Fix typo in README (#1306)

[etc/vim.git] / black.py

diff --git a/black.py b/black.py
index 5b2e0171c484d2ed5d94ad3066d4fb2a13068ce7..31859d1a499411d60d027e4b71feb208def8a7e9 100644 (file)
--- a/black.py
+++ b/black.py
@@ -37,9 +37,11 @@ from typing import (
     Union,
     cast,
 )
     Union,
     cast,
 )

+from typing_extensions import Final
+from mypy_extensions import mypyc_attr

 
 from appdirs import user_cache_dir
 
 from appdirs import user_cache_dir

-from attr import dataclass, evolve, Factory
+from dataclasses import dataclass, field, replace

 import click
 import toml
 from typed_ast import ast3, ast27
 import click
 import toml
 from typed_ast import ast3, ast27


@@ -184,8 +186,8 @@ VERSION_TO_FEATURES: Dict[TargetVersion, Set[Feature]] = {
 
 
 @dataclass
 
 
 @dataclass

-class FileMode:
-    target_versions: Set[TargetVersion] = Factory(set)
+class Mode:
+    target_versions: Set[TargetVersion] = field(default_factory=set)

     line_length: int = DEFAULT_LINE_LENGTH
     string_normalization: bool = True
     is_pyi: bool = False
     line_length: int = DEFAULT_LINE_LENGTH
     string_normalization: bool = True
     is_pyi: bool = False


@@ -207,10 +209,31 @@ class FileMode:
         return ".".join(parts)
 
 
         return ".".join(parts)
 
 

+# Legacy name, left for integrations.
+FileMode = Mode
+
+

 def supports_feature(target_versions: Set[TargetVersion], feature: Feature) -> bool:
     return all(feature in VERSION_TO_FEATURES[version] for version in target_versions)
 
 
 def supports_feature(target_versions: Set[TargetVersion], feature: Feature) -> bool:
     return all(feature in VERSION_TO_FEATURES[version] for version in target_versions)
 
 

+def find_pyproject_toml(path_search_start: str) -> Optional[str]:
+    """Find the absolute filepath to a pyproject.toml if it exists"""
+    path_project_root = find_project_root(path_search_start)
+    path_pyproject_toml = path_project_root / "pyproject.toml"
+    return str(path_pyproject_toml) if path_pyproject_toml.is_file() else None
+
+
+def parse_pyproject_toml(path_config: str) -> Dict[str, Any]:
+    """Parse a pyproject toml file, pulling out relevant parts for Black
+
+    If parsing fails, will raise a toml.TomlDecodeError
+    """
+    pyproject_toml = toml.load(path_config)
+    config = pyproject_toml.get("tool", {}).get("black", {})
+    return {k.replace("--", "").replace("-", "_"): v for k, v in config.items()}
+
+

 def read_pyproject_toml(
     ctx: click.Context, param: click.Parameter, value: Union[str, int, bool, None]
 ) -> Optional[str]:
 def read_pyproject_toml(
     ctx: click.Context, param: click.Parameter, value: Union[str, int, bool, None]
 ) -> Optional[str]:


@@ -221,16 +244,12 @@ def read_pyproject_toml(
     """
     assert not isinstance(value, (int, bool)), "Invalid parameter type passed"
     if not value:
     """
     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:
+        value = find_pyproject_toml(ctx.params.get("src", ()))
+        if value is None:

             return None
 
     try:
             return None
 
     try:

-        pyproject_toml = toml.load(value)
-        config = pyproject_toml.get("tool", {}).get("black", {})
+        config = parse_pyproject_toml(value)

     except (toml.TomlDecodeError, OSError) as e:
         raise click.FileError(
             filename=value, hint=f"Error reading configuration file: {e}"
     except (toml.TomlDecodeError, OSError) as e:
         raise click.FileError(
             filename=value, hint=f"Error reading configuration file: {e}"


