Update README with missing fixes in Change Log

[etc/vim.git] / black.py

diff --git a/black.py b/black.py
index a31aa7ac4402812d3c54e98125b7e8e3e2a6feb6..f51b10ef7d0a282e60a8064f2d871c43739cd90d 100644 (file)
--- a/black.py
+++ b/black.py
@@ -1,18 +1,20 @@
 import asyncio
 import asyncio

-import pickle

 from asyncio.base_events import BaseEventLoop
 from concurrent.futures import Executor, ProcessPoolExecutor
 from asyncio.base_events import BaseEventLoop
 from concurrent.futures import Executor, ProcessPoolExecutor

-from enum import Enum
-from functools import partial, wraps
+from datetime import datetime
+from enum import Enum, Flag
+from functools import lru_cache, partial, wraps
+import io

 import keyword
 import logging
 from multiprocessing import Manager
 import os
 from pathlib import Path
 import keyword
 import logging
 from multiprocessing import Manager
 import os
 from pathlib import Path

+import pickle

 import re
 import re

-import tokenize

 import signal
 import sys
 import signal
 import sys

+import tokenize

 from typing import (
     Any,
     Callable,
 from typing import (
     Any,
     Callable,


@@ -36,6 +38,7 @@ from typing import (
 from appdirs import user_cache_dir
 from attr import dataclass, Factory
 import click
 from appdirs import user_cache_dir
 from attr import dataclass, Factory
 import click

+import toml

 
 # lib2to3 fork
 from blib2to3.pytree import Node, Leaf, type_repr
 
 # lib2to3 fork
 from blib2to3.pytree import Node, Leaf, type_repr


@@ -44,14 +47,19 @@ from blib2to3.pgen2 import driver, token
 from blib2to3.pgen2.parse import ParseError
 
 
 from blib2to3.pgen2.parse import ParseError
 
 

-__version__ = "18.5b0"
+__version__ = "18.6b2"

 DEFAULT_LINE_LENGTH = 88
 DEFAULT_LINE_LENGTH = 88

+DEFAULT_EXCLUDES = (
+    r"/(\.git|\.hg|\.mypy_cache|\.tox|\.venv|_build|buck-out|build|dist)/"
+)
+DEFAULT_INCLUDES = r"\.pyi?$"

 CACHE_DIR = Path(user_cache_dir("black", version=__version__))
 
 
 # types
 FileContent = str
 Encoding = str
 CACHE_DIR = Path(user_cache_dir("black", version=__version__))
 
 
 # types
 FileContent = str
 Encoding = str

+NewLine = str

 Depth = int
 NodeType = int
 LeafID = int
 Depth = int
 NodeType = int
 LeafID = int


@@ -115,6 +123,13 @@ class WriteBack(Enum):
     YES = 1
     DIFF = 2
 
     YES = 1
     DIFF = 2
 

+    @classmethod
+    def from_configuration(cls, *, check: bool, diff: bool) -> "WriteBack":
+        if check and not diff:
+            return cls.NO
+
+        return cls.DIFF if diff else cls.YES
+

 
 class Changed(Enum):
     NO = 0
 
 class Changed(Enum):
     NO = 0


@@ -122,7 +137,61 @@ class Changed(Enum):
     YES = 2
 
 
     YES = 2
 
 

-@click.command()
+class FileMode(Flag):
+    AUTO_DETECT = 0
+    PYTHON36 = 1
+    PYI = 2
+    NO_STRING_NORMALIZATION = 4
+
+    @classmethod
+    def from_configuration(
+        cls, *, py36: bool, pyi: bool, skip_string_normalization: bool
+    ) -> "FileMode":
+        mode = cls.AUTO_DETECT
+        if py36:
+            mode |= cls.PYTHON36
+        if pyi:
+            mode |= cls.PYI
+        if skip_string_normalization:
+            mode |= cls.NO_STRING_NORMALIZATION
+        return mode
+
+
+def read_pyproject_toml(
+    ctx: click.Context, param: click.Parameter, value: Union[str, int, bool, None]
+) -> Optional[str]:
+    """Inject Black configuration from "pyproject.toml" into defaults in `ctx`.
+
+    Returns the path to a successfully found and read configuration file, None
+    otherwise.
+    """
+    assert not isinstance(value, (int, bool)), "Invalid parameter type passed"
+    if not value:
+        root = find_project_root(ctx.params.get("src", ()))
+        path = root / "pyproject.toml"
+        if path.is_file():
+            value = str(path)
+        else:
+            return None
+
+    try:
+        pyproject_toml = toml.load(value)
+        config = pyproject_toml.get("tool", {}).get("black", {})
+    except (toml.TomlDecodeError, OSError) as e:
+        raise click.BadOptionUsage(f"Error reading configuration file: {e}", ctx)
+
+    if not config:
+        return None
+
+    if ctx.default_map is None:
+        ctx.default_map = {}
+    ctx.default_map.update(  # type: ignore  # bad types in .pyi
+        {k.replace("--", "").replace("-", "_"): v for k, v in config.items()}
+    )
+    return value
+
+
+@click.command(context_settings=dict(help_option_names=["-h", "--help"]))

 @click.option(
     "-l",
     "--line-length",
 @click.option(
     "-l",
     "--line-length",


@@ -131,6 +200,29 @@ class Changed(Enum):
     help="How many character per line to allow.",
     show_default=True,
 )
     help="How many character per line to allow.",
     show_default=True,
 )

+@click.option(
+    "--py36",
+    is_flag=True,
+    help=(
+        "Allow using Python 3.6-only syntax on all input files.  This will put "
+        "trailing commas in function signatures and calls also after *args and "
+        "**kwargs.  [default: per-file auto-detection]"
+    ),
+)
+@click.option(
+    "--pyi",
+    is_flag=True,
+    help=(
+        "Format all input files like typing stubs regardless of file extension "
+        "(useful when piping source on standard input)."
+    ),
+)
+@click.option(
+    "-S",
+    "--skip-string-normalization",
+    is_flag=True,
+    help="Don't normalize string quotes or prefixes.",
+)

 @click.option(
     "--check",
     is_flag=True,
 @click.option(
     "--check",
     is_flag=True,


@@ -151,29 +243,46 @@ class Changed(Enum):
     help="If --fast given, skip temporary sanity checks. [default: --safe]",
 )
 @click.option(
     help="If --fast given, skip temporary sanity checks. [default: --safe]",
 )
 @click.option(

-    "-q",
-    "--quiet",
-    is_flag=True,
+    "--include",
+    type=str,
+    default=DEFAULT_INCLUDES,

     help=(
     help=(

-        "Don't emit non-error messages to stderr. Errors are still emitted, "
-        "silence those with 2>/dev/null."
+        "A regular expression that matches files and directories that should be "
+        "included on recursive searches.  An empty value means all files are "
+        "included regardless of the name.  Use forward slashes for directories on "
+        "all platforms (Windows, too).  Exclusions are calculated first, inclusions "
+        "later."

     ),
     ),

+    show_default=True,

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

-    "--pyi",
+    "--exclude",
+    type=str,
+    default=DEFAULT_EXCLUDES,
+    help=(
+        "A regular expression that matches files and directories that should be "
+        "excluded on recursive searches.  An empty value means no paths are excluded. "
+        "Use forward slashes for directories on all platforms (Windows, too).  "
+        "Exclusions are calculated first, inclusions later."
+    ),
+    show_default=True,
+)
+@click.option(
+    "-q",
+    "--quiet",

     is_flag=True,
     help=(
     is_flag=True,
     help=(

-        "Consider all input files typing stubs regardless of file extension "
-        "(useful when piping source on standard input)."
+        "Don't emit non-error messages to stderr. Errors are still emitted, "
+        "silence those with 2>/dev/null."

