18.6b3

[etc/vim.git] / black.py

diff --git a/black.py b/black.py
index ce4a44f392f3daadf1e1f4be88aded372a6c7d96..0da2fad34a98422e732415776e893d98916209cf 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 datetime import datetime

 from enum import Enum, Flag
 from enum import Enum, Flag

-from functools import partial, wraps
+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,


@@ -27,7 +29,6 @@ from typing import (
     Sequence,
     Set,
     Tuple,
     Sequence,
     Set,
     Tuple,

-    Type,

     TypeVar,
     Union,
     cast,
     TypeVar,
     Union,
     cast,


@@ -36,6 +37,7 @@ 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


@@ -44,10 +46,10 @@ from blib2to3.pgen2 import driver, token
 from blib2to3.pgen2.parse import ParseError
 
 
 from blib2to3.pgen2.parse import ParseError
 
 

-__version__ = "18.5b1"
+__version__ = "18.6b3"

 DEFAULT_LINE_LENGTH = 88
 DEFAULT_EXCLUDES = (
 DEFAULT_LINE_LENGTH = 88
 DEFAULT_EXCLUDES = (

-    r"build/|buck-out/|dist/|_build/|\.git/|\.hg/|\.mypy_cache/|\.tox/|\.venv/"
+    r"/(\.git|\.hg|\.mypy_cache|\.tox|\.venv|_build|buck-out|build|dist)/"

 )
 DEFAULT_INCLUDES = r"\.pyi?$"
 CACHE_DIR = Path(user_cache_dir("black", version=__version__))
 )
 DEFAULT_INCLUDES = r"\.pyi?$"
 CACHE_DIR = Path(user_cache_dir("black", version=__version__))


@@ -56,6 +58,7 @@ CACHE_DIR = Path(user_cache_dir("black", version=__version__))
 # types
 FileContent = str
 Encoding = str
 # types
 FileContent = str
 Encoding = str

+NewLine = str

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


@@ -86,39 +89,18 @@ class CannotSplit(Exception):
     """
 
 
     """
 
 

-class FormatError(Exception):
-    """Base exception for `# fmt: on` and `# fmt: off` handling.
-
-    It holds the number of bytes of the prefix consumed before the format
-    control comment appeared.
-    """
-
-    def __init__(self, consumed: int) -> None:
-        super().__init__(consumed)
-        self.consumed = consumed
-
-    def trim_prefix(self, leaf: Leaf) -> None:
-        leaf.prefix = leaf.prefix[self.consumed :]
-
-    def leaf_from_consumed(self, leaf: Leaf) -> Leaf:
-        """Returns a new Leaf from the consumed part of the prefix."""
-        unformatted_prefix = leaf.prefix[: self.consumed]
-        return Leaf(token.NEWLINE, unformatted_prefix)
-
-
-class FormatOn(FormatError):
-    """Found a comment like `# fmt: on` in the file."""
-
-
-class FormatOff(FormatError):
-    """Found a comment like `# fmt: off` in the file."""
-
-

 class WriteBack(Enum):
     NO = 0
     YES = 1
     DIFF = 2
 
 class WriteBack(Enum):
     NO = 0
     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


@@ -132,8 +114,55 @@ class FileMode(Flag):
     PYI = 2
     NO_STRING_NORMALIZATION = 4
 
     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

 
 

-@click.command()
+    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",


@@ -143,55 +172,46 @@ class FileMode(Flag):
     show_default=True,
 )
 @click.option(
     show_default=True,
 )
 @click.option(

-    "--check",
+    "--py36",

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

-        "Don't write the files back, just return the status.  Return code 0 "
-        "means nothing would change.  Return code 1 means some files would be "
-        "reformatted.  Return code 123 means there was an internal error."
+        "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(
     ),
 )
 @click.option(

-    "--diff",
-    is_flag=True,
-    help="Don't write the files back, just output a diff for each file on stdout.",
-)
-@click.option(
-    "--fast/--safe",
+    "--pyi",

     is_flag=True,
     is_flag=True,

-    help="If --fast given, skip temporary sanity checks. [default: --safe]",
+    help=(
+        "Format all input files like typing stubs regardless of file extension "
+        "(useful when piping source on standard input)."
+    ),

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

-    "-q",
-    "--quiet",
+    "-S",
+    "--skip-string-normalization",

     is_flag=True,
     is_flag=True,

-    help=(
-        "Don't emit non-error messages to stderr. Errors are still emitted, "
-        "silence those with 2>/dev/null."
-    ),
+    help="Don't normalize string quotes or prefixes.",

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

-    "--pyi",
+    "--check",

     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 write the files back, just return the status.  Return code 0 "
+        "means nothing would change.  Return code 1 means some files would be "
+        "reformatted.  Return code 123 means there was an internal error."