@@ -241,12 +260,21 @@ def read_pyproject_toml(
 
     if ctx.default_map is None:
         ctx.default_map = {}
 
     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()}
-    )
+    ctx.default_map.update(config)  # type: ignore  # bad types in .pyi

     return value
 
 
     return value
 
 

+def target_version_option_callback(
+    c: click.Context, p: Union[click.Option, click.Parameter], v: Tuple[str, ...]
+) -> List[TargetVersion]:
+    """Compute the target versions from a --target-version flag.
+
+    This is its own function because mypy couldn't infer the type correctly
+    when it was a lambda, causing mypyc trouble.
+    """
+    return [TargetVersion[val.upper()] for val in v]
+
+

 @click.command(context_settings=dict(help_option_names=["-h", "--help"]))
 @click.option("-c", "--code", type=str, help="Format the code passed in as a string.")
 @click.option(
 @click.command(context_settings=dict(help_option_names=["-h", "--help"]))
 @click.option("-c", "--code", type=str, help="Format the code passed in as a string.")
 @click.option(


@@ -261,7 +289,7 @@ def read_pyproject_toml(
     "-t",
     "--target-version",
     type=click.Choice([v.name.lower() for v in TargetVersion]),
     "-t",
     "--target-version",
     type=click.Choice([v.name.lower() for v in TargetVersion]),

-    callback=lambda c, p, v: [TargetVersion[val.upper()] for val in v],
+    callback=target_version_option_callback,

     multiple=True,
     help=(
         "Python versions that should be supported by Black's output. [default: "
     multiple=True,
     help=(
         "Python versions that should be supported by Black's output. [default: "


@@ -388,7 +416,7 @@ def main(
     verbose: bool,
     include: str,
     exclude: str,
     verbose: bool,
     include: str,
     exclude: str,

-    src: Tuple[str],
+    src: Tuple[str, ...],

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


@@ -408,7 +436,7 @@ def main(
     else:
         # We'll autodetect later.
         versions = set()
     else:
         # We'll autodetect later.
         versions = set()

-    mode = FileMode(
+    mode = Mode(

         target_versions=versions,
         line_length=line_length,
         is_pyi=pyi,
         target_versions=versions,
         line_length=line_length,
         is_pyi=pyi,


@@ -429,7 +457,7 @@ def main(
     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)
+    report = Report(check=check, diff=diff, quiet=quiet, verbose=verbose)

     root = find_project_root(src)
     sources: Set[Path] = set()
     path_empty(src, quiet, verbose, ctx)
     root = find_project_root(src)
     sources: Set[Path] = set()
     path_empty(src, quiet, verbose, ctx)


@@ -470,7 +498,9 @@ def main(
     ctx.exit(report.return_code)
 
 
     ctx.exit(report.return_code)
 
 

-def path_empty(src: Tuple[str], quiet: bool, verbose: bool, ctx: click.Context) -> None:
+def path_empty(
+    src: Tuple[str, ...], quiet: bool, verbose: bool, ctx: click.Context
+) -> None:

     """
     Exit if there is no `src` provided for formatting
     """
     """
     Exit if there is no `src` provided for formatting
     """


@@ -481,7 +511,7 @@ def path_empty(src: Tuple[str], quiet: bool, verbose: bool, ctx: click.Context)
 
 
 def reformat_one(
 
 
 def reformat_one(

-    src: Path, fast: bool, write_back: WriteBack, mode: FileMode, report: "Report"
+    src: Path, fast: bool, write_back: WriteBack, mode: Mode, report: "Report"

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


@@ -514,11 +544,7 @@ def reformat_one(
 
 
 def reformat_many(
 
 
 def reformat_many(

-    sources: Set[Path],
-    fast: bool,
-    write_back: WriteBack,
-    mode: FileMode,
-    report: "Report",
+    sources: Set[Path], fast: bool, write_back: WriteBack, mode: Mode, report: "Report"

 ) -> None:
     """Reformat multiple files using a ProcessPoolExecutor."""
     loop = asyncio.get_event_loop()
 ) -> None:
     """Reformat multiple files using a ProcessPoolExecutor."""
     loop = asyncio.get_event_loop()