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

-    "--py36",
+    "-v",
+    "--verbose",

     is_flag=True,
     help=(
     is_flag=True,
     help=(

-        "Allow using Python 3.6-only syntax on all input files.  This will put "
-        "trailing commas in function signatures and calls also after *args and "
-        "**kwargs.  [default: per-file auto-detection]"
+        "Also emit messages to stderr about files that were not changed or were "
+        "ignored due to --exclude=."

     ),
 )
 @click.version_option(version=__version__)
     ),
 )
 @click.version_option(version=__version__)


@@ -183,6 +292,16 @@ class Changed(Enum):
     type=click.Path(
         exists=True, file_okay=True, dir_okay=True, readable=True, allow_dash=True
     ),
     type=click.Path(
         exists=True, file_okay=True, dir_okay=True, readable=True, allow_dash=True
     ),

+    is_eager=True,
+)
+@click.option(
+    "--config",
+    type=click.Path(
+        exists=False, file_okay=True, dir_okay=False, readable=True, allow_dash=False
+    ),
+    is_eager=True,
+    callback=read_pyproject_toml,
+    help="Read configuration from PATH.",

 )
 @click.pass_context
 def main(
 )
 @click.pass_context
 def main(


@@ -193,43 +312,57 @@ def main(
     fast: bool,
     pyi: bool,
     py36: bool,
     fast: bool,
     pyi: bool,
     py36: bool,

+    skip_string_normalization: bool,

     quiet: bool,
     quiet: bool,

-    src: List[str],
+    verbose: bool,
+    include: str,
+    exclude: str,
+    src: Tuple[str],
+    config: Optional[str],

 ) -> None:
     """The uncompromising code formatter."""
 ) -> None:
     """The uncompromising code formatter."""

-    sources: List[Path] = []
+    write_back = WriteBack.from_configuration(check=check, diff=diff)
+    mode = FileMode.from_configuration(
+        py36=py36, pyi=pyi, skip_string_normalization=skip_string_normalization
+    )
+    if config and verbose:
+        out(f"Using configuration from {config}.", bold=False, fg="blue")
+    try:
+        include_regex = re_compile_maybe_verbose(include)
+    except re.error:
+        err(f"Invalid regular expression for include given: {include!r}")
+        ctx.exit(2)
+    try:
+        exclude_regex = re_compile_maybe_verbose(exclude)
+    except re.error:
+        err(f"Invalid regular expression for exclude given: {exclude!r}")
+        ctx.exit(2)
+    report = Report(check=check, quiet=quiet, verbose=verbose)
+    root = find_project_root(src)
+    sources: Set[Path] = set()

     for s in src:
         p = Path(s)
         if p.is_dir():
     for s in src:
         p = Path(s)
         if p.is_dir():

-            sources.extend(gen_python_files_in_dir(p))
-        elif p.is_file():
+            sources.update(
+                gen_python_files_in_dir(p, root, include_regex, exclude_regex, report)
+            )
+        elif p.is_file() or s == "-":

             # if a file was explicitly given, we don't care about its extension
             # if a file was explicitly given, we don't care about its extension

-            sources.append(p)
-        elif s == "-":
-            sources.append(Path("-"))
+            sources.add(p)

         else:
             err(f"invalid path: {s}")
         else:
             err(f"invalid path: {s}")

-
-    if check and not diff:
-        write_back = WriteBack.NO
-    elif diff:
-        write_back = WriteBack.DIFF
-    else:
-        write_back = WriteBack.YES
-    report = Report(check=check, quiet=quiet)

     if len(sources) == 0:
     if len(sources) == 0:

-        out("No paths given. Nothing to do 😴")
+        if verbose or not quiet:
+            out("No paths given. Nothing to do 😴")

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

-        return

 
 

-    elif len(sources) == 1:
+    if len(sources) == 1:

         reformat_one(
         reformat_one(

-            src=sources[0],
+            src=sources.pop(),

             line_length=line_length,
             fast=fast,
             line_length=line_length,
             fast=fast,

-            pyi=pyi,
-            py36=py36,

             write_back=write_back,
             write_back=write_back,

+            mode=mode,

             report=report,
         )
     else:
             report=report,
         )
     else:


@@ -241,9 +374,8 @@ def main(
                     sources=sources,
                     line_length=line_length,
                     fast=fast,
                     sources=sources,
                     line_length=line_length,
                     fast=fast,

-                    pyi=pyi,
-                    py36=py36,

                     write_back=write_back,
                     write_back=write_back,

+                    mode=mode,

                     report=report,
                     loop=loop,
                     executor=executor,
                     report=report,
                     loop=loop,
                     executor=executor,


@@ -251,9 +383,10 @@ def main(
             )
         finally:
             shutdown(loop)
             )
         finally:
             shutdown(loop)

-        if not quiet:
-            out("All done! ✨ 🍰 ✨")
-            click.echo(str(report))
+    if verbose or not quiet:
+        bang = "💥 💔 💥" if report.return_code else "✨ 🍰 ✨"
+        out(f"All done! {bang}")
+        click.secho(str(report), err=True)

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


@@ -261,9 +394,8 @@ def reformat_one(
     src: Path,
     line_length: int,
     fast: bool,
     src: Path,
     line_length: int,
     fast: bool,

-    pyi: bool,
-    py36: bool,

     write_back: WriteBack,
     write_back: WriteBack,

+    mode: FileMode,

     report: "Report",
 ) -> None:
     """Reformat a single file under `src` without spawning child processes.
     report: "Report",
 ) -> None:
     """Reformat a single file under `src` without spawning child processes.


@@ -276,43 +408,37 @@ def reformat_one(
         changed = Changed.NO
         if not src.is_file() and str(src) == "-":
             if format_stdin_to_stdout(
         changed = Changed.NO
         if not src.is_file() and str(src) == "-":
             if format_stdin_to_stdout(

-                line_length=line_length,
-                fast=fast,
-                is_pyi=pyi,
-                force_py36=py36,
-                write_back=write_back,
+                line_length=line_length, fast=fast, write_back=write_back, mode=mode

             ):
                 changed = Changed.YES
         else:
             cache: Cache = {}
             if write_back != WriteBack.DIFF:
             ):
                 changed = Changed.YES
         else:
             cache: Cache = {}
             if write_back != WriteBack.DIFF:

-                cache = read_cache(line_length, pyi, py36)
-                src = src.resolve()
-                if src in cache and cache[src] == get_cache_info(src):
+                cache = read_cache(line_length, mode)
+                res_src = src.resolve()
+                if res_src in cache and cache[res_src] == get_cache_info(res_src):

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

-                force_pyi=pyi,
-                force_py36=py36,

                 write_back=write_back,
                 write_back=write_back,

+                mode=mode,

             ):
                 changed = Changed.YES
             if write_back == WriteBack.YES and changed is not Changed.NO:
             ):
                 changed = Changed.YES
             if write_back == WriteBack.YES and changed is not Changed.NO:

-                write_cache(cache, [src], line_length, pyi, py36)
+                write_cache(cache, [src], line_length, mode)

         report.done(src, changed)
     except Exception as exc:
         report.failed(src, str(exc))
 
 
 async def schedule_formatting(
         report.done(src, changed)
     except Exception as exc:
         report.failed(src, str(exc))
 
 
 async def schedule_formatting(

-    sources: List[Path],
+    sources: Set[Path],

     line_length: int,
     fast: bool,
     line_length: int,
     fast: bool,

-    pyi: bool,
-    py36: bool,

     write_back: WriteBack,
     write_back: WriteBack,

+    mode: FileMode,

     report: "Report",
     loop: BaseEventLoop,
     executor: Executor,
     report: "Report",
     loop: BaseEventLoop,
     executor: Executor,


