Guarantee nullary funs/macros are allowed in guards, closes #1997

Author: José Valim

lib/elixir/lib/macro.ex

@@ -672,19 +672,18 @@ defmodule Macro do
 
   defp do_expand_once({ atom, meta, args } = original, env)
       when is_atom(atom) and is_list(args) and is_list(meta) do
-    module = env.module
-
-    extra  = if function_exported?(module, :__info__, 1) do
-      [{ module, module.__info__(:macros) }]
-    else
-      []
-    end
-
     arity = length(args)
 
     if :elixir_import.special_form(atom, arity) do
       { original, false }
     else
+      module = env.module
+      extra  = if function_exported?(module, :__info__, 1) do
+        [{ module, module.__info__(:macros) }]
+      else
+        []
+      end
+
       expand = :elixir_dispatch.expand_import(meta, { atom, length(args) }, args,
                                               :elixir_env.ex_to_env(env), extra)
 

lib/elixir/src/elixir_exp.erl

@@ -296,9 +296,6 @@ expand({ Name, Meta, Kind } = Var, #elixir_env{vars=Vars} = E) when is_atom(Name
 
           compile_error(Meta, E#elixir_env.file, "expected var ~ts~ts to expand to an existing "
                         "variable or be a part of a match", [Name, Extra]);
-        E#elixir_env.context == guard ->
-          compile_error(Meta, E#elixir_env.file, "unknown variable ~ts or cannot invoke "
-                        "function ~ts/0 inside guard", [Name, Name]);
         true ->
           expand({ Name, Meta, [] }, E)
       end

lib/elixir/test/elixir/kernel/expansion_test.exs

@@ -162,6 +162,11 @@ defmodule Kernel.ExpansionTest do
            quote(do: :"Elixir.Hello".a())
   end
 
+  test "locals: in guards" do
+    assert expand(quote(do: fn pid when pid == self -> pid end)) ==
+           quote(do: fn pid when __op__(:==, pid, :erlang.self()) -> pid end)
+  end
+
   test "locals: custom imports" do
     assert expand(quote do: (import Kernel.ExpansionTarget; seventeen)) ==
            quote do: (import :"Elixir.Kernel.ExpansionTarget", []; 17)