Always wrap binary operators in groups

Author: José Valim

lib/elixir/lib/code/formatter.ex

@@ -647,11 +647,11 @@ defmodule Code.Formatter do
     doc =
       cond do
         op in @no_space_binary_operators ->
-          concat(concat(left, op_string), right)
+          group(concat(concat(left, op_string), right))
 
         op in @no_newline_binary_operators ->
           op_string = " " <> op_string <> " "
-          concat(concat(left, op_string), right)
+          group(concat(concat(left, op_string), right))
 
         op in @left_new_line_before_binary_operators ->
           op_string = op_string <> " "
@@ -688,7 +688,7 @@ defmodule Code.Formatter do
 
           with_next_break_fits(next_break_fits?, right, fn right ->
             op_string = " " <> op_string
-            concat(left, group(nest(glue(op_string, group(right)), nesting, :break)))
+            group(concat(left, group(nest(glue(op_string, group(right)), nesting, :break))))
           end)
       end
 

lib/elixir/test/elixir/code_formatter/integration_test.exs

@@ -231,6 +231,16 @@ defmodule Code.Formatter.IntegrationTest do
     """
   end
 
+  test "comprehensions with when" do
+    assert_same """
+    for {key, value} when is_atom(key) <- Map.to_list(map),
+        key = Atom.to_string(key),
+        String.starts_with?(key, hint) do
+      %{kind: :map_key, name: key, value_is_map: is_map(value)}
+    end
+    """
+  end
+
   test "next break fits followed by inline tuple" do
     assert_same """
     assert ExUnit.Filters.eval([line: "1"], [:line], %{line: 3, describe_line: 2}, tests) ==