@@ -326,9 +452,9 @@ async def schedule_formatting(
     """
     cache: Cache = {}
     if write_back != WriteBack.DIFF:
     """
     cache: Cache = {}
     if write_back != WriteBack.DIFF:

-        cache = read_cache(line_length, pyi, py36)
+        cache = read_cache(line_length, mode)

         sources, cached = filter_cached(cache, sources)
         sources, cached = filter_cached(cache, sources)

-        for src in cached:
+        for src in sorted(cached):

             report.done(src, Changed.CACHED)
     cancelled = []
     formatted = []
             report.done(src, Changed.CACHED)
     cancelled = []
     formatted = []


@@ -346,9 +472,8 @@ async def schedule_formatting(
                 src,
                 line_length,
                 fast,
                 src,
                 line_length,
                 fast,

-                pyi,
-                py36,

                 write_back,
                 write_back,

+                mode,

                 lock,
             ): src
             for src in sorted(sources)
                 lock,
             ): src
             for src in sorted(sources)


@@ -374,16 +499,15 @@ async def schedule_formatting(
     if cancelled:
         await asyncio.gather(*cancelled, loop=loop, return_exceptions=True)
     if write_back == WriteBack.YES and formatted:
     if cancelled:
         await asyncio.gather(*cancelled, loop=loop, return_exceptions=True)
     if write_back == WriteBack.YES and formatted:

-        write_cache(cache, formatted, line_length, pyi, py36)
+        write_cache(cache, formatted, line_length, mode)

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

-    force_pyi: bool = False,
-    force_py36: bool = False,

     write_back: WriteBack = WriteBack.NO,
     write_back: WriteBack = WriteBack.NO,

+    mode: FileMode = FileMode.AUTO_DETECT,

     lock: Any = None,  # multiprocessing.Manager().Lock() is some crazy proxy
 ) -> bool:
     """Format file under `src` path. Return True if changed.
     lock: Any = None,  # multiprocessing.Manager().Lock() is some crazy proxy
 ) -> bool:
     """Format file under `src` path. Return True if changed.


@@ -391,32 +515,38 @@ def format_file_in_place(
     If `write_back` is True, write reformatted code back to stdout.
     `line_length` and `fast` options are passed to :func:`format_file_contents`.
     """
     If `write_back` is True, write reformatted code back to stdout.
     `line_length` and `fast` options are passed to :func:`format_file_contents`.
     """

-    is_pyi = force_pyi or src.suffix == ".pyi"
+    if src.suffix == ".pyi":
+        mode |= FileMode.PYI

 
 

-    with tokenize.open(src) as src_buffer:
-        src_contents = src_buffer.read()
+    then = datetime.utcfromtimestamp(src.stat().st_mtime)
+    with open(src, "rb") as buf:
+        src_contents, encoding, newline = decode_bytes(buf.read())

     try:
         dst_contents = format_file_contents(
     try:
         dst_contents = format_file_contents(

-            src_contents,
-            line_length=line_length,
-            fast=fast,
-            is_pyi=is_pyi,
-            force_py36=force_py36,
+            src_contents, line_length=line_length, fast=fast, mode=mode

         )
     except NothingChanged:
         return False
 
     if write_back == write_back.YES:
         )
     except NothingChanged:
         return False
 
     if write_back == write_back.YES:

-        with open(src, "w", encoding=src_buffer.encoding) as f:
+        with open(src, "w", encoding=encoding, newline=newline) as f:

             f.write(dst_contents)
     elif write_back == write_back.DIFF:
             f.write(dst_contents)
     elif write_back == write_back.DIFF:

-        src_name = f"{src}  (original)"
-        dst_name = f"{src}  (formatted)"
+        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 lock:
             lock.acquire()
         try:
         diff_contents = diff(src_contents, dst_contents, src_name, dst_name)
         if lock:
             lock.acquire()
         try:

-            sys.stdout.write(diff_contents)
+            f = io.TextIOWrapper(
+                sys.stdout.buffer,
+                encoding=encoding,
+                newline=newline,
+                write_through=True,
+            )
+            f.write(diff_contents)
+            f.detach()

         finally:
             if lock:
                 lock.release()
         finally:
             if lock:
                 lock.release()


@@ -426,9 +556,8 @@ def format_file_in_place(
 def format_stdin_to_stdout(
     line_length: int,
     fast: bool,
 def format_stdin_to_stdout(
     line_length: int,
     fast: bool,

-    is_pyi: bool = False,
-    force_py36: bool = False,

     write_back: WriteBack = WriteBack.NO,
     write_back: WriteBack = WriteBack.NO,

+    mode: FileMode = FileMode.AUTO_DETECT,

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


@@ -436,28 +565,28 @@ def format_stdin_to_stdout(
     `line_length`, `fast`, `is_pyi`, and `force_py36` arguments are passed to
     :func:`format_file_contents`.
     """
     `line_length`, `fast`, `is_pyi`, and `force_py36` arguments are passed to
     :func:`format_file_contents`.
     """

-    src = sys.stdin.read()
+    then = datetime.utcnow()
+    src, encoding, newline = decode_bytes(sys.stdin.buffer.read())

     dst = src
     try:
     dst = src
     try:

-        dst = format_file_contents(
-            src,
-            line_length=line_length,
-            fast=fast,
-            is_pyi=is_pyi,
-            force_py36=force_py36,
-        )
+        dst = format_file_contents(src, line_length=line_length, fast=fast, mode=mode)

         return True
 
     except NothingChanged:
         return False
 
     finally:
         return True
 
     except NothingChanged:
         return False
 
     finally:

+        f = io.TextIOWrapper(
+            sys.stdout.buffer, encoding=encoding, newline=newline, write_through=True
+        )

         if write_back == WriteBack.YES:
         if write_back == WriteBack.YES:

-            sys.stdout.write(dst)
+            f.write(dst)

         elif write_back == WriteBack.DIFF:
         elif write_back == WriteBack.DIFF:

-            src_name = "<stdin>  (original)"
-            dst_name = "<stdin>  (formatted)"
-            sys.stdout.write(diff(src, dst, src_name, dst_name))
+            now = datetime.utcnow()
+            src_name = f"STDIN\t{then} +0000"
+            dst_name = f"STDOUT\t{now} +0000"
+            f.write(diff(src, dst, src_name, dst_name))
+        f.detach()

 
 
 def format_file_contents(
 
 
 def format_file_contents(


@@ -465,8 +594,7 @@ def format_file_contents(
     *,
     line_length: int,
     fast: bool,
     *,
     line_length: int,
     fast: bool,

-    is_pyi: bool = False,
-    force_py36: bool = False,
+    mode: FileMode = FileMode.AUTO_DETECT,

 ) -> FileContent:
     """Reformat contents a file and return new contents.
 
 ) -> FileContent:
     """Reformat contents a file and return new contents.
 