@@ -548,7 +574,7 @@ async def schedule_formatting(
     sources: Set[Path],
     fast: bool,
     write_back: WriteBack,
     sources: Set[Path],
     fast: bool,
     write_back: WriteBack,

-    mode: FileMode,
+    mode: Mode,

     report: "Report",
     loop: asyncio.AbstractEventLoop,
     executor: Executor,
     report: "Report",
     loop: asyncio.AbstractEventLoop,
     executor: Executor,


@@ -585,7 +611,7 @@ async def schedule_formatting(
         ): src
         for src in sorted(sources)
     }
         ): src
         for src in sorted(sources)
     }

-    pending: Iterable[asyncio.Future] = tasks.keys()
+    pending: Iterable["asyncio.Future[bool]"] = tasks.keys()

     try:
         loop.add_signal_handler(signal.SIGINT, cancel, pending)
         loop.add_signal_handler(signal.SIGTERM, cancel, pending)
     try:
         loop.add_signal_handler(signal.SIGINT, cancel, pending)
         loop.add_signal_handler(signal.SIGTERM, cancel, pending)


@@ -618,7 +644,7 @@ async def schedule_formatting(
 def format_file_in_place(
     src: Path,
     fast: bool,
 def format_file_in_place(
     src: Path,
     fast: bool,

-    mode: FileMode,
+    mode: Mode,

     write_back: WriteBack = WriteBack.NO,
     lock: Any = None,  # multiprocessing.Manager().Lock() is some crazy proxy
 ) -> bool:
     write_back: WriteBack = WriteBack.NO,
     lock: Any = None,  # multiprocessing.Manager().Lock() is some crazy proxy
 ) -> bool:


@@ -629,7 +655,7 @@ def format_file_in_place(
     `mode` and `fast` options are passed to :func:`format_file_contents`.
     """
     if src.suffix == ".pyi":
     `mode` and `fast` options are passed to :func:`format_file_contents`.
     """
     if src.suffix == ".pyi":

-        mode = evolve(mode, is_pyi=True)
+        mode = replace(mode, is_pyi=True)

 
     then = datetime.utcfromtimestamp(src.stat().st_mtime)
     with open(src, "rb") as buf:
 
     then = datetime.utcfromtimestamp(src.stat().st_mtime)
     with open(src, "rb") as buf:


@@ -639,10 +665,10 @@ def format_file_in_place(
     except NothingChanged:
         return False
 
     except NothingChanged:
         return False
 

-    if write_back == write_back.YES:
+    if write_back == WriteBack.YES:

         with open(src, "w", encoding=encoding, newline=newline) as f:
             f.write(dst_contents)
         with open(src, "w", encoding=encoding, newline=newline) as f:
             f.write(dst_contents)

-    elif write_back == write_back.DIFF:
+    elif write_back == WriteBack.DIFF:

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


@@ -662,7 +688,7 @@ def format_file_in_place(
 
 
 def format_stdin_to_stdout(
 
 
 def format_stdin_to_stdout(

-    fast: bool, *, write_back: WriteBack = WriteBack.NO, mode: FileMode
+    fast: bool, *, write_back: WriteBack = WriteBack.NO, mode: Mode

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


@@ -694,9 +720,7 @@ def format_stdin_to_stdout(
         f.detach()
 
 
         f.detach()
 
 

-def format_file_contents(
-    src_contents: str, *, fast: bool, mode: FileMode
-) -> FileContent:
+def format_file_contents(src_contents: str, *, fast: bool, mode: Mode) -> FileContent:

     """Reformat contents a file and return new contents.
 
     If `fast` is False, additionally confirm that the reformatted code is
     """Reformat contents a file and return new contents.
 