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

-    "--py36",
+    "--diff",

     is_flag=True,
     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]"
-    ),
+    help="Don't write the files back, just output a diff for each file on stdout.",

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

-    "-S",
-    "--skip-string-normalization",
+    "--fast/--safe",

     is_flag=True,
     is_flag=True,

-    help="Don't normalize string quotes or prefixes.",
+    help="If --fast given, skip temporary sanity checks. [default: --safe]",

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


@@ -199,8 +219,10 @@ class FileMode(Flag):
     default=DEFAULT_INCLUDES,
     help=(
         "A regular expression that matches files and directories that should be "
     default=DEFAULT_INCLUDES,
     help=(
         "A regular expression that matches files and directories that should be "

-        "included on recursive searches. On Windows, use forward slashes for "
-        "directories."
+        "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,
 )
     ),
     show_default=True,
 )


@@ -210,11 +232,30 @@ class FileMode(Flag):
     default=DEFAULT_EXCLUDES,
     help=(
         "A regular expression that matches files and directories that should be "
     default=DEFAULT_EXCLUDES,
     help=(
         "A regular expression that matches files and directories that should be "

-        "excluded on recursive searches. On Windows, use forward slashes for "
-        "directories."
+        "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,
 )
     ),
     show_default=True,
 )

+@click.option(
+    "-q",
+    "--quiet",
+    is_flag=True,
+    help=(
+        "Don't emit non-error messages to stderr. Errors are still emitted, "
+        "silence those with 2>/dev/null."
+    ),
+)
+@click.option(
+    "-v",
+    "--verbose",
+    is_flag=True,
+    help=(
+        "Also emit messages to stderr about files that were not changed or were "
+        "ignored due to --exclude=."
+    ),
+)

 @click.version_option(version=__version__)
 @click.argument(
     "src",
 @click.version_option(version=__version__)
 @click.argument(
     "src",


@@ -222,6 +263,16 @@ class FileMode(Flag):
     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(


@@ -234,56 +285,51 @@ def main(
     py36: bool,
     skip_string_normalization: bool,
     quiet: bool,
     py36: bool,
     skip_string_normalization: bool,
     quiet: bool,

+    verbose: bool,

     include: str,
     exclude: str,
     include: str,
     exclude: str,

-    src: List[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:
     try:

-        include_regex = re.compile(include)
+        include_regex = re_compile_maybe_verbose(include)

     except re.error:
         err(f"Invalid regular expression for include given: {include!r}")
         ctx.exit(2)
     try:
     except re.error:
         err(f"Invalid regular expression for include given: {include!r}")
         ctx.exit(2)
     try:

-        exclude_regex = re.compile(exclude)
+        exclude_regex = re_compile_maybe_verbose(exclude)

     except re.error:
         err(f"Invalid regular expression for exclude given: {exclude!r}")
         ctx.exit(2)
     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, include_regex, exclude_regex))
-        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
-    mode = FileMode.AUTO_DETECT
-    if py36:
-        mode |= FileMode.PYTHON36
-    if pyi:
-        mode |= FileMode.PYI
-    if skip_string_normalization:
-        mode |= FileMode.NO_STRING_NORMALIZATION
-    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,
             write_back=write_back,
             line_length=line_length,
             fast=fast,
             write_back=write_back,


@@ -308,9 +354,10 @@ 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)
 
 


@@ -339,8 +386,8 @@ def reformat_one(
             cache: Cache = {}
             if write_back != WriteBack.DIFF:
                 cache = read_cache(line_length, mode)
             cache: Cache = {}
             if write_back != WriteBack.DIFF:
                 cache = read_cache(line_length, mode)

