Raise a more meaningful error when using attributes inside match in module

[josevalim]

defmodule Oops do
    @my_const = 42
end

[whatyouhide]

I'm very new to the interiors of Elixir and to Erlang as well, but I'd like to give this a try.

The error you get (on Elixir 1.0.2) when running the snippet above is:

** (CompileError) iex:1: cannot invoke remote function Module.get_attribute/3 inside match

The key function should be elixir_translator:assert_allowed_in_context/5, whose implementation is:

assert_allowed_in_context(Meta, Left, Right, Arity, #elixir_scope{context=Context} = S)
    when (Context == match) orelse (Context == guard) ->
  case (Left == erlang) andalso erl_internal:guard_bif(Right, Arity) of
    true  -> ok;
    false ->
      compile_error(Meta, S#elixir_scope.file, "cannot invoke remote function ~ts.~ts/~B inside ~ts",
        ['Elixir.Macro':to_string(Left), Right, Arity, Context])
  end;
assert_allowed_in_context(_, _, _, _, _) ->
  ok.

Should one just check that Left, Right and Arity match Module.get_attribute/3 or the issue should be solved in a more generic way?

[josevalim]

You can solve it more generic way in the @ implementation:

https://github.com/elixir-lang/elixir/blob/master/lib/elixir/lib/kernel.ex#L2001

Basically, if you are not inside a function and inside a match context (this information is available in the __CALLER__), we need to raise. :) Let me know if you have further questions.

[lexmag]

@whatyouhide any further work on it? I'd like to pick it up .

[whatyouhide]

@lexmag I haven't been able to come up with a working solution, my Elixir-fu is still rough 😄 I'll be happy to learn something from your solution, so go ahead! 👍

[lexmag]

@whatyouhide great. Thank you.
Here is a PR: #3005