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e455a5075392e6405b6c2472c371bbce36a7d1d5
[etc/vim.git] / src / black / lines.py
1 from dataclasses import dataclass, field
2 import itertools
3 import sys
4 from typing import (
5     Callable,
6     Dict,
7     Iterator,
8     List,
9     Optional,
10     Sequence,
11     Tuple,
12     TypeVar,
13     cast,
14 )
15
16 from blib2to3.pytree import Node, Leaf
17 from blib2to3.pgen2 import token
18
19 from black.brackets import BracketTracker, DOT_PRIORITY
20 from black.mode import Mode, Preview
21 from black.nodes import STANDALONE_COMMENT, TEST_DESCENDANTS
22 from black.nodes import BRACKETS, OPENING_BRACKETS, CLOSING_BRACKETS
23 from black.nodes import syms, whitespace, replace_child, child_towards
24 from black.nodes import is_multiline_string, is_import, is_type_comment
25 from black.nodes import is_one_sequence_between
26
27 # types
28 T = TypeVar("T")
29 Index = int
30 LeafID = int
31
32
33 @dataclass
34 class Line:
35     """Holds leaves and comments. Can be printed with `str(line)`."""
36
37     mode: Mode
38     depth: int = 0
39     leaves: List[Leaf] = field(default_factory=list)
40     # keys ordered like `leaves`
41     comments: Dict[LeafID, List[Leaf]] = field(default_factory=dict)
42     bracket_tracker: BracketTracker = field(default_factory=BracketTracker)
43     inside_brackets: bool = False
44     should_split_rhs: bool = False
45     magic_trailing_comma: Optional[Leaf] = None
46
47     def append(self, leaf: Leaf, preformatted: bool = False) -> None:
48         """Add a new `leaf` to the end of the line.
49
50         Unless `preformatted` is True, the `leaf` will receive a new consistent
51         whitespace prefix and metadata applied by :class:`BracketTracker`.
52         Trailing commas are maybe removed, unpacked for loop variables are
53         demoted from being delimiters.
54
55         Inline comments are put aside.
56         """
57         has_value = leaf.type in BRACKETS or bool(leaf.value.strip())
58         if not has_value:
59             return
60
61         if token.COLON == leaf.type and self.is_class_paren_empty:
62             del self.leaves[-2:]
63         if self.leaves and not preformatted:
64             # Note: at this point leaf.prefix should be empty except for
65             # imports, for which we only preserve newlines.
66             leaf.prefix += whitespace(
67                 leaf, complex_subscript=self.is_complex_subscript(leaf)
68             )
69         if self.inside_brackets or not preformatted:
70             self.bracket_tracker.mark(leaf)
71             if self.mode.magic_trailing_comma:
72                 if self.has_magic_trailing_comma(leaf):
73                     self.magic_trailing_comma = leaf
74             elif self.has_magic_trailing_comma(leaf, ensure_removable=True):
75                 self.remove_trailing_comma()
76         if not self.append_comment(leaf):
77             self.leaves.append(leaf)
78
79     def append_safe(self, leaf: Leaf, preformatted: bool = False) -> None:
80         """Like :func:`append()` but disallow invalid standalone comment structure.
81
82         Raises ValueError when any `leaf` is appended after a standalone comment
83         or when a standalone comment is not the first leaf on the line.
84         """
85         if self.bracket_tracker.depth == 0:
86             if self.is_comment:
87                 raise ValueError("cannot append to standalone comments")
88
89             if self.leaves and leaf.type == STANDALONE_COMMENT:
90                 raise ValueError(
91                     "cannot append standalone comments to a populated line"
92                 )
93
94         self.append(leaf, preformatted=preformatted)
95
96     @property
97     def is_comment(self) -> bool:
98         """Is this line a standalone comment?"""
99         return len(self.leaves) == 1 and self.leaves[0].type == STANDALONE_COMMENT
100
101     @property
102     def is_decorator(self) -> bool:
103         """Is this line a decorator?"""
104         return bool(self) and self.leaves[0].type == token.AT
105
106     @property
107     def is_import(self) -> bool:
108         """Is this an import line?"""
109         return bool(self) and is_import(self.leaves[0])
110
111     @property
112     def is_class(self) -> bool:
113         """Is this line a class definition?"""