-                src = src.resolve()
-                if src in cache and cache[src] == get_cache_info(src):
+                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,
                     changed = Changed.CACHED
             if changed is not Changed.CACHED and format_file_in_place(
                 src,


@@ -358,7 +405,7 @@ def reformat_one(
 
 
 async def schedule_formatting(
 
 
 async def schedule_formatting(

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

     line_length: int,
     fast: bool,
     write_back: WriteBack,
     line_length: int,
     fast: bool,
     write_back: WriteBack,


@@ -378,7 +425,7 @@ async def schedule_formatting(
     if write_back != WriteBack.DIFF:
         cache = read_cache(line_length, mode)
         sources, cached = filter_cached(cache, sources)
     if write_back != WriteBack.DIFF:
         cache = read_cache(line_length, mode)
         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 = []


@@ -441,8 +488,10 @@ def format_file_in_place(
     """
     if src.suffix == ".pyi":
         mode |= FileMode.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(
             src_contents, line_length=line_length, fast=fast, mode=mode
     try:
         dst_contents = format_file_contents(
             src_contents, line_length=line_length, fast=fast, mode=mode


@@ -451,16 +500,24 @@ def format_file_in_place(
         return False
 
     if write_back == write_back.YES:
         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()


@@ -479,7 +536,8 @@ 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 = format_file_contents(src, line_length=line_length, fast=fast, mode=mode)
     dst = src
     try:
         dst = format_file_contents(src, line_length=line_length, fast=fast, mode=mode)


@@ -489,12 +547,17 @@ def format_stdin_to_stdout(
         return False
 
     finally:
         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(


@@ -536,6 +599,7 @@ def format_str(
     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)
     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)

+    normalize_fmt_off(src_node)

     lines = LineGenerator(
         remove_u_prefix=py36 or "unicode_literals" in future_imports,
         is_pyi=is_pyi,
     lines = LineGenerator(
         remove_u_prefix=py36 or "unicode_literals" in future_imports,
         is_pyi=is_pyi,


@@ -555,6 +619,23 @@ 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,


@@ -565,9 +646,8 @@ 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:


@@ -650,13 +730,15 @@ class DebugVisitor(Visitor[T]):
             out(f" {node.value!r}", fg="blue", bold=False)
 
     @classmethod
             out(f" {node.value!r}", fg="blue", bold=False)
 
     @classmethod

-    def show(cls, code: str) -> None:
+    def show(cls, code: Union[str, Leaf, Node]) -> None:

         """Pretty-print the lib2to3 AST of a given string of `code`.
 
         Convenience method for debugging.
         """
         v: DebugVisitor[None] = DebugVisitor()
         """Pretty-print the lib2to3 AST of a given string of `code`.
 
         Convenience method for debugging.
         """
         v: DebugVisitor[None] = DebugVisitor()

-        list(v.visit(lib2to3_parse(code)))
+        if isinstance(code, str):
+            code = lib2to3_parse(code)
+        list(v.visit(code))

 
 
 KEYWORDS = set(keyword.kwlist)
 
 
 KEYWORDS = set(keyword.kwlist)


@@ -673,6 +755,7 @@ STATEMENT = {
     syms.classdef,
 }
 STANDALONE_COMMENT = 153
     syms.classdef,
 }
 STANDALONE_COMMENT = 153

+token.tok_name[STANDALONE_COMMENT] = "STANDALONE_COMMENT"

 LOGIC_OPERATORS = {"and", "or"}
 COMPARATORS = {
     token.LESS,
 LOGIC_OPERATORS = {"and", "or"}
 COMPARATORS = {
     token.LESS,


@@ -711,6 +794,19 @@ UNPACKING_PARENTS = {
     syms.dictsetmaker,
     syms.listmaker,
     syms.testlist_gexp,
     syms.dictsetmaker,
     syms.listmaker,
     syms.testlist_gexp,

+    syms.testlist_star_expr,
+}
+SURROUNDED_BY_BRACKETS = {
+    syms.typedargslist,
+    syms.arglist,
+    syms.subscriptlist,
+    syms.vfplist,
+    syms.import_as_names,
+    syms.yield_expr,
+    syms.testlist_gexp,
+    syms.testlist_star_expr,
+    syms.listmaker,
+    syms.dictsetmaker,

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


@@ -1033,6 +1129,13 @@ 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 (


@@ -1114,6 +1217,9 @@ 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:


@@ -1137,18 +1243,18 @@ 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()
         )


@@ -1173,55 +1279,6 @@ class Line:
         return bool(self.leaves or self.comments)
 
 
         return bool(self.leaves or self.comments)
 
 

-class UnformattedLines(Line):
-    """Just like :class:`Line` but stores lines which aren't reformatted."""
-
-    def append(self, leaf: Leaf, preformatted: bool = True) -> None:
-        """Just add a new `leaf` to the end of the lines.
-
-        The `preformatted` argument is ignored.
-
-        Keeps track of indentation `depth`, which is useful when the user
-        says `# fmt: on`. Otherwise, doesn't do anything with the `leaf`.
-        """
-        try:
-            list(generate_comments(leaf))
-        except FormatOn as f_on:
-            self.leaves.append(f_on.leaf_from_consumed(leaf))
-            raise
-
-        self.leaves.append(leaf)
-        if leaf.type == token.INDENT:
-            self.depth += 1
-        elif leaf.type == token.DEDENT:
-            self.depth -= 1
-
-    def __str__(self) -> str:
-        """Render unformatted lines from leaves which were added with `append()`.
-
-        `depth` is not used for indentation in this case.
-        """
-        if not self:
-            return "\n"
-
-        res = ""
-        for leaf in self.leaves:
-            res += str(leaf)
-        return res
-
-    def append_comment(self, comment: Leaf) -> bool:
-        """Not implemented in this class. Raises `NotImplementedError`."""
-        raise NotImplementedError("Unformatted lines don't store comments separately.")
-
-    def maybe_remove_trailing_comma(self, closing: Leaf) -> bool:
-        """Does nothing and returns False."""
-        return False
-
-    def maybe_increment_for_loop_variable(self, leaf: Leaf) -> bool:
-        """Does nothing and returns False."""
-        return False
-
-

 @dataclass
 class EmptyLineTracker:
     """Provides a stateful method that returns the number of potential extra
 @dataclass
 class EmptyLineTracker:
     """Provides a stateful method that returns the number of potential extra


@@ -1243,9 +1300,6 @@ class EmptyLineTracker:
         This is for separating `def`, `async def` and `class` with extra empty
         lines (two on module-level).
         """
         This is for separating `def`, `async def` and `class` with extra empty
         lines (two on module-level).
         """

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

         before, after = self._maybe_empty_lines(current_line)
         before -= self.previous_after
         self.previous_after = after
         before, after = self._maybe_empty_lines(current_line)
         before -= self.previous_after
         self.previous_after = after


@@ -1271,44 +1325,8 @@ 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.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:
-                        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


@@ -1327,6 +1345,50 @@ class EmptyLineTracker:
 
         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]):


@@ -1341,7 +1403,7 @@ class LineGenerator(Visitor[Line]):
     current_line: Line = Factory(Line)
     remove_u_prefix: bool = False
 
     current_line: Line = Factory(Line)
     remove_u_prefix: bool = False
 

-    def line(self, indent: int = 0, type: Type[Line] = Line) -> Iterator[Line]:
+    def line(self, indent: int = 0) -> Iterator[Line]:

         """Generate a line.
 
         If the line is empty, only emit if it makes sense.
         """Generate a line.
 
         If the line is empty, only emit if it makes sense.


@@ -1350,67 +1412,39 @@ class LineGenerator(Visitor[Line]):
         If any lines were generated, set up a new current_line.
         """
         if not self.current_line:
         If any lines were generated, set up a new current_line.
         """
         if not self.current_line:

-            if self.current_line.__class__ == type:
-                self.current_line.depth += indent
-            else:
-                self.current_line = type(depth=self.current_line.depth + indent)
+            self.current_line.depth += indent

             return  # Line is empty, don't emit. Creating a new one unnecessary.
 
         complete_line = self.current_line
             return  # Line is empty, don't emit. Creating a new one unnecessary.
 
