Document the future style changes introduced in #3489 and #3440 (#3541)

[etc/vim.git] / src / black / __init__.py

diff --git a/src/black/__init__.py b/src/black/__init__.py
index c61bc8c1d60e2f2b681a663e2b94435ce1439bf0..4ebf28821c39ca339b05f372de2695246f6fcc99 100644 (file)
--- a/src/black/__init__.py
+++ b/src/black/__init__.py
@@ -1,59 +1,92 @@
-import asyncio
-from concurrent.futures import Executor, ThreadPoolExecutor, ProcessPoolExecutor
-from contextlib import contextmanager
-from datetime import datetime
-from enum import Enum

 import io
 import io

-from multiprocessing import Manager, freeze_support
-import os
-from pathlib import Path
-import regex as re
-import signal
+import json
+import platform
+import re

 import sys
 import tokenize
 import traceback
 import sys
 import tokenize
 import traceback

+from contextlib import contextmanager
+from dataclasses import replace
+from datetime import datetime
+from enum import Enum
+from json.decoder import JSONDecodeError
+from pathlib import Path

 from typing import (
     Any,
     Dict,
     Generator,
     Iterator,
     List,
 from typing import (
     Any,
     Dict,
     Generator,
     Iterator,
     List,

+    MutableMapping,

     Optional,
     Pattern,
     Optional,
     Pattern,

+    Sequence,

     Set,
     Sized,
     Tuple,
     Union,
 )
 
     Set,
     Sized,
     Tuple,
     Union,
 )
 

-from dataclasses import replace

 import click
 import click

+from click.core import ParameterSource
+from mypy_extensions import mypyc_attr
+from pathspec import PathSpec
+from pathspec.patterns.gitwildmatch import GitWildMatchPatternError

 
 

-from black.const import DEFAULT_LINE_LENGTH, DEFAULT_INCLUDES, DEFAULT_EXCLUDES
-from black.const import STDIN_PLACEHOLDER
-from black.nodes import STARS, syms, is_simple_decorator_expression
-from black.lines import Line, EmptyLineTracker
-from black.linegen import transform_line, LineGenerator, LN
+from _black_version import version as __version__
+from black.cache import Cache, get_cache_info, read_cache, write_cache

 from black.comments import normalize_fmt_off
 from black.comments import normalize_fmt_off

-from black.mode import Mode, TargetVersion
-from black.mode import Feature, supports_feature, VERSION_TO_FEATURES
-from black.cache import read_cache, write_cache, get_cache_info, filter_cached, Cache
-from black.concurrency import cancel, shutdown
-from black.output import dump_to_file, diff, color_diff, out, err
-from black.report import Report, Changed
-from black.files import find_project_root, find_pyproject_toml, parse_pyproject_toml
-from black.files import gen_python_files, get_gitignore, normalize_path_maybe_ignore
-from black.files import wrap_stream_for_windows
+from black.const import (
+    DEFAULT_EXCLUDES,
+    DEFAULT_INCLUDES,
+    DEFAULT_LINE_LENGTH,
+    STDIN_PLACEHOLDER,
+)
+from black.files import (
+    find_project_root,
+    find_pyproject_toml,
+    find_user_pyproject_toml,
+    gen_python_files,
+    get_gitignore,
+    normalize_path_maybe_ignore,
+    parse_pyproject_toml,
+    wrap_stream_for_windows,
+)
+from black.handle_ipynb_magics import (
+    PYTHON_CELL_MAGICS,
+    TRANSFORMED_MAGICS,
+    jupyter_dependencies_are_installed,
+    mask_cell,
+    put_trailing_semicolon_back,
+    remove_trailing_semicolon,
+    unmask_cell,
+)
+from black.linegen import LN, LineGenerator, transform_line
+from black.lines import EmptyLineTracker, LinesBlock
+from black.mode import (
+    FUTURE_FLAG_TO_FEATURE,
+    VERSION_TO_FEATURES,
+    Feature,
+    Mode,
+    TargetVersion,
+    supports_feature,
+)
+from black.nodes import (
+    STARS,
+    is_number_token,
+    is_simple_decorator_expression,
+    is_string_token,
+    syms,
+)
+from black.output import color_diff, diff, dump_to_file, err, ipynb_diff, out

 from black.parsing import InvalidInput  # noqa F401
 from black.parsing import lib2to3_parse, parse_ast, stringify_ast
 from black.parsing import InvalidInput  # noqa F401
 from black.parsing import lib2to3_parse, parse_ast, stringify_ast

-
-
-# lib2to3 fork
-from blib2to3.pytree import Node, Leaf
+from black.report import Changed, NothingChanged, Report
+from black.trans import iter_fexpr_spans

 from blib2to3.pgen2 import token
 from blib2to3.pgen2 import token

+from blib2to3.pytree import Leaf, Node

 
 

-from _black_version import version as __version__
-
+COMPILED = Path(__file__).suffix in (".pyd", ".so")

 
 # types
 FileContent = str
 
 # types
 FileContent = str


@@ -61,10 +94,6 @@ Encoding = str
 NewLine = str
 
 
 NewLine = str
 
 

-class NothingChanged(UserWarning):
-    """Raised when reformatted code is the same as source."""
-
-

 class WriteBack(Enum):
     NO = 0
     YES = 1
 class WriteBack(Enum):
     NO = 0
     YES = 1


@@ -107,7 +136,7 @@ def read_pyproject_toml(
     except (OSError, ValueError) as e:
         raise click.FileError(
             filename=value, hint=f"Error reading configuration file: {e}"
     except (OSError, ValueError) as e:
         raise click.FileError(
             filename=value, hint=f"Error reading configuration file: {e}"

-        )
+        ) from None

 
     if not config:
         return None
 
     if not config:
         return None


@@ -161,14 +190,19 @@ def validate_regex(
     ctx: click.Context,
     param: click.Parameter,
     value: Optional[str],
     ctx: click.Context,
     param: click.Parameter,
     value: Optional[str],

-) -> Optional[Pattern]:
+) -> Optional[Pattern[str]]:

     try:
         return re_compile_maybe_verbose(value) if value is not None else None
     try:
         return re_compile_maybe_verbose(value) if value is not None else None

-    except re.error:
-        raise click.BadParameter("Not a valid regular expression")
+    except re.error as e:
+        raise click.BadParameter(f"Not a valid regular expression: {e}") from None

 
 
 
 

-@click.command(context_settings=dict(help_option_names=["-h", "--help"]))
+@click.command(
+    context_settings={"help_option_names": ["-h", "--help"]},
+    # While Click does set this field automatically using the docstring, mypyc
+    # (annoyingly) strips 'em so we need to set it here too.
+    help="The uncompromising code formatter.",
+)

 @click.option("-c", "--code", type=str, help="Format the code passed in as a string.")
 @click.option(
     "-l",
 @click.option("-c", "--code", type=str, help="Format the code passed in as a string.")
 @click.option(
     "-l",


@@ -185,8 +219,9 @@ def validate_regex(
     callback=target_version_option_callback,
     multiple=True,
     help=(
     callback=target_version_option_callback,
     multiple=True,
     help=(

-        "Python versions that should be supported by Black's output. [default: per-file"
-        " auto-detection]"
+        "Python versions that should be supported by Black's output. By default, Black"
+        " will try to infer this from the project metadata in pyproject.toml. If this"
+        " does not yield conclusive results, Black will use per-file auto-detection."

