Properly handle optional keys in map intersection

Author: josevalim

lib/elixir/lib/module/types/descr.ex

@@ -1330,11 +1330,10 @@ defmodule Module.Types.Descr do
         :maps.next(iterator) |> map_literal_intersection_loop(acc)
 
       _ ->
-        # If the key is marked as not_set in the open map, we can ignore it.
-        if type1 == @not_set do
-          :maps.next(iterator) |> map_literal_intersection_loop(acc)
-        else
-          throw(:empty)
+        # If the key is optional in the open map, we can ignore it
+        case type1 do
+          %{optional: 1} -> :maps.next(iterator) |> map_literal_intersection_loop(acc)
+          _ -> throw(:empty)
         end
     end
   end

lib/elixir/test/elixir/module/types/descr_test.exs

@@ -167,6 +167,9 @@ defmodule Module.Types.DescrTest do
       assert intersection(closed_map(a: integer()), open_map(b: not_set())) ==
                closed_map(a: integer())
 
+      assert intersection(closed_map(a: integer()), open_map(b: if_set(integer()))) ==
+               closed_map(a: integer())
+
       assert equal?(
                intersection(closed_map(a: integer()), closed_map(a: if_set(integer()))),
                closed_map(a: integer())