         complete_line = self.current_line

-        self.current_line = type(depth=complete_line.depth + indent)
+        self.current_line = Line(depth=complete_line.depth + indent)

         yield complete_line
 
         yield complete_line
 

-    def visit(self, node: LN) -> Iterator[Line]:
-        """Main method to visit `node` and its children.
-
-        Yields :class:`Line` objects.
-        """
-        if isinstance(self.current_line, UnformattedLines):
-            # File contained `# fmt: off`
-            yield from self.visit_unformatted(node)
-
-        else:
-            yield from super().visit(node)
-

     def visit_default(self, node: LN) -> Iterator[Line]:
         """Default `visit_*()` implementation. Recurses to children of `node`."""
         if isinstance(node, Leaf):
             any_open_brackets = self.current_line.bracket_tracker.any_open_brackets()
     def visit_default(self, node: LN) -> Iterator[Line]:
         """Default `visit_*()` implementation. Recurses to children of `node`."""
         if isinstance(node, Leaf):
             any_open_brackets = self.current_line.bracket_tracker.any_open_brackets()

-            try:
-                for comment in generate_comments(node):
-                    if any_open_brackets:
-                        # any comment within brackets is subject to splitting
-                        self.current_line.append(comment)
-                    elif comment.type == token.COMMENT:
-                        # regular trailing comment
-                        self.current_line.append(comment)
-                        yield from self.line()
-
-                    else:
-                        # regular standalone comment
-                        yield from self.line()
-
-                        self.current_line.append(comment)
-                        yield from self.line()
-
-            except FormatOff as f_off:
-                f_off.trim_prefix(node)
-                yield from self.line(type=UnformattedLines)
-                yield from self.visit(node)
-
-            except FormatOn as f_on:
-                # This only happens here if somebody says "fmt: on" multiple
-                # times in a row.
-                f_on.trim_prefix(node)
-                yield from self.visit_default(node)
+            for comment in generate_comments(node):
+                if any_open_brackets:
+                    # any comment within brackets is subject to splitting
+                    self.current_line.append(comment)
+                elif comment.type == token.COMMENT:
+                    # regular trailing comment
+                    self.current_line.append(comment)
+                    yield from self.line()

 
 

-            else:
-                normalize_prefix(node, inside_brackets=any_open_brackets)
-                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:
-                    self.current_line.append(node)
+                else:
+                    # regular standalone comment
+                    yield from self.line()
+
+                    self.current_line.append(comment)
+                    yield from self.line()
+
+            normalize_prefix(node, inside_brackets=any_open_brackets)
+            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:
+                self.current_line.append(node)

         yield from super().visit_default(node)
 
     def visit_INDENT(self, node: Node) -> Iterator[Line]:
         yield from super().visit_default(node)
 
     def visit_INDENT(self, node: Node) -> Iterator[Line]:


@@ -1507,23 +1541,10 @@ class LineGenerator(Visitor[Line]):
         yield from self.visit_default(leaf)
         yield from self.line()
 
         yield from self.visit_default(leaf)
         yield from self.line()
 

-    def visit_unformatted(self, node: LN) -> Iterator[Line]:
-        """Used when file contained a `# fmt: off`."""
-        if isinstance(node, Node):
-            for child in node.children:
-                yield from self.visit(child)
-
-        else:
-            try:
-                self.current_line.append(node)
-            except FormatOn as f_on:
-                f_on.trim_prefix(node)
-                yield from self.line()
-                yield from self.visit(node)
-
-            if node.type == token.ENDMARKER:
-                # somebody decided not to put a final `# fmt: on`
-                yield from self.line()
+    def visit_STANDALONE_COMMENT(self, leaf: Leaf) -> Iterator[Line]:
+        if not self.current_line.bracket_tracker.any_open_brackets():
+            yield from self.line()
+        yield from self.visit_default(leaf)

 
     def __attrs_post_init__(self) -> None:
         """You are in a twisty little maze of passages."""
 
     def __attrs_post_init__(self) -> None:
         """You are in a twisty little maze of passages."""


