generate a module at runtime and compile it and for it what is happening will be “compile time”. You really should revise what you really want to achieve with this and consider other ways, this can very easily bite you in the rear in the most inopportune moment in the future.

Yes, I’m aware of that and clarified what I meant in the comment that you’re replying to: I’m interested to know if the code is being called during compilation. I assume hissssst’s expression would evaluate to true in the scenario you describe, which is exactly what I want.

To be precise, expression evaluates to true, only if the process is compiling the Elixir module. Some processes can be present during the compilation, but this expression would return false in them, since these processes are not compiling anything.

I see, yes, thanks for the clarification, hissssst.

We’re talking past each other. What I described is also “during compilation”.

What I described is also “during compilation”

Yes, I know. And I want the expression to evaluate to true in that context, so I don’t see the problem.

I use the following code in ex_cldr to detect if Elixir is compiling. The mechanism changed from Elixir 1.11, hence the conditional check:

  def compiling? do
    # TODO: When we depend on Elixir v1.11+ only, remove function_exported and elixir_compiler_pid
    process_alive?(:can_await_module_compilation?) ||
      process_alive?(:elixir_compiler_pid)
  end

  defp process_alive?(:can_await_module_compilation?) do
    Code.ensure_loaded?(Code) &&
      function_exported?(Code, :can_await_module_compilation?, 0) &&
      apply(Code, :can_await_module_compilation?, [])
  end

  defp process_alive?(name) do
    case Process.get(name) do
      nil -> false
      pid when is_pid(pid) -> true
    end
  end