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Docs: clarify fmt:on/off requirements (#2985) (#3048)
[etc/vim.git] / src / black / __init__.py
1 import asyncio
2 from json.decoder import JSONDecodeError
3 import json
4 from contextlib import contextmanager
5 from datetime import datetime
6 from enum import Enum
7 import io
8 from multiprocessing import Manager, freeze_support
9 import os
10 from pathlib import Path
11 from pathspec.patterns.gitwildmatch import GitWildMatchPatternError
12 import platform
13 import re
14 import signal
15 import sys
16 import tokenize
17 import traceback
18 from typing import (
19     TYPE_CHECKING,
20     Any,
21     Dict,
22     Generator,
23     Iterator,
24     List,
25     MutableMapping,
26     Optional,
27     Pattern,
28     Sequence,
29     Set,
30     Sized,
31     Tuple,
32     Union,
33 )
34
35 import click
36 from click.core import ParameterSource
37 from dataclasses import replace
38 from mypy_extensions import mypyc_attr
39
40 from black.const import DEFAULT_LINE_LENGTH, DEFAULT_INCLUDES, DEFAULT_EXCLUDES
41 from black.const import STDIN_PLACEHOLDER
42 from black.nodes import STARS, syms, is_simple_decorator_expression
43 from black.nodes import is_string_token
44 from black.lines import Line, EmptyLineTracker
45 from black.linegen import transform_line, LineGenerator, LN
46 from black.comments import normalize_fmt_off
47 from black.mode import FUTURE_FLAG_TO_FEATURE, Mode, TargetVersion
48 from black.mode import Feature, supports_feature, VERSION_TO_FEATURES
49 from black.cache import read_cache, write_cache, get_cache_info, filter_cached, Cache
50 from black.concurrency import cancel, shutdown, maybe_install_uvloop
51 from black.output import dump_to_file, ipynb_diff, diff, color_diff, out, err
52 from black.report import Report, Changed, NothingChanged
53 from black.files import (
54     find_project_root,
55     find_pyproject_toml,
56     parse_pyproject_toml,
57     find_user_pyproject_toml,
58 )
59 from black.files import gen_python_files, get_gitignore, normalize_path_maybe_ignore
60 from black.files import wrap_stream_for_windows
61 from black.parsing import InvalidInput  # noqa F401
62 from black.parsing import lib2to3_parse, parse_ast, stringify_ast
63 from black.handle_ipynb_magics import (
64     mask_cell,
65     unmask_cell,
66     remove_trailing_semicolon,
67     put_trailing_semicolon_back,
68     TRANSFORMED_MAGICS,
69     PYTHON_CELL_MAGICS,
70     jupyter_dependencies_are_installed,
71 )
72
73
74 # lib2to3 fork
75 from blib2to3.pytree import Node, Leaf
76 from blib2to3.pgen2 import token
77
78 from _black_version import version as __version__
79
80 if TYPE_CHECKING:
81     from concurrent.futures import Executor
82
83 COMPILED = Path(__file__).suffix in (".pyd", ".so")
84
85 # types
86 FileContent = str
87 Encoding = str
88 NewLine = str
89
90
91 class WriteBack(Enum):
92     NO = 0
93     YES = 1
94     DIFF = 2
95     CHECK = 3
96     COLOR_DIFF = 4
97
98     @classmethod
99     def from_configuration(
100         cls, *, check: bool, diff: bool, color: bool = False
101     ) -> "WriteBack":
102         if check and not diff:
103             return cls.CHECK
104
105         if diff and color:
106             return cls.COLOR_DIFF
107
108         return cls.DIFF if diff else cls.YES
109
110
111 # Legacy name, left for integrations.
112 FileMode = Mode
113
114 DEFAULT_WORKERS = os.cpu_count()
115
116
117 def read_pyproject_toml(
118     ctx: click.Context, param: click.Parameter, value: Optional[str]
119 ) -> Optional[str]:
120     """Inject Black configuration from "pyproject.toml" into defaults in `ctx`.
121
122     Returns the path to a successfully found and read configuration file, None
123     otherwise.
124     """
125     if not value:
126         value = find_pyproject_toml(ctx.params.get("src", ()))
127         if value is None:
128             return None
129
130     try:
131         config = parse_pyproject_toml(value)
132     except (OSError, ValueError) as e:
133         raise click.FileError(
134             filename=value, hint=f"Error reading configuration file: {e}"
135         ) from None
136
137     if not config:
138         return None
139     else:
140         # Sanitize the values to be Click friendly. For more information please see:
141         # https://github.com/psf/black/issues/1458
142         # https://github.com/pallets/click/issues/1567
143         config = {
144             k: str(v) if not isinstance(v, (list, dict)) else v
145             for k, v in config.items()
146         }
147
148     target_version = config.get("target_version")
149     if target_version is not None and not isinstance(target_version, list):
150         raise click.BadOptionUsage(
151             "target-version", "Config key target-version must be a list"
152         )
153
154     default_map: Dict[str, Any] = {}
155     if ctx.default_map:
156         default_map.update(ctx.default_map)
157     default_map.update(config)
158
159     ctx.default_map = default_map
160     return value
161
162
163 def target_version_option_callback(
164     c: click.Context, p: Union[click.Option, click.Parameter], v: Tuple[str, ...]
165 ) -> List[TargetVersion]:
166     """Compute the target versions from a --target-version flag.
167
168     This is its own function because mypy couldn't infer the type correctly
169     when it was a lambda, causing mypyc trouble.
170     """
171     return [TargetVersion[val.upper()] for val in v]
172
173
174 def re_compile_maybe_verbose(regex: str) -> Pattern[str]:
175     """Compile a regular expression string in `regex`.
176
177     If it contains newlines, use verbose mode.
178     """
179     if "\n" in regex:
180         regex = "(?x)" + regex
181     compiled: Pattern[str] = re.compile(regex)
182     return compiled
183
184
185 def validate_regex(
186     ctx: click.Context,
187     param: click.Parameter,
188     value: Optional[str],
189 ) -> Optional[Pattern[str]]:
190     try:
191         return re_compile_maybe_verbose(value) if value is not None else None
192     except re.error as e:
193         raise click.BadParameter(f"Not a valid regular expression: {e}") from None
194
195
196 @click.command(
197     context_settings={"help_option_names": ["-h", "--help"]},
198     # While Click does set this field automatically using the docstring, mypyc
199     # (annoyingly) strips 'em so we need to set it here too.