     If `fast` is False, additionally confirm that the reformatted code is


@@ -716,11 +740,34 @@ def format_file_contents(
     return dst_contents
 
 
     return dst_contents
 
 

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

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

-    allowed.
+    allowed.  Example:
+
+    >>> import black
+    >>> print(black.format_str("def f(arg:str='')->None:...", mode=Mode()))
+    def f(arg: str = "") -> None:
+        ...
+
+    A more complex example:
+    >>> print(
+    ...   black.format_str(
+    ...     "def f(arg:str='')->None: hey",
+    ...     mode=black.Mode(
+    ...       target_versions={black.TargetVersion.PY36},
+    ...       line_length=10,
+    ...       string_normalization=False,
+    ...       is_pyi=False,
+    ...     ),
+    ...   ),
+    ... )
+    def f(
+        arg: str = '',
+    ) -> None:
+        hey
+

     """
     src_node = lib2to3_parse(src_contents.lstrip(), mode.target_versions)
     dst_contents = []
     """
     src_node = lib2to3_parse(src_contents.lstrip(), mode.target_versions)
     dst_contents = []


@@ -745,11 +792,9 @@ def format_str(src_contents: str, *, mode: FileMode) -> FileContent:
         if supports_feature(versions, feature)
     }
     for current_line in lines.visit(src_node):
         if supports_feature(versions, feature)
     }
     for current_line in lines.visit(src_node):

-        for _ in range(after):
-            dst_contents.append(str(empty_line))
+        dst_contents.append(str(empty_line) * after)

         before, after = elt.maybe_empty_lines(current_line)
         before, after = elt.maybe_empty_lines(current_line)

-        for _ in range(before):
-            dst_contents.append(str(empty_line))
+        dst_contents.append(str(empty_line) * before)

         for line in split_line(
             current_line, line_length=mode.line_length, features=split_line_features
         ):
         for line in split_line(
             current_line, line_length=mode.line_length, features=split_line_features
         ):


@@ -787,7 +832,8 @@ def get_grammars(target_versions: Set[TargetVersion]) -> List[Grammar]:
             # Python 2.7
             pygram.python_grammar,
         ]
             # Python 2.7
             pygram.python_grammar,
         ]

-    elif all(version.is_python2() for version in target_versions):
+
+    if all(version.is_python2() for version in target_versions):

         # Python 2-only code, so try Python 2 grammars.
         return [
             # Python 2.7 with future print_function import
         # Python 2-only code, so try Python 2 grammars.
         return [
             # Python 2.7 with future print_function import


@@ -795,21 +841,21 @@ def get_grammars(target_versions: Set[TargetVersion]) -> List[Grammar]:
             # Python 2.7
             pygram.python_grammar,
         ]
             # Python 2.7
             pygram.python_grammar,
         ]

-    else:
-        # Python 3-compatible code, so only try Python 3 grammar.
-        grammars = []
-        # If we have to parse both, try to parse async as a keyword first
-        if not supports_feature(target_versions, Feature.ASYNC_IDENTIFIERS):
-            # Python 3.7+
-            grammars.append(
-                pygram.python_grammar_no_print_statement_no_exec_statement_async_keywords  # noqa: B950
-            )
-        if not supports_feature(target_versions, Feature.ASYNC_KEYWORDS):
-            # Python 3.0-3.6
-            grammars.append(pygram.python_grammar_no_print_statement_no_exec_statement)
-        # At least one of the above branches must have been taken, because every Python
-        # version has exactly one of the two 'ASYNC_*' flags
-        return grammars
+
+    # Python 3-compatible code, so only try Python 3 grammar.
+    grammars = []
+    # If we have to parse both, try to parse async as a keyword first
+    if not supports_feature(target_versions, Feature.ASYNC_IDENTIFIERS):
+        # Python 3.7+
+        grammars.append(
+            pygram.python_grammar_no_print_statement_no_exec_statement_async_keywords
+        )
+    if not supports_feature(target_versions, Feature.ASYNC_KEYWORDS):
+        # Python 3.0-3.6
+        grammars.append(pygram.python_grammar_no_print_statement_no_exec_statement)
+    # At least one of the above branches must have been taken, because every Python
+    # version has exactly one of the two 'ASYNC_*' flags
+    return grammars

