Keep parens on unary operators on the left of in

lib/elixir/lib/code/formatter.ex

@@ -875,6 +875,16 @@ defmodule Code.Formatter do
     operand_to_algebra_with_comments(pipes, meta, state, fun)
   end
 
+  # TODO: We can remove this workaround once we remove
+  # ?rearrange_uop from the parser on v2.0.
+  # (! left) in right
+  # (not left) in right
+  defp binary_op_to_algebra(:in, "in", meta, {op, _, [_]} = left, right, context, state, nesting)
+       when op in [:not, :!] do
+    left = {:__block__, [], [left]}
+    binary_op_to_algebra(:in, "in", meta, left, right, context, state, nesting)
+  end
+
   defp binary_op_to_algebra(op, op_string, meta, left_arg, right_arg, context, state, nesting) do
     op_info = augmented_binary_op(op)
     left_context = left_op_context(context)

lib/elixir/test/elixir/code_formatter/operators_test.exs

@@ -171,6 +171,10 @@ defmodule Code.Formatter.OperatorsTest do
       assert_same "foo not in bar"
       assert_same "(not foo) in bar"
       assert_same "(!foo) in bar"
+      assert_same "!foo not in bar"
+
+      assert_format "!!foo in bar", "!((!foo) in bar)"
+      assert_format "!not foo in bar", "!((not foo) in bar)"
     end
 
     test "bitwise precedence" do

lib/elixir/test/elixir/code_normalizer/quoted_ast_test.exs

@@ -245,6 +245,8 @@ defmodule Code.Normalizer.QuotedASTTest do
 
     test "not in" do
       assert quoted_to_string(quote(do: false not in [])) == "false not in []"
+      assert quoted_to_string({:in, [], [quote(do: !foo), []]}) == "(!foo) in []"
+      assert quoted_to_string({:in, [], [quote(do: not foo), []]}) == "(not foo) in []"
     end
 
     test "if else" do