Fix <<"x"::utf8>> false positive in clause check

2 files changed, 16 insertions, 3 deletions

diff --git a/lib/elixir/lib/module/types/infer.ex b/lib/elixir/lib/module/types/infer.ex
index 02f87deb8..3a6299779 100644
--- a/lib/elixir/lib/module/types/infer.ex
+++ b/lib/elixir/lib/module/types/infer.ex
@@ -264,9 +264,15 @@ defmodule Module.Types.Infer do
       end
 
     expr_stack(full_expr, context, fn context ->
-      with {:ok, type, context} <- of_pattern(expr, context),
-           {:ok, _type, context} <- unify(type, expected_type, context),
-           do: {:ok, context}
+      # Special case utf specifiers with binary literals since they allow
+      # both integer and binary literals but variables are always integer
+      if is_binary(expr) and utf_specifier?(specifiers) do
+        {:ok, context}
+      else
+        with {:ok, type, context} <- of_pattern(expr, context),
+             {:ok, _type, context} <- unify(type, expected_type, context),
+             do: {:ok, context}
+      end
     end)
   end
 
@@ -284,6 +290,10 @@ defmodule Module.Types.Infer do
     end
   end
 
+  defp utf_specifier?(specifiers) do
+    :utf8 in specifiers or :utf16 in specifiers or :utf32 in specifiers
+  end
+
   # Collect binary type specifiers,
   # from `<<pattern::integer-size(10)>>` collect `integer`
   defp collect_specifiers({:-, _meta, [left, right]}) do
diff --git a/lib/elixir/test/elixir/module/types/infer_test.exs b/lib/elixir/test/elixir/module/types/infer_test.exs
index 71bb5c697..61820cdf2 100644
--- a/lib/elixir/test/elixir/module/types/infer_test.exs
+++ b/lib/elixir/test/elixir/module/types/infer_test.exs
@@ -124,9 +124,12 @@ defmodule Module.Types.InferTest do
       assert quoted_pattern(<<"foo"::binary>>) == {:ok, :binary}
       assert quoted_pattern(<<123::integer>>) == {:ok, :binary}
       assert quoted_pattern(<<foo::integer>>) == {:ok, :binary}
+      assert quoted_pattern(<<123::utf8>>) == {:ok, :binary}
+      assert quoted_pattern(<<"foo"::utf8>>) == {:ok, :binary}
 
       assert quoted_pattern({<<foo::integer>>, foo}) == {:ok, {:tuple, [:binary, :integer]}}
       assert quoted_pattern({<<foo::binary>>, foo}) == {:ok, {:tuple, [:binary, :binary]}}
+      assert quoted_pattern({<<foo::utf8>>, foo}) == {:ok, {:tuple, [:binary, :integer]}}
 
       assert {:error, {{:unable_unify, :integer, :binary, _, _}, _}} =
                quoted_pattern(<<123::binary>>)