@@ -477,30 +605,18 @@ def format_file_contents(
     if src_contents.strip() == "":
         raise NothingChanged
 
     if src_contents.strip() == "":
         raise NothingChanged
 

-    dst_contents = format_str(
-        src_contents, line_length=line_length, is_pyi=is_pyi, force_py36=force_py36
-    )
+    dst_contents = format_str(src_contents, line_length=line_length, mode=mode)

     if src_contents == dst_contents:
         raise NothingChanged
 
     if not fast:
         assert_equivalent(src_contents, dst_contents)
     if src_contents == dst_contents:
         raise NothingChanged
 
     if not fast:
         assert_equivalent(src_contents, dst_contents)

-        assert_stable(
-            src_contents,
-            dst_contents,
-            line_length=line_length,
-            is_pyi=is_pyi,
-            force_py36=force_py36,
-        )
+        assert_stable(src_contents, dst_contents, line_length=line_length, mode=mode)

     return dst_contents
 
 
 def format_str(
     return dst_contents
 
 
 def format_str(

-    src_contents: str,
-    line_length: int,
-    *,
-    is_pyi: bool = False,
-    force_py36: bool = False,
+    src_contents: str, line_length: int, *, mode: FileMode = FileMode.AUTO_DETECT

 ) -> FileContent:
     """Reformat a string and return new contents.
 
 ) -> FileContent:
     """Reformat a string and return new contents.
 


@@ -509,11 +625,15 @@ def format_str(
     src_node = lib2to3_parse(src_contents)
     dst_contents = ""
     future_imports = get_future_imports(src_node)
     src_node = lib2to3_parse(src_contents)
     dst_contents = ""
     future_imports = get_future_imports(src_node)

-    elt = EmptyLineTracker(is_pyi=is_pyi)
-    py36 = force_py36 or is_python36(src_node)
+    is_pyi = bool(mode & FileMode.PYI)
+    py36 = bool(mode & FileMode.PYTHON36) or is_python36(src_node)
+    normalize_strings = not bool(mode & FileMode.NO_STRING_NORMALIZATION)

     lines = LineGenerator(
     lines = LineGenerator(

-        remove_u_prefix=py36 or "unicode_literals" in future_imports, is_pyi=is_pyi
+        remove_u_prefix=py36 or "unicode_literals" in future_imports,
+        is_pyi=is_pyi,
+        normalize_strings=normalize_strings,

     )
     )

+    elt = EmptyLineTracker(is_pyi=is_pyi)

     empty_line = Line()
     after = 0
     for current_line in lines.visit(src_node):
     empty_line = Line()
     after = 0
     for current_line in lines.visit(src_node):


@@ -527,6 +647,23 @@ def format_str(
     return dst_contents
 
 
     return dst_contents
 
 

+def decode_bytes(src: bytes) -> Tuple[FileContent, Encoding, NewLine]:
+    """Return a tuple of (decoded_contents, encoding, newline).
+
+    `newline` is either CRLF or LF but `decoded_contents` is decoded with
+    universal newlines (i.e. only contains LF).
+    """
+    srcbuf = io.BytesIO(src)
+    encoding, lines = tokenize.detect_encoding(srcbuf.readline)
+    if not lines:
+        return "", encoding, "\n"
+
+    newline = "\r\n" if b"\r\n" == lines[0][-2:] else "\n"
+    srcbuf.seek(0)
+    with io.TextIOWrapper(srcbuf, encoding) as tiow:
+        return tiow.read(), encoding, newline
+
+

 GRAMMARS = [
     pygram.python_grammar_no_print_statement_no_exec_statement,
     pygram.python_grammar_no_print_statement,
 GRAMMARS = [
     pygram.python_grammar_no_print_statement_no_exec_statement,
     pygram.python_grammar_no_print_statement,


@@ -537,9 +674,8 @@ GRAMMARS = [
 def lib2to3_parse(src_txt: str) -> Node:
     """Given a string with source, return the lib2to3 Node."""
     grammar = pygram.python_grammar_no_print_statement
 def lib2to3_parse(src_txt: str) -> Node:
     """Given a string with source, return the lib2to3 Node."""
     grammar = pygram.python_grammar_no_print_statement

-    if src_txt[-1] != "\n":
-        nl = "\r\n" if "\r\n" in src_txt[:1024] else "\n"
-        src_txt += nl
+    if src_txt[-1:] != "\n":
+        src_txt += "\n"

     for grammar in GRAMMARS:
         drv = driver.Driver(grammar, pytree.convert)
         try:
     for grammar in GRAMMARS:
         drv = driver.Driver(grammar, pytree.convert)
         try:


@@ -683,6 +819,7 @@ UNPACKING_PARENTS = {
     syms.dictsetmaker,
     syms.listmaker,
     syms.testlist_gexp,
     syms.dictsetmaker,
     syms.listmaker,
     syms.testlist_gexp,

+    syms.testlist_star_expr,

 }
 TEST_DESCENDANTS = {
     syms.test,
 }
 TEST_DESCENDANTS = {
     syms.test,


@@ -971,27 +1108,6 @@ class Line:
             and second_leaf.value == "def"
         )
 
             and second_leaf.value == "def"
         )
 

-    @property
-    def is_flow_control(self) -> bool:
-        """Is this line a flow control statement?
-
-        Those are `return`, `raise`, `break`, and `continue`.
-        """
-        return (
-            bool(self)
-            and self.leaves[0].type == token.NAME
-            and self.leaves[0].value in FLOW_CONTROL
-        )
-
-    @property
-    def is_yield(self) -> bool:
-        """Is this line a yield statement?"""
-        return (
-            bool(self)
-            and self.leaves[0].type == token.NAME
-            and self.leaves[0].value == "yield"
-        )
-

     @property
     def is_class_paren_empty(self) -> bool:
         """Is this a class with no base classes but using parentheses?
     @property
     def is_class_paren_empty(self) -> bool:
         """Is this a class with no base classes but using parentheses?


@@ -1008,6 +1124,15 @@ class Line:
             and self.leaves[3].value == ")"
         )
 
             and self.leaves[3].value == ")"
         )
 

+    @property
+    def is_triple_quoted_string(self) -> bool:
+        """Is the line a triple quoted string?"""
+        return (
+            bool(self)
+            and self.leaves[0].type == token.STRING
+            and self.leaves[0].value.startswith(('"""', "'''"))
+        )
+

     def contains_standalone_comments(self, depth_limit: int = sys.maxsize) -> bool:
         """If so, needs to be split before emitting."""
         for leaf in self.leaves:
     def contains_standalone_comments(self, depth_limit: int = sys.maxsize) -> bool:
         """If so, needs to be split before emitting."""
         for leaf in self.leaves:


@@ -1017,6 +1142,13 @@ class Line:
 
         return False
 
 
         return False
 

+    def contains_multiline_strings(self) -> bool:
+        for leaf in self.leaves:
+            if is_multiline_string(leaf):
+                return True
+
+        return False
+

     def maybe_remove_trailing_comma(self, closing: Leaf) -> bool:
         """Remove trailing comma if there is one and it's safe."""
         if not (
     def maybe_remove_trailing_comma(self, closing: Leaf) -> bool:
         """Remove trailing comma if there is one and it's safe."""
         if not (


@@ -1098,6 +1230,9 @@ class Line:
 
         Provide a non-negative leaf `_index` to speed up the function.
         """
 
         Provide a non-negative leaf `_index` to speed up the function.
         """

+        if not self.comments:
+            return
+

         if _index == -1:
             for _index, _leaf in enumerate(self.leaves):
                 if leaf is _leaf:
         if _index == -1:
             for _index, _leaf in enumerate(self.leaves):
                 if leaf is _leaf:


@@ -1121,18 +1256,18 @@ class Line:
 
     def is_complex_subscript(self, leaf: Leaf) -> bool:
         """Return True iff `leaf` is part of a slice with non-trivial exprs."""
 
     def is_complex_subscript(self, leaf: Leaf) -> bool:
         """Return True iff `leaf` is part of a slice with non-trivial exprs."""

