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Enable `PYTHONWARNDEFAULTENCODING = 1` in CI (#3763)
[etc/vim.git] / src / black / __init__.py
index 2a5c750a5835562ddf5c743b01ab0cc58b4cb75c..222cb3ca03d98ca059c3c09d270b97700558105a 100644 (file)
@@ -1,22 +1,17 @@
-import asyncio
 import io
 import json
 import io
 import json
-import os
 import platform
 import re
 import platform
 import re
-import signal
 import sys
 import tokenize
 import traceback
 from contextlib import contextmanager
 from dataclasses import replace
 import sys
 import tokenize
 import traceback
 from contextlib import contextmanager
 from dataclasses import replace
-from datetime import datetime
+from datetime import datetime, timezone
 from enum import Enum
 from json.decoder import JSONDecodeError
 from enum import Enum
 from json.decoder import JSONDecodeError
-from multiprocessing import Manager, freeze_support
 from pathlib import Path
 from typing import (
 from pathlib import Path
 from typing import (
-    TYPE_CHECKING,
     Any,
     Dict,
     Generator,
     Any,
     Dict,
     Generator,
@@ -35,12 +30,12 @@ from typing import (
 import click
 from click.core import ParameterSource
 from mypy_extensions import mypyc_attr
 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_version import version as __version__
 from pathspec.patterns.gitwildmatch import GitWildMatchPatternError
 
 from _black_version import version as __version__
-from black.cache import Cache, filter_cached, get_cache_info, read_cache, write_cache
+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.concurrency import cancel, maybe_install_uvloop, shutdown
 from black.const import (
     DEFAULT_EXCLUDES,
     DEFAULT_INCLUDES,
 from black.const import (
     DEFAULT_EXCLUDES,
     DEFAULT_INCLUDES,
@@ -67,7 +62,7 @@ from black.handle_ipynb_magics import (
     unmask_cell,
 )
 from black.linegen import LN, LineGenerator, transform_line
     unmask_cell,
 )
 from black.linegen import LN, LineGenerator, transform_line
-from black.lines import EmptyLineTracker, Line
+from black.lines import EmptyLineTracker, LinesBlock
 from black.mode import (
     FUTURE_FLAG_TO_FEATURE,
     VERSION_TO_FEATURES,
 from black.mode import (
     FUTURE_FLAG_TO_FEATURE,
     VERSION_TO_FEATURES,
@@ -87,12 +82,10 @@ 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.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.pytree import Leaf, Node
 
 from blib2to3.pgen2 import token
 from blib2to3.pytree import Leaf, Node
 
-if TYPE_CHECKING:
-    from concurrent.futures import Executor
-
 COMPILED = Path(__file__).suffix in (".pyd", ".so")
 
 # types
 COMPILED = Path(__file__).suffix in (".pyd", ".so")
 
 # types
@@ -124,8 +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]
@@ -136,7 +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
 
@@ -228,8 +221,9 @@ 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(
@@ -253,11 +247,17 @@ 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",
@@ -364,6 +364,7 @@ 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 "
@@ -374,9 +375,11 @@ 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",
@@ -439,6 +442,7 @@ 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,
@@ -451,7 +455,7 @@ 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:
@@ -468,7 +472,9 @@ 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:
@@ -478,20 +484,6 @@ 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())
@@ -508,6 +500,9 @@ 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 (
@@ -535,6 +530,7 @@ 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,
@@ -587,6 +583,8 @@ 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,
@@ -620,12 +618,12 @@ def get_sources(
 ) -> Set[Path]:
     """Compute the set of files to be formatted."""
     sources: Set[Path] = set()
 ) -> Set[Path]:
     """Compute the set of files to be formatted."""
     sources: Set[Path] = set()
+    root = ctx.obj["root"]
 
 
-    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:
@@ -636,9 +634,15 @@ 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, ctx.obj["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.
@@ -660,6 +664,15 @@ def get_sources(
 
             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 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(),
@@ -675,9 +688,12 @@ 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
 
 
@@ -771,132 +787,6 @@ 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."""
-    from concurrent.futures import Executor, ProcessPoolExecutor, ThreadPoolExecutor
-
-    executor: Executor
-    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)
-
-    loop = asyncio.new_event_loop()
-    asyncio.set_event_loop(loop)
-    try:
-        loop.run_until_complete(
-            schedule_formatting(
-                sources=sources,
-                fast=fast,
-                write_back=write_back,
-                mode=mode,
-                report=report,
-                loop=loop,
-                executor=executor,
-            )
-        )
-    finally:
-        try:
-            shutdown(loop)
-        finally:
-            asyncio.set_event_loop(None)
-        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,
@@ -915,8 +805,11 @@ 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)
@@ -926,14 +819,16 @@ 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:
@@ -971,7 +866,7 @@ 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())
@@ -996,9 +891,9 @@ 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)
@@ -1027,9 +922,6 @@ 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:
@@ -1124,6 +1016,9 @@ 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)
@@ -1188,31 +1083,46 @@ 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 = []
+    dst_blocks: List[LinesBlock] = []
     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)
 
     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)
 
-    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)
 
 
@@ -1240,6 +1150,7 @@ 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;
@@ -1247,6 +1158,10 @@ 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:
@@ -1261,6 +1176,11 @@ 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 is_number_token(n):
             if "_" in n.value:
 
         elif is_number_token(n):
             if "_" in n.value:
@@ -1317,6 +1237,23 @@ 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
         elif (
             n.type == syms.except_clause
             and len(n.children) >= 2
@@ -1336,6 +1273,9 @@ def get_features_used(  # noqa: C901
         ):
             features.add(Feature.VARIADIC_GENERICS)
 
         ):
             features.add(Feature.VARIADIC_GENERICS)
 
+        elif n.type in (syms.type_stmt, syms.typeparams):
+            features.add(Feature.TYPE_PARAMS)
+
     return features
 
 
     return features
 
 
@@ -1489,14 +1429,19 @@ def patch_click() -> None:
 
     for module in modules:
         if hasattr(module, "_verify_python3_env"):
 
     for module in modules:
         if hasattr(module, "_verify_python3_env"):
-            module._verify_python3_env = lambda: None  # type: ignore
+            module._verify_python3_env = lambda: None
         if hasattr(module, "_verify_python_env"):
         if hasattr(module, "_verify_python_env"):
-            module._verify_python_env = lambda: None  # type: ignore
+            module._verify_python_env = lambda: None
 
 
 def patched_main() -> None:
 
 
 def patched_main() -> None:
-    maybe_install_uvloop()
-    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()