200     help="The uncompromising code formatter.",
201 )
202 @click.option("-c", "--code", type=str, help="Format the code passed in as a string.")
203 @click.option(
204     "-l",
205     "--line-length",
206     type=int,
207     default=DEFAULT_LINE_LENGTH,
208     help="How many characters per line to allow.",
209     show_default=True,
210 )
211 @click.option(
212     "-t",
213     "--target-version",
214     type=click.Choice([v.name.lower() for v in TargetVersion]),
215     callback=target_version_option_callback,
216     multiple=True,
217     help=(
218         "Python versions that should be supported by Black's output. [default: per-file"
219         " auto-detection]"
220     ),
221 )
222 @click.option(
223     "--pyi",
224     is_flag=True,
225     help=(
226         "Format all input files like typing stubs regardless of file extension (useful"
227         " when piping source on standard input)."
228     ),
229 )
230 @click.option(
231     "--ipynb",
232     is_flag=True,
233     help=(
234         "Format all input files like Jupyter Notebooks regardless of file extension "
235         "(useful when piping source on standard input)."
236     ),
237 )
238 @click.option(
239     "--python-cell-magics",
240     multiple=True,
241     help=(
242         "When processing Jupyter Notebooks, add the given magic to the list"
243         f" of known python-magics ({', '.join(PYTHON_CELL_MAGICS)})."
244         " Useful for formatting cells with custom python magics."
245     ),
246     default=[],
247 )
248 @click.option(
249     "-S",
250     "--skip-string-normalization",
251     is_flag=True,
252     help="Don't normalize string quotes or prefixes.",
253 )
254 @click.option(
255     "-C",
256     "--skip-magic-trailing-comma",
257     is_flag=True,
258     help="Don't use trailing commas as a reason to split lines.",
259 )
260 @click.option(
261     "--experimental-string-processing",
262     is_flag=True,
263     hidden=True,
264     help="(DEPRECATED and now included in --preview) Normalize string literals.",
265 )
266 @click.option(
267     "--preview",
268     is_flag=True,
269     help=(
270         "Enable potentially disruptive style changes that may be added to Black's main"
271         " functionality in the next major release."
272     ),
273 )
274 @click.option(
275     "--check",
276     is_flag=True,
277     help=(
278         "Don't write the files back, just return the status. Return code 0 means"
279         " nothing would change. Return code 1 means some files would be reformatted."
280         " Return code 123 means there was an internal error."
281     ),
282 )
283 @click.option(
284     "--diff",
285     is_flag=True,
286     help="Don't write the files back, just output a diff for each file on stdout.",
287 )
288 @click.option(
289     "--color/--no-color",
290     is_flag=True,
291     help="Show colored diff. Only applies when `--diff` is given.",
292 )
293 @click.option(
294     "--fast/--safe",
295     is_flag=True,
296     help="If --fast given, skip temporary sanity checks. [default: --safe]",
297 )
298 @click.option(
299     "--required-version",
300     type=str,
301     help=(
302         "Require a specific version of Black to be running (useful for unifying results"
303         " across many environments e.g. with a pyproject.toml file). It can be"
304         " either a major version number or an exact version."
305     ),
306 )
307 @click.option(
308     "--include",
309     type=str,
310     default=DEFAULT_INCLUDES,
311     callback=validate_regex,
312     help=(
313         "A regular expression that matches files and directories that should be"
314         " included on recursive searches. An empty value means all files are included"
315         " regardless of the name. Use forward slashes for directories on all platforms"
316         " (Windows, too). Exclusions are calculated first, inclusions later."
317     ),
318     show_default=True,
319 )
320 @click.option(
321     "--exclude",
322     type=str,
323     callback=validate_regex,
324     help=(
325         "A regular expression that matches files and directories that should be"
326         " excluded on recursive searches. An empty value means no paths are excluded."
327         " Use forward slashes for directories on all platforms (Windows, too)."
328         " Exclusions are calculated first, inclusions later. [default:"
329         f" {DEFAULT_EXCLUDES}]"
330     ),
331     show_default=False,
332 )
333 @click.option(
334     "--extend-exclude",
335     type=str,
336     callback=validate_regex,
337     help=(
338         "Like --exclude, but adds additional files and directories on top of the"
339         " excluded ones. (Useful if you simply want to add to the default)"
340     ),
341 )
342 @click.option(
343     "--force-exclude",
344     type=str,
345     callback=validate_regex,
346     help=(
347         "Like --exclude, but files and directories matching this regex will be "
348         "excluded even when they are passed explicitly as arguments."
349     ),
350 )
351 @click.option(
352     "--stdin-filename",
353     type=str,
354     help=(
355         "The name of the file when passing it through stdin. Useful to make "
356         "sure Black will respect --force-exclude option on some "
357         "editors that rely on using stdin."
358     ),
359 )
360 @click.option(
361     "-W",
362     "--workers",
363     type=click.IntRange(min=1),
364     default=DEFAULT_WORKERS,
365     show_default=True,
366     help="Number of parallel workers",
367 )
368 @click.option(
369     "-q",
370     "--quiet",
371     is_flag=True,
372     help=(
373         "Don't emit non-error messages to stderr. Errors are still emitted; silence"
374         " those with 2>/dev/null."
375     ),
376 )
377 @click.option(
378     "-v",
379     "--verbose",
380     is_flag=True,
381     help=(
382         "Also emit messages to stderr about files that were not changed or were ignored"
383         " due to exclusion patterns."
