Correctly handle trailing commas that are inside a line's leading non-nested parens

CHANGES.md

@@ -17,6 +17,8 @@
 - Enforce empty lines before classes and functions with sticky leading comments (#3302)
 - Implicitly concatenated strings used as function args are now wrapped inside
   parentheses (#3307)
+- Correctly handle trailing commas that are inside a line's leading non-nested parens
+  (#3370)
 
 ### Configuration
 

src/black/brackets.py

@@ -2,7 +2,7 @@
 
 import sys
 from dataclasses import dataclass, field
-from typing import Dict, Iterable, List, Optional, Tuple, Union
+from typing import Dict, Iterable, List, Optional, Sequence, Set, Tuple, Union
 
 if sys.version_info < (3, 8):
     from typing_extensions import Final
@@ -340,3 +340,35 @@ def max_delimiter_priority_in_atom(node: LN) -> Priority:
 
     except ValueError:
         return 0
+
+
+def get_leaves_inside_matching_brackets(leaves: Sequence[Leaf]) -> Set[LeafID]:
+    """Return leaves that are inside matching brackets.
+
+    The input `leaves` can have non-matching brackets at the head or tail parts.
+    Matching brackets are included.
+    """
+    try:
+        # Only track brackets from the first opening bracket to the last closing
+        # bracket.
+        start_index = next(
+            i for i, l in enumerate(leaves) if l.type in OPENING_BRACKETS
+        )
+        end_index = next(
+            len(leaves) - i
+            for i, l in enumerate(reversed(leaves))
+            if l.type in CLOSING_BRACKETS
+        )
+    except StopIteration:
+        return set()
+    ids = set()
+    depth = 0
+    for i in range(end_index, start_index - 1, -1):
+        leaf = leaves[i]
+        if leaf.type in CLOSING_BRACKETS:
+            depth += 1
+        if depth > 0:
+            ids.add(id(leaf))
+        if leaf.type in OPENING_BRACKETS:
+            depth -= 1
+    return ids

src/black/linegen.py

@@ -2,10 +2,16 @@
 Generating lines of code.
 """
 import sys
+from enum import Enum, auto
 from functools import partial, wraps
 from typing import Collection, Iterator, List, Optional, Set, Union, cast
 
-from black.brackets import COMMA_PRIORITY, DOT_PRIORITY, max_delimiter_priority_in_atom
+from black.brackets import (
+    COMMA_PRIORITY,
+    DOT_PRIORITY,
+    get_leaves_inside_matching_brackets,
+    max_delimiter_priority_in_atom,
+)
 from black.comments import FMT_OFF, generate_comments, list_comments
 from black.lines import (
     Line,
@@ -561,6 +567,12 @@ def _rhs(
         yield line
 
 
+class _BracketSplitComponent(Enum):
+    head = auto()
+    body = auto()
+    tail = auto()
+
+
 def left_hand_split(line: Line, _features: Collection[Feature] = ()) -> Iterator[Line]:
     """Split line into many lines, starting with the first matching bracket pair.
 
@@ -591,9 +603,15 @@ def left_hand_split(line: Line, _features: Collection[Feature] = ()) -> Iterator
     if not matching_bracket:
         raise CannotSplit("No brackets found")
 
-    head = bracket_split_build_line(head_leaves, line, matching_bracket)
-    body = bracket_split_build_line(body_leaves, line, matching_bracket, is_body=True)
-    tail = bracket_split_build_line(tail_leaves, line, matching_bracket)
+    head = bracket_split_build_line(
+        head_leaves, line, matching_bracket, component=_BracketSplitComponent.head
+    )
+    body = bracket_split_build_line(
+        body_leaves, line, matching_bracket, component=_BracketSplitComponent.body
+    )
+    tail = bracket_split_build_line(
+        tail_leaves, line, matching_bracket, component=_BracketSplitComponent.tail
+    )
     bracket_split_succeeded_or_raise(head, body, tail)
     for result in (head, body, tail):
         if result:
@@ -639,9 +657,15 @@ def right_hand_split(
     tail_leaves.reverse()
     body_leaves.reverse()
     head_leaves.reverse()
-    head = bracket_split_build_line(head_leaves, line, opening_bracket)
-    body = bracket_split_build_line(body_leaves, line, opening_bracket, is_body=True)
-    tail = bracket_split_build_line(tail_leaves, line, opening_bracket)
+    head = bracket_split_build_line(
+        head_leaves, line, opening_bracket, component=_BracketSplitComponent.head
+    )
+    body = bracket_split_build_line(
+        body_leaves, line, opening_bracket, component=_BracketSplitComponent.body
+    )
+    tail = bracket_split_build_line(
+        tail_leaves, line, opening_bracket, component=_BracketSplitComponent.tail
+    )
     bracket_split_succeeded_or_raise(head, body, tail)
     if (
         Feature.FORCE_OPTIONAL_PARENTHESES not in features
@@ -715,15 +739,23 @@ def bracket_split_succeeded_or_raise(head: Line, body: Line, tail: Line) -> None
 