-        open_lsqb = (
-            leaf if leaf.type == token.LSQB else self.bracket_tracker.get_open_lsqb()
-        )
+        open_lsqb = self.bracket_tracker.get_open_lsqb()

         if open_lsqb is None:
             return False
 
         subscript_start = open_lsqb.next_sibling
         if open_lsqb is None:
             return False
 
         subscript_start = open_lsqb.next_sibling

-        if (
-            isinstance(subscript_start, Node)
-            and subscript_start.type == syms.subscriptlist
-        ):
-            subscript_start = child_towards(subscript_start, leaf)
+
+        if isinstance(subscript_start, Node):
+            if subscript_start.type == syms.listmaker:
+                return False
+
+            if subscript_start.type == syms.subscriptlist:
+                subscript_start = child_towards(subscript_start, leaf)

         return subscript_start is not None and any(
             n.type in TEST_DESCENDANTS for n in subscript_start.pre_order()
         )
         return subscript_start is not None and any(
             n.type in TEST_DESCENDANTS for n in subscript_start.pre_order()
         )


@@ -1215,6 +1350,7 @@ class EmptyLineTracker:
     the prefix of the first leaf consists of optional newlines.  Those newlines
     are consumed by `maybe_empty_lines()` and included in the computation.
     """
     the prefix of the first leaf consists of optional newlines.  Those newlines
     are consumed by `maybe_empty_lines()` and included in the computation.
     """

+

     is_pyi: bool = False
     previous_line: Optional[Line] = None
     previous_after: int = 0
     is_pyi: bool = False
     previous_line: Optional[Line] = None
     previous_after: int = 0


@@ -1224,8 +1360,7 @@ class EmptyLineTracker:
         """Return the number of extra empty lines before and after the `current_line`.
 
         This is for separating `def`, `async def` and `class` with extra empty
         """Return the number of extra empty lines before and after the `current_line`.
 
         This is for separating `def`, `async def` and `class` with extra empty

-        lines (two on module-level), as well as providing an extra empty line
-        after flow control keywords to make them more prominent.
+        lines (two on module-level).

         """
         if isinstance(current_line, UnformattedLines):
             return 0, 0
         """
         if isinstance(current_line, UnformattedLines):
             return 0, 0


@@ -1255,39 +1390,8 @@ class EmptyLineTracker:
                 before = 0 if depth else 1
             else:
                 before = 1 if depth else 2
                 before = 0 if depth else 1
             else:
                 before = 1 if depth else 2

-        is_decorator = current_line.is_decorator
-        if is_decorator or current_line.is_def or current_line.is_class:
-            if not is_decorator:
-                self.previous_defs.append(depth)
-            if self.previous_line is None:
-                # Don't insert empty lines before the first line in the file.
-                return 0, 0
-
-            if self.previous_line.is_decorator:
-                return 0, 0
-
-            if (
-                self.previous_line.is_comment
-                and self.previous_line.depth == current_line.depth
-                and before == 0
-            ):
-                return 0, 0
-
-            if self.is_pyi:
-                if self.previous_line.depth > current_line.depth:
-                    newlines = 1
-                elif current_line.is_class or self.previous_line.is_class:
-                    if current_line.is_stub_class and self.previous_line.is_stub_class:
-                        newlines = 0
-                    else:
-                        newlines = 1
-                else:
-                    newlines = 0
-            else:
-                newlines = 2
-            if current_line.depth and newlines:
-                newlines -= 1
-            return newlines, 0
+        if current_line.is_decorator or current_line.is_def or current_line.is_class:
+            return self._maybe_empty_lines_for_class_or_def(current_line, before)

 
         if (
             self.previous_line
 
         if (
             self.previous_line


@@ -1297,8 +1401,59 @@ class EmptyLineTracker:
         ):
             return (before or 1), 0
 
         ):
             return (before or 1), 0
 

+        if (
+            self.previous_line
+            and self.previous_line.is_class
+            and current_line.is_triple_quoted_string
+        ):
+            return before, 1
+

         return before, 0
 
         return before, 0
 

+    def _maybe_empty_lines_for_class_or_def(
+        self, current_line: Line, before: int
+    ) -> Tuple[int, int]:
+        if not current_line.is_decorator:
+            self.previous_defs.append(current_line.depth)
+        if self.previous_line is None:
+            # Don't insert empty lines before the first line in the file.
+            return 0, 0
+
+        if self.previous_line.is_decorator:
+            return 0, 0
+
+        if self.previous_line.depth < current_line.depth and (
+            self.previous_line.is_class or self.previous_line.is_def
+        ):
+            return 0, 0
+
+        if (
+            self.previous_line.is_comment
+            and self.previous_line.depth == current_line.depth
+            and before == 0
+        ):
+            return 0, 0
+
+        if self.is_pyi:
+            if self.previous_line.depth > current_line.depth:
+                newlines = 1
+            elif current_line.is_class or self.previous_line.is_class:
+                if current_line.is_stub_class and self.previous_line.is_stub_class:
+                    # No blank line between classes with an emty body
+                    newlines = 0
+                else:
+                    newlines = 1
+            elif current_line.is_def and not self.previous_line.is_def:
+                # Blank line between a block of functions and a block of non-functions
+                newlines = 1
+            else:
+                newlines = 0
+        else:
+            newlines = 2
+        if current_line.depth and newlines:
+            newlines -= 1
+        return newlines, 0
+

 
 @dataclass
 class LineGenerator(Visitor[Line]):
 
 @dataclass
 class LineGenerator(Visitor[Line]):


@@ -1307,7 +1462,9 @@ class LineGenerator(Visitor[Line]):
     Note: destroys the tree it's visiting by mutating prefixes of its leaves
     in ways that will no longer stringify to valid Python code on the tree.
     """
     Note: destroys the tree it's visiting by mutating prefixes of its leaves
     in ways that will no longer stringify to valid Python code on the tree.
     """

+

     is_pyi: bool = False
     is_pyi: bool = False

+    normalize_strings: bool = True

     current_line: Line = Factory(Line)
     remove_u_prefix: bool = False
 
     current_line: Line = Factory(Line)
     remove_u_prefix: bool = False
 


@@ -1376,7 +1533,7 @@ class LineGenerator(Visitor[Line]):
 
             else:
                 normalize_prefix(node, inside_brackets=any_open_brackets)
 
             else:
                 normalize_prefix(node, inside_brackets=any_open_brackets)

-                if node.type == token.STRING:
+                if self.normalize_strings and node.type == token.STRING:

                     normalize_string_prefix(node, remove_u_prefix=self.remove_u_prefix)
                     normalize_string_quotes(node)
                 if node.type not in WHITESPACE:
                     normalize_string_prefix(node, remove_u_prefix=self.remove_u_prefix)
                     normalize_string_quotes(node)
                 if node.type not in WHITESPACE:


@@ -1736,7 +1893,7 @@ def whitespace(leaf: Leaf, *, complex_subscript: bool) -> str:  # noqa C901
             elif prevp.type == token.EQUAL and prevp_parent.type == syms.argument:
                 return NO
 
             elif prevp.type == token.EQUAL and prevp_parent.type == syms.argument:
                 return NO
 

-        elif t == token.NAME or t == token.NUMBER:
+        elif t in {token.NAME, token.NUMBER, token.STRING}:

             return NO
 
     elif p.type == syms.import_from:
             return NO
 
     elif p.type == syms.import_from:


@@ -1888,6 +2045,10 @@ def is_split_before_delimiter(leaf: Leaf, previous: Leaf = None) -> int:
     return 0
 
 
     return 0
 
 

+FMT_OFF = {"# fmt: off", "# fmt:off", "# yapf: disable"}
+FMT_ON = {"# fmt: on", "# fmt:on", "# yapf: enable"}
+
+

 def generate_comments(leaf: LN) -> Iterator[Leaf]:
     """Clean the prefix of the `leaf` and generate comments from it, if any.
 
 def generate_comments(leaf: LN) -> Iterator[Leaf]:
     """Clean the prefix of the `leaf` and generate comments from it, if any.
 