114         return (
115             bool(self)
116             and self.leaves[0].type == token.NAME
117             and self.leaves[0].value == "class"
118         )
119
120     @property
121     def is_stub_class(self) -> bool:
122         """Is this line a class definition with a body consisting only of "..."?"""
123         return self.is_class and self.leaves[-3:] == [
124             Leaf(token.DOT, ".") for _ in range(3)
125         ]
126
127     @property
128     def is_def(self) -> bool:
129         """Is this a function definition? (Also returns True for async defs.)"""
130         try:
131             first_leaf = self.leaves[0]
132         except IndexError:
133             return False
134
135         try:
136             second_leaf: Optional[Leaf] = self.leaves[1]
137         except IndexError:
138             second_leaf = None
139         return (first_leaf.type == token.NAME and first_leaf.value == "def") or (
140             first_leaf.type == token.ASYNC
141             and second_leaf is not None
142             and second_leaf.type == token.NAME
143             and second_leaf.value == "def"
144         )
145
146     @property
147     def is_class_paren_empty(self) -> bool:
148         """Is this a class with no base classes but using parentheses?
149
150         Those are unnecessary and should be removed.
151         """
152         return (
153             bool(self)
154             and len(self.leaves) == 4
155             and self.is_class
156             and self.leaves[2].type == token.LPAR
157             and self.leaves[2].value == "("
158             and self.leaves[3].type == token.RPAR
159             and self.leaves[3].value == ")"
160         )
161
162     @property
163     def is_triple_quoted_string(self) -> bool:
164         """Is the line a triple quoted string?"""
165         return (
166             bool(self)
167             and self.leaves[0].type == token.STRING
168             and self.leaves[0].value.startswith(('"""', "'''"))
169         )
170
171     def contains_standalone_comments(self, depth_limit: int = sys.maxsize) -> bool:
172         """If so, needs to be split before emitting."""
173         for leaf in self.leaves:
174             if leaf.type == STANDALONE_COMMENT and leaf.bracket_depth <= depth_limit:
175                 return True
176
177         return False
178
179     def contains_uncollapsable_type_comments(self) -> bool:
180         ignored_ids = set()
181         try:
182             last_leaf = self.leaves[-1]
183             ignored_ids.add(id(last_leaf))
184             if last_leaf.type == token.COMMA or (
185                 last_leaf.type == token.RPAR and not last_leaf.value
186             ):
187                 # When trailing commas or optional parens are inserted by Black for
188                 # consistency, comments after the previous last element are not moved
189                 # (they don't have to, rendering will still be correct).  So we ignore
190                 # trailing commas and invisible.
191                 last_leaf = self.leaves[-2]
192                 ignored_ids.add(id(last_leaf))
193         except IndexError:
194             return False
195
196         # A type comment is uncollapsable if it is attached to a leaf
197         # that isn't at the end of the line (since that could cause it
198         # to get associated to a different argument) or if there are
199         # comments before it (since that could cause it to get hidden
200         # behind a comment.
201         comment_seen = False
202         for leaf_id, comments in self.comments.items():
203             for comment in comments:
204                 if is_type_comment(comment):
205                     if comment_seen or (
206                         not is_type_comment(comment, " ignore")
207                         and leaf_id not in ignored_ids
208                     ):
209                         return True
210
211                 comment_seen = True
212
213         return False
214
215     def contains_unsplittable_type_ignore(self) -> bool:
216         if not self.leaves:
217             return False
218
219         # If a 'type: ignore' is attached to the end of a line, we
220         # can't split the line, because we can't know which of the
221         # subexpressions the ignore was meant to apply to.
222         #
223         # We only want this to apply to actual physical lines from the
224         # original source, though: we don't want the presence of a
225         # 'type: ignore' at the end of a multiline expression to
226         # justify pushing it all onto one line. Thus we
227         # (unfortunately) need to check the actual source lines and
228         # only report an unsplittable 'type: ignore' if this line was
229         # one line in the original code.
230
231         # Grab the first and last line numbers, skipping generated leaves
232         first_line = next((leaf.lineno for leaf in self.leaves if leaf.lineno != 0), 0)
233         last_line = next(
234             (leaf.lineno for leaf in reversed(self.leaves) if leaf.lineno != 0), 0
235         )
236
237         if first_line == last_line:
238             # We look at the last two leaves since a comma or an
239             # invisible paren could have been added at the end of the
240             # line.