 
 def bracket_split_build_line(
-    leaves: List[Leaf], original: Line, opening_bracket: Leaf, *, is_body: bool = False
+    leaves: List[Leaf],
+    original: Line,
+    opening_bracket: Leaf,
+    *,
+    component: _BracketSplitComponent,
 ) -> Line:
     """Return a new line with given `leaves` and respective comments from `original`.
 
-    If `is_body` is True, the result line is one-indented inside brackets and as such
-    has its first leaf's prefix normalized and a trailing comma added when expected.
+    If it's the head component, brackets will be tracked so trailing commas are
+    respected.
+
+    If it's the body component, the result line is one-indented inside brackets and as
+    such has its first leaf's prefix normalized and a trailing comma added when
+    expected.
     """
     result = Line(mode=original.mode, depth=original.depth)
-    if is_body:
+    if component is _BracketSplitComponent.body:
         result.inside_brackets = True
         result.depth += 1
         if leaves:
@@ -761,12 +793,24 @@ def bracket_split_build_line(
                         leaves.insert(i + 1, new_comma)
                     break
 
+    leaves_to_track: Set[LeafID] = set()
+    if (
+        Preview.handle_trailing_commas_in_head in original.mode
+        and component is _BracketSplitComponent.head
+    ):
+        leaves_to_track = get_leaves_inside_matching_brackets(leaves)
     # Populate the line
     for leaf in leaves:
-        result.append(leaf, preformatted=True)
+        result.append(
+            leaf,
+            preformatted=True,
+            track_bracket=id(leaf) in leaves_to_track,
+        )
         for comment_after in original.comments_after(leaf):
             result.append(comment_after, preformatted=True)
-    if is_body and should_split_line(result, opening_bracket):
+    if component is _BracketSplitComponent.body and should_split_line(
+        result, opening_bracket
+    ):
         result.should_split_rhs = True
     return result
 

src/black/lines.py

@@ -53,7 +53,9 @@ class Line:
     should_split_rhs: bool = False
     magic_trailing_comma: Optional[Leaf] = None
 
-    def append(self, leaf: Leaf, preformatted: bool = False) -> None:
+    def append(
+        self, leaf: Leaf, preformatted: bool = False, track_bracket: bool = False
+    ) -> None:
         """Add a new `leaf` to the end of the line.
 
         Unless `preformatted` is True, the `leaf` will receive a new consistent
@@ -75,7 +77,7 @@ def append(self, leaf: Leaf, preformatted: bool = False) -> None:
             leaf.prefix += whitespace(
                 leaf, complex_subscript=self.is_complex_subscript(leaf)
             )
-        if self.inside_brackets or not preformatted:
+        if self.inside_brackets or not preformatted or track_bracket:
             self.bracket_tracker.mark(leaf)
             if self.mode.magic_trailing_comma:
                 if self.has_magic_trailing_comma(leaf):

src/black/mode.py

@@ -151,6 +151,7 @@ class Preview(Enum):
 
     annotation_parens = auto()
     empty_lines_before_class_or_def_with_leading_comments = auto()
+    handle_trailing_commas_in_head = auto()
     long_docstring_quotes_on_newline = auto()
     normalize_docstring_quotes_and_prefixes_properly = auto()
     one_element_subscript = auto()

tests/data/preview/skip_magic_trailing_comma.py

@@ -15,6 +15,37 @@
 # Except single element tuples
 small_tuple = (1,)
 