384     ),
385 )
386 @click.version_option(
387     version=__version__,
388     message=(
389         f"%(prog)s, %(version)s (compiled: {'yes' if COMPILED else 'no'})\n"
390         f"Python ({platform.python_implementation()}) {platform.python_version()}"
391     ),
392 )
393 @click.argument(
394     "src",
395     nargs=-1,
396     type=click.Path(
397         exists=True, file_okay=True, dir_okay=True, readable=True, allow_dash=True
398     ),
399     is_eager=True,
400     metavar="SRC ...",
401 )
402 @click.option(
403     "--config",
404     type=click.Path(
405         exists=True,
406         file_okay=True,
407         dir_okay=False,
408         readable=True,
409         allow_dash=False,
410         path_type=str,
411     ),
412     is_eager=True,
413     callback=read_pyproject_toml,
414     help="Read configuration from FILE path.",
415 )
416 @click.pass_context
417 def main(  # noqa: C901
418     ctx: click.Context,
419     code: Optional[str],
420     line_length: int,
421     target_version: List[TargetVersion],
422     check: bool,
423     diff: bool,
424     color: bool,
425     fast: bool,
426     pyi: bool,
427     ipynb: bool,
428     python_cell_magics: Sequence[str],
429     skip_string_normalization: bool,
430     skip_magic_trailing_comma: bool,
431     experimental_string_processing: bool,
432     preview: bool,
433     quiet: bool,
434     verbose: bool,
435     required_version: Optional[str],
436     include: Pattern[str],
437     exclude: Optional[Pattern[str]],
438     extend_exclude: Optional[Pattern[str]],
439     force_exclude: Optional[Pattern[str]],
440     stdin_filename: Optional[str],
441     workers: int,
442     src: Tuple[str, ...],
443     config: Optional[str],
444 ) -> None:
445     """The uncompromising code formatter."""
446     ctx.ensure_object(dict)
447
448     if src and code is not None:
449         out(
450             main.get_usage(ctx)
451             + "\n\n'SRC' and 'code' cannot be passed simultaneously."
452         )
453         ctx.exit(1)
454     if not src and code is None:
455         out(main.get_usage(ctx) + "\n\nOne of 'SRC' or 'code' is required.")
456         ctx.exit(1)
457
458     root, method = find_project_root(src) if code is None else (None, None)
459     ctx.obj["root"] = root
460
461     if verbose:
462         if root:
463             out(
464                 f"Identified `{root}` as project root containing a {method}.",
465                 fg="blue",
466             )
467
468             normalized = [
469                 (normalize_path_maybe_ignore(Path(source), root), source)
470                 for source in src
471             ]
472             srcs_string = ", ".join(
473                 [
474                     f'"{_norm}"'
475                     if _norm
476                     else f'\033[31m"{source} (skipping - invalid)"\033[34m'
477                     for _norm, source in normalized
478                 ]
479             )
480             out(f"Sources to be formatted: {srcs_string}", fg="blue")
481
482         if config:
483             config_source = ctx.get_parameter_source("config")
484             user_level_config = str(find_user_pyproject_toml())
485             if config == user_level_config:
486                 out(
487                     "Using configuration from user-level config at "
488                     f"'{user_level_config}'.",
489                     fg="blue",
490                 )
491             elif config_source in (
492                 ParameterSource.DEFAULT,
493                 ParameterSource.DEFAULT_MAP,
494             ):
495                 out("Using configuration from project root.", fg="blue")
496             else:
497                 out(f"Using configuration in '{config}'.", fg="blue")
498
499     error_msg = "Oh no! 💥 💔 💥"
500     if (
501         required_version
502         and required_version != __version__
503         and required_version != __version__.split(".")[0]
504     ):
505         err(
506             f"{error_msg} The required version `{required_version}` does not match"
507             f" the running version `{__version__}`!"
508         )
509         ctx.exit(1)
510     if ipynb and pyi:
511         err("Cannot pass both `pyi` and `ipynb` flags!")
512         ctx.exit(1)
513
514     write_back = WriteBack.from_configuration(check=check, diff=diff, color=color)
515     if target_version:
516         versions = set(target_version)
517     else:
518         # We'll autodetect later.
519         versions = set()
520     mode = Mode(
521         target_versions=versions,
522         line_length=line_length,
523         is_pyi=pyi,
524         is_ipynb=ipynb,
525         string_normalization=not skip_string_normalization,
526         magic_trailing_comma=not skip_magic_trailing_comma,
527         experimental_string_processing=experimental_string_processing,
528         preview=preview,
529         python_cell_magics=set(python_cell_magics),
530     )
531
532     if code is not None:
533         # Run in quiet mode by default with -c; the extra output isn't useful.
534         # You can still pass -v to get verbose output.
535         quiet = True
536
537     report = Report(check=check, diff=diff, quiet=quiet, verbose=verbose)
538
539     if code is not None:
540         reformat_code(
541             content=code, fast=fast, write_back=write_back, mode=mode, report=report
542         )
543     else:
544         try:
545             sources = get_sources(
546                 ctx=ctx,
547                 src=src,
548                 quiet=quiet,
549                 verbose=verbose,
550                 include=include,
551                 exclude=exclude,
552                 extend_exclude=extend_exclude,
553                 force_exclude=force_exclude,
554                 report=report,
555                 stdin_filename=stdin_filename,
556             )
557         except GitWildMatchPatternError:
558             ctx.exit(1)
559
560         path_empty(
561             sources,
562             "No Python files are present to be formatted. Nothing to do 😴",
563             quiet,
564             verbose,
565             ctx,
566         )
567
568         if len(sources) == 1:
569             reformat_one(
570                 src=sources.pop(),
571                 fast=fast,
572                 write_back=write_back,
573                 mode=mode,
574                 report=report,
575             )
576         else:
577             reformat_many(
578                 sources=sources,
579                 fast=fast,
580                 write_back=write_back,
581                 mode=mode,
582                 report=report,
583                 workers=workers,
584             )
585
586     if verbose or not quiet:
587         if code is None and (verbose or report.change_count or report.failure_count):
588             out()
589         out(error_msg if report.return_code else "All done! ✨ 🍰 ✨")
590         if code is None:
591             click.echo(str(report), err=True)
592     ctx.exit(report.return_code)
593
594
595 def get_sources(
596     *,
597     ctx: click.Context,
598     src: Tuple[str, ...],
599     quiet: bool,
600     verbose: bool,
601     include: Pattern[str],
602     exclude: Optional[Pattern[str]],
603     extend_exclude: Optional[Pattern[str]],
604     force_exclude: Optional[Pattern[str]],
605     report: "Report",
606     stdin_filename: Optional[str],
607 ) -> Set[Path]:
608     """Compute the set of files to be formatted."""