 
 
 def lib2to3_parse(src_txt: str, target_versions: Iterable[TargetVersion] = ()) -> Node:
 
 
 def lib2to3_parse(src_txt: str, target_versions: Iterable[TargetVersion] = ()) -> Node:


@@ -864,8 +910,16 @@ class Visitor(Generic[T]):
         if node.type < 256:
             name = token.tok_name[node.type]
         else:
         if node.type < 256:
             name = token.tok_name[node.type]
         else:

-            name = type_repr(node.type)
-        yield from getattr(self, f"visit_{name}", self.visit_default)(node)
+            name = str(type_repr(node.type))
+        # We explicitly branch on whether a visitor exists (instead of
+        # using self.visit_default as the default arg to getattr) in order
+        # to save needing to create a bound method object and so mypyc can
+        # generate a native call to visit_default.
+        visitf = getattr(self, f"visit_{name}", None)
+        if visitf:
+            yield from visitf(node)
+        else:
+            yield from self.visit_default(node)

 
     def visit_default(self, node: LN) -> Iterator[T]:
         """Default `visit_*()` implementation. Recurses to children of `node`."""
 
     def visit_default(self, node: LN) -> Iterator[T]:
         """Default `visit_*()` implementation. Recurses to children of `node`."""


@@ -910,8 +964,8 @@ class DebugVisitor(Visitor[T]):
         list(v.visit(code))
 
 
         list(v.visit(code))
 
 

-WHITESPACE = {token.DEDENT, token.INDENT, token.NEWLINE}
-STATEMENT = {
+WHITESPACE: Final = {token.DEDENT, token.INDENT, token.NEWLINE}
+STATEMENT: Final = {

     syms.if_stmt,
     syms.while_stmt,
     syms.for_stmt,
     syms.if_stmt,
     syms.while_stmt,
     syms.for_stmt,


@@ -921,10 +975,10 @@ STATEMENT = {
     syms.funcdef,
     syms.classdef,
 }
     syms.funcdef,
     syms.classdef,
 }

-STANDALONE_COMMENT = 153
+STANDALONE_COMMENT: Final = 153

 token.tok_name[STANDALONE_COMMENT] = "STANDALONE_COMMENT"
 token.tok_name[STANDALONE_COMMENT] = "STANDALONE_COMMENT"

-LOGIC_OPERATORS = {"and", "or"}
-COMPARATORS = {
+LOGIC_OPERATORS: Final = {"and", "or"}
+COMPARATORS: Final = {

     token.LESS,
     token.GREATER,
     token.EQEQUAL,
     token.LESS,
     token.GREATER,
     token.EQEQUAL,


@@ -932,7 +986,7 @@ COMPARATORS = {
     token.LESSEQUAL,
     token.GREATEREQUAL,
 }
     token.LESSEQUAL,
     token.GREATEREQUAL,
 }

-MATH_OPERATORS = {
+MATH_OPERATORS: Final = {

     token.VBAR,
     token.CIRCUMFLEX,
     token.AMPER,
     token.VBAR,
     token.CIRCUMFLEX,
     token.AMPER,


@@ -948,23 +1002,23 @@ MATH_OPERATORS = {
     token.TILDE,
     token.DOUBLESTAR,
 }
     token.TILDE,
     token.DOUBLESTAR,
 }

-STARS = {token.STAR, token.DOUBLESTAR}
-VARARGS_SPECIALS = STARS | {token.SLASH}
-VARARGS_PARENTS = {
+STARS: Final = {token.STAR, token.DOUBLESTAR}
+VARARGS_SPECIALS: Final = STARS | {token.SLASH}
+VARARGS_PARENTS: Final = {

     syms.arglist,
     syms.argument,  # double star in arglist
     syms.trailer,  # single argument to call
     syms.typedargslist,
     syms.varargslist,  # lambdas
 }
     syms.arglist,
     syms.argument,  # double star in arglist
     syms.trailer,  # single argument to call
     syms.typedargslist,
     syms.varargslist,  # lambdas
 }