+# Trailing commas in multiple chained non-nested parens.
+zero(
+    one,
+).two(
+    three,
+).four(
+    five,
+)
+
+func1(arg1).func2(arg2,).func3(arg3).func4(arg4,).func5(arg5)
+
+(
+    a,
+    b,
+    c,
+    d,
+) = func1(
+    arg1
+) and func2(arg2)
+
+func(
+    argument1,
+    (
+        one,
+        two,
+    ),
+    argument4,
+    argument5,
+    argument6,
+)
+
 # output
 # We should not remove the trailing comma in a single-element subscript.
 a: tuple[int,]
@@ -32,3 +63,12 @@
 
 # Except single element tuples
 small_tuple = (1,)
+
+# Trailing commas in multiple chained non-nested parens.
+zero(one).two(three).four(five)
+
+func1(arg1).func2(arg2).func3(arg3).func4(arg4).func5(arg5)
+
+(a, b, c, d) = func1(arg1) and func2(arg2)
+
+func(argument1, (one, two), argument4, argument5, argument6)

tests/data/preview/trailing_commas_in_leading_parts.py

@@ -0,0 +1,74 @@
+zero(one,).two(three,).four(five,)
+
+func1(arg1).func2(arg2,).func3(arg3).func4(arg4,).func5(arg5)
+
+# Inner one-element tuple shouldn't explode
+func1(arg1).func2(arg1, (one_tuple,)).func3(arg3)
+
+(a, b, c, d,) = func1(arg1) and func2(arg2)
+
+
+# Example from https://github.com/psf/black/issues/3229
+def refresh_token(self, device_family, refresh_token, api_key):
+    return self.orchestration.refresh_token(
+        data={
+            "refreshToken": refresh_token,
+        },
+        api_key=api_key,
+    )["extensions"]["sdk"]["token"]
+
+
+# Edge case where a bug in a working-in-progress version of
+# https://github.com/psf/black/pull/3370 causes an infinite recursion.
+assert (
+    long_module.long_class.long_func().another_func()
+    == long_module.long_class.long_func()["some_key"].another_func(arg1)
+)
+
+
+# output
+
+
+zero(
+    one,
+).two(
+    three,
+).four(
+    five,
+)
+
+func1(arg1).func2(
+    arg2,
+).func3(arg3).func4(
+    arg4,
+).func5(arg5)
+
+# Inner one-element tuple shouldn't explode
+func1(arg1).func2(arg1, (one_tuple,)).func3(arg3)
+
+(
+    a,
+    b,
+    c,
+    d,
+) = func1(
+    arg1
+) and func2(arg2)
+
+
+# Example from https://github.com/psf/black/issues/3229
+def refresh_token(self, device_family, refresh_token, api_key):
+    return self.orchestration.refresh_token(
+        data={
+            "refreshToken": refresh_token,
+        },
+        api_key=api_key,
+    )["extensions"]["sdk"]["token"]
+
+
+# Edge case where a bug in a working-in-progress version of
+# https://github.com/psf/black/pull/3370 causes an infinite recursion.
+assert (
+    long_module.long_class.long_func().another_func()
+    == long_module.long_class.long_func()["some_key"].another_func(arg1)
+)

tests/data/simple_cases/function_trailing_comma.py

@@ -49,6 +49,17 @@ def func() -> ((also_super_long_type_annotation_that_may_cause_an_AST_related_cr
 ):
     pass
 
+
+# Make sure inner one-element tuple won't explode
+some_module.some_function(
+    argument1, (one_element_tuple,), argument4, argument5, argument6
+)
+
+# Inner trailing comma causes outer to explode
+some_module.some_function(
+    argument1, (one, two,), argument4, argument5, argument6
+)
+
 # output
 
 def f(
@@ -151,3 +162,21 @@ def func() -> (
     )
 ):
     pass
+
+
+# Make sure inner one-element tuple won't explode
+some_module.some_function(
+    argument1, (one_element_tuple,), argument4, argument5, argument6
+)
+
+# Inner trailing comma causes outer to explode
+some_module.some_function(
+    argument1,
+    (
+        one,
+        two,
+    ),
+    argument4,
+    argument5,
+    argument6,
+)