     ),
 )
 @click.option(
     ),
 )
 @click.option(


@@ -197,6 +232,30 @@ def validate_regex(
         " when piping source on standard input)."
     ),
 )
         " when piping source on standard input)."
     ),
 )

+@click.option(
+    "--ipynb",
+    is_flag=True,
+    help=(
+        "Format all input files like Jupyter Notebooks regardless of file extension "
+        "(useful when piping source on standard input)."
+    ),
+)
+@click.option(
+    "--python-cell-magics",
+    multiple=True,
+    help=(
+        "When processing Jupyter Notebooks, add the given magic to the list"
+        f" of known python-magics ({', '.join(sorted(PYTHON_CELL_MAGICS))})."
+        " Useful for formatting cells with custom python magics."
+    ),
+    default=[],
+)
+@click.option(
+    "-x",
+    "--skip-source-first-line",
+    is_flag=True,
+    help="Skip the first line of the source code.",
+)

 @click.option(
     "-S",
     "--skip-string-normalization",
 @click.option(
     "-S",
     "--skip-string-normalization",


@@ -213,9 +272,14 @@ def validate_regex(
     "--experimental-string-processing",
     is_flag=True,
     hidden=True,
     "--experimental-string-processing",
     is_flag=True,
     hidden=True,

+    help="(DEPRECATED and now included in --preview) Normalize string literals.",
+)
+@click.option(
+    "--preview",
+    is_flag=True,

     help=(
     help=(

-        "Experimental option that performs more normalization on string literals."
-        " Currently disabled because it leads to some crashes."
+        "Enable potentially disruptive style changes that may be added to Black's main"
+        " functionality in the next major release."

     ),
 )
 @click.option(
     ),
 )
 @click.option(


@@ -242,6 +306,15 @@ def validate_regex(
     is_flag=True,
     help="If --fast given, skip temporary sanity checks. [default: --safe]",
 )
     is_flag=True,
     help="If --fast given, skip temporary sanity checks. [default: --safe]",
 )

+@click.option(
+    "--required-version",
+    type=str,
+    help=(
+        "Require a specific version of Black to be running (useful for unifying results"
+        " across many environments e.g. with a pyproject.toml file). It can be"
+        " either a major version number or an exact version."
+    ),
+)

 @click.option(
     "--include",
     type=str,
 @click.option(
     "--include",
     type=str,


@@ -295,6 +368,13 @@ def validate_regex(
         "editors that rely on using stdin."
     ),
 )
         "editors that rely on using stdin."
     ),
 )

+@click.option(
+    "-W",
+    "--workers",
+    type=click.IntRange(min=1),
+    default=None,
+    help="Number of parallel workers [default: number of CPUs in the system]",
+)

 @click.option(
     "-q",
     "--quiet",
 @click.option(
     "-q",
     "--quiet",


@@ -313,7 +393,13 @@ def validate_regex(
         " due to exclusion patterns."
     ),
 )
         " due to exclusion patterns."
     ),
 )

-@click.version_option(version=__version__)
+@click.version_option(
+    version=__version__,
+    message=(
+        f"%(prog)s, %(version)s (compiled: {'yes' if COMPILED else 'no'})\n"
+        f"Python ({platform.python_implementation()}) {platform.python_version()}"
+    ),
+)

 @click.argument(
     "src",
     nargs=-1,
 @click.argument(
     "src",
     nargs=-1,


@@ -321,6 +407,7 @@ def validate_regex(
         exists=True, file_okay=True, dir_okay=True, readable=True, allow_dash=True
     ),
     is_eager=True,
         exists=True, file_okay=True, dir_okay=True, readable=True, allow_dash=True
     ),
     is_eager=True,

+    metavar="SRC ...",

 )
 @click.option(
     "--config",
 )
 @click.option(
     "--config",


@@ -337,7 +424,7 @@ def validate_regex(
     help="Read configuration from FILE path.",
 )
 @click.pass_context
     help="Read configuration from FILE path.",
 )
 @click.pass_context

-def main(
+def main(  # noqa: C901

     ctx: click.Context,
     code: Optional[str],
     line_length: int,
     ctx: click.Context,
     code: Optional[str],
     line_length: int,


@@ -347,20 +434,107 @@ def main(
     color: bool,
     fast: bool,
     pyi: bool,
     color: bool,
     fast: bool,
     pyi: bool,

+    ipynb: bool,
+    python_cell_magics: Sequence[str],
+    skip_source_first_line: bool,

     skip_string_normalization: bool,
     skip_magic_trailing_comma: bool,
     experimental_string_processing: bool,
     skip_string_normalization: bool,
     skip_magic_trailing_comma: bool,
     experimental_string_processing: bool,

+    preview: bool,

     quiet: bool,
     verbose: bool,
     quiet: bool,
     verbose: bool,

-    include: Pattern,
-    exclude: Optional[Pattern],
-    extend_exclude: Optional[Pattern],
-    force_exclude: Optional[Pattern],
+    required_version: Optional[str],
+    include: Pattern[str],
+    exclude: Optional[Pattern[str]],
+    extend_exclude: Optional[Pattern[str]],
+    force_exclude: Optional[Pattern[str]],

     stdin_filename: Optional[str],
     stdin_filename: Optional[str],

+    workers: Optional[int],

     src: Tuple[str, ...],
     config: Optional[str],
 ) -> None:
     """The uncompromising code formatter."""
     src: Tuple[str, ...],
     config: Optional[str],
 ) -> None:
     """The uncompromising code formatter."""