-UNPACKING_PARENTS = {
+UNPACKING_PARENTS: Final = {

     syms.atom,  # single element of a list or set literal
     syms.dictsetmaker,
     syms.listmaker,
     syms.testlist_gexp,
     syms.testlist_star_expr,
 }
     syms.atom,  # single element of a list or set literal
     syms.dictsetmaker,
     syms.listmaker,
     syms.testlist_gexp,
     syms.testlist_star_expr,
 }

-TEST_DESCENDANTS = {
+TEST_DESCENDANTS: Final = {

     syms.test,
     syms.lambdef,
     syms.or_test,
     syms.test,
     syms.lambdef,
     syms.or_test,


@@ -981,7 +1035,7 @@ TEST_DESCENDANTS = {
     syms.term,
     syms.power,
 }
     syms.term,
     syms.power,
 }

-ASSIGNMENTS = {
+ASSIGNMENTS: Final = {

     "=",
     "+=",
     "-=",
     "=",
     "+=",
     "-=",


@@ -997,13 +1051,13 @@ ASSIGNMENTS = {
     "**=",
     "//=",
 }
     "**=",
     "//=",
 }

-COMPREHENSION_PRIORITY = 20
-COMMA_PRIORITY = 18
-TERNARY_PRIORITY = 16
-LOGIC_PRIORITY = 14
-STRING_PRIORITY = 12
-COMPARATOR_PRIORITY = 10
-MATH_PRIORITIES = {
+COMPREHENSION_PRIORITY: Final = 20
+COMMA_PRIORITY: Final = 18
+TERNARY_PRIORITY: Final = 16
+LOGIC_PRIORITY: Final = 14
+STRING_PRIORITY: Final = 12
+COMPARATOR_PRIORITY: Final = 10
+MATH_PRIORITIES: Final = {

     token.VBAR: 9,
     token.CIRCUMFLEX: 8,
     token.AMPER: 7,
     token.VBAR: 9,
     token.CIRCUMFLEX: 8,
     token.AMPER: 7,


@@ -1019,7 +1073,7 @@ MATH_PRIORITIES = {
     token.TILDE: 3,
     token.DOUBLESTAR: 2,
 }
     token.TILDE: 3,
     token.DOUBLESTAR: 2,
 }

-DOT_PRIORITY = 1
+DOT_PRIORITY: Final = 1

 
 
 @dataclass
 
 
 @dataclass


@@ -1027,11 +1081,11 @@ class BracketTracker:
     """Keeps track of brackets on a line."""
 
     depth: int = 0
     """Keeps track of brackets on a line."""
 
     depth: int = 0

-    bracket_match: Dict[Tuple[Depth, NodeType], Leaf] = Factory(dict)
-    delimiters: Dict[LeafID, Priority] = Factory(dict)
+    bracket_match: Dict[Tuple[Depth, NodeType], Leaf] = field(default_factory=dict)
+    delimiters: Dict[LeafID, Priority] = field(default_factory=dict)

     previous: Optional[Leaf] = None
     previous: Optional[Leaf] = None

-    _for_loop_depths: List[int] = Factory(list)
-    _lambda_argument_depths: List[int] = Factory(list)
+    _for_loop_depths: List[int] = field(default_factory=list)
+    _lambda_argument_depths: List[int] = field(default_factory=list)

 
     def mark(self, leaf: Leaf) -> None:
         """Mark `leaf` with bracket-related metadata. Keep track of delimiters.
 
     def mark(self, leaf: Leaf) -> None:
         """Mark `leaf` with bracket-related metadata. Keep track of delimiters.


