Ensure structs can be expanded in dynamic module names, closes #4894

Signed-off-by: José Valim <[email protected]>

Author: José Valim

lib/elixir/src/elixir_map.erl

@@ -31,7 +31,9 @@ expand_struct(Meta, Left, Right, #{context := Context} = E) ->
   end,
 
   EMeta =
-    case lists:member(ELeft, ?m(E, context_modules)) of
+    %% We also include the current module because it won't be present
+    %% in context module in case the module name is defined dynamically.
+    case lists:member(ELeft, [?m(E, module) | ?m(E, context_modules)]) of
       true  -> [{struct, context} | Meta];
       false -> Meta
     end,

lib/elixir/test/elixir/map_test.exs

@@ -147,6 +147,16 @@ defmodule MapTest do
     %^struct{name: "john"} = user
   end
 
+  test "structs when using dynamic modules" do
+    defmodule Module.concat(MapTest, DynamicUser) do
+      defstruct [:name, :age]
+
+      def sample do
+        %__MODULE__{}
+      end
+    end
+  end
+
   test "structs when quoted" do
     assert (quote do
       %User{foo: 1}