241             for node in self.leaves[-2:]:
242                 for comment in self.comments.get(id(node), []):
243                     if is_type_comment(comment, " ignore"):
244                         return True
245
246         return False
247
248     def contains_multiline_strings(self) -> bool:
249         return any(is_multiline_string(leaf) for leaf in self.leaves)
250
251     def has_magic_trailing_comma(
252         self, closing: Leaf, ensure_removable: bool = False
253     ) -> bool:
254         """Return True if we have a magic trailing comma, that is when:
255         - there's a trailing comma here
256         - it's not a one-tuple
257         - it's not a single-element subscript
258         Additionally, if ensure_removable:
259         - it's not from square bracket indexing
260         """
261         if not (
262             closing.type in CLOSING_BRACKETS
263             and self.leaves
264             and self.leaves[-1].type == token.COMMA
265         ):
266             return False
267
268         if closing.type == token.RBRACE:
269             return True
270
271         if closing.type == token.RSQB:
272             if (
273                 Preview.one_element_subscript in self.mode
274                 and closing.parent
275                 and closing.parent.type == syms.trailer
276                 and closing.opening_bracket
277                 and is_one_sequence_between(
278                     closing.opening_bracket,
279                     closing,
280                     self.leaves,
281                     brackets=(token.LSQB, token.RSQB),
282                 )
283             ):
284                 return False
285
286             if not ensure_removable:
287                 return True
288             comma = self.leaves[-1]
289             return bool(comma.parent and comma.parent.type == syms.listmaker)
290
291         if self.is_import:
292             return True
293
294         if closing.opening_bracket is not None and not is_one_sequence_between(
295             closing.opening_bracket, closing, self.leaves
296         ):
297             return True
298
299         return False
300
301     def append_comment(self, comment: Leaf) -> bool:
302         """Add an inline or standalone comment to the line."""
303         if (
304             comment.type == STANDALONE_COMMENT
305             and self.bracket_tracker.any_open_brackets()
306         ):
307             comment.prefix = ""
308             return False
309
310         if comment.type != token.COMMENT:
311             return False
312
313         if not self.leaves:
314             comment.type = STANDALONE_COMMENT
315             comment.prefix = ""
316             return False
317
318         last_leaf = self.leaves[-1]
319         if (
320             last_leaf.type == token.RPAR
321             and not last_leaf.value
322             and last_leaf.parent
323             and len(list(last_leaf.parent.leaves())) <= 3
324             and not is_type_comment(comment)
325         ):
326             # Comments on an optional parens wrapping a single leaf should belong to
327             # the wrapped node except if it's a type comment. Pinning the comment like
328             # this avoids unstable formatting caused by comment migration.
329             if len(self.leaves) < 2:
330                 comment.type = STANDALONE_COMMENT
331                 comment.prefix = ""
332                 return False
333
334             last_leaf = self.leaves[-2]
335         self.comments.setdefault(id(last_leaf), []).append(comment)
336         return True
337
338     def comments_after(self, leaf: Leaf) -> List[Leaf]:
339         """Generate comments that should appear directly after `leaf`."""
340         return self.comments.get(id(leaf), [])
341
342     def remove_trailing_comma(self) -> None:
343         """Remove the trailing comma and moves the comments attached to it."""
344         trailing_comma = self.leaves.pop()
345         trailing_comma_comments = self.comments.pop(id(trailing_comma), [])
346         self.comments.setdefault(id(self.leaves[-1]), []).extend(
347             trailing_comma_comments
348         )
349
350     def is_complex_subscript(self, leaf: Leaf) -> bool:
351         """Return True iff `leaf` is part of a slice with non-trivial exprs."""
352         open_lsqb = self.bracket_tracker.get_open_lsqb()
353         if open_lsqb is None:
354             return False
355
356         subscript_start = open_lsqb.next_sibling
357
358         if isinstance(subscript_start, Node):
359             if subscript_start.type == syms.listmaker:
360                 return False
361
362             if subscript_start.type == syms.subscriptlist:
363                 subscript_start = child_towards(subscript_start, leaf)
364         return subscript_start is not None and any(
365             n.type in TEST_DESCENDANTS for n in subscript_start.pre_order()
366         )
367
368     def enumerate_with_length(
369         self, reversed: bool = False
370     ) -> Iterator[Tuple[Index, Leaf, int]]:
371         """Return an enumeration of leaves with their length.