+    ctx.ensure_object(dict)
+
+    if src and code is not None:
+        out(
+            main.get_usage(ctx)
+            + "\n\n'SRC' and 'code' cannot be passed simultaneously."
+        )
+        ctx.exit(1)
+    if not src and code is None:
+        out(main.get_usage(ctx) + "\n\nOne of 'SRC' or 'code' is required.")
+        ctx.exit(1)
+
+    root, method = (
+        find_project_root(src, stdin_filename) if code is None else (None, None)
+    )
+    ctx.obj["root"] = root
+
+    if verbose:
+        if root:
+            out(
+                f"Identified `{root}` as project root containing a {method}.",
+                fg="blue",
+            )
+
+            normalized = [
+                (
+                    (source, source)
+                    if source == "-"
+                    else (normalize_path_maybe_ignore(Path(source), root), source)
+                )
+                for source in src
+            ]
+            srcs_string = ", ".join(
+                [
+                    (
+                        f'"{_norm}"'
+                        if _norm
+                        else f'\033[31m"{source} (skipping - invalid)"\033[34m'
+                    )
+                    for _norm, source in normalized
+                ]
+            )
+            out(f"Sources to be formatted: {srcs_string}", fg="blue")
+
+        if config:
+            config_source = ctx.get_parameter_source("config")
+            user_level_config = str(find_user_pyproject_toml())
+            if config == user_level_config:
+                out(
+                    (
+                        "Using configuration from user-level config at "
+                        f"'{user_level_config}'."
+                    ),
+                    fg="blue",
+                )
+            elif config_source in (
+                ParameterSource.DEFAULT,
+                ParameterSource.DEFAULT_MAP,
+            ):
+                out("Using configuration from project root.", fg="blue")
+            else:
+                out(f"Using configuration in '{config}'.", fg="blue")
+            if ctx.default_map:
+                for param, value in ctx.default_map.items():
+                    out(f"{param}: {value}")
+
+    error_msg = "Oh no! 💥 💔 💥"
+    if (
+        required_version
+        and required_version != __version__
+        and required_version != __version__.split(".")[0]
+    ):
+        err(
+            f"{error_msg} The required version `{required_version}` does not match"
+            f" the running version `{__version__}`!"
+        )
+        ctx.exit(1)
+    if ipynb and pyi:
+        err("Cannot pass both `pyi` and `ipynb` flags!")
+        ctx.exit(1)
+

     write_back = WriteBack.from_configuration(check=check, diff=diff, color=color)
     if target_version:
         versions = set(target_version)
     write_back = WriteBack.from_configuration(check=check, diff=diff, color=color)
     if target_version:
         versions = set(target_version)


@@ -371,53 +545,77 @@ def main(
         target_versions=versions,
         line_length=line_length,
         is_pyi=pyi,
         target_versions=versions,
         line_length=line_length,
         is_pyi=pyi,

+        is_ipynb=ipynb,
+        skip_source_first_line=skip_source_first_line,

         string_normalization=not skip_string_normalization,
         magic_trailing_comma=not skip_magic_trailing_comma,
         experimental_string_processing=experimental_string_processing,
         string_normalization=not skip_string_normalization,
         magic_trailing_comma=not skip_magic_trailing_comma,
         experimental_string_processing=experimental_string_processing,

+        preview=preview,
+        python_cell_magics=set(python_cell_magics),

     )
     )

-    if config and verbose:
-        out(f"Using configuration from {config}.", bold=False, fg="blue")
+

     if code is not None:
     if code is not None:

-        print(format_str(code, mode=mode))
-        ctx.exit(0)
-    report = Report(check=check, diff=diff, quiet=quiet, verbose=verbose)
-    sources = get_sources(
-        ctx=ctx,
-        src=src,
-        quiet=quiet,
-        verbose=verbose,
-        include=include,
-        exclude=exclude,
-        extend_exclude=extend_exclude,
-        force_exclude=force_exclude,
-        report=report,
-        stdin_filename=stdin_filename,
-    )
+        # Run in quiet mode by default with -c; the extra output isn't useful.
+        # You can still pass -v to get verbose output.
+        quiet = True

 
 

-    path_empty(
-        sources,
-        "No Python files are present to be formatted. Nothing to do 😴",
-        quiet,
-        verbose,
-        ctx,
-    )
+    report = Report(check=check, diff=diff, quiet=quiet, verbose=verbose)

 
 

-    if len(sources) == 1:
-        reformat_one(
-            src=sources.pop(),
-            fast=fast,
-            write_back=write_back,
-            mode=mode,
-            report=report,
+    if code is not None:
+        reformat_code(
+            content=code, fast=fast, write_back=write_back, mode=mode, report=report

         )
     else:
         )
     else:

-        reformat_many(
-            sources=sources, fast=fast, write_back=write_back, mode=mode, report=report
+        try:
+            sources = get_sources(
+                ctx=ctx,
+                src=src,
+                quiet=quiet,
+                verbose=verbose,
+                include=include,
+                exclude=exclude,
+                extend_exclude=extend_exclude,
+                force_exclude=force_exclude,
+                report=report,
+                stdin_filename=stdin_filename,
+            )
+        except GitWildMatchPatternError:
+            ctx.exit(1)
+
+        path_empty(
+            sources,
+            "No Python files are present to be formatted. Nothing to do 😴",
+            quiet,
+            verbose,
+            ctx,

         )
 
         )
 

+        if len(sources) == 1:
+            reformat_one(
+                src=sources.pop(),
+                fast=fast,
+                write_back=write_back,
+                mode=mode,
+                report=report,
+            )
+        else:
+            from black.concurrency import reformat_many
+
+            reformat_many(
+                sources=sources,
+                fast=fast,
+                write_back=write_back,
+                mode=mode,
+                report=report,
+                workers=workers,
+            )
+

     if verbose or not quiet:
     if verbose or not quiet:

-        out("Oh no! 💥 💔 💥" if report.return_code else "All done! ✨ 🍰 ✨")
-        click.secho(str(report), err=True)
+        if code is None and (verbose or report.change_count or report.failure_count):
+            out()
+        out(error_msg if report.return_code else "All done! ✨ 🍰 ✨")
+        if code is None:
+            click.echo(str(report), err=True)

     ctx.exit(report.return_code)
 
 
     ctx.exit(report.return_code)
 
 


@@ -435,16 +633,13 @@ def get_sources(
     stdin_filename: Optional[str],
 ) -> Set[Path]:
     """Compute the set of files to be formatted."""
     stdin_filename: Optional[str],
 ) -> Set[Path]:
     """Compute the set of files to be formatted."""

