Upgrade mypy (#3864)

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

diff --git a/src/black/__init__.py b/src/black/__init__.py
index e9d3c1b795a8fa167a9c3bcb69320e9d5a39a302..6fc91d2e6d379d6d631caf142b7006af7f6c3d2a 100644 (file)
--- a/src/black/__init__.py
+++ b/src/black/__init__.py
@@ -1,20 +1,16 @@
-import asyncio
-from json.decoder import JSONDecodeError
-import json
-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
-from pathspec.patterns.gitwildmatch import GitWildMatchPatternError
+import json
+import platform

 import re
 import re

-import signal

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

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

 from typing import (
     Any,
     Dict,
 from typing import (
     Any,
     Dict,


@@ -33,48 +29,62 @@ from typing import (
 
 import click
 from click.core import ParameterSource
 
 import click
 from click.core import ParameterSource

-from dataclasses import replace

 from mypy_extensions import mypyc_attr
 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.nodes import is_string_token
-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

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

-from black.mode import FUTURE_FLAG_TO_FEATURE, 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, maybe_install_uvloop
-from black.output import dump_to_file, ipynb_diff, diff, color_diff, out, err
-from black.report import Report, Changed, NothingChanged
+from black.const import (
+    DEFAULT_EXCLUDES,
+    DEFAULT_INCLUDES,
+    DEFAULT_LINE_LENGTH,
+    STDIN_PLACEHOLDER,
+)

 from black.files import (
     find_project_root,
     find_pyproject_toml,
 from black.files import (
     find_project_root,
     find_pyproject_toml,

-    parse_pyproject_toml,

     find_user_pyproject_toml,
     find_user_pyproject_toml,

+    gen_python_files,
+    get_gitignore,
+    normalize_path_maybe_ignore,
+    parse_pyproject_toml,
+    wrap_stream_for_windows,

 )
 )

-from black.files import gen_python_files, get_gitignore, normalize_path_maybe_ignore
-from black.files import wrap_stream_for_windows
-from black.parsing import InvalidInput  # noqa F401
-from black.parsing import lib2to3_parse, parse_ast, stringify_ast

 from black.handle_ipynb_magics import (
 from black.handle_ipynb_magics import (

-    mask_cell,
-    unmask_cell,
-    remove_trailing_semicolon,
-    put_trailing_semicolon_back,
-    TRANSFORMED_MAGICS,

     PYTHON_CELL_MAGICS,
     PYTHON_CELL_MAGICS,

+    TRANSFORMED_MAGICS,

     jupyter_dependencies_are_installed,
     jupyter_dependencies_are_installed,

+    mask_cell,
+    put_trailing_semicolon_back,
+    remove_trailing_semicolon,
+    unmask_cell,

 )
 )

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

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

-
-from _black_version import version as __version__
+from blib2to3.pytree import Leaf, Node

 
 COMPILED = Path(__file__).suffix in (".pyd", ".so")
 
 
 COMPILED = Path(__file__).suffix in (".pyd", ".so")
 


@@ -107,8 +117,6 @@ class WriteBack(Enum):
 # Legacy name, left for integrations.
 FileMode = Mode
 
 # Legacy name, left for integrations.
 FileMode = Mode
 

-DEFAULT_WORKERS = os.cpu_count()
-

 
 def read_pyproject_toml(
     ctx: click.Context, param: click.Parameter, value: Optional[str]
 
 def read_pyproject_toml(
     ctx: click.Context, param: click.Parameter, value: Optional[str]


@@ -119,7 +127,9 @@ def read_pyproject_toml(
     otherwise.
     """
     if not value:
     otherwise.
     """
     if not value:

-        value = find_pyproject_toml(ctx.params.get("src", ()))
+        value = find_pyproject_toml(
+            ctx.params.get("src", ()), ctx.params.get("stdin_filename", None)
+        )

         if value is None:
             return None
 
         if value is None:
             return None
 


@@ -147,6 +157,16 @@ def read_pyproject_toml(
             "target-version", "Config key target-version must be a list"
         )
 
             "target-version", "Config key target-version must be a list"
         )
 

+    exclude = config.get("exclude")
+    if exclude is not None and not isinstance(exclude, str):
+        raise click.BadOptionUsage("exclude", "Config key exclude must be a string")
+
+    extend_exclude = config.get("extend_exclude")
+    if extend_exclude is not None and not isinstance(extend_exclude, str):
+        raise click.BadOptionUsage(
+            "extend-exclude", "Config key extend-exclude must be a string"
+        )
+

     default_map: Dict[str, Any] = {}
     if ctx.default_map:
         default_map.update(ctx.default_map)
     default_map: Dict[str, Any] = {}
     if ctx.default_map:
         default_map.update(ctx.default_map)