609     sources: Set[Path] = set()
610
611     if exclude is None:
612         exclude = re_compile_maybe_verbose(DEFAULT_EXCLUDES)
613         gitignore = get_gitignore(ctx.obj["root"])
614     else:
615         gitignore = None
616
617     for s in src:
618         if s == "-" and stdin_filename:
619             p = Path(stdin_filename)
620             is_stdin = True
621         else:
622             p = Path(s)
623             is_stdin = False
624
625         if is_stdin or p.is_file():
626             normalized_path = normalize_path_maybe_ignore(p, ctx.obj["root"], report)
627             if normalized_path is None:
628                 continue
629
630             normalized_path = "/" + normalized_path
631             # Hard-exclude any files that matches the `--force-exclude` regex.
632             if force_exclude:
633                 force_exclude_match = force_exclude.search(normalized_path)
634             else:
635                 force_exclude_match = None
636             if force_exclude_match and force_exclude_match.group(0):
637                 report.path_ignored(p, "matches the --force-exclude regular expression")
638                 continue
639
640             if is_stdin:
641                 p = Path(f"{STDIN_PLACEHOLDER}{str(p)}")
642
643             if p.suffix == ".ipynb" and not jupyter_dependencies_are_installed(
644                 verbose=verbose, quiet=quiet
645             ):
646                 continue
647
648             sources.add(p)
649         elif p.is_dir():
650             sources.update(
651                 gen_python_files(
652                     p.iterdir(),
653                     ctx.obj["root"],
654                     include,
655                     exclude,
656                     extend_exclude,
657                     force_exclude,
658                     report,
659                     gitignore,
660                     verbose=verbose,
661                     quiet=quiet,
662                 )
663             )
664         elif s == "-":
665             sources.add(p)
666         else:
667             err(f"invalid path: {s}")
668     return sources
669
670
671 def path_empty(
672     src: Sized, msg: str, quiet: bool, verbose: bool, ctx: click.Context
673 ) -> None:
674     """
675     Exit if there is no `src` provided for formatting
676     """
677     if not src:
678         if verbose or not quiet:
679             out(msg)
680         ctx.exit(0)
681
682
683 def reformat_code(
684     content: str, fast: bool, write_back: WriteBack, mode: Mode, report: Report
685 ) -> None:
686     """
687     Reformat and print out `content` without spawning child processes.
688     Similar to `reformat_one`, but for string content.
689
690     `fast`, `write_back`, and `mode` options are passed to
691     :func:`format_file_in_place` or :func:`format_stdin_to_stdout`.
692     """
693     path = Path("<string>")
694     try:
695         changed = Changed.NO
696         if format_stdin_to_stdout(
697             content=content, fast=fast, write_back=write_back, mode=mode
698         ):
699             changed = Changed.YES
700         report.done(path, changed)
701     except Exception as exc:
702         if report.verbose:
703             traceback.print_exc()
704         report.failed(path, str(exc))
705
706
707 # diff-shades depends on being to monkeypatch this function to operate. I know it's
708 # not ideal, but this shouldn't cause any issues ... hopefully. ~ichard26
709 @mypyc_attr(patchable=True)
710 def reformat_one(
711     src: Path, fast: bool, write_back: WriteBack, mode: Mode, report: "Report"
712 ) -> None:
713     """Reformat a single file under `src` without spawning child processes.
714
715     `fast`, `write_back`, and `mode` options are passed to
716     :func:`format_file_in_place` or :func:`format_stdin_to_stdout`.
717     """
718     try:
719         changed = Changed.NO
720
721         if str(src) == "-":
722             is_stdin = True
723         elif str(src).startswith(STDIN_PLACEHOLDER):
724             is_stdin = True
725             # Use the original name again in case we want to print something
726             # to the user
727             src = Path(str(src)[len(STDIN_PLACEHOLDER) :])
728         else:
729             is_stdin = False
730
731         if is_stdin:
732             if src.suffix == ".pyi":
733                 mode = replace(mode, is_pyi=True)
734             elif src.suffix == ".ipynb":
735                 mode = replace(mode, is_ipynb=True)
736             if format_stdin_to_stdout(fast=fast, write_back=write_back, mode=mode):
737                 changed = Changed.YES
738         else:
739             cache: Cache = {}
740             if write_back not in (WriteBack.DIFF, WriteBack.COLOR_DIFF):
741                 cache = read_cache(mode)
742                 res_src = src.resolve()
743                 res_src_s = str(res_src)
744                 if res_src_s in cache and cache[res_src_s] == get_cache_info(res_src):
745                     changed = Changed.CACHED
746             if changed is not Changed.CACHED and format_file_in_place(
747                 src, fast=fast, write_back=write_back, mode=mode
748             ):
749                 changed = Changed.YES
750             if (write_back is WriteBack.YES and changed is not Changed.CACHED) or (
751                 write_back is WriteBack.CHECK and changed is Changed.NO
752             ):
753                 write_cache(cache, [src], mode)
754         report.done(src, changed)
755     except Exception as exc:
756         if report.verbose:
757             traceback.print_exc()
758         report.failed(src, str(exc))
759
760
761 # diff-shades depends on being to monkeypatch this function to operate. I know it's
762 # not ideal, but this shouldn't cause any issues ... hopefully. ~ichard26
763 @mypyc_attr(patchable=True)
764 def reformat_many(
765     sources: Set[Path],
766     fast: bool,
767     write_back: WriteBack,
768     mode: Mode,
769     report: "Report",
770     workers: Optional[int],
771 ) -> None:
772     """Reformat multiple files using a ProcessPoolExecutor."""
773     from concurrent.futures import Executor, ThreadPoolExecutor, ProcessPoolExecutor
774
775     executor: Executor
776     loop = asyncio.get_event_loop()
777     worker_count = workers if workers is not None else DEFAULT_WORKERS
778     if sys.platform == "win32":
779         # Work around https://bugs.python.org/issue26903
780         assert worker_count is not None
781         worker_count = min(worker_count, 60)
782     try:
783         executor = ProcessPoolExecutor(max_workers=worker_count)
784     except (ImportError, NotImplementedError, OSError):
785         # we arrive here if the underlying system does not support multi-processing
786         # like in AWS Lambda or Termux, in which case we gracefully fallback to
787         # a ThreadPoolExecutor with just a single worker (more workers would not do us
788         # any good due to the Global Interpreter Lock)
789         executor = ThreadPoolExecutor(max_workers=1)
790
791     try:
792         loop.run_until_complete(
793             schedule_formatting(
794                 sources=sources,
795                 fast=fast,
796                 write_back=write_back,
797                 mode=mode,
798                 report=report,
799                 loop=loop,
800                 executor=executor,
801             )
802         )
803     finally:
804         shutdown(loop)
805         if executor is not None:
806             executor.shutdown()
807
808
809 async def schedule_formatting(
810     sources: Set[Path],
811     fast: bool,
812     write_back: WriteBack,
813     mode: Mode,
814     report: "Report",
815     loop: asyncio.AbstractEventLoop,
816     executor: "Executor",
817 ) -> None:
818     """Run formatting of `sources` in parallel using the provided `executor`.