372
373         Stops prematurely on multiline strings and standalone comments.
374         """
375         op = cast(
376             Callable[[Sequence[Leaf]], Iterator[Tuple[Index, Leaf]]],
377             enumerate_reversed if reversed else enumerate,
378         )
379         for index, leaf in op(self.leaves):
380             length = len(leaf.prefix) + len(leaf.value)
381             if "\n" in leaf.value:
382                 return  # Multiline strings, we can't continue.
383
384             for comment in self.comments_after(leaf):
385                 length += len(comment.value)
386
387             yield index, leaf, length
388
389     def clone(self) -> "Line":
390         return Line(
391             mode=self.mode,
392             depth=self.depth,
393             inside_brackets=self.inside_brackets,
394             should_split_rhs=self.should_split_rhs,
395             magic_trailing_comma=self.magic_trailing_comma,
396         )
397
398     def __str__(self) -> str:
399         """Render the line."""
400         if not self:
401             return "\n"
402
403         indent = "    " * self.depth
404         leaves = iter(self.leaves)
405         first = next(leaves)
406         res = f"{first.prefix}{indent}{first.value}"
407         for leaf in leaves:
408             res += str(leaf)
409         for comment in itertools.chain.from_iterable(self.comments.values()):
410             res += str(comment)
411
412         return res + "\n"
413
414     def __bool__(self) -> bool:
415         """Return True if the line has leaves or comments."""
416         return bool(self.leaves or self.comments)
417
418
419 @dataclass
420 class EmptyLineTracker:
421     """Provides a stateful method that returns the number of potential extra
422     empty lines needed before and after the currently processed line.
423
424     Note: this tracker works on lines that haven't been split yet.  It assumes
425     the prefix of the first leaf consists of optional newlines.  Those newlines
426     are consumed by `maybe_empty_lines()` and included in the computation.
427     """
428
429     is_pyi: bool = False
430     previous_line: Optional[Line] = None
431     previous_after: int = 0
432     previous_defs: List[int] = field(default_factory=list)
433
434     def maybe_empty_lines(self, current_line: Line) -> Tuple[int, int]:
435         """Return the number of extra empty lines before and after the `current_line`.
436
437         This is for separating `def`, `async def` and `class` with extra empty
438         lines (two on module-level).
439         """
440         before, after = self._maybe_empty_lines(current_line)
441         before = (
442             # Black should not insert empty lines at the beginning
443             # of the file
444             0
445             if self.previous_line is None
446             else before - self.previous_after
447         )
448         self.previous_after = after
449         self.previous_line = current_line
450         return before, after
451
452     def _maybe_empty_lines(self, current_line: Line) -> Tuple[int, int]:
453         max_allowed = 1
454         if current_line.depth == 0:
455             max_allowed = 1 if self.is_pyi else 2
456         if current_line.leaves:
457             # Consume the first leaf's extra newlines.
458             first_leaf = current_line.leaves[0]
459             before = first_leaf.prefix.count("\n")
460             before = min(before, max_allowed)
461             first_leaf.prefix = ""
462         else:
463             before = 0
464         depth = current_line.depth
465         while self.previous_defs and self.previous_defs[-1] >= depth:
466             if self.is_pyi:
467                 assert self.previous_line is not None
468                 if depth and not current_line.is_def and self.previous_line.is_def:
469                     # Empty lines between attributes and methods should be preserved.
470                     before = min(1, before)
471                 elif depth:
472                     before = 0
473                 else:
474                     before = 1
475             else:
476                 if depth:
477                     before = 1
478                 elif (
479                     not depth
480                     and self.previous_defs[-1]
481                     and current_line.leaves[-1].type == token.COLON
482                     and (
483                         current_line.leaves[0].value
484                         not in ("with", "try", "for", "while", "if", "match")
485                     )
486                 ):
487                     # We shouldn't add two newlines between an indented function and
488                     # a dependent non-indented clause. This is to avoid issues with
489                     # conditional function definitions that are technically top-level
490                     # and therefore get two trailing newlines, but look weird and
491                     # inconsistent when they're followed by elif, else, etc. This is
492                     # worse because these functions only get *one* preceding newline
493                     # already.