-
-    root = find_project_root(src)

     sources: Set[Path] = set()
     sources: Set[Path] = set()

-    path_empty(src, "No Path provided. Nothing to do 😴", quiet, verbose, ctx)
+    root = ctx.obj["root"]

 
 

-    if exclude is None:
-        exclude = re_compile_maybe_verbose(DEFAULT_EXCLUDES)
-        gitignore = get_gitignore(root)
-    else:
-        gitignore = None
+    using_default_exclude = exclude is None
+    exclude = re_compile_maybe_verbose(DEFAULT_EXCLUDES) if exclude is None else exclude
+    gitignore: Optional[Dict[Path, PathSpec]] = None
+    root_gitignore = get_gitignore(root)

 
     for s in src:
         if s == "-" and stdin_filename:
 
     for s in src:
         if s == "-" and stdin_filename:


@@ -455,7 +650,7 @@ def get_sources(
             is_stdin = False
 
         if is_stdin or p.is_file():
             is_stdin = False
 
         if is_stdin or p.is_file():

-            normalized_path = normalize_path_maybe_ignore(p, root, report)
+            normalized_path = normalize_path_maybe_ignore(p, ctx.obj["root"], report)

             if normalized_path is None:
                 continue
 
             if normalized_path is None:
                 continue
 


@@ -472,18 +667,31 @@ def get_sources(
             if is_stdin:
                 p = Path(f"{STDIN_PLACEHOLDER}{str(p)}")
 
             if is_stdin:
                 p = Path(f"{STDIN_PLACEHOLDER}{str(p)}")
 

+            if p.suffix == ".ipynb" and not jupyter_dependencies_are_installed(
+                verbose=verbose, quiet=quiet
+            ):
+                continue
+

             sources.add(p)
         elif p.is_dir():
             sources.add(p)
         elif p.is_dir():

+            p = root / normalize_path_maybe_ignore(p, ctx.obj["root"], report)
+            if using_default_exclude:
+                gitignore = {
+                    root: root_gitignore,
+                    p: get_gitignore(p),
+                }

             sources.update(
                 gen_python_files(
                     p.iterdir(),
             sources.update(
                 gen_python_files(
                     p.iterdir(),

-                    root,
+                    ctx.obj["root"],

                     include,
                     exclude,
                     extend_exclude,
                     force_exclude,
                     report,
                     gitignore,
                     include,
                     exclude,
                     extend_exclude,
                     force_exclude,
                     report,
                     gitignore,

+                    verbose=verbose,
+                    quiet=quiet,

                 )
             )
         elif s == "-":
                 )
             )
         elif s == "-":


@@ -499,11 +707,39 @@ def path_empty(
     """
     Exit if there is no `src` provided for formatting
     """
     """
     Exit if there is no `src` provided for formatting
     """

-    if not src and (verbose or not quiet):
-        out(msg)
+    if not src:
+        if verbose or not quiet:
+            out(msg)

         ctx.exit(0)
 
 
         ctx.exit(0)
 
 

+def reformat_code(
+    content: str, fast: bool, write_back: WriteBack, mode: Mode, report: Report
+) -> None:
+    """
+    Reformat and print out `content` without spawning child processes.
+    Similar to `reformat_one`, but for string content.
+
+    `fast`, `write_back`, and `mode` options are passed to
+    :func:`format_file_in_place` or :func:`format_stdin_to_stdout`.
+    """
+    path = Path("<string>")
+    try:
+        changed = Changed.NO
+        if format_stdin_to_stdout(
+            content=content, fast=fast, write_back=write_back, mode=mode
+        ):
+            changed = Changed.YES
+        report.done(path, changed)
+    except Exception as exc:
+        if report.verbose:
+            traceback.print_exc()
+        report.failed(path, str(exc))
+
+
+# diff-shades depends on being to monkeypatch this function to operate. I know it's
+# not ideal, but this shouldn't cause any issues ... hopefully. ~ichard26
+@mypyc_attr(patchable=True)

 def reformat_one(
     src: Path, fast: bool, write_back: WriteBack, mode: Mode, report: "Report"
 ) -> None:
 def reformat_one(
     src: Path, fast: bool, write_back: WriteBack, mode: Mode, report: "Report"
 ) -> None:


@@ -528,6 +764,8 @@ def reformat_one(
         if is_stdin:
             if src.suffix == ".pyi":
                 mode = replace(mode, is_pyi=True)
         if is_stdin:
             if src.suffix == ".pyi":
                 mode = replace(mode, is_pyi=True)

+            elif src.suffix == ".ipynb":
+                mode = replace(mode, is_ipynb=True)

             if format_stdin_to_stdout(fast=fast, write_back=write_back, mode=mode):
                 changed = Changed.YES
         else:
             if format_stdin_to_stdout(fast=fast, write_back=write_back, mode=mode):
                 changed = Changed.YES
         else:


@@ -553,114 +791,6 @@ def reformat_one(
         report.failed(src, str(exc))
 
 
         report.failed(src, str(exc))
 
 

-def reformat_many(
-    sources: Set[Path], fast: bool, write_back: WriteBack, mode: Mode, report: "Report"
-) -> None:
-    """Reformat multiple files using a ProcessPoolExecutor."""
-    executor: Executor
-    loop = asyncio.get_event_loop()
-    worker_count = os.cpu_count()
-    if sys.platform == "win32":
-        # Work around https://bugs.python.org/issue26903
-        worker_count = min(worker_count, 60)
-    try:
-        executor = ProcessPoolExecutor(max_workers=worker_count)
-    except (ImportError, OSError):
-        # we arrive here if the underlying system does not support multi-processing
-        # like in AWS Lambda or Termux, in which case we gracefully fallback to
-        # a ThreadPoolExecutor with just a single worker (more workers would not do us
-        # any good due to the Global Interpreter Lock)
-        executor = ThreadPoolExecutor(max_workers=1)
-
-    try:
-        loop.run_until_complete(
-            schedule_formatting(
-                sources=sources,
-                fast=fast,
-                write_back=write_back,
-                mode=mode,
-                report=report,
-                loop=loop,
-                executor=executor,
-            )
-        )
-    finally:
-        shutdown(loop)
-        if executor is not None:
-            executor.shutdown()
-
-
-async def schedule_formatting(
-    sources: Set[Path],
-    fast: bool,
-    write_back: WriteBack,
-    mode: Mode,
-    report: "Report",
-    loop: asyncio.AbstractEventLoop,
-    executor: Executor,
-) -> None:
-    """Run formatting of `sources` in parallel using the provided `executor`.
-
-    (Use ProcessPoolExecutors for actual parallelism.)
-
-    `write_back`, `fast`, and `mode` options are passed to
-    :func:`format_file_in_place`.
-    """
-    cache: Cache = {}
-    if write_back not in (WriteBack.DIFF, WriteBack.COLOR_DIFF):
-        cache = read_cache(mode)
-        sources, cached = filter_cached(cache, sources)
-        for src in sorted(cached):
-            report.done(src, Changed.CACHED)
-    if not sources:
-        return
-
-    cancelled = []
-    sources_to_cache = []
-    lock = None
-    if write_back in (WriteBack.DIFF, WriteBack.COLOR_DIFF):
-        # For diff output, we need locks to ensure we don't interleave output
-        # from different processes.
-        manager = Manager()
-        lock = manager.Lock()
-    tasks = {
-        asyncio.ensure_future(
-            loop.run_in_executor(
-                executor, format_file_in_place, src, fast, mode, write_back, lock
-            )
-        ): src
-        for src in sorted(sources)
-    }
-    pending = tasks.keys()
-    try:
-        loop.add_signal_handler(signal.SIGINT, cancel, pending)
-        loop.add_signal_handler(signal.SIGTERM, cancel, pending)
-    except NotImplementedError:
-        # There are no good alternatives for these on Windows.
-        pass
-    while pending:
-        done, _ = await asyncio.wait(pending, return_when=asyncio.FIRST_COMPLETED)
-        for task in done:
-            src = tasks.pop(task)
-            if task.cancelled():
-                cancelled.append(task)
-            elif task.exception():
-                report.failed(src, str(task.exception()))
-            else:
-                changed = Changed.YES if task.result() else Changed.NO
-                # If the file was written back or was successfully checked as
-                # well-formatted, store this information in the cache.
-                if write_back is WriteBack.YES or (
-                    write_back is WriteBack.CHECK and changed is Changed.NO
-                ):
-                    sources_to_cache.append(src)
-                report.done(src, changed)
-    if cancelled:
-        await asyncio.gather(*cancelled, loop=loop, return_exceptions=True)
-    if sources_to_cache:
-        write_cache(cache, sources_to_cache, mode)
-
-