@@ -1907,16 +2068,37 @@ def generate_comments(leaf: LN) -> Iterator[Leaf]:
     Inline comments are emitted as regular token.COMMENT leaves.  Standalone
     are emitted with a fake STANDALONE_COMMENT token identifier.
     """
     Inline comments are emitted as regular token.COMMENT leaves.  Standalone
     are emitted with a fake STANDALONE_COMMENT token identifier.
     """

-    p = leaf.prefix
-    if not p:
-        return
+    for pc in list_comments(leaf.prefix, is_endmarker=leaf.type == token.ENDMARKER):
+        yield Leaf(pc.type, pc.value, prefix="\n" * pc.newlines)
+        if pc.value in FMT_ON:
+            raise FormatOn(pc.consumed)

 
 

-    if "#" not in p:
-        return
+        if pc.value in FMT_OFF:
+            if pc.type == STANDALONE_COMMENT:
+                raise FormatOff(pc.consumed)
+
+            prev = preceding_leaf(leaf)
+            if not prev or prev.type in WHITESPACE:  # standalone comment in disguise
+                raise FormatOff(pc.consumed)
+
+
+@dataclass
+class ProtoComment:
+    type: int  # token.COMMENT or STANDALONE_COMMENT
+    value: str  # content of the comment
+    newlines: int  # how many newlines before the comment
+    consumed: int  # how many characters of the original leaf's prefix did we consume
+
+
+@lru_cache(maxsize=4096)
+def list_comments(prefix: str, is_endmarker: bool) -> List[ProtoComment]:
+    result: List[ProtoComment] = []
+    if not prefix or "#" not in prefix:
+        return result

 
     consumed = 0
     nlines = 0
 
     consumed = 0
     nlines = 0

-    for index, line in enumerate(p.split("\n")):
+    for index, line in enumerate(prefix.split("\n")):

         consumed += len(line) + 1  # adding the length of the split '\n'
         line = line.lstrip()
         if not line:
         consumed += len(line) + 1  # adding the length of the split '\n'
         line = line.lstrip()
         if not line:


@@ -1924,25 +2106,18 @@ def generate_comments(leaf: LN) -> Iterator[Leaf]:
         if not line.startswith("#"):
             continue
 
         if not line.startswith("#"):
             continue
 

-        if index == 0 and leaf.type != token.ENDMARKER:
+        if index == 0 and not is_endmarker:

             comment_type = token.COMMENT  # simple trailing comment
         else:
             comment_type = STANDALONE_COMMENT
         comment = make_comment(line)
             comment_type = token.COMMENT  # simple trailing comment
         else:
             comment_type = STANDALONE_COMMENT
         comment = make_comment(line)

-        yield Leaf(comment_type, comment, prefix="\n" * nlines)
-
-        if comment in {"# fmt: on", "# yapf: enable"}:
-            raise FormatOn(consumed)
-
-        if comment in {"# fmt: off", "# yapf: disable"}:
-            if comment_type == STANDALONE_COMMENT:
-                raise FormatOff(consumed)
-
-            prev = preceding_leaf(leaf)
-            if not prev or prev.type in WHITESPACE:  # standalone comment in disguise
-                raise FormatOff(consumed)
-
+        result.append(
+            ProtoComment(
+                type=comment_type, value=comment, newlines=nlines, consumed=consumed
+            )
+        )

         nlines = 0
         nlines = 0

+    return result

 
 
 def make_comment(content: str) -> str:
 
 
 def make_comment(content: str) -> str:


@@ -2122,32 +2297,50 @@ def right_hand_split(
             result.append(leaf, preformatted=True)
             for comment_after in line.comments_after(leaf):
                 result.append(comment_after, preformatted=True)
             result.append(leaf, preformatted=True)
             for comment_after in line.comments_after(leaf):
                 result.append(comment_after, preformatted=True)

-    bracket_split_succeeded_or_raise(head, body, tail)

     assert opening_bracket and closing_bracket
     assert opening_bracket and closing_bracket

+    body.should_explode = should_explode(body, opening_bracket)
+    bracket_split_succeeded_or_raise(head, body, tail)

     if (
     if (

+        # the body shouldn't be exploded
+        not body.should_explode

         # the opening bracket is an optional paren
         # the opening bracket is an optional paren

-        opening_bracket.type == token.LPAR
+        and opening_bracket.type == token.LPAR

         and not opening_bracket.value
         # the closing bracket is an optional paren
         and closing_bracket.type == token.RPAR
         and not closing_bracket.value
         and not opening_bracket.value
         # the closing bracket is an optional paren
         and closing_bracket.type == token.RPAR
         and not closing_bracket.value

-        # there are no standalone comments in the body
-        and not line.contains_standalone_comments(0)
-        # and it's not an import (optional parens are the only thing we can split
-        # on in this case; attempting a split without them is a waste of time)
+        # it's not an import (optional parens are the only thing we can split on
+        # in this case; attempting a split without them is a waste of time)

         and not line.is_import
         and not line.is_import

+        # there are no standalone comments in the body
+        and not body.contains_standalone_comments(0)
+        # and we can actually remove the parens
+        and can_omit_invisible_parens(body, line_length)

     ):
         omit = {id(closing_bracket), *omit}
     ):
         omit = {id(closing_bracket), *omit}

-        if can_omit_invisible_parens(body, line_length):
-            try:
-                yield from right_hand_split(line, line_length, py36=py36, omit=omit)
-                return
-            except CannotSplit:
-                pass
+        try:
+            yield from right_hand_split(line, line_length, py36=py36, omit=omit)
+            return
+
+        except CannotSplit:
+            if not (
+                can_be_split(body)
+                or is_line_short_enough(body, line_length=line_length)
+            ):
+                raise CannotSplit(
+                    "Splitting failed, body is still too long and can't be split."
+                )
+
+            elif head.contains_multiline_strings() or tail.contains_multiline_strings():
+                raise CannotSplit(
+                    "The current optional pair of parentheses is bound to fail to "
+                    "satisfy the splitting algorithm because the head or the tail "
+                    "contains multiline strings which by definition never fit one "
+                    "line."
+                )

 
     ensure_visible(opening_bracket)
     ensure_visible(closing_bracket)
 
     ensure_visible(opening_bracket)
     ensure_visible(closing_bracket)

-    body.should_explode = should_explode(body, opening_bracket)

     for result in (head, body, tail):
         if result:
             yield result
     for result in (head, body, tail):
         if result:
             yield result


@@ -2362,8 +2555,8 @@ def normalize_string_quotes(leaf: Leaf) -> None:
 
     prefix = leaf.value[:first_quote_pos]
     unescaped_new_quote = re.compile(rf"(([^\\]|^)(\\\\)*){new_quote}")
 
     prefix = leaf.value[:first_quote_pos]
     unescaped_new_quote = re.compile(rf"(([^\\]|^)(\\\\)*){new_quote}")

-    escaped_new_quote = re.compile(rf"([^\\]|^)\\(\\\\)*{new_quote}")
-    escaped_orig_quote = re.compile(rf"([^\\]|^)\\(\\\\)*{orig_quote}")
+    escaped_new_quote = re.compile(rf"([^\\]|^)\\((?:\\\\)*){new_quote}")
+    escaped_orig_quote = re.compile(rf"([^\\]|^)\\((?:\\\\)*){orig_quote}")

     body = leaf.value[first_quote_pos + len(orig_quote) : -len(orig_quote)]
     if "r" in prefix.casefold():
         if unescaped_new_quote.search(body):
     body = leaf.value[first_quote_pos + len(orig_quote) : -len(orig_quote)]
     if "r" in prefix.casefold():
         if unescaped_new_quote.search(body):