494                     before = 1
495                 else:
496                     before = 2
497             self.previous_defs.pop()
498         if current_line.is_decorator or current_line.is_def or current_line.is_class:
499             return self._maybe_empty_lines_for_class_or_def(current_line, before)
500
501         if (
502             self.previous_line
503             and self.previous_line.is_import
504             and not current_line.is_import
505             and depth == self.previous_line.depth
506         ):
507             return (before or 1), 0
508
509         if (
510             self.previous_line
511             and self.previous_line.is_class
512             and current_line.is_triple_quoted_string
513         ):
514             return before, 1
515
516         return before, 0
517
518     def _maybe_empty_lines_for_class_or_def(
519         self, current_line: Line, before: int
520     ) -> Tuple[int, int]:
521         if not current_line.is_decorator:
522             self.previous_defs.append(current_line.depth)
523         if self.previous_line is None:
524             # Don't insert empty lines before the first line in the file.
525             return 0, 0
526
527         if self.previous_line.is_decorator:
528             if self.is_pyi and current_line.is_stub_class:
529                 # Insert an empty line after a decorated stub class
530                 return 0, 1
531
532             return 0, 0
533
534         if self.previous_line.depth < current_line.depth and (
535             self.previous_line.is_class or self.previous_line.is_def
536         ):
537             return 0, 0
538
539         if (
540             self.previous_line.is_comment
541             and self.previous_line.depth == current_line.depth
542             and before == 0
543         ):
544             return 0, 0
545
546         if self.is_pyi:
547             if current_line.is_class or self.previous_line.is_class:
548                 if self.previous_line.depth < current_line.depth:
549                     newlines = 0
550                 elif self.previous_line.depth > current_line.depth:
551                     newlines = 1
552                 elif current_line.is_stub_class and self.previous_line.is_stub_class:
553                     # No blank line between classes with an empty body
554                     newlines = 0
555                 else:
556                     newlines = 1
557             elif (
558                 current_line.is_def or current_line.is_decorator
559             ) and not self.previous_line.is_def:
560                 if current_line.depth:
561                     # In classes empty lines between attributes and methods should
562                     # be preserved.
563                     newlines = min(1, before)
564                 else:
565                     # Blank line between a block of functions (maybe with preceding
566                     # decorators) and a block of non-functions
567                     newlines = 1
568             elif self.previous_line.depth > current_line.depth:
569                 newlines = 1
570             else:
571                 newlines = 0
572         else:
573             newlines = 1 if current_line.depth else 2
574         return newlines, 0
575
576
577 def enumerate_reversed(sequence: Sequence[T]) -> Iterator[Tuple[Index, T]]:
578     """Like `reversed(enumerate(sequence))` if that were possible."""
579     index = len(sequence) - 1
580     for element in reversed(sequence):
581         yield (index, element)
582         index -= 1
583
584
585 def append_leaves(
586     new_line: Line, old_line: Line, leaves: List[Leaf], preformatted: bool = False
587 ) -> None:
588     """
589     Append leaves (taken from @old_line) to @new_line, making sure to fix the
590     underlying Node structure where appropriate.
591
592     All of the leaves in @leaves are duplicated. The duplicates are then
593     appended to @new_line and used to replace their originals in the underlying
594     Node structure. Any comments attached to the old leaves are reattached to
595     the new leaves.
596
597     Pre-conditions:
598         set(@leaves) is a subset of set(@old_line.leaves).
599     """
600     for old_leaf in leaves:
601         new_leaf = Leaf(old_leaf.type, old_leaf.value)
602         replace_child(old_leaf, new_leaf)
603         new_line.append(new_leaf, preformatted=preformatted)
604
605         for comment_leaf in old_line.comments_after(old_leaf):
606             new_line.append(comment_leaf, preformatted=True)
607
608
609 def is_line_short_enough(line: Line, *, line_length: int, line_str: str = "") -> bool:
610     """Return True if `line` is no longer than `line_length`.
611
612     Uses the provided `line_str` rendering, if any, otherwise computes a new one.
613     """
614     if not line_str:
615         line_str = line_to_string(line)
616     return (
617         len(line_str) <= line_length
618         and "\n" not in line_str  # multiline strings
619         and not line.contains_standalone_comments()
620     )
621
622
623 def can_be_split(line: Line) -> bool:
624     """Return False if the line cannot be split *for sure*.
625
626     This is not an exhaustive search but a cheap heuristic that we can use to
627     avoid some unfortunate formattings (mostly around wrapping unsplittable code
628     in unnecessary parentheses).