819
820     (Use ProcessPoolExecutors for actual parallelism.)
821
822     `write_back`, `fast`, and `mode` options are passed to
823     :func:`format_file_in_place`.
824     """
825     cache: Cache = {}
826     if write_back not in (WriteBack.DIFF, WriteBack.COLOR_DIFF):
827         cache = read_cache(mode)
828         sources, cached = filter_cached(cache, sources)
829         for src in sorted(cached):
830             report.done(src, Changed.CACHED)
831     if not sources:
832         return
833
834     cancelled = []
835     sources_to_cache = []
836     lock = None
837     if write_back in (WriteBack.DIFF, WriteBack.COLOR_DIFF):
838         # For diff output, we need locks to ensure we don't interleave output
839         # from different processes.
840         manager = Manager()
841         lock = manager.Lock()
842     tasks = {
843         asyncio.ensure_future(
844             loop.run_in_executor(
845                 executor, format_file_in_place, src, fast, mode, write_back, lock
846             )
847         ): src
848         for src in sorted(sources)
849     }
850     pending = tasks.keys()
851     try:
852         loop.add_signal_handler(signal.SIGINT, cancel, pending)
853         loop.add_signal_handler(signal.SIGTERM, cancel, pending)
854     except NotImplementedError:
855         # There are no good alternatives for these on Windows.
856         pass
857     while pending:
858         done, _ = await asyncio.wait(pending, return_when=asyncio.FIRST_COMPLETED)
859         for task in done:
860             src = tasks.pop(task)
861             if task.cancelled():
862                 cancelled.append(task)
863             elif task.exception():
864                 report.failed(src, str(task.exception()))
865             else:
866                 changed = Changed.YES if task.result() else Changed.NO
867                 # If the file was written back or was successfully checked as
868                 # well-formatted, store this information in the cache.
869                 if write_back is WriteBack.YES or (
870                     write_back is WriteBack.CHECK and changed is Changed.NO
871                 ):
872                     sources_to_cache.append(src)
873                 report.done(src, changed)
874     if cancelled:
875         if sys.version_info >= (3, 7):
876             await asyncio.gather(*cancelled, return_exceptions=True)
877         else:
878             await asyncio.gather(*cancelled, loop=loop, return_exceptions=True)
879     if sources_to_cache:
880         write_cache(cache, sources_to_cache, mode)
881
882
883 def format_file_in_place(
884     src: Path,
885     fast: bool,
886     mode: Mode,
887     write_back: WriteBack = WriteBack.NO,
888     lock: Any = None,  # multiprocessing.Manager().Lock() is some crazy proxy
889 ) -> bool:
890     """Format file under `src` path. Return True if changed.
891
892     If `write_back` is DIFF, write a diff to stdout. If it is YES, write reformatted
893     code to the file.
894     `mode` and `fast` options are passed to :func:`format_file_contents`.
895     """
896     if src.suffix == ".pyi":
897         mode = replace(mode, is_pyi=True)
898     elif src.suffix == ".ipynb":
899         mode = replace(mode, is_ipynb=True)
900
901     then = datetime.utcfromtimestamp(src.stat().st_mtime)
902     with open(src, "rb") as buf:
903         src_contents, encoding, newline = decode_bytes(buf.read())
904     try:
905         dst_contents = format_file_contents(src_contents, fast=fast, mode=mode)
906     except NothingChanged:
907         return False
908     except JSONDecodeError:
909         raise ValueError(
910             f"File '{src}' cannot be parsed as valid Jupyter notebook."
911         ) from None
912
913     if write_back == WriteBack.YES:
914         with open(src, "w", encoding=encoding, newline=newline) as f:
915             f.write(dst_contents)
916     elif write_back in (WriteBack.DIFF, WriteBack.COLOR_DIFF):
917         now = datetime.utcnow()
918         src_name = f"{src}\t{then} +0000"
919         dst_name = f"{src}\t{now} +0000"
920         if mode.is_ipynb:
921             diff_contents = ipynb_diff(src_contents, dst_contents, src_name, dst_name)
922         else:
923             diff_contents = diff(src_contents, dst_contents, src_name, dst_name)
924
925         if write_back == WriteBack.COLOR_DIFF:
926             diff_contents = color_diff(diff_contents)
927
928         with lock or nullcontext():
929             f = io.TextIOWrapper(
930                 sys.stdout.buffer,
931                 encoding=encoding,
932                 newline=newline,
933                 write_through=True,
934             )
935             f = wrap_stream_for_windows(f)
936             f.write(diff_contents)
937             f.detach()
938
939     return True
940
941
942 def format_stdin_to_stdout(
943     fast: bool,
944     *,
945     content: Optional[str] = None,
946     write_back: WriteBack = WriteBack.NO,
947     mode: Mode,
948 ) -> bool:
949     """Format file on stdin. Return True if changed.
950
951     If content is None, it's read from sys.stdin.
952
953     If `write_back` is YES, write reformatted code back to stdout. If it is DIFF,
954     write a diff to stdout. The `mode` argument is passed to
955     :func:`format_file_contents`.
956     """
957     then = datetime.utcnow()
958
959     if content is None:
960         src, encoding, newline = decode_bytes(sys.stdin.buffer.read())
961     else:
962         src, encoding, newline = content, "utf-8", ""
963
964     dst = src
965     try:
966         dst = format_file_contents(src, fast=fast, mode=mode)
967         return True
968
969     except NothingChanged:
970         return False
971
972     finally:
973         f = io.TextIOWrapper(
974             sys.stdout.buffer, encoding=encoding, newline=newline, write_through=True
975         )
976         if write_back == WriteBack.YES:
977             # Make sure there's a newline after the content
978             if dst and dst[-1] != "\n":
979                 dst += "\n"
980             f.write(dst)
981         elif write_back in (WriteBack.DIFF, WriteBack.COLOR_DIFF):
982             now = datetime.utcnow()
983             src_name = f"STDIN\t{then} +0000"
984             dst_name = f"STDOUT\t{now} +0000"
985             d = diff(src, dst, src_name, dst_name)
986             if write_back == WriteBack.COLOR_DIFF:
987                 d = color_diff(d)
988                 f = wrap_stream_for_windows(f)
989             f.write(d)
990         f.detach()
991
992
993 def check_stability_and_equivalence(
994     src_contents: str, dst_contents: str, *, mode: Mode
995 ) -> None:
996     """Perform stability and equivalence checks.