@@ -211,8 +231,9 @@ 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(


@@ -236,11 +257,17 @@ def validate_regex(
     multiple=True,
     help=(
         "When processing Jupyter Notebooks, add the given magic to the list"
     multiple=True,
     help=(
         "When processing Jupyter Notebooks, add the given magic to the list"

-        f" of known python-magics ({', '.join(PYTHON_CELL_MAGICS)})."
+        f" of known python-magics ({', '.join(sorted(PYTHON_CELL_MAGICS))})."

         " Useful for formatting cells with custom python magics."
     ),
     default=[],
 )
         " 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",


@@ -347,6 +374,7 @@ def validate_regex(
 @click.option(
     "--stdin-filename",
     type=str,
 @click.option(
     "--stdin-filename",
     type=str,

+    is_eager=True,

     help=(
         "The name of the file when passing it through stdin. Useful to make "
         "sure Black will respect --force-exclude option on some "
     help=(
         "The name of the file when passing it through stdin. Useful to make "
         "sure Black will respect --force-exclude option on some "


@@ -357,9 +385,11 @@ def validate_regex(
     "-W",
     "--workers",
     type=click.IntRange(min=1),
     "-W",
     "--workers",
     type=click.IntRange(min=1),

-    default=DEFAULT_WORKERS,
-    show_default=True,
-    help="Number of parallel workers",
+    default=None,
+    help=(
+        "Number of parallel workers [default: BLACK_NUM_WORKERS environment variable "
+        "or number of CPUs in the system]"
+    ),

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


@@ -381,7 +411,10 @@ def validate_regex(
 )
 @click.version_option(
     version=__version__,
 )
 @click.version_option(
     version=__version__,

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

 )
 @click.argument(
     "src",
 )
 @click.argument(
     "src",


@@ -419,6 +452,7 @@ def main(  # noqa: C901
     pyi: bool,
     ipynb: bool,
     python_cell_magics: Sequence[str],
     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,


@@ -431,7 +465,7 @@ def main(  # noqa: C901
     extend_exclude: Optional[Pattern[str]],
     force_exclude: Optional[Pattern[str]],
     stdin_filename: Optional[str],
     extend_exclude: Optional[Pattern[str]],
     force_exclude: Optional[Pattern[str]],
     stdin_filename: Optional[str],

-    workers: int,
+    workers: Optional[int],

     src: Tuple[str, ...],
     config: Optional[str],
 ) -> None:
     src: Tuple[str, ...],
     config: Optional[str],
 ) -> None:


@@ -448,7 +482,9 @@ def main(  # noqa: C901
         out(main.get_usage(ctx) + "\n\nOne of 'SRC' or 'code' is required.")
         ctx.exit(1)
 
         out(main.get_usage(ctx) + "\n\nOne of 'SRC' or 'code' is required.")
         ctx.exit(1)
 

-    root, method = find_project_root(src) if code is None else (None, None)
+    root, method = (
+        find_project_root(src, stdin_filename) if code is None else (None, None)
+    )

     ctx.obj["root"] = root
 
     if verbose:
     ctx.obj["root"] = root
 
     if verbose:


@@ -458,20 +494,6 @@ def main(  # noqa: C901
                 fg="blue",
             )
 
                 fg="blue",
             )
 

-            normalized = [
-                (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:
             config_source = ctx.get_parameter_source("config")
             user_level_config = str(find_user_pyproject_toml())


@@ -488,6 +510,9 @@ def main(  # noqa: C901
                 out("Using configuration from project root.", fg="blue")
             else:
                 out(f"Using configuration in '{config}'.", fg="blue")
                 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 (
 
     error_msg = "Oh no! 💥 💔 💥"
     if (


@@ -515,6 +540,7 @@ def main(  # noqa: C901
         line_length=line_length,
         is_pyi=pyi,
         is_ipynb=ipynb,
         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,


@@ -534,9 +560,10 @@ def main(  # noqa: C901
             content=code, fast=fast, write_back=write_back, mode=mode, report=report
         )
     else:
             content=code, fast=fast, write_back=write_back, mode=mode, report=report
         )
     else:

+        assert root is not None  # root is only None if code is not None

         try:
             sources = get_sources(
         try:
             sources = get_sources(

-                ctx=ctx,
+                root=root,

                 src=src,
                 quiet=quiet,
                 verbose=verbose,
                 src=src,
                 quiet=quiet,
                 verbose=verbose,


@@ -567,6 +594,8 @@ def main(  # noqa: C901
                 report=report,
             )
         else:
                 report=report,
             )
         else:

+            from black.concurrency import reformat_many
+

             reformat_many(
                 sources=sources,
                 fast=fast,
             reformat_many(
                 sources=sources,
                 fast=fast,


@@ -587,7 +616,7 @@ def main(  # noqa: C901
 
 def get_sources(
     *,
 
 def get_sources(
     *,

-    ctx: click.Context,
+    root: Path,

     src: Tuple[str, ...],
     quiet: bool,
     verbose: bool,
     src: Tuple[str, ...],
     quiet: bool,
     verbose: bool,


@@ -601,11 +630,10 @@ def get_sources(
     """Compute the set of files to be formatted."""
     sources: Set[Path] = set()
 
     """Compute the set of files to be formatted."""
     sources: Set[Path] = set()
 

-    if exclude is None:
-        exclude = re_compile_maybe_verbose(DEFAULT_EXCLUDES)
-        gitignore = get_gitignore(ctx.obj["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:


@@ -616,9 +644,15 @@ 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, ctx.obj["root"], report)
+            normalized_path: Optional[str] = normalize_path_maybe_ignore(
+                p, root, report
+            )

             if normalized_path is None:
             if normalized_path is None:

+                if verbose:
+                    out(f'Skipping invalid source: "{normalized_path}"', fg="red")

                 continue
                 continue

+            if verbose:
+                out(f'Found input source: "{normalized_path}"', fg="blue")

 
             normalized_path = "/" + normalized_path
             # Hard-exclude any files that matches the `--force-exclude` regex.
 
             normalized_path = "/" + normalized_path
             # Hard-exclude any files that matches the `--force-exclude` regex.


@@ -634,16 +668,27 @@ def get_sources(
                 p = Path(f"{STDIN_PLACEHOLDER}{str(p)}")
 
             if p.suffix == ".ipynb" and not jupyter_dependencies_are_installed(
                 p = Path(f"{STDIN_PLACEHOLDER}{str(p)}")
 
             if p.suffix == ".ipynb" and not jupyter_dependencies_are_installed(

-                verbose=verbose, quiet=quiet
+                warn=verbose or not quiet

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

+            p_relative = normalize_path_maybe_ignore(p, root, report)
+            assert p_relative is not None
+            p = root / p_relative
+            if verbose:
+                out(f'Found input source directory: "{p}"', fg="blue")
+
+            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(),

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

                     include,
                     exclude,
                     extend_exclude,
                     include,
                     exclude,
                     extend_exclude,


@@ -655,9 +700,12 @@ def get_sources(
                 )
             )
         elif s == "-":
                 )
             )
         elif s == "-":

+            if verbose:
+                out("Found input source stdin", fg="blue")

             sources.add(p)
         else:
             err(f"invalid path: {s}")
             sources.add(p)
         else:
             err(f"invalid path: {s}")

+

     return sources
 
 
     return sources
 
 


@@ -729,12 +777,9 @@ def reformat_one(
             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:

-            cache: Cache = {}
+            cache = Cache.read(mode)

             if write_back not in (WriteBack.DIFF, WriteBack.COLOR_DIFF):
             if write_back not in (WriteBack.DIFF, WriteBack.COLOR_DIFF):

-                cache = read_cache(mode)
-                res_src = src.resolve()
-                res_src_s = str(res_src)
-                if res_src_s in cache and cache[res_src_s] == get_cache_info(res_src):
+                if not cache.is_changed(src):

                     changed = Changed.CACHED
             if changed is not Changed.CACHED and format_file_in_place(
                 src, fast=fast, write_back=write_back, mode=mode
                     changed = Changed.CACHED
             if changed is not Changed.CACHED and format_file_in_place(
                 src, fast=fast, write_back=write_back, mode=mode


@@ -743,7 +788,7 @@ def reformat_one(
             if (write_back is WriteBack.YES and changed is not Changed.CACHED) or (
                 write_back is WriteBack.CHECK and changed is Changed.NO
             ):
             if (write_back is WriteBack.YES and changed is not Changed.CACHED) or (
                 write_back is WriteBack.CHECK and changed is Changed.NO
             ):