 def format_file_in_place(
     src: Path,
     fast: bool,
 def format_file_in_place(
     src: Path,
     fast: bool,


@@ -676,14 +806,25 @@ def format_file_in_place(
     """
     if src.suffix == ".pyi":
         mode = replace(mode, is_pyi=True)
     """
     if src.suffix == ".pyi":
         mode = replace(mode, is_pyi=True)

+    elif src.suffix == ".ipynb":
+        mode = replace(mode, is_ipynb=True)

 
     then = datetime.utcfromtimestamp(src.stat().st_mtime)
 
     then = datetime.utcfromtimestamp(src.stat().st_mtime)

+    header = b""

     with open(src, "rb") as buf:
     with open(src, "rb") as buf:

+        if mode.skip_source_first_line:
+            header = buf.readline()

         src_contents, encoding, newline = decode_bytes(buf.read())
     try:
         dst_contents = format_file_contents(src_contents, fast=fast, mode=mode)
     except NothingChanged:
         return False
         src_contents, encoding, newline = decode_bytes(buf.read())
     try:
         dst_contents = format_file_contents(src_contents, fast=fast, mode=mode)
     except NothingChanged:
         return False

+    except JSONDecodeError:
+        raise ValueError(
+            f"File '{src}' cannot be parsed as valid Jupyter notebook."
+        ) from None
+    src_contents = header.decode(encoding) + src_contents
+    dst_contents = header.decode(encoding) + dst_contents

 
     if write_back == WriteBack.YES:
         with open(src, "w", encoding=encoding, newline=newline) as f:
 
     if write_back == WriteBack.YES:
         with open(src, "w", encoding=encoding, newline=newline) as f:


@@ -692,7 +833,10 @@ def format_file_in_place(
         now = datetime.utcnow()
         src_name = f"{src}\t{then} +0000"
         dst_name = f"{src}\t{now} +0000"
         now = datetime.utcnow()
         src_name = f"{src}\t{then} +0000"
         dst_name = f"{src}\t{now} +0000"

-        diff_contents = diff(src_contents, dst_contents, src_name, dst_name)
+        if mode.is_ipynb:
+            diff_contents = ipynb_diff(src_contents, dst_contents, src_name, dst_name)
+        else:
+            diff_contents = diff(src_contents, dst_contents, src_name, dst_name)

 
         if write_back == WriteBack.COLOR_DIFF:
             diff_contents = color_diff(diff_contents)
 
         if write_back == WriteBack.COLOR_DIFF:
             diff_contents = color_diff(diff_contents)


@@ -712,16 +856,27 @@ def format_file_in_place(
 
 
 def format_stdin_to_stdout(
 
 
 def format_stdin_to_stdout(

-    fast: bool, *, write_back: WriteBack = WriteBack.NO, mode: Mode
+    fast: bool,
+    *,
+    content: Optional[str] = None,
+    write_back: WriteBack = WriteBack.NO,
+    mode: Mode,

 ) -> bool:
     """Format file on stdin. Return True if changed.
 
 ) -> bool:
     """Format file on stdin. Return True if changed.
 

+    If content is None, it's read from sys.stdin.
+

     If `write_back` is YES, write reformatted code back to stdout. If it is DIFF,
     write a diff to stdout. The `mode` argument is passed to
     :func:`format_file_contents`.
     """
     then = datetime.utcnow()
     If `write_back` is YES, write reformatted code back to stdout. If it is DIFF,
     write a diff to stdout. The `mode` argument is passed to
     :func:`format_file_contents`.
     """
     then = datetime.utcnow()

-    src, encoding, newline = decode_bytes(sys.stdin.buffer.read())
+
+    if content is None:
+        src, encoding, newline = decode_bytes(sys.stdin.buffer.read())
+    else:
+        src, encoding, newline = content, "utf-8", ""
+

     dst = src
     try:
         dst = format_file_contents(src, fast=fast, mode=mode)
     dst = src
     try:
         dst = format_file_contents(src, fast=fast, mode=mode)


@@ -735,6 +890,9 @@ def format_stdin_to_stdout(
             sys.stdout.buffer, encoding=encoding, newline=newline, write_through=True
         )
         if write_back == WriteBack.YES:
             sys.stdout.buffer, encoding=encoding, newline=newline, write_through=True
         )
         if write_back == WriteBack.YES:

+            # Make sure there's a newline after the content
+            if dst and dst[-1] != "\n":
+                dst += "\n"

             f.write(dst)
         elif write_back in (WriteBack.DIFF, WriteBack.COLOR_DIFF):
             now = datetime.utcnow()
             f.write(dst)
         elif write_back in (WriteBack.DIFF, WriteBack.COLOR_DIFF):
             now = datetime.utcnow()


@@ -748,6 +906,19 @@ def format_stdin_to_stdout(
         f.detach()
 
 
         f.detach()
 
 

+def check_stability_and_equivalence(
+    src_contents: str, dst_contents: str, *, mode: Mode
+) -> None:
+    """Perform stability and equivalence checks.
+
+    Raise AssertionError if source and destination contents are not
+    equivalent, or if a second pass of the formatter would format the
+    content differently.
+    """
+    assert_equivalent(src_contents, dst_contents)
+    assert_stable(src_contents, dst_contents, mode=mode)
+
+

 def format_file_contents(src_contents: str, *, fast: bool, mode: Mode) -> FileContent:
     """Reformat contents of a file and return new contents.
 
 def format_file_contents(src_contents: str, *, fast: bool, mode: Mode) -> FileContent:
     """Reformat contents of a file and return new contents.
 