@@ -1766,7 +1787,7 @@ 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:


@@ -1813,6 +1834,31 @@ def child_towards(ancestor: Node, descendant: LN) -> Optional[LN]:
     return node
 
 
     return node
 
 

+def container_of(leaf: Leaf) -> LN:
+    """Return `leaf` or one of its ancestors that is the topmost container of it.
+
+    By "container" we mean a node where `leaf` is the very first child.
+    """
+    same_prefix = leaf.prefix
+    container: LN = leaf
+    while container:
+        parent = container.parent
+        if parent is None:
+            break
+
+        if parent.children[0].prefix != same_prefix:
+            break
+
+        if parent.type == syms.file_input:
+            break
+
+        if parent.type in SURROUNDED_BY_BRACKETS:
+            break
+
+        container = parent
+    return container
+
+

 def is_split_after_delimiter(leaf: Leaf, previous: Leaf = None) -> int:
     """Return the priority of the `leaf` delimiter, given a line break after it.
 
 def is_split_after_delimiter(leaf: Leaf, previous: Leaf = None) -> int:
     """Return the priority of the `leaf` delimiter, given a line break after it.
 


@@ -1918,6 +1964,10 @@ 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.
 


@@ -1937,16 +1987,27 @@ 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 "#" not in p:
-        return
+
+@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:


@@ -1954,25 +2015,18 @@ 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:


@@ -2007,7 +2061,7 @@ def split_line(
     If `py36` is True, splitting may generate syntax that is only compatible
     with Python 3.6 and later.
     """
     If `py36` is True, splitting may generate syntax that is only compatible
     with Python 3.6 and later.
     """

-    if isinstance(line, UnformattedLines) or line.is_comment:
+    if line.is_comment:

         yield line
         return
 
         yield line
         return
 


@@ -2152,32 +2206,50 @@ 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


@@ -2392,8 +2464,8 @@ 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):


@@ -2404,15 +2476,21 @@ 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("\\")


@@ -2435,10 +2513,10 @@ 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)):


@@ -2474,8 +2552,85 @@ def normalize_invisible_parens(node: Node, parens_after: Set[str]) -> None:
         check_lpar = isinstance(child, Leaf) and child.value in parens_after
 
 
         check_lpar = isinstance(child, Leaf) and child.value in parens_after
 
 

+def normalize_fmt_off(node: Node) -> None:
+    """Convert content between `# fmt: off`/`# fmt: on` into standalone comments."""
+    try_again = True
+    while try_again:
+        try_again = convert_one_fmt_off_pair(node)
+
+
+def convert_one_fmt_off_pair(node: Node) -> bool:
+    """Convert content of a single `# fmt: off`/`# fmt: on` into a standalone comment.
+
+    Returns True if a pair was converted.
+    """
+    for leaf in node.leaves():
+        previous_consumed = 0
+        for comment in list_comments(leaf.prefix, is_endmarker=False):
+            if comment.value in FMT_OFF:
+                # We only want standalone comments. If there's no previous leaf or
+                # the previous leaf is indentation, it's a standalone comment in
+                # disguise.
+                if comment.type != STANDALONE_COMMENT:
+                    prev = preceding_leaf(leaf)
+                    if prev and prev.type not in WHITESPACE:
+                        continue
+
+                ignored_nodes = list(generate_ignored_nodes(leaf))
+                if not ignored_nodes:
+                    continue
+
+                first = ignored_nodes[0]  # Can be a container node with the `leaf`.
+                parent = first.parent
+                prefix = first.prefix
+                first.prefix = prefix[comment.consumed :]
+                hidden_value = (
+                    comment.value + "\n" + "".join(str(n) for n in ignored_nodes)
+                )
+                if hidden_value.endswith("\n"):
+                    # That happens when one of the `ignored_nodes` ended with a NEWLINE
+                    # leaf (possibly followed by a DEDENT).
+                    hidden_value = hidden_value[:-1]
+                first_idx = None
+                for ignored in ignored_nodes:
+                    index = ignored.remove()
+                    if first_idx is None:
+                        first_idx = index
+                assert parent is not None, "INTERNAL ERROR: fmt: on/off handling (1)"
+                assert first_idx is not None, "INTERNAL ERROR: fmt: on/off handling (2)"
+                parent.insert_child(
+                    first_idx,
+                    Leaf(
+                        STANDALONE_COMMENT,
+                        hidden_value,
+                        prefix=prefix[:previous_consumed] + "\n" * comment.newlines,
+                    ),
+                )
+                return True
+
+            previous_consumed += comment.consumed
+
+    return False
+
+
+def generate_ignored_nodes(leaf: Leaf) -> Iterator[LN]:
+    """Starting from the container of `leaf`, generate all leaves until `# fmt: on`.
+
+    Stops at the end of the block.
+    """
+    container: Optional[LN] = container_of(leaf)
+    while container is not None and container.type != token.ENDMARKER:
+        for comment in list_comments(container.prefix, is_endmarker=False):
+            if comment.value in FMT_ON:
+                return
+
+        yield container
+
+        container = container.next_sibling
+
+

