Format type hints after comments

CHANGES.md

@@ -125,6 +125,7 @@ wheels in a future release as soon as the mypyc bug is fixed.
 - Implicitly concatenated strings used as function args are no longer wrapped inside
   parentheses (#3640)
 - Remove blank lines between a class definition and its docstring (#3692)
+- Stop wrapping unnecessarily when there are comments inside brackets (#3362).
 
 ### Configuration
 

src/black/linegen.py

@@ -561,7 +561,7 @@ def transform_line(
     if (
         not line.contains_uncollapsable_type_comments()
         and not line.should_split_rhs
-        and not line.magic_trailing_comma
+        and not line.bracket_after_magic_trailing_comma
         and (
             is_line_short_enough(line, mode=mode, line_str=line_str)
             or line.contains_unsplittable_type_ignore()
@@ -619,6 +619,24 @@ def _rhs(
                     string_paren_wrap,
                     rhs,
                 ]
+
+                # If there are comments at the beginning or end of the line, call
+                # standalone_comment_split before delimiter_split. Else, call
+                # delimiter_split first. This means that when there is a comment in the
+                # middle of an expression or list, it will perform a delimiter split.
+                # But when the comment is at the top or bottom, it won't perform a
+                # delimiter split (if it doesn't have to).
+                if (
+                    Preview.stop_some_unnecessary_wrapping_inside_brackets in mode
+                    and line.contains_standalone_comments()
+                    and len(line.comments) == 0
+                    and all(
+                        leaf.type != STANDALONE_COMMENT for leaf in line.leaves[1:-1]
+                    )
+                    and line.magic_trailing_comma is None
+                ):
+                    transformers.remove(standalone_comment_split)
+                    transformers.insert(0, standalone_comment_split)
             else:
                 transformers = [
                     string_merge,
@@ -800,6 +818,7 @@ def _first_right_hand_split(
     body = bracket_split_build_line(
         body_leaves, line, opening_bracket, component=_BracketSplitComponent.body
     )
+    body.magic_trailing_comma = line.magic_trailing_comma
     tail = bracket_split_build_line(
         tail_leaves, line, opening_bracket, component=_BracketSplitComponent.tail
     )
@@ -848,7 +867,7 @@ def _maybe_split_omitting_optional_parens(
                 )
                 # the left side of assignment won't explode further because of magic
                 # trailing comma
-                and rhs.head.magic_trailing_comma is None
+                and rhs.head.bracket_after_magic_trailing_comma is None
                 # the split by omitting optional parens isn't preferred by some other
                 # reason
                 and not _prefer_split_rhs_oop(rhs_oop, mode)
@@ -1526,7 +1545,7 @@ def generate_trailers_to_omit(line: Line, line_length: int) -> Iterator[Set[Leaf
     """
 
     omit: Set[LeafID] = set()
-    if not line.magic_trailing_comma:
+    if not line.bracket_after_magic_trailing_comma:
         yield omit
 
     length = 4 * line.depth

src/black/lines.py

@@ -57,6 +57,7 @@ class Line:
     bracket_tracker: BracketTracker = field(default_factory=BracketTracker)
     inside_brackets: bool = False
     should_split_rhs: bool = False
+    bracket_after_magic_trailing_comma: Optional[Leaf] = None
     magic_trailing_comma: Optional[Leaf] = None
 
     def append(
@@ -89,7 +90,8 @@ def append(
             self.bracket_tracker.mark(leaf)
             if self.mode.magic_trailing_comma:
                 if self.has_magic_trailing_comma(leaf):
-                    self.magic_trailing_comma = leaf
+                    self.bracket_after_magic_trailing_comma = leaf
+                    self.magic_trailing_comma = self.get_last_non_comment_leaf()
             elif self.has_magic_trailing_comma(leaf, ensure_removable=True):
                 self.remove_trailing_comma()
         if not self.append_comment(leaf):
@@ -306,6 +308,13 @@ def contains_unsplittable_type_ignore(self) -> bool:
     def contains_multiline_strings(self) -> bool:
         return any(is_multiline_string(leaf) for leaf in self.leaves)
 
+    def get_last_non_comment_leaf(self) -> Optional[Leaf]:
+        for leaf in reversed(self.leaves):
+            if leaf.type != STANDALONE_COMMENT:
+                return leaf
+
+        return None
+
     def has_magic_trailing_comma(
         self, closing: Leaf, ensure_removable: bool = False
     ) -> bool:
@@ -317,10 +326,18 @@ def has_magic_trailing_comma(
         - it's not from square bracket indexing
         (specifically, single-element square bracket indexing)
         """
+        if Preview.stop_some_unnecessary_wrapping_inside_brackets in self.mode:
+            leaf_to_check = self.get_last_non_comment_leaf()
+        elif len(self.leaves) > 0:
+            leaf_to_check = self.leaves[-1]
+        else:
+            return False
+
         if not (
             closing.type in CLOSING_BRACKETS
             and self.leaves
-            and self.leaves[-1].type == token.COMMA
+            and leaf_to_check is not None
+            and leaf_to_check.type == token.COMMA
         ):
             return False
 
