Avoid race conditions in the struct detection

Author: José Valim

lib/elixir/lib/kernel/error_handler.ex

@@ -29,7 +29,7 @@ defmodule Kernel.ErrorHandler do
       {:error, _} ->
         parent = :erlang.get(:elixir_compiler_pid)
         ref    = :erlang.make_ref
-        send parent, {:waiting, module, self(), ref, module}
+        send parent, {:waiting, :module, self(), ref, module}
         :erlang.garbage_collect(self)
         receive do
           {^ref, :ready}   -> :ok

lib/elixir/src/elixir_map.erl

@@ -82,7 +82,7 @@ load_struct(Meta, Name, S) ->
   Context = lists:keyfind(struct, 1, Meta) == {struct, context},
 
   Local =
-    elixir_module:is_open(Name) andalso
+    not(ensure_loaded(Name)) andalso
       (Context orelse wait_for_struct(Name)),
 
   try
@@ -112,6 +112,12 @@ load_struct(Meta, Name, S) ->
       end
   end.
 
+ensure_loaded(Module) ->
+  case code:ensure_loaded(Module) of
+    {module, Module} -> true;
+    {error, _} -> false
+  end.
+
 wait_for_struct(Module) ->
   case erlang:get(elixir_compiler_pid) of
     undefined ->