@@ -755,30 +926,127 @@ def format_file_contents(src_contents: str, *, fast: bool, mode: Mode) -> FileCo
     valid by calling :func:`assert_equivalent` and :func:`assert_stable` on it.
     `mode` is passed to :func:`format_str`.
     """
     valid by calling :func:`assert_equivalent` and :func:`assert_stable` on it.
     `mode` is passed to :func:`format_str`.
     """

-    if not src_contents.strip():
+    if mode.is_ipynb:
+        dst_contents = format_ipynb_string(src_contents, fast=fast, mode=mode)
+    else:
+        dst_contents = format_str(src_contents, mode=mode)
+    if src_contents == dst_contents:

         raise NothingChanged
 
         raise NothingChanged
 

-    dst_contents = format_str(src_contents, mode=mode)
-    if src_contents == dst_contents:
+    if not fast and not mode.is_ipynb:
+        # Jupyter notebooks will already have been checked above.
+        check_stability_and_equivalence(src_contents, dst_contents, mode=mode)
+    return dst_contents
+
+
+def validate_cell(src: str, mode: Mode) -> None:
+    """Check that cell does not already contain TransformerManager transformations,
+    or non-Python cell magics, which might cause tokenizer_rt to break because of
+    indentations.
+
+    If a cell contains ``!ls``, then it'll be transformed to
+    ``get_ipython().system('ls')``. However, if the cell originally contained
+    ``get_ipython().system('ls')``, then it would get transformed in the same way:
+
+        >>> TransformerManager().transform_cell("get_ipython().system('ls')")
+        "get_ipython().system('ls')\n"
+        >>> TransformerManager().transform_cell("!ls")
+        "get_ipython().system('ls')\n"
+
+    Due to the impossibility of safely roundtripping in such situations, cells
+    containing transformed magics will be ignored.
+    """
+    if any(transformed_magic in src for transformed_magic in TRANSFORMED_MAGICS):
+        raise NothingChanged
+    if (
+        src[:2] == "%%"
+        and src.split()[0][2:] not in PYTHON_CELL_MAGICS | mode.python_cell_magics
+    ):

         raise NothingChanged
 
         raise NothingChanged
 

+
+def format_cell(src: str, *, fast: bool, mode: Mode) -> str:
+    """Format code in given cell of Jupyter notebook.
+
+    General idea is:
+
+      - if cell has trailing semicolon, remove it;
+      - if cell has IPython magics, mask them;
+      - format cell;
+      - reinstate IPython magics;
+      - reinstate trailing semicolon (if originally present);
+      - strip trailing newlines.
+
+    Cells with syntax errors will not be processed, as they
+    could potentially be automagics or multi-line magics, which
+    are currently not supported.
+    """
+    validate_cell(src, mode)
+    src_without_trailing_semicolon, has_trailing_semicolon = remove_trailing_semicolon(
+        src
+    )
+    try:
+        masked_src, replacements = mask_cell(src_without_trailing_semicolon)
+    except SyntaxError:
+        raise NothingChanged from None
+    masked_dst = format_str(masked_src, mode=mode)

     if not fast:
     if not fast:

-        assert_equivalent(src_contents, dst_contents)
-
-        # Forced second pass to work around optional trailing commas (becoming
-        # forced trailing commas on pass 2) interacting differently with optional
-        # parentheses.  Admittedly ugly.
-        dst_contents_pass2 = format_str(dst_contents, mode=mode)
-        if dst_contents != dst_contents_pass2:
-            dst_contents = dst_contents_pass2
-            assert_equivalent(src_contents, dst_contents, pass_num=2)
-            assert_stable(src_contents, dst_contents, mode=mode)
-        # Note: no need to explicitly call `assert_stable` if `dst_contents` was
-        # the same as `dst_contents_pass2`.
-    return dst_contents
+        check_stability_and_equivalence(masked_src, masked_dst, mode=mode)
+    dst_without_trailing_semicolon = unmask_cell(masked_dst, replacements)
+    dst = put_trailing_semicolon_back(
+        dst_without_trailing_semicolon, has_trailing_semicolon
+    )
+    dst = dst.rstrip("\n")
+    if dst == src:
+        raise NothingChanged from None
+    return dst
+
+
+def validate_metadata(nb: MutableMapping[str, Any]) -> None:
+    """If notebook is marked as non-Python, don't format it.
+
+    All notebook metadata fields are optional, see
+    https://nbformat.readthedocs.io/en/latest/format_description.html. So
+    if a notebook has empty metadata, we will try to parse it anyway.
+    """
+    language = nb.get("metadata", {}).get("language_info", {}).get("name", None)
+    if language is not None and language != "python":
+        raise NothingChanged from None
+
+
+def format_ipynb_string(src_contents: str, *, fast: bool, mode: Mode) -> FileContent:
+    """Format Jupyter notebook.
+
+    Operate cell-by-cell, only on code cells, only for Python notebooks.
+    If the ``.ipynb`` originally had a trailing newline, it'll be preserved.
+    """
+    if not src_contents:
+        raise NothingChanged
+
+    trailing_newline = src_contents[-1] == "\n"
+    modified = False
+    nb = json.loads(src_contents)
+    validate_metadata(nb)
+    for cell in nb["cells"]:
+        if cell.get("cell_type", None) == "code":
+            try:
+                src = "".join(cell["source"])
+                dst = format_cell(src, fast=fast, mode=mode)
+            except NothingChanged:
+                pass
+            else:
+                cell["source"] = dst.splitlines(keepends=True)
+                modified = True
+    if modified:
+        dst_contents = json.dumps(nb, indent=1, ensure_ascii=False)
+        if trailing_newline:
+            dst_contents = dst_contents + "\n"
+        return dst_contents
+    else:
+        raise NothingChanged

 
 
 
 

-def format_str(src_contents: str, *, mode: Mode) -> FileContent:
+def format_str(src_contents: str, *, mode: Mode) -> str:

     """Reformat a string and return new contents.
 
     `mode` determines formatting options, such as how many characters per line are
     """Reformat a string and return new contents.
 
     `mode` determines formatting options, such as how many characters per line are


@@ -808,35 +1076,57 @@ def format_str(src_contents: str, *, mode: Mode) -> FileContent:
         hey
 
     """
         hey
 
     """

+    dst_contents = _format_str_once(src_contents, mode=mode)
+    # Forced second pass to work around optional trailing commas (becoming
+    # forced trailing commas on pass 2) interacting differently with optional
+    # parentheses.  Admittedly ugly.
+    if src_contents != dst_contents:
+        return _format_str_once(dst_contents, mode=mode)
+    return dst_contents
+
+
+def _format_str_once(src_contents: str, *, mode: Mode) -> str:

     src_node = lib2to3_parse(src_contents.lstrip(), mode.target_versions)
     src_node = lib2to3_parse(src_contents.lstrip(), mode.target_versions)

-    dst_contents = []
-    future_imports = get_future_imports(src_node)
+    dst_blocks: List[LinesBlock] = []

     if mode.target_versions:
         versions = mode.target_versions
     else:
     if mode.target_versions:
         versions = mode.target_versions
     else:

-        versions = detect_target_versions(src_node)
+        future_imports = get_future_imports(src_node)
+        versions = detect_target_versions(src_node, future_imports=future_imports)
+
+    context_manager_features = {
+        feature
+        for feature in {Feature.PARENTHESIZED_CONTEXT_MANAGERS}
+        if supports_feature(versions, feature)
+    }

     normalize_fmt_off(src_node)
     normalize_fmt_off(src_node)

-    lines = LineGenerator(
-        mode=mode,
-        remove_u_prefix="unicode_literals" in future_imports
-        or supports_feature(versions, Feature.UNICODE_LITERALS),
-    )
-    elt = EmptyLineTracker(is_pyi=mode.is_pyi)
-    empty_line = Line(mode=mode)
-    after = 0
+    lines = LineGenerator(mode=mode, features=context_manager_features)
+    elt = EmptyLineTracker(mode=mode)

     split_line_features = {
         feature
         for feature in {Feature.TRAILING_COMMA_IN_CALL, Feature.TRAILING_COMMA_IN_DEF}
         if supports_feature(versions, feature)
     }
     split_line_features = {
         feature
         for feature in {Feature.TRAILING_COMMA_IN_CALL, Feature.TRAILING_COMMA_IN_DEF}
         if supports_feature(versions, feature)
     }

+    block: Optional[LinesBlock] = None

     for current_line in lines.visit(src_node):
     for current_line in lines.visit(src_node):

-        dst_contents.append(str(empty_line) * after)
-        before, after = elt.maybe_empty_lines(current_line)
-        dst_contents.append(str(empty_line) * before)
+        block = elt.maybe_empty_lines(current_line)
+        dst_blocks.append(block)

         for line in transform_line(
             current_line, mode=mode, features=split_line_features
         ):
         for line in transform_line(
             current_line, mode=mode, features=split_line_features
         ):

-            dst_contents.append(str(line))
+            block.content_lines.append(str(line))
+    if dst_blocks:
+        dst_blocks[-1].after = 0
+    dst_contents = []
+    for block in dst_blocks:
+        dst_contents.extend(block.all_lines())
+    if not dst_contents:
+        # Use decode_bytes to retrieve the correct source newline (CRLF or LF),
+        # and check if normalized_content has more than one line
+        normalized_content, _, newline = decode_bytes(src_contents.encode("utf-8"))
+        if "\n" in normalized_content:
+            return newline
+        return ""

     return "".join(dst_contents)
 
 
     return "".join(dst_contents)
 
 


@@ -857,30 +1147,55 @@ def decode_bytes(src: bytes) -> Tuple[FileContent, Encoding, NewLine]:
         return tiow.read(), encoding, newline
 
 
         return tiow.read(), encoding, newline
 
 

-def get_features_used(node: Node) -> Set[Feature]:
+def get_features_used(  # noqa: C901
+    node: Node, *, future_imports: Optional[Set[str]] = None
+) -> Set[Feature]:

     """Return a set of (relatively) new Python features used in this file.
 
     Currently looking for:
     - f-strings;
     """Return a set of (relatively) new Python features used in this file.
 
     Currently looking for:
     - f-strings;

+    - self-documenting expressions in f-strings (f"{x=}");

     - underscores in numeric literals;
     - trailing commas after * or ** in function signatures and calls;
     - positional only arguments in function signatures and lambdas;
     - assignment expression;
     - relaxed decorator syntax;
     - underscores in numeric literals;
     - trailing commas after * or ** in function signatures and calls;
     - positional only arguments in function signatures and lambdas;
     - assignment expression;
     - relaxed decorator syntax;

+    - usage of __future__ flags (annotations);
+    - print / exec statements;
+    - parenthesized context managers;
+    - match statements;
+    - except* clause;
+    - variadic generics;

     """
     features: Set[Feature] = set()
     """
     features: Set[Feature] = set()

+    if future_imports:
+        features |= {
+            FUTURE_FLAG_TO_FEATURE[future_import]
+            for future_import in future_imports
+            if future_import in FUTURE_FLAG_TO_FEATURE
+        }
+

     for n in node.pre_order():
     for n in node.pre_order():

-        if n.type == token.STRING:
-            value_head = n.value[:2]  # type: ignore
+        if is_string_token(n):
+            value_head = n.value[:2]

             if value_head in {'f"', 'F"', "f'", "F'", "rf", "fr", "RF", "FR"}:
                 features.add(Feature.F_STRINGS)
             if value_head in {'f"', 'F"', "f'", "F'", "rf", "fr", "RF", "FR"}:
                 features.add(Feature.F_STRINGS)

-
-        elif n.type == token.NUMBER:
-            if "_" in n.value:  # type: ignore
+                if Feature.DEBUG_F_STRINGS not in features:
+                    for span_beg, span_end in iter_fexpr_spans(n.value):
+                        if n.value[span_beg : span_end - 1].rstrip().endswith("="):
+                            features.add(Feature.DEBUG_F_STRINGS)
+                            break
+
+        elif is_number_token(n):
+            if "_" in n.value:

                 features.add(Feature.NUMERIC_UNDERSCORES)
 
         elif n.type == token.SLASH:
                 features.add(Feature.NUMERIC_UNDERSCORES)
 
         elif n.type == token.SLASH:

-            if n.parent and n.parent.type in {syms.typedargslist, syms.arglist}:
+            if n.parent and n.parent.type in {
+                syms.typedargslist,
+                syms.arglist,
+                syms.varargslist,
+            }:

                 features.add(Feature.POS_ONLY_ARGUMENTS)
 
         elif n.type == token.COLONEQUAL:
                 features.add(Feature.POS_ONLY_ARGUMENTS)
 
         elif n.type == token.COLONEQUAL:


@@ -911,12 +1226,65 @@ def get_features_used(node: Node) -> Set[Feature]:
                         if argch.type in STARS:
                             features.add(feature)
 
                         if argch.type in STARS:
                             features.add(feature)
 

+        elif (
+            n.type in {syms.return_stmt, syms.yield_expr}
+            and len(n.children) >= 2
+            and n.children[1].type == syms.testlist_star_expr
+            and any(child.type == syms.star_expr for child in n.children[1].children)
+        ):
+            features.add(Feature.UNPACKING_ON_FLOW)
+
+        elif (
+            n.type == syms.annassign
+            and len(n.children) >= 4
+            and n.children[3].type == syms.testlist_star_expr
+        ):
+            features.add(Feature.ANN_ASSIGN_EXTENDED_RHS)
+
+        elif (
+            n.type == syms.with_stmt
+            and len(n.children) > 2
+            and n.children[1].type == syms.atom
+        ):
+            atom_children = n.children[1].children
+            if (
+                len(atom_children) == 3
+                and atom_children[0].type == token.LPAR
+                and atom_children[1].type == syms.testlist_gexp
+                and atom_children[2].type == token.RPAR
+            ):
+                features.add(Feature.PARENTHESIZED_CONTEXT_MANAGERS)
+
+        elif n.type == syms.match_stmt:
+            features.add(Feature.PATTERN_MATCHING)
+
+        elif (
+            n.type == syms.except_clause
+            and len(n.children) >= 2
+            and n.children[1].type == token.STAR
+        ):
+            features.add(Feature.EXCEPT_STAR)
+
+        elif n.type in {syms.subscriptlist, syms.trailer} and any(
+            child.type == syms.star_expr for child in n.children
+        ):
+            features.add(Feature.VARIADIC_GENERICS)
+
+        elif (
+            n.type == syms.tname_star
+            and len(n.children) == 3
+            and n.children[2].type == syms.star_expr
+        ):
+            features.add(Feature.VARIADIC_GENERICS)
+

     return features
 
 
     return features
 
 

