Fix loop while unifying type variables, closes #11658

Author: josevalim

lib/elixir/lib/module/types/unify.ex

@@ -130,10 +130,15 @@ defmodule Module.Types.Unify do
 
       %{^var => {:var, new_var} = var_type} ->
         unify_result =
-          if var_source? do
-            unify(var_type, type, stack, context)
-          else
-            unify(type, var_type, stack, context)
+          cond do
+            recursive_type?(var_type, [], context) ->
+              {:ok, var_type, put_in(context.types[var], var_type)}
+
+            var_source? ->
+              unify(var_type, type, stack, context)
+
+            true ->
+              unify(type, var_type, stack, context)
           end
 
         case unify_result do

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

@@ -744,5 +744,17 @@ defmodule Module.Types.TypesTest do
                )
              ) == :none
     end
+
+    test "nested map updates" do
+      assert warning(
+               [state],
+               (
+                 _foo = state.key.user_id
+                 _bar = state.key.user_id
+                 state = %{state | key: %{state.key | other_id: 1}}
+                 _baz = state.key.user_id
+               )
+             ) == :none
+    end
   end
 end