997
998     Raise AssertionError if source and destination contents are not
999     equivalent, or if a second pass of the formatter would format the
1000     content differently.
1001     """
1002     assert_equivalent(src_contents, dst_contents)
1003     assert_stable(src_contents, dst_contents, mode=mode)
1004
1005
1006 def format_file_contents(src_contents: str, *, fast: bool, mode: Mode) -> FileContent:
1007     """Reformat contents of a file and return new contents.
1008
1009     If `fast` is False, additionally confirm that the reformatted code is
1010     valid by calling :func:`assert_equivalent` and :func:`assert_stable` on it.
1011     `mode` is passed to :func:`format_str`.
1012     """
1013     if not src_contents.strip():
1014         raise NothingChanged
1015
1016     if mode.is_ipynb:
1017         dst_contents = format_ipynb_string(src_contents, fast=fast, mode=mode)
1018     else:
1019         dst_contents = format_str(src_contents, mode=mode)
1020     if src_contents == dst_contents:
1021         raise NothingChanged
1022
1023     if not fast and not mode.is_ipynb:
1024         # Jupyter notebooks will already have been checked above.
1025         check_stability_and_equivalence(src_contents, dst_contents, mode=mode)
1026     return dst_contents
1027
1028
1029 def validate_cell(src: str, mode: Mode) -> None:
1030     """Check that cell does not already contain TransformerManager transformations,
1031     or non-Python cell magics, which might cause tokenizer_rt to break because of
1032     indentations.
1033
1034     If a cell contains ``!ls``, then it'll be transformed to
1035     ``get_ipython().system('ls')``. However, if the cell originally contained
1036     ``get_ipython().system('ls')``, then it would get transformed in the same way:
1037
1038         >>> TransformerManager().transform_cell("get_ipython().system('ls')")
1039         "get_ipython().system('ls')\n"
1040         >>> TransformerManager().transform_cell("!ls")
1041         "get_ipython().system('ls')\n"
1042
1043     Due to the impossibility of safely roundtripping in such situations, cells
1044     containing transformed magics will be ignored.
1045     """
1046     if any(transformed_magic in src for transformed_magic in TRANSFORMED_MAGICS):
1047         raise NothingChanged
1048     if (
1049         src[:2] == "%%"
1050         and src.split()[0][2:] not in PYTHON_CELL_MAGICS | mode.python_cell_magics
1051     ):
1052         raise NothingChanged
1053
1054
1055 def format_cell(src: str, *, fast: bool, mode: Mode) -> str:
1056     """Format code in given cell of Jupyter notebook.
1057
1058     General idea is:
1059
1060       - if cell has trailing semicolon, remove it;
1061       - if cell has IPython magics, mask them;
1062       - format cell;
1063       - reinstate IPython magics;
1064       - reinstate trailing semicolon (if originally present);
1065       - strip trailing newlines.
1066
1067     Cells with syntax errors will not be processed, as they
1068     could potentially be automagics or multi-line magics, which
1069     are currently not supported.
1070     """
1071     validate_cell(src, mode)
1072     src_without_trailing_semicolon, has_trailing_semicolon = remove_trailing_semicolon(
1073         src
1074     )
1075     try:
1076         masked_src, replacements = mask_cell(src_without_trailing_semicolon)
1077     except SyntaxError:
1078         raise NothingChanged from None
1079     masked_dst = format_str(masked_src, mode=mode)
1080     if not fast:
1081         check_stability_and_equivalence(masked_src, masked_dst, mode=mode)
1082     dst_without_trailing_semicolon = unmask_cell(masked_dst, replacements)
1083     dst = put_trailing_semicolon_back(
1084         dst_without_trailing_semicolon, has_trailing_semicolon
1085     )
1086     dst = dst.rstrip("\n")
1087     if dst == src:
1088         raise NothingChanged from None
1089     return dst
1090
1091
1092 def validate_metadata(nb: MutableMapping[str, Any]) -> None:
1093     """If notebook is marked as non-Python, don't format it.
1094
1095     All notebook metadata fields are optional, see
1096     https://nbformat.readthedocs.io/en/latest/format_description.html. So
1097     if a notebook has empty metadata, we will try to parse it anyway.
1098     """
1099     language = nb.get("metadata", {}).get("language_info", {}).get("name", None)
1100     if language is not None and language != "python":
1101         raise NothingChanged from None
1102
1103
1104 def format_ipynb_string(src_contents: str, *, fast: bool, mode: Mode) -> FileContent:
1105     """Format Jupyter notebook.
1106
1107     Operate cell-by-cell, only on code cells, only for Python notebooks.
1108     If the ``.ipynb`` originally had a trailing newline, it'll be preserved.
1109     """
1110     trailing_newline = src_contents[-1] == "\n"
1111     modified = False
1112     nb = json.loads(src_contents)
1113     validate_metadata(nb)
1114     for cell in nb["cells"]:
1115         if cell.get("cell_type", None) == "code":
1116             try:
1117                 src = "".join(cell["source"])
1118                 dst = format_cell(src, fast=fast, mode=mode)
1119             except NothingChanged:
1120                 pass
1121             else:
1122                 cell["source"] = dst.splitlines(keepends=True)
1123                 modified = True
1124     if modified:
1125         dst_contents = json.dumps(nb, indent=1, ensure_ascii=False)
1126         if trailing_newline:
1127             dst_contents = dst_contents + "\n"
1128         return dst_contents
1129     else:
1130         raise NothingChanged
1131
1132
1133 def format_str(src_contents: str, *, mode: Mode) -> str:
1134     """Reformat a string and return new contents.
1135
1136     `mode` determines formatting options, such as how many characters per line are
1137     allowed.  Example:
1138
1139     >>> import black
1140     >>> print(black.format_str("def f(arg:str='')->None:...", mode=black.Mode()))
1141     def f(arg: str = "") -> None:
1142         ...
