Consider hygienic vars in defguard, closes #7566

2 files changed, 41 insertions, 8 deletions

diff --git a/lib/elixir/lib/kernel/utils.ex b/lib/elixir/lib/kernel/utils.ex
index 52242196d..9138c60f6 100644
--- a/lib/elixir/lib/kernel/utils.ex
+++ b/lib/elixir/lib/kernel/utils.ex
@@ -201,8 +201,8 @@ defmodule Kernel.Utils do
 
   defp extract_refs_from_args(args) do
     Macro.postwalk(args, [], fn
-      {ref, _meta, context} = var, acc when is_atom(ref) and is_atom(context) ->
-        {var, [{ref, context} | acc]}
+      {ref, meta, context} = var, acc when is_atom(ref) and is_atom(context) ->
+        {var, [{ref, var_context(meta, context)} | acc]}
 
       node, acc ->
         {node, acc}
@@ -212,8 +212,8 @@ defmodule Kernel.Utils do
   # Finds every reference to `refs` in `guard` and wraps them in an unquote.
   defp unquote_every_ref(guard, refs) do
     Macro.postwalk(guard, fn
-      {ref, _meta, context} = var when is_atom(ref) and is_atom(context) ->
-        case {ref, context} in refs do
+      {ref, meta, context} = var when is_atom(ref) and is_atom(context) ->
+        case {ref, var_context(meta, context)} in refs do
           true -> literal_unquote(var)
           false -> var
         end
@@ -227,9 +227,11 @@ defmodule Kernel.Utils do
   defp unquote_refs_once(guard, refs) do
     {_, used_refs} =
       Macro.postwalk(guard, [], fn
-        {ref, _meta, context} = var, acc when is_atom(ref) and is_atom(context) ->
-          case {ref, context} in refs and {ref, context} not in acc do
-            true -> {var, [{ref, context} | acc]}
+        {ref, meta, context} = var, acc when is_atom(ref) and is_atom(context) ->
+          pair = {ref, var_context(meta, context)}
+
+          case pair in refs and pair not in acc do
+            true -> {var, [pair | acc]}
             false -> {var, acc}
           end
 
@@ -237,7 +239,7 @@ defmodule Kernel.Utils do
           {node, acc}
       end)
 
-    vars = for {ref, context} <- :lists.reverse(used_refs), do: {ref, [], context}
+    vars = for {ref, context} <- :lists.reverse(used_refs), do: context_to_var(ref, context)
     exprs = for var <- vars, do: literal_unquote(var)
 
     quote do
@@ -253,4 +255,14 @@ defmodule Kernel.Utils do
   defp literal_unquote(ast) do
     {:unquote, [], List.wrap(ast)}
   end
+
+  defp context_to_var(ref, ctx) when is_atom(ctx), do: {ref, [], ctx}
+  defp context_to_var(ref, ctx) when is_integer(ctx), do: {ref, [counter: ctx], nil}
+
+  defp var_context(meta, kind) do
+    case :lists.keyfind(:counter, 1, meta) do
+      {:counter, counter} -> counter
+      false -> kind
+    end
+  end
 end
diff --git a/lib/elixir/test/elixir/kernel/guard_test.exs b/lib/elixir/test/elixir/kernel/guard_test.exs
index cbf1d0899..e18e1e326 100644
--- a/lib/elixir/test/elixir/kernel/guard_test.exs
+++ b/lib/elixir/test/elixir/kernel/guard_test.exs
@@ -109,6 +109,27 @@ defmodule Kernel.GuardTest do
       end
     end
 
+    defmodule GuardFromMacro do
+      defmacro __using__(_) do
+        quote do
+          defguard is_even(value) when is_integer(value) and rem(value, 2) == 0
+        end
+      end
+    end
+
+    test "defguard defines a guard from inside another macro" do
+      defmodule UseGuardFromMacro do
+        use GuardFromMacro
+
+        def assert! do
+          assert is_even(0)
+          refute is_even(1)
+        end
+      end
+
+      UseGuardFromMacro.assert!()
+    end
+
     defmodule IntegerPrivateGuards do
       defguardp is_even(value) when is_integer(value) and rem(value, 2) == 0