Ensure macro expansion does not expand on variables

Author: José Valim

lib/elixir/lib/macro.ex

@@ -588,12 +588,20 @@ defmodule Macro do
     do: { env, true, cache }
 
   # Expand possible macro import invocation
-  defp expand_once({ atom, meta, args } = original, env, cache) when is_atom(atom) and is_list(meta) do
-    args = case is_atom(args) do
-      true  -> []
-      false -> args
+  defp expand_once({ atom, meta, context } = original, env, cache)
+      when is_atom(atom) and is_list(meta) and is_atom(context) do
+    if :lists.member({ atom, Keyword.get(meta, :counter, context) }, env.vars) do
+      { original, false, cache }
+    else
+      case expand_once({ atom, meta, [] }, env, cache) do
+        { _, true, _ } = exp -> exp
+        { _, false, cache }  -> { original, false, cache }
+      end
     end
+  end
 
+  defp expand_once({ atom, meta, args } = original, env, cache)
+      when is_atom(atom) and is_list(args) and is_list(meta) do
     case not is_partial?(args) do
       false -> { original, false, cache }
       true  ->

lib/elixir/test/elixir/macro_test.exs

@@ -156,6 +156,13 @@ defmodule MacroTest do
     assert Macro.expand_once(quote(do: local_macro), __ENV__) == :local_macro
   end
 
+  test :expand_once_checks_vars do
+    local_macro = 1
+    assert local_macro == 1
+    quote = quote(hygiene: [vars: false], do: local_macro)
+    assert Macro.expand_once(quote, __ENV__) == quote
+  end
+
   test :expand_once_with_imported_macro do
     temp_var = { :x, [temp: true], Kernel }
     assert Macro.expand_once(quote(do: 1 || false), __ENV__) == (quote context: Kernel do