-                write_cache(cache, [src], mode)
+                cache.write([src])

         report.done(src, changed)
     except Exception as exc:
         if report.verbose:
         report.done(src, changed)
     except Exception as exc:
         if report.verbose:


@@ -751,126 +796,6 @@ def reformat_one(
         report.failed(src, str(exc))
 
 
         report.failed(src, 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_many(
-    sources: Set[Path],
-    fast: bool,
-    write_back: WriteBack,
-    mode: Mode,
-    report: "Report",
-    workers: Optional[int],
-) -> None:
-    """Reformat multiple files using a ProcessPoolExecutor."""
-    executor: Executor
-    loop = asyncio.get_event_loop()
-    worker_count = workers if workers is not None else DEFAULT_WORKERS
-    if sys.platform == "win32":
-        # Work around https://bugs.python.org/issue26903
-        assert worker_count is not None
-        worker_count = min(worker_count, 60)
-    try:
-        executor = ProcessPoolExecutor(max_workers=worker_count)
-    except (ImportError, NotImplementedError, 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:
-        if sys.version_info >= (3, 7):
-            await asyncio.gather(*cancelled, return_exceptions=True)
-        else:
-            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,


@@ -889,8 +814,11 @@ def format_file_in_place(
     elif src.suffix == ".ipynb":
         mode = replace(mode, is_ipynb=True)
 
     elif src.suffix == ".ipynb":
         mode = replace(mode, is_ipynb=True)
 

-    then = datetime.utcfromtimestamp(src.stat().st_mtime)
+    then = datetime.fromtimestamp(src.stat().st_mtime, timezone.utc)
+    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)
         src_contents, encoding, newline = decode_bytes(buf.read())
     try:
         dst_contents = format_file_contents(src_contents, fast=fast, mode=mode)


@@ -900,14 +828,16 @@ def format_file_in_place(
         raise ValueError(
             f"File '{src}' cannot be parsed as valid Jupyter notebook."
         ) from None
         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:
             f.write(dst_contents)
     elif write_back in (WriteBack.DIFF, WriteBack.COLOR_DIFF):
 
     if write_back == WriteBack.YES:
         with open(src, "w", encoding=encoding, newline=newline) as f:
             f.write(dst_contents)
     elif write_back in (WriteBack.DIFF, WriteBack.COLOR_DIFF):

-        now = datetime.utcnow()
-        src_name = f"{src}\t{then} +0000"
-        dst_name = f"{src}\t{now} +0000"
+        now = datetime.now(timezone.utc)
+        src_name = f"{src}\t{then}"
+        dst_name = f"{src}\t{now}"

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


@@ -945,7 +875,7 @@ def format_stdin_to_stdout(
     write a diff to stdout. The `mode` argument is passed to
     :func:`format_file_contents`.
     """
     write a diff to stdout. The `mode` argument is passed to
     :func:`format_file_contents`.
     """

-    then = datetime.utcnow()
+    then = datetime.now(timezone.utc)

 
     if content is None:
         src, encoding, newline = decode_bytes(sys.stdin.buffer.read())
 
     if content is None:
         src, encoding, newline = decode_bytes(sys.stdin.buffer.read())


@@ -970,9 +900,9 @@ def format_stdin_to_stdout(
                 dst += "\n"
             f.write(dst)
         elif write_back in (WriteBack.DIFF, WriteBack.COLOR_DIFF):
                 dst += "\n"
             f.write(dst)
         elif write_back in (WriteBack.DIFF, WriteBack.COLOR_DIFF):

-            now = datetime.utcnow()
-            src_name = f"STDIN\t{then} +0000"
-            dst_name = f"STDOUT\t{now} +0000"
+            now = datetime.now(timezone.utc)
+            src_name = f"STDIN\t{then}"
+            dst_name = f"STDOUT\t{now}"

             d = diff(src, dst, src_name, dst_name)
             if write_back == WriteBack.COLOR_DIFF:
                 d = color_diff(d)
             d = diff(src, dst, src_name, dst_name)
             if write_back == WriteBack.COLOR_DIFF:
                 d = color_diff(d)


@@ -1001,9 +931,6 @@ 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():
-        raise NothingChanged
-

     if mode.is_ipynb:
         dst_contents = format_ipynb_string(src_contents, fast=fast, mode=mode)
     else:
     if mode.is_ipynb:
         dst_contents = format_ipynb_string(src_contents, fast=fast, mode=mode)
     else:


@@ -1098,6 +1025,9 @@ def format_ipynb_string(src_contents: str, *, fast: bool, mode: Mode) -> FileCon
     Operate cell-by-cell, only on code cells, only for Python notebooks.
     If the ``.ipynb`` originally had a trailing newline, it'll be preserved.
     """
     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)
     trailing_newline = src_contents[-1] == "\n"
     modified = False
     nb = json.loads(src_contents)


@@ -1162,31 +1092,46 @@ def format_str(src_contents: str, *, mode: Mode) -> str:
 
 def _format_str_once(src_contents: str, *, mode: Mode) -> str:
     src_node = lib2to3_parse(src_contents.lstrip(), mode.target_versions)
 
 def _format_str_once(src_contents: str, *, mode: Mode) -> str:
     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:

+        future_imports = get_future_imports(src_node)

         versions = detect_target_versions(src_node, future_imports=future_imports)
 
         versions = detect_target_versions(src_node, future_imports=future_imports)
 

-    normalize_fmt_off(src_node, preview=mode.preview)
-    lines = LineGenerator(mode=mode)
-    elt = EmptyLineTracker(is_pyi=mode.is_pyi)
-    empty_line = Line(mode=mode)
-    after = 0
+    context_manager_features = {
+        feature
+        for feature in {Feature.PARENTHESIZED_CONTEXT_MANAGERS}
+        if supports_feature(versions, feature)
+    }
+    normalize_fmt_off(src_node)
+    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)
 
 


@@ -1214,6 +1159,7 @@ def get_features_used(  # noqa: C901
 
     Currently looking for:
     - f-strings;
 
     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;
     - underscores in numeric literals;
     - trailing commas after * or ** in function signatures and calls;
     - positional only arguments in function signatures and lambdas;


@@ -1221,6 +1167,10 @@ def get_features_used(  # noqa: C901
     - relaxed decorator syntax;
     - usage of __future__ flags (annotations);
     - print / exec statements;
     - relaxed decorator syntax;
     - usage of __future__ flags (annotations);
     - print / exec statements;

+    - parenthesized context managers;
+    - match statements;
+    - except* clause;
+    - variadic generics;

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


@@ -1235,9 +1185,13 @@ def get_features_used(  # noqa: C901
             value_head = n.value[:2]
             if value_head in {'f"', 'F"', "f'", "F'", "rf", "fr", "RF", "FR"}:
                 features.add(Feature.F_STRINGS)
             value_head = n.value[:2]
             if value_head in {'f"', 'F"', "f'", "F'", "rf", "fr", "RF", "FR"}:
                 features.add(Feature.F_STRINGS)

+                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 n.type == token.NUMBER:
-            assert isinstance(n, Leaf)
+        elif is_number_token(n):

             if "_" in n.value:
                 features.add(Feature.NUMERIC_UNDERSCORES)
 
             if "_" in n.value:
                 features.add(Feature.NUMERIC_UNDERSCORES)
 


@@ -1292,6 +1246,45 @@ def get_features_used(  # noqa: C901
         ):
             features.add(Feature.ANN_ASSIGN_EXTENDED_RHS)
 
         ):
             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)
+
+        elif n.type in (syms.type_stmt, syms.typeparams):
+            features.add(Feature.TYPE_PARAMS)
+

     return features
 
 
     return features
 
 


@@ -1416,42 +1409,14 @@ def nullcontext() -> Iterator[None]:
     yield
 
 
     yield
 
 

-def patch_click() -> None:
-    """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
-    application.  Click refuses to work in this scenario by raising a RuntimeError.
-
-    In case of Black the likelihood that non-ASCII characters are going to be used in
-    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
-    except ImportError:
-        pass
-    else:
-        modules.append(core)
-    try:
-        from click import _unicodefun
-    except ImportError:
-        pass
-    else:
-        modules.append(_unicodefun)
-
-    for module in modules:
-        if hasattr(module, "_verify_python3_env"):
-            module._verify_python3_env = lambda: None  # type: ignore
-        if hasattr(module, "_verify_python_env"):
-            module._verify_python_env = lambda: None  # type: ignore
+def patched_main() -> None:
+    # 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()

 
 

-def patched_main() -> None:
-    maybe_install_uvloop()
-    freeze_support()
-    patch_click()

     main()
 
 
     main()