Ensure Registry.match/4 works with :_ as key

Author: José Valim

lib/elixir/lib/registry.ex

@@ -534,7 +534,8 @@ defmodule Registry do
   """
   @spec match(registry, key, match_pattern :: atom() | tuple(), guards :: list()) :: [{pid, term}]
   def match(registry, key, pattern, guards \\ []) when is_atom(registry) and is_list(guards) do
-    spec = [{{key, {:_, pattern}}, guards, [{:element, 2, :"$_"}]}]
+    guards = [{:"=:=", {:element, 1, :"$_"}, {:const, key}} | guards]
+    spec = [{{:_, {:_, pattern}}, guards, [{:element, 2, :"$_"}]}]
 
     case key_info!(registry) do
       {:unique, partitions, key_ets} ->

lib/elixir/test/elixir/registry_test.exs

@@ -69,6 +69,10 @@ defmodule RegistryTest do
                [{self(), value}]
         assert Registry.match(registry, "hello", {:"$1", :_, :"$1"}) ==
                [{self(), value}]
+        assert Registry.match(registry, "hello", :_) ==
+               [{self(), value}]
+        assert Registry.match(registry, :_, :_) ==
+               []
       end
 
       test "supports guard conditions", %{registry: registry} do