1143
1144     A more complex example:
1145
1146     >>> print(
1147     ...   black.format_str(
1148     ...     "def f(arg:str='')->None: hey",
1149     ...     mode=black.Mode(
1150     ...       target_versions={black.TargetVersion.PY36},
1151     ...       line_length=10,
1152     ...       string_normalization=False,
1153     ...       is_pyi=False,
1154     ...     ),
1155     ...   ),
1156     ... )
1157     def f(
1158         arg: str = '',
1159     ) -> None:
1160         hey
1161
1162     """
1163     dst_contents = _format_str_once(src_contents, mode=mode)
1164     # Forced second pass to work around optional trailing commas (becoming
1165     # forced trailing commas on pass 2) interacting differently with optional
1166     # parentheses.  Admittedly ugly.
1167     if src_contents != dst_contents:
1168         return _format_str_once(dst_contents, mode=mode)
1169     return dst_contents
1170
1171
1172 def _format_str_once(src_contents: str, *, mode: Mode) -> str:
1173     src_node = lib2to3_parse(src_contents.lstrip(), mode.target_versions)
1174     dst_contents = []
1175     future_imports = get_future_imports(src_node)
1176     if mode.target_versions:
1177         versions = mode.target_versions
1178     else:
1179         versions = detect_target_versions(src_node, future_imports=future_imports)
1180
1181     normalize_fmt_off(src_node, preview=mode.preview)
1182     lines = LineGenerator(mode=mode)
1183     elt = EmptyLineTracker(is_pyi=mode.is_pyi)
1184     empty_line = Line(mode=mode)
1185     after = 0
1186     split_line_features = {
1187         feature
1188         for feature in {Feature.TRAILING_COMMA_IN_CALL, Feature.TRAILING_COMMA_IN_DEF}
1189         if supports_feature(versions, feature)
1190     }
1191     for current_line in lines.visit(src_node):
1192         dst_contents.append(str(empty_line) * after)
1193         before, after = elt.maybe_empty_lines(current_line)
1194         dst_contents.append(str(empty_line) * before)
1195         for line in transform_line(
1196             current_line, mode=mode, features=split_line_features
1197         ):
1198             dst_contents.append(str(line))
1199     return "".join(dst_contents)
1200
1201
1202 def decode_bytes(src: bytes) -> Tuple[FileContent, Encoding, NewLine]:
1203     """Return a tuple of (decoded_contents, encoding, newline).
1204
1205     `newline` is either CRLF or LF but `decoded_contents` is decoded with
1206     universal newlines (i.e. only contains LF).
1207     """
1208     srcbuf = io.BytesIO(src)
1209     encoding, lines = tokenize.detect_encoding(srcbuf.readline)
1210     if not lines:
1211         return "", encoding, "\n"
1212
1213     newline = "\r\n" if b"\r\n" == lines[0][-2:] else "\n"
1214     srcbuf.seek(0)
1215     with io.TextIOWrapper(srcbuf, encoding) as tiow:
1216         return tiow.read(), encoding, newline
1217
1218
1219 def get_features_used(  # noqa: C901
1220     node: Node, *, future_imports: Optional[Set[str]] = None
1221 ) -> Set[Feature]:
1222     """Return a set of (relatively) new Python features used in this file.
1223
1224     Currently looking for:
1225     - f-strings;
1226     - underscores in numeric literals;
1227     - trailing commas after * or ** in function signatures and calls;
1228     - positional only arguments in function signatures and lambdas;
1229     - assignment expression;
1230     - relaxed decorator syntax;
1231     - usage of __future__ flags (annotations);
1232     - print / exec statements;
1233     """
1234     features: Set[Feature] = set()
1235     if future_imports:
1236         features |= {
1237             FUTURE_FLAG_TO_FEATURE[future_import]
1238             for future_import in future_imports
1239             if future_import in FUTURE_FLAG_TO_FEATURE
1240         }
1241
1242     for n in node.pre_order():
1243         if is_string_token(n):
1244             value_head = n.value[:2]
1245             if value_head in {'f"', 'F"', "f'", "F'", "rf", "fr", "RF", "FR"}:
1246                 features.add(Feature.F_STRINGS)
1247
1248         elif n.type == token.NUMBER:
1249             assert isinstance(n, Leaf)
1250             if "_" in n.value:
1251                 features.add(Feature.NUMERIC_UNDERSCORES)
1252
1253         elif n.type == token.SLASH:
1254             if n.parent and n.parent.type in {
1255                 syms.typedargslist,
1256                 syms.arglist,
1257                 syms.varargslist,
1258             }:
1259                 features.add(Feature.POS_ONLY_ARGUMENTS)
1260
1261         elif n.type == token.COLONEQUAL:
1262             features.add(Feature.ASSIGNMENT_EXPRESSIONS)
1263
1264         elif n.type == syms.decorator:
1265             if len(n.children) > 1 and not is_simple_decorator_expression(
1266                 n.children[1]
1267             ):
1268                 features.add(Feature.RELAXED_DECORATORS)
1269
1270         elif (
1271             n.type in {syms.typedargslist, syms.arglist}
1272             and n.children
1273             and n.children[-1].type == token.COMMA
1274         ):
1275             if n.type == syms.typedargslist:
1276                 feature = Feature.TRAILING_COMMA_IN_DEF
1277             else:
1278                 feature = Feature.TRAILING_COMMA_IN_CALL
1279
1280             for ch in n.children:
1281                 if ch.type in STARS:
1282                     features.add(feature)
1283
1284                 if ch.type == syms.argument:
1285                     for argch in ch.children:
1286                         if argch.type in STARS:
1287                             features.add(feature)
1288
1289         elif (
1290             n.type in {syms.return_stmt, syms.yield_expr}
1291             and len(n.children) >= 2
1292             and n.children[1].type == syms.testlist_star_expr
1293             and any(child.type == syms.star_expr for child in n.children[1].children)
1294         ):
1295             features.add(Feature.UNPACKING_ON_FLOW)
1296
1297         elif (
1298             n.type == syms.annassign
1299             and len(n.children) >= 4
1300             and n.children[3].type == syms.testlist_star_expr
1301         ):
1302             features.add(Feature.ANN_ASSIGN_EXTENDED_RHS)
1303
1304         elif (
1305             n.type == syms.except_clause
1306             and len(n.children) >= 2
1307             and n.children[1].type == token.STAR
1308         ):
1309             features.add(Feature.EXCEPT_STAR)
1310
1311     return features
1312
1313
1314 def detect_target_versions(
1315     node: Node, *, future_imports: Optional[Set[str]] = None
1316 ) -> Set[TargetVersion]:
1317     """Detect the version to target based on the nodes used."""