-def detect_target_versions(node: Node) -> Set[TargetVersion]:
+def detect_target_versions(
+    node: Node, *, future_imports: Optional[Set[str]] = None
+) -> Set[TargetVersion]:

     """Detect the version to target based on the nodes used."""
     """Detect the version to target based on the nodes used."""

-    features = get_features_used(node)
+    features = get_features_used(node, future_imports=future_imports)

     return {
         version for version in TargetVersion if features <= VERSION_TO_FEATURES[version]
     }
     return {
         version for version in TargetVersion if features <= VERSION_TO_FEATURES[version]
     }


@@ -972,22 +1340,24 @@ def get_future_imports(node: Node) -> Set[str]:
     return imports
 
 
     return imports
 
 

-def assert_equivalent(src: str, dst: str, *, pass_num: int = 1) -> None:
+def assert_equivalent(src: str, dst: str) -> None:

     """Raise AssertionError if `src` and `dst` aren't equivalent."""
     try:
         src_ast = parse_ast(src)
     except Exception as exc:
         raise AssertionError(
     """Raise AssertionError if `src` and `dst` aren't equivalent."""
     try:
         src_ast = parse_ast(src)
     except Exception as exc:
         raise AssertionError(

-            "cannot use --safe with this file; failed to parse source file.  AST"
-            f" error message: {exc}"
-        )
+            "cannot use --safe with this file; failed to parse source file AST: "
+            f"{exc}\n"
+            "This could be caused by running Black with an older Python version "
+            "that does not support new syntax used in your source file."
+        ) from exc

 
     try:
         dst_ast = parse_ast(dst)
     except Exception as exc:
         log = dump_to_file("".join(traceback.format_tb(exc.__traceback__)), dst)
         raise AssertionError(
 
     try:
         dst_ast = parse_ast(dst)
     except Exception as exc:
         log = dump_to_file("".join(traceback.format_tb(exc.__traceback__)), dst)
         raise AssertionError(

-            f"INTERNAL ERROR: Black produced invalid code on pass {pass_num}: {exc}. "
+            f"INTERNAL ERROR: Black produced invalid code: {exc}. "

             "Please report a bug on https://github.com/psf/black/issues.  "
             f"This invalid output might be helpful: {log}"
         ) from None
             "Please report a bug on https://github.com/psf/black/issues.  "
             f"This invalid output might be helpful: {log}"
         ) from None


@@ -998,14 +1368,17 @@ def assert_equivalent(src: str, dst: str, *, pass_num: int = 1) -> None:
         log = dump_to_file(diff(src_ast_str, dst_ast_str, "src", "dst"))
         raise AssertionError(
             "INTERNAL ERROR: Black produced code that is not equivalent to the"
         log = dump_to_file(diff(src_ast_str, dst_ast_str, "src", "dst"))
         raise AssertionError(
             "INTERNAL ERROR: Black produced code that is not equivalent to the"

-            f" source on pass {pass_num}.  Please report a bug on "
+            " source.  Please report a bug on "

             f"https://github.com/psf/black/issues.  This diff might be helpful: {log}"
         ) from None
 
 
 def assert_stable(src: str, dst: str, mode: Mode) -> None:
     """Raise AssertionError if `dst` reformats differently the second time."""
             f"https://github.com/psf/black/issues.  This diff might be helpful: {log}"
         ) from None
 
 
 def assert_stable(src: str, dst: str, mode: Mode) -> None:
     """Raise AssertionError if `dst` reformats differently the second time."""

-    newdst = format_str(dst, mode=mode)
+    # We shouldn't call format_str() here, because that formats the string
+    # twice and may hide a bug where we bounce back and forth between two
+    # versions.
+    newdst = _format_str_once(dst, mode=mode)

     if dst != newdst:
         log = dump_to_file(
             str(mode),
     if dst != newdst:
         log = dump_to_file(
             str(mode),


@@ -1029,7 +1402,7 @@ def nullcontext() -> Iterator[None]:
 
 
 def patch_click() -> None:
 
 
 def patch_click() -> None:

-    """Make Click not crash.
+    """Make Click not crash on Python 3.6 with LANG=C.

 
     On certain misconfigured environments, Python 3 selects the ASCII encoding as the
     default which restricts paths that it can access during the lifetime of the
 
     On certain misconfigured environments, Python 3 selects the ASCII encoding as the
     default which restricts paths that it can access during the lifetime of the


@@ -1039,19 +1412,37 @@ def patch_click() -> None:
     file paths is minimal since it's Python source code.  Moreover, this crash was
     spurious on Python 3.7 thanks to PEP 538 and PEP 540.
     """
     file paths is minimal since it's Python source code.  Moreover, this crash was
     spurious on Python 3.7 thanks to PEP 538 and PEP 540.
     """

+    modules: List[Any] = []

     try:
         from click import core
     try:
         from click import core

+    except ImportError:
+        pass
+    else:
+        modules.append(core)
+    try:
+        # Removed in Click 8.1.0 and newer; we keep this around for users who have
+        # older versions installed.

         from click import _unicodefun  # type: ignore
         from click import _unicodefun  # type: ignore

-    except ModuleNotFoundError:
-        return
+    except ImportError:
+        pass
+    else:
+        modules.append(_unicodefun)

 
 

-    for module in (core, _unicodefun):
+    for module in modules:

         if hasattr(module, "_verify_python3_env"):
             module._verify_python3_env = lambda: None
         if hasattr(module, "_verify_python3_env"):
             module._verify_python3_env = lambda: None

+        if hasattr(module, "_verify_python_env"):
+            module._verify_python_env = lambda: None

 
 
 def patched_main() -> None:
 
 
 def patched_main() -> None:

-    freeze_support()
+    # PyInstaller patches multiprocessing to need freeze_support() even in non-Windows
+    # environments so just assume we always need to call it if frozen.
+    if getattr(sys, "frozen", False):
+        from multiprocessing import freeze_support
+
+        freeze_support()
+

     patch_click()
     main()
 
     patch_click()
     main()