@@ -2374,15 +2567,21 @@ def normalize_string_quotes(leaf: Leaf) -> None:
         # Do not introduce or remove backslashes in raw strings
         new_body = body
     else:
         # Do not introduce or remove backslashes in raw strings
         new_body = body
     else:

-        # remove unnecessary quotes
+        # remove unnecessary escapes

         new_body = sub_twice(escaped_new_quote, rf"\1\2{new_quote}", body)
         if body != new_body:
         new_body = sub_twice(escaped_new_quote, rf"\1\2{new_quote}", body)
         if body != new_body:

-            # Consider the string without unnecessary quotes as the original
+            # Consider the string without unnecessary escapes as the original

             body = new_body
             leaf.value = f"{prefix}{orig_quote}{body}{orig_quote}"
         new_body = sub_twice(escaped_orig_quote, rf"\1\2{orig_quote}", new_body)
         new_body = sub_twice(unescaped_new_quote, rf"\1\\{new_quote}", new_body)
             body = new_body
             leaf.value = f"{prefix}{orig_quote}{body}{orig_quote}"
         new_body = sub_twice(escaped_orig_quote, rf"\1\2{orig_quote}", new_body)
         new_body = sub_twice(unescaped_new_quote, rf"\1\\{new_quote}", new_body)

-    if new_quote == '"""' and new_body[-1] == '"':
+    if "f" in prefix.casefold():
+        matches = re.findall(r"[^{]\{(.*?)\}[^}]", new_body)
+        for m in matches:
+            if "\\" in str(m):
+                # Do not introduce backslashes in interpolated expressions
+                return
+    if new_quote == '"""' and new_body[-1:] == '"':

         # edge case:
         new_body = new_body[:-1] + '\\"'
     orig_escape_count = body.count("\\")
         # edge case:
         new_body = new_body[:-1] + '\\"'
     orig_escape_count = body.count("\\")


@@ -2405,10 +2604,10 @@ def normalize_invisible_parens(node: Node, parens_after: Set[str]) -> None:
     Standardizes on visible parentheses for single-element tuples, and keeps
     existing visible parentheses for other tuples and generator expressions.
     """
     Standardizes on visible parentheses for single-element tuples, and keeps
     existing visible parentheses for other tuples and generator expressions.
     """

-    try:
-        list(generate_comments(node))
-    except FormatOff:
-        return  # This `node` has a prefix with `# fmt: off`, don't mess with parens.
+    for pc in list_comments(node.prefix, is_endmarker=False):
+        if pc.value in FMT_OFF:
+            # This `node` has a prefix with `# fmt: off`, don't mess with parens.
+            return

 
     check_lpar = False
     for index, child in enumerate(list(node.children)):
 
     check_lpar = False
     for index, child in enumerate(list(node.children)):


@@ -2445,7 +2644,7 @@ def normalize_invisible_parens(node: Node, parens_after: Set[str]) -> None:
 
 
 def maybe_make_parens_invisible_in_atom(node: LN) -> bool:
 
 
 def maybe_make_parens_invisible_in_atom(node: LN) -> bool:

-    """If it's safe, make the parens in the atom `node` invisible, recusively."""
+    """If it's safe, make the parens in the atom `node` invisible, recursively."""

     if (
         node.type != syms.atom
         or is_empty_tuple(node)
     if (
         node.type != syms.atom
         or is_empty_tuple(node)


@@ -2758,40 +2957,87 @@ def get_future_imports(node: Node) -> Set[str]:
     return imports
 
 
     return imports
 
 

-PYTHON_EXTENSIONS = {".py", ".pyi"}
-BLACKLISTED_DIRECTORIES = {
-    "build",
-    "buck-out",
-    "dist",
-    "_build",
-    ".git",
-    ".hg",
-    ".mypy_cache",
-    ".tox",
-    ".venv",
-}
+def gen_python_files_in_dir(
+    path: Path,
+    root: Path,
+    include: Pattern[str],
+    exclude: Pattern[str],
+    report: "Report",
+) -> Iterator[Path]:
+    """Generate all files under `path` whose paths are not excluded by the
+    `exclude` regex, but are included by the `include` regex.

 
 

+    Symbolic links pointing outside of the root directory are ignored.

 
 

-def gen_python_files_in_dir(path: Path) -> Iterator[Path]:
-    """Generate all files under `path` which aren't under BLACKLISTED_DIRECTORIES
-    and have one of the PYTHON_EXTENSIONS.
+    `report` is where output about exclusions goes.

     """
     """

+    assert root.is_absolute(), f"INTERNAL ERROR: `root` must be absolute but is {root}"

     for child in path.iterdir():
     for child in path.iterdir():

-        if child.is_dir():
-            if child.name in BLACKLISTED_DIRECTORIES:
+        try:
+            normalized_path = "/" + child.resolve().relative_to(root).as_posix()
+        except ValueError:
+            if child.is_symlink():
+                report.path_ignored(
+                    child,
+                    "is a symbolic link that points outside of the root directory",
+                )

                 continue
 
                 continue
 

-            yield from gen_python_files_in_dir(child)
+            raise
+
+        if child.is_dir():
+            normalized_path += "/"
+        exclude_match = exclude.search(normalized_path)
+        if exclude_match and exclude_match.group(0):
+            report.path_ignored(child, f"matches the --exclude regular expression")
+            continue
+
+        if child.is_dir():
+            yield from gen_python_files_in_dir(child, root, include, exclude, report)
+
+        elif child.is_file():
+            include_match = include.search(normalized_path)
+            if include_match:
+                yield child

 
 

-        elif child.is_file() and child.suffix in PYTHON_EXTENSIONS:
-            yield child
+
+@lru_cache()
+def find_project_root(srcs: Iterable[str]) -> Path:
+    """Return a directory containing .git, .hg, or pyproject.toml.
+
+    That directory can be one of the directories passed in `srcs` or their
+    common parent.
+
+    If no directory in the tree contains a marker that would specify it's the
+    project root, the root of the file system is returned.
+    """
+    if not srcs:
+        return Path("/").resolve()
+
+    common_base = min(Path(src).resolve() for src in srcs)
+    if common_base.is_dir():
+        # Append a fake file so `parents` below returns `common_base_dir`, too.
+        common_base /= "fake-file"
+    for directory in common_base.parents:
+        if (directory / ".git").is_dir():
+            return directory
+
+        if (directory / ".hg").is_dir():
+            return directory
+
+        if (directory / "pyproject.toml").is_file():
+            return directory
+
+    return directory

 
 
 @dataclass
 class Report:
     """Provides a reformatting counter. Can be rendered with `str(report)`."""
 
 
 @dataclass
 class Report:
     """Provides a reformatting counter. Can be rendered with `str(report)`."""