1318     features = get_features_used(node, future_imports=future_imports)
1319     return {
1320         version for version in TargetVersion if features <= VERSION_TO_FEATURES[version]
1321     }
1322
1323
1324 def get_future_imports(node: Node) -> Set[str]:
1325     """Return a set of __future__ imports in the file."""
1326     imports: Set[str] = set()
1327
1328     def get_imports_from_children(children: List[LN]) -> Generator[str, None, None]:
1329         for child in children:
1330             if isinstance(child, Leaf):
1331                 if child.type == token.NAME:
1332                     yield child.value
1333
1334             elif child.type == syms.import_as_name:
1335                 orig_name = child.children[0]
1336                 assert isinstance(orig_name, Leaf), "Invalid syntax parsing imports"
1337                 assert orig_name.type == token.NAME, "Invalid syntax parsing imports"
1338                 yield orig_name.value
1339
1340             elif child.type == syms.import_as_names:
1341                 yield from get_imports_from_children(child.children)
1342
1343             else:
1344                 raise AssertionError("Invalid syntax parsing imports")
1345
1346     for child in node.children:
1347         if child.type != syms.simple_stmt:
1348             break
1349
1350         first_child = child.children[0]
1351         if isinstance(first_child, Leaf):
1352             # Continue looking if we see a docstring; otherwise stop.
1353             if (
1354                 len(child.children) == 2
1355                 and first_child.type == token.STRING
1356                 and child.children[1].type == token.NEWLINE
1357             ):
1358                 continue
1359
1360             break
1361
1362         elif first_child.type == syms.import_from:
1363             module_name = first_child.children[1]
1364             if not isinstance(module_name, Leaf) or module_name.value != "__future__":
1365                 break
1366
1367             imports |= set(get_imports_from_children(first_child.children[3:]))
1368         else:
1369             break
1370
1371     return imports
1372
1373
1374 def assert_equivalent(src: str, dst: str) -> None:
1375     """Raise AssertionError if `src` and `dst` aren't equivalent."""
1376     try:
1377         src_ast = parse_ast(src)
1378     except Exception as exc:
1379         raise AssertionError(
1380             "cannot use --safe with this file; failed to parse source file AST: "
1381             f"{exc}\n"
1382             "This could be caused by running Black with an older Python version "
1383             "that does not support new syntax used in your source file."
1384         ) from exc
1385
1386     try:
1387         dst_ast = parse_ast(dst)
1388     except Exception as exc:
1389         log = dump_to_file("".join(traceback.format_tb(exc.__traceback__)), dst)
1390         raise AssertionError(
1391             f"INTERNAL ERROR: Black produced invalid code: {exc}. "
1392             "Please report a bug on https://github.com/psf/black/issues.  "
1393             f"This invalid output might be helpful: {log}"
1394         ) from None
1395
1396     src_ast_str = "\n".join(stringify_ast(src_ast))
1397     dst_ast_str = "\n".join(stringify_ast(dst_ast))
1398     if src_ast_str != dst_ast_str:
1399         log = dump_to_file(diff(src_ast_str, dst_ast_str, "src", "dst"))
1400         raise AssertionError(
1401             "INTERNAL ERROR: Black produced code that is not equivalent to the"
1402             " source.  Please report a bug on "
1403             f"https://github.com/psf/black/issues.  This diff might be helpful: {log}"
1404         ) from None
1405
1406
1407 def assert_stable(src: str, dst: str, mode: Mode) -> None:
1408     """Raise AssertionError if `dst` reformats differently the second time."""
1409     # We shouldn't call format_str() here, because that formats the string
1410     # twice and may hide a bug where we bounce back and forth between two
1411     # versions.
1412     newdst = _format_str_once(dst, mode=mode)
1413     if dst != newdst:
1414         log = dump_to_file(
1415             str(mode),
1416             diff(src, dst, "source", "first pass"),
1417             diff(dst, newdst, "first pass", "second pass"),
1418         )
1419         raise AssertionError(
1420             "INTERNAL ERROR: Black produced different code on the second pass of the"
1421             " formatter.  Please report a bug on https://github.com/psf/black/issues."
1422             f"  This diff might be helpful: {log}"
1423         ) from None
1424
1425
1426 @contextmanager
1427 def nullcontext() -> Iterator[None]:
1428     """Return an empty context manager.
1429
1430     To be used like `nullcontext` in Python 3.7.
1431     """
1432     yield
1433
1434
1435 def patch_click() -> None:
1436     """Make Click not crash on Python 3.6 with LANG=C.
1437
1438     On certain misconfigured environments, Python 3 selects the ASCII encoding as the
1439     default which restricts paths that it can access during the lifetime of the
1440     application.  Click refuses to work in this scenario by raising a RuntimeError.
1441
1442     In case of Black the likelihood that non-ASCII characters are going to be used in
1443     file paths is minimal since it's Python source code.  Moreover, this crash was
1444     spurious on Python 3.7 thanks to PEP 538 and PEP 540.
1445     """
1446     modules: List[Any] = []
1447     try:
1448         from click import core
1449     except ImportError:
1450         pass
1451     else:
1452         modules.append(core)
1453     try:
1454         # Removed in Click 8.1.0 and newer; we keep this around for users who have
1455         # older versions installed.
1456         from click import _unicodefun  # type: ignore
1457     except ImportError:
1458         pass
1459     else:
1460         modules.append(_unicodefun)
1461
1462     for module in modules:
1463         if hasattr(module, "_verify_python3_env"):
1464             module._verify_python3_env = lambda: None  # type: ignore
1465         if hasattr(module, "_verify_python_env"):
1466             module._verify_python_env = lambda: None  # type: ignore
1467
1468
1469 def patched_main() -> None:
1470     maybe_install_uvloop()
1471     freeze_support()
1472     patch_click()
1473     main()
1474
1475
1476 if __name__ == "__main__":
1477     patched_main()