Refine types from case on inference

Author: josevalim

lib/elixir/lib/module/types/expr.ex

@@ -487,7 +487,7 @@ defmodule Module.Types.Expr do
         end)
 
       context =
-        if none? do
+        if none? or stack.mode != :static do
           head_type = Enum.reduce(clauses_acc, none(), &union(elem(&1, 0), &2))
 
           {_, refined_context} =

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

@@ -1919,7 +1919,7 @@ defmodule Module.Types.ExprTest do
              ) == dynamic()
     end
 
-    test "refine types when there are branches (case)" do
+    test "refine types when there are dead branches (case)" do
       assert typecheck!(
                [x, key],
                (
@@ -1958,6 +1958,32 @@ defmodule Module.Types.ExprTest do
              ) == dynamic(open_map())
     end
 
+    test "refine types when it is dynamic" do
+      assert typecheck!(
+               [x],
+               (
+                 case x do
+                   {} -> :tuple
+                   %{} -> :empty_list
+                 end
+
+                 x
+               )
+             ) == dynamic()
+
+      assert typedyn(
+               [x],
+               (
+                 case x do
+                   {} -> :tuple
+                   %{} -> :empty_list
+                 end
+
+                 x
+               )
+             ) == dynamic(union(open_map(), tuple([])))
+    end
+
     test "warns on redundant clauses" do
       assert typewarn!(
                [x],