 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)


@@ -2789,42 +2944,85 @@ def get_future_imports(node: Node) -> Set[str]:
 
 
 def gen_python_files_in_dir(
 
 
 def gen_python_files_in_dir(

-    path: Path, include: Pattern[str], exclude: Pattern[str]
+    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.
 ) -> 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.
+
+    `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():

-        searchable_path = str(child.as_posix())
-        if Path(child.parts[0]).is_dir():
-            searchable_path = "/" + searchable_path
-        if child.is_dir():
-            searchable_path = searchable_path + "/"
-            exclude_match = exclude.search(searchable_path)
-            if exclude_match and len(exclude_match.group()) > 0:
+        try:
+            normalized_path = "/" + child.resolve().relative_to(root).as_posix()
+        except ValueError:
+            if child.is_symlink():
+                report.path_ignored(
+                    child, f"is a symbolic link that points outside {root}"
+                )

                 continue
 
                 continue
 

-            yield from gen_python_files_in_dir(child, include, exclude)
+            raise

 
 

-        else:
-            include_match = include.search(searchable_path)
-            exclude_match = exclude.search(searchable_path)
-            if (
-                child.is_file()
-                and include_match
-                and len(include_match.group()) > 0
-                and (not exclude_match or len(exclude_match.group()) == 0)
-            ):
+        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
 
 
                 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)`."""
 
     check: bool = False
     quiet: bool = False
 @dataclass
 class Report:
     """Provides a reformatting counter. Can be rendered with `str(report)`."""
 
     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


@@ -2833,11 +3031,11 @@ 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:


@@ -2850,6 +3048,10 @@ 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.


@@ -3043,6 +3245,16 @@ 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


@@ -3088,6 +3300,42 @@ 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?
 


@@ -3178,12 +3426,7 @@ def can_omit_invisible_parens(line: Line, line_length: int) -> bool:
 
 
 def get_cache_file(line_length: int, mode: FileMode) -> Path:
 
 
 def get_cache_file(line_length: int, mode: FileMode) -> Path:

-    pyi = bool(mode & FileMode.PYI)
-    py36 = bool(mode & FileMode.PYTHON36)
-    return (
-        CACHE_DIR
-        / f"cache.{line_length}{'.pyi' if pyi else ''}{'.py36' if py36 else ''}.pickle"
-    )
+    return CACHE_DIR / f"cache.{line_length}.{mode.value}.pickle"

 
 
 def read_cache(line_length: int, mode: FileMode) -> Cache:
 
 
 def read_cache(line_length: int, mode: FileMode) -> Cache:


@@ -3210,26 +3453,24 @@ 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, mode: FileMode
+    cache: Cache, sources: Iterable[Path], line_length: int, mode: FileMode

 ) -> None:
     """Update the cache file."""
     cache_file = get_cache_file(line_length, mode)
 ) -> None:
     """Update the cache file."""
     cache_file = get_cache_file(line_length, mode)


@@ -3243,5 +3484,28 @@ def write_cache(
         pass
 
 
         pass
 
 

+def patch_click() -> None:
+    """Make Click not crash.
+
+    On certain misconfigured environments, Python 3 selects the ASCII encoding as the
+    default which restricts paths that it can access during the lifetime of the
+    application.  Click refuses to work in this scenario by raising a RuntimeError.
+
+    In case of Black the likelihood that non-ASCII characters are going to be used in
+    file paths is minimal since it's Python source code.  Moreover, this crash was
+    spurious on Python 3.7 thanks to PEP 538 and PEP 540.
+    """
+    try:
+        from click import core
+        from click import _unicodefun  # type: ignore
+    except ModuleNotFoundError:
+        return
+
+    for module in (core, _unicodefun):
+        if hasattr(module, "_verify_python3_env"):
+            module._verify_python3_env = lambda: None
+
+

 if __name__ == "__main__":
 if __name__ == "__main__":

+    patch_click()

     main()
     main()