629     """
630     leaves = line.leaves
631     if len(leaves) < 2:
632         return False
633
634     if leaves[0].type == token.STRING and leaves[1].type == token.DOT:
635         call_count = 0
636         dot_count = 0
637         next = leaves[-1]
638         for leaf in leaves[-2::-1]:
639             if leaf.type in OPENING_BRACKETS:
640                 if next.type not in CLOSING_BRACKETS:
641                     return False
642
643                 call_count += 1
644             elif leaf.type == token.DOT:
645                 dot_count += 1
646             elif leaf.type == token.NAME:
647                 if not (next.type == token.DOT or next.type in OPENING_BRACKETS):
648                     return False
649
650             elif leaf.type not in CLOSING_BRACKETS:
651                 return False
652
653             if dot_count > 1 and call_count > 1:
654                 return False
655
656     return True
657
658
659 def can_omit_invisible_parens(
660     line: Line,
661     line_length: int,
662 ) -> bool:
663     """Does `line` have a shape safe to reformat without optional parens around it?
664
665     Returns True for only a subset of potentially nice looking formattings but
666     the point is to not return false positives that end up producing lines that
667     are too long.
668     """
669     bt = line.bracket_tracker
670     if not bt.delimiters:
671         # Without delimiters the optional parentheses are useless.
672         return True
673
674     max_priority = bt.max_delimiter_priority()
675     if bt.delimiter_count_with_priority(max_priority) > 1:
676         # With more than one delimiter of a kind the optional parentheses read better.
677         return False
678
679     if max_priority == DOT_PRIORITY:
680         # A single stranded method call doesn't require optional parentheses.
681         return True
682
683     assert len(line.leaves) >= 2, "Stranded delimiter"
684
685     # With a single delimiter, omit if the expression starts or ends with
686     # a bracket.
687     first = line.leaves[0]
688     second = line.leaves[1]
689     if first.type in OPENING_BRACKETS and second.type not in CLOSING_BRACKETS:
690         if _can_omit_opening_paren(line, first=first, line_length=line_length):
691             return True
692
693         # Note: we are not returning False here because a line might have *both*
694         # a leading opening bracket and a trailing closing bracket.  If the
695         # opening bracket doesn't match our rule, maybe the closing will.
696
697     penultimate = line.leaves[-2]
698     last = line.leaves[-1]
699
700     if (
701         last.type == token.RPAR
702         or last.type == token.RBRACE
703         or (
704             # don't use indexing for omitting optional parentheses;
705             # it looks weird
706             last.type == token.RSQB
707             and last.parent
708             and last.parent.type != syms.trailer
709         )
710     ):
711         if penultimate.type in OPENING_BRACKETS:
712             # Empty brackets don't help.
713             return False
714
715         if is_multiline_string(first):
716             # Additional wrapping of a multiline string in this situation is
717             # unnecessary.
718             return True
719
720         if _can_omit_closing_paren(line, last=last, line_length=line_length):
721             return True
722
723     return False
724
725
726 def _can_omit_opening_paren(line: Line, *, first: Leaf, line_length: int) -> bool:
727     """See `can_omit_invisible_parens`."""
728     remainder = False
729     length = 4 * line.depth
730     _index = -1
731     for _index, leaf, leaf_length in line.enumerate_with_length():
732         if leaf.type in CLOSING_BRACKETS and leaf.opening_bracket is first:
733             remainder = True
734         if remainder:
735             length += leaf_length
736             if length > line_length:
737                 break
738
739             if leaf.type in OPENING_BRACKETS:
740                 # There are brackets we can further split on.
741                 remainder = False
742
743     else:
744         # checked the entire string and line length wasn't exceeded
745         if len(line.leaves) == _index + 1:
746             return True
747
748     return False
749
750
751 def _can_omit_closing_paren(line: Line, *, last: Leaf, line_length: int) -> bool:
752     """See `can_omit_invisible_parens`."""
753     length = 4 * line.depth
754     seen_other_brackets = False
755     for _index, leaf, leaf_length in line.enumerate_with_length():
756         length += leaf_length
757         if leaf is last.opening_bracket:
758             if seen_other_brackets or length <= line_length:
759                 return True
760
761         elif leaf.type in OPENING_BRACKETS:
762             # There are brackets we can further split on.
763             seen_other_brackets = True
764
765     return False
766
767
768 def line_to_string(line: Line) -> str:
769     """Returns the string representation of @line.
770
771     WARNING: This is known to be computationally expensive.
772     """
773     return str(line).strip("\n")