+

     check: bool = False
     quiet: bool = False
     check: bool = False
     quiet: bool = False

+    verbose: bool = False

     change_count: int = 0
     same_count: int = 0
     failure_count: int = 0
     change_count: int = 0
     same_count: int = 0
     failure_count: int = 0


@@ -2800,11 +3046,11 @@ class Report:
         """Increment the counter for successful reformatting. Write out a message."""
         if changed is Changed.YES:
             reformatted = "would reformat" if self.check else "reformatted"
         """Increment the counter for successful reformatting. Write out a message."""
         if changed is Changed.YES:
             reformatted = "would reformat" if self.check else "reformatted"

-            if not self.quiet:
+            if self.verbose or not self.quiet:

                 out(f"{reformatted} {src}")
             self.change_count += 1
         else:
                 out(f"{reformatted} {src}")
             self.change_count += 1
         else:

-            if not self.quiet:
+            if self.verbose:

                 if changed is Changed.NO:
                     msg = f"{src} already well formatted, good job."
                 else:
                 if changed is Changed.NO:
                     msg = f"{src} already well formatted, good job."
                 else:


@@ -2817,6 +3063,10 @@ class Report:
         err(f"error: cannot format {src}: {message}")
         self.failure_count += 1
 
         err(f"error: cannot format {src}: {message}")
         self.failure_count += 1
 

+    def path_ignored(self, path: Path, message: str) -> None:
+        if self.verbose:
+            out(f"{path} ignored: {message}", bold=False)
+

     @property
     def return_code(self) -> int:
         """Return the exit code that the app should use.
     @property
     def return_code(self) -> int:
         """Return the exit code that the app should use.


@@ -2930,12 +3180,10 @@ def assert_equivalent(src: str, dst: str) -> None:
 
 
 def assert_stable(
 
 
 def assert_stable(

-    src: str, dst: str, line_length: int, is_pyi: bool = False, force_py36: bool = False
+    src: str, dst: str, line_length: int, mode: FileMode = FileMode.AUTO_DETECT

 ) -> None:
     """Raise AssertionError if `dst` reformats differently the second time."""
 ) -> None:
     """Raise AssertionError if `dst` reformats differently the second time."""

-    newdst = format_str(
-        dst, line_length=line_length, is_pyi=is_pyi, force_py36=force_py36
-    )
+    newdst = format_str(dst, line_length=line_length, mode=mode)

     if dst != newdst:
         log = dump_to_file(
             diff(src, dst, "source", "first pass"),
     if dst != newdst:
         log = dump_to_file(
             diff(src, dst, "source", "first pass"),


@@ -3012,6 +3260,16 @@ def sub_twice(regex: Pattern[str], replacement: str, original: str) -> str:
     return regex.sub(replacement, regex.sub(replacement, original))
 
 
     return regex.sub(replacement, regex.sub(replacement, original))
 
 

+def re_compile_maybe_verbose(regex: str) -> Pattern[str]:
+    """Compile a regular expression string in `regex`.
+
+    If it contains newlines, use verbose mode.
+    """
+    if "\n" in regex:
+        regex = "(?x)" + regex
+    return re.compile(regex)
+
+

 def enumerate_reversed(sequence: Sequence[T]) -> Iterator[Tuple[Index, T]]:
     """Like `reversed(enumerate(sequence))` if that were possible."""
     index = len(sequence) - 1
 def enumerate_reversed(sequence: Sequence[T]) -> Iterator[Tuple[Index, T]]:
     """Like `reversed(enumerate(sequence))` if that were possible."""
     index = len(sequence) - 1


@@ -3057,6 +3315,42 @@ def is_line_short_enough(line: Line, *, line_length: int, line_str: str = "") ->
     )
 
 
     )
 
 

+def can_be_split(line: Line) -> bool:
+    """Return False if the line cannot be split *for sure*.
+
+    This is not an exhaustive search but a cheap heuristic that we can use to
+    avoid some unfortunate formattings (mostly around wrapping unsplittable code
+    in unnecessary parentheses).
+    """
+    leaves = line.leaves
+    if len(leaves) < 2:
+        return False
+
+    if leaves[0].type == token.STRING and leaves[1].type == token.DOT:
+        call_count = 0
+        dot_count = 0
+        next = leaves[-1]
+        for leaf in leaves[-2::-1]:
+            if leaf.type in OPENING_BRACKETS:
+                if next.type not in CLOSING_BRACKETS:
+                    return False
+
+                call_count += 1
+            elif leaf.type == token.DOT:
+                dot_count += 1
+            elif leaf.type == token.NAME:
+                if not (next.type == token.DOT or next.type in OPENING_BRACKETS):
+                    return False
+
+            elif leaf.type not in CLOSING_BRACKETS:
+                return False
+
+            if dot_count > 1 and call_count > 1:
+                return False
+
+    return True
+
+

 def can_omit_invisible_parens(line: Line, line_length: int) -> bool:
     """Does `line` have a shape safe to reformat without optional parens around it?
 
 def can_omit_invisible_parens(line: Line, line_length: int) -> bool:
     """Does `line` have a shape safe to reformat without optional parens around it?
 


@@ -3146,19 +3440,16 @@ def can_omit_invisible_parens(line: Line, line_length: int) -> bool:
     return False
 
 
     return False
 
 

-def get_cache_file(line_length: int, pyi: bool = False, py36: bool = False) -> Path:
-    return (
-        CACHE_DIR
-        / f"cache.{line_length}{'.pyi' if pyi else ''}{'.py36' if py36 else ''}.pickle"
-    )
+def get_cache_file(line_length: int, mode: FileMode) -> Path:
+    return CACHE_DIR / f"cache.{line_length}.{mode.value}.pickle"

 
 
 
 

-def read_cache(line_length: int, pyi: bool = False, py36: bool = False) -> Cache:
+def read_cache(line_length: int, mode: FileMode) -> Cache:

     """Read the cache if it exists and is well formed.
 
     If it is not well formed, the call to write_cache later should resolve the issue.
     """
     """Read the cache if it exists and is well formed.
 
     If it is not well formed, the call to write_cache later should resolve the issue.
     """

-    cache_file = get_cache_file(line_length, pyi, py36)
+    cache_file = get_cache_file(line_length, mode)

     if not cache_file.exists():
         return {}
 
     if not cache_file.exists():
         return {}
 


@@ -3177,33 +3468,27 @@ def get_cache_info(path: Path) -> CacheInfo:
     return stat.st_mtime, stat.st_size
 
 
     return stat.st_mtime, stat.st_size
 
 

-def filter_cached(
-    cache: Cache, sources: Iterable[Path]
-) -> Tuple[List[Path], List[Path]]:
-    """Split a list of paths into two.
+def filter_cached(cache: Cache, sources: Iterable[Path]) -> Tuple[Set[Path], Set[Path]]:
+    """Split an iterable of paths in `sources` into two sets.

 
 

-    The first list contains paths of files that modified on disk or are not in the
-    cache. The other list contains paths to non-modified files.
+    The first contains paths of files that modified on disk or are not in the
+    cache. The other contains paths to non-modified files.

     """
     """

-    todo, done = [], []
+    todo, done = set(), set()

     for src in sources:
         src = src.resolve()
         if cache.get(src) != get_cache_info(src):
     for src in sources:
         src = src.resolve()
         if cache.get(src) != get_cache_info(src):

-            todo.append(src)
+            todo.add(src)

         else:
         else:

-            done.append(src)
+            done.add(src)

     return todo, done
 
 
 def write_cache(
     return todo, done
 
 
 def write_cache(

-    cache: Cache,
-    sources: List[Path],
-    line_length: int,
-    pyi: bool = False,
-    py36: bool = False,
+    cache: Cache, sources: Iterable[Path], line_length: int, mode: FileMode

 ) -> None:
     """Update the cache file."""
 ) -> None:
     """Update the cache file."""

-    cache_file = get_cache_file(line_length, pyi, py36)
+    cache_file = get_cache_file(line_length, mode)

     try:
         if not CACHE_DIR.exists():
             CACHE_DIR.mkdir(parents=True)
     try:
         if not CACHE_DIR.exists():
             CACHE_DIR.mkdir(parents=True)