@@ -411,7 +428,16 @@ def comments_after(self, leaf: Leaf) -> List[Leaf]:
 
     def remove_trailing_comma(self) -> None:
         """Remove the trailing comma and moves the comments attached to it."""
-        trailing_comma = self.leaves.pop()
+        if Preview.stop_some_unnecessary_wrapping_inside_brackets in self.mode:
+            # There might be comments after the magic trailing comma, so we must search
+            # backwards to find it.
+            for i in range(len(self.leaves) - 1, -1, -1):
+                if self.leaves[i].type == token.COMMA:
+                    trailing_comma = self.leaves.pop(i)
+                    break
+        else:
+            trailing_comma = self.leaves.pop()
+
         trailing_comma_comments = self.comments.pop(id(trailing_comma), [])
         self.comments.setdefault(id(self.leaves[-1]), []).extend(
             trailing_comma_comments
@@ -463,6 +489,7 @@ def clone(self) -> "Line":
             inside_brackets=self.inside_brackets,
             should_split_rhs=self.should_split_rhs,
             magic_trailing_comma=self.magic_trailing_comma,
+            bracket_after_magic_trailing_comma=self.bracket_after_magic_trailing_comma,
         )
 
     def __str__(self) -> str:

src/black/mode.py

@@ -185,6 +185,7 @@ class Preview(Enum):
     skip_magic_trailing_comma_in_subscript = auto()
     wrap_long_dict_values_in_parens = auto()
     wrap_multiple_context_managers_in_parens = auto()
+    stop_some_unnecessary_wrapping_inside_brackets = auto()
     dummy_implementations = auto()
     walrus_subscript = auto()
 

src/black/trans.py

@@ -2133,6 +2133,7 @@ def do_transform(
             inside_brackets=True,
             should_split_rhs=line.should_split_rhs,
             magic_trailing_comma=line.magic_trailing_comma,
+            bracket_after_magic_trailing_comma=line.bracket_after_magic_trailing_comma,
         )
         string_leaf = Leaf(token.STRING, string_value)
         insert_str_child(string_leaf)

tests/data/miscellaneous/skip_magic_trailing_comma.py

@@ -0,0 +1,5 @@
+def func(
+    x,
+    # this comment shouldn't be deleted
+):
+    pass

tests/data/miscellaneous/trailing_comma_and_comment.pyi

@@ -0,0 +1,5 @@
+def func(
+    x,
+    y,
+    # comment
+): ...

tests/data/preview/trailing_comma.py

@@ -7,19 +7,19 @@
 f = [
     arg1,
     arg2,
-    arg3, arg4
+    arg3, arg4, arg5, arg6, arg7, arg8, arg9, arg10, arg11, arg12, arg13, arg14, arg15, arg16, arg17, arg18
     # comment
 ]
 g = (
     arg1,
     arg2,
-    arg3, arg4
+    arg3, arg4, arg5, arg6, arg7, arg8, arg9, arg10, arg11, arg12, arg13, arg14, arg15, arg16, arg17, arg18
     # comment
 )
 h = {
     arg1,
     arg2,
-    arg3, arg4
+    arg3, arg4, arg5, arg6, arg7, arg8, arg9, arg10, arg11, arg12, arg13, arg14, arg15, arg16, arg17, arg18
     # comment
 }
 
@@ -37,19 +37,61 @@
     arg2,
     arg3,
     arg4,
+    arg5,
+    arg6,
+    arg7,
+    arg8,
+    arg9,
+    arg10,
+    arg11,
+    arg12,
+    arg13,
+    arg14,
+    arg15,
+    arg16,
+    arg17,
+    arg18,
     # comment
 ]
 g = (
     arg1,
     arg2,
     arg3,
     arg4,
+    arg5,
+    arg6,
+    arg7,
+    arg8,
+    arg9,
+    arg10,
+    arg11,
+    arg12,
+    arg13,
+    arg14,
+    arg15,
+    arg16,
+    arg17,
+    arg18,
     # comment
 )
 h = {
     arg1,
     arg2,
     arg3,
     arg4,
+    arg5,
+    arg6,
+    arg7,
+    arg8,
+    arg9,
+    arg10,
+    arg11,
+    arg12,
+    arg13,
+    arg14,
+    arg15,
+    arg16,
+    arg17,
+    arg18,
     # comment
 }

tests/data/preview/trailing_comma_with_comment.py

@@ -0,0 +1,6 @@
+li = [
+    1,
+    2,
+    3,
+    # comment
+]

tests/data/preview/wrapping_with_comments_in_brackets.py

@@ -0,0 +1,19 @@
+def get_requires_for_build_sdist(
+    # pylint: disable-next=unused-argument
+    config_settings: dict[str, str | list[str]] | None = None,
+) -> list[str]:
+    return ["pathspec", "pyproject_metadata"]
+
+
+(
+    a
+    and b
+    # comment
+    and c
+    and d
+)
+
+(
+    # comment
+    a and b and c and d
+)

tests/test_format.py

@@ -218,3 +218,24 @@ def test_type_comment_syntax_error() -> None:
     source, expected = read_data("type_comments", "type_comment_syntax_error")
     assert_format(source, expected)
     black.assert_equivalent(source, expected)
+
+
+def test_skip_magic_trailing_comma() -> None:
+    """
+    Test a case where the --skip-magic-trailing-comma option used
+    """
+    source, expected = read_data("miscellaneous", "skip_magic_trailing_comma")
+    mode = replace(DEFAULT_MODE, magic_trailing_comma=False, preview=True)
+    assert_format(source, expected, mode)
+
+
+def test_trailing_comma_and_comment_in_pyi() -> None:
+    source, expected = read_data("miscellaneous", "trailing_comma_and_comment.pyi")
+    mode = replace(
+        DEFAULT_MODE,
+        magic_trailing_comma=False,
+        preview=False,
+        line_length=130,
+        is_pyi=True,
+    )
+    assert_format(source, expected, mode)