@@ -1159,9 +1213,10 @@ class Line:
     """Holds leaves and comments. Can be printed with `str(line)`."""
 
     depth: int = 0
     """Holds leaves and comments. Can be printed with `str(line)`."""
 
     depth: int = 0

-    leaves: List[Leaf] = Factory(list)
-    comments: Dict[LeafID, List[Leaf]] = Factory(dict)  # keys ordered like `leaves`
-    bracket_tracker: BracketTracker = Factory(BracketTracker)
+    leaves: List[Leaf] = field(default_factory=list)
+    # keys ordered like `leaves`
+    comments: Dict[LeafID, List[Leaf]] = field(default_factory=dict)
+    bracket_tracker: BracketTracker = field(default_factory=BracketTracker)

     inside_brackets: bool = False
     should_explode: bool = False
 
     inside_brackets: bool = False
     should_explode: bool = False
 


@@ -1249,6 +1304,7 @@ class Line:
         """
         if not self.leaves or len(self.leaves) < 4:
             return False
         """
         if not self.leaves or len(self.leaves) < 4:
             return False

+

         # Look for and address a trailing colon.
         if self.leaves[-1].type == token.COLON:
             closer = self.leaves[-2]
         # Look for and address a trailing colon.
         if self.leaves[-1].type == token.COLON:
             closer = self.leaves[-2]


@@ -1258,6 +1314,7 @@ class Line:
             close_index = -1
         if closer.type not in CLOSING_BRACKETS or self.inside_brackets:
             return False
             close_index = -1
         if closer.type not in CLOSING_BRACKETS or self.inside_brackets:
             return False

+

         if closer.type == token.RPAR:
             # Tuples require an extra check, because if there's only
             # one element in the tuple removing the comma unmakes the
         if closer.type == token.RPAR:
             # Tuples require an extra check, because if there's only
             # one element in the tuple removing the comma unmakes the


@@ -1272,9 +1329,11 @@ class Line:
             for _open_index, leaf in enumerate(self.leaves):
                 if leaf is opener:
                     break
             for _open_index, leaf in enumerate(self.leaves):
                 if leaf is opener:
                     break

+

             else:
                 # Couldn't find the matching opening paren, play it safe.
                 return False
             else:
                 # Couldn't find the matching opening paren, play it safe.
                 return False

+

             commas = 0
             comma_depth = self.leaves[close_index - 1].bracket_depth
             for leaf in self.leaves[_open_index + 1 : close_index]:
             commas = 0
             comma_depth = self.leaves[close_index - 1].bracket_depth
             for leaf in self.leaves[_open_index + 1 : close_index]:


@@ -1284,16 +1343,20 @@ class Line:
                 # We haven't looked yet for the trailing comma because
                 # we might also have caught noop parens.
                 return self.leaves[close_index - 1].type == token.COMMA
                 # We haven't looked yet for the trailing comma because
                 # we might also have caught noop parens.
                 return self.leaves[close_index - 1].type == token.COMMA

+

             elif commas == 1:
                 return False  # it's either a one-tuple or didn't have a trailing comma
             elif commas == 1:
                 return False  # it's either a one-tuple or didn't have a trailing comma

+

             if self.leaves[close_index - 1].type in CLOSING_BRACKETS:
                 close_index -= 1
                 closer = self.leaves[close_index]
                 if closer.type == token.RPAR:
                     # TODO: this is a gut feeling. Will we ever see this?
                     return False
             if self.leaves[close_index - 1].type in CLOSING_BRACKETS:
                 close_index -= 1
                 closer = self.leaves[close_index]
                 if closer.type == token.RPAR:
                     # TODO: this is a gut feeling. Will we ever see this?
                     return False

+

         if self.leaves[close_index - 1].type != token.COMMA:
             return False
         if self.leaves[close_index - 1].type != token.COMMA:
             return False

+

         return True
 
     @property
         return True
 
     @property


@@ -1343,9 +1406,9 @@ class Line:
     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:

-            if leaf.type == STANDALONE_COMMENT:
-                if leaf.bracket_depth <= depth_limit:
-                    return True
+            if leaf.type == STANDALONE_COMMENT and leaf.bracket_depth <= depth_limit:
+                return True
+

         return False
 
     def contains_uncollapsable_type_comments(self) -> bool:
         return False
 
     def contains_uncollapsable_type_comments(self) -> bool:


@@ -1374,7 +1437,10 @@ class Line:
         for leaf_id, comments in self.comments.items():
             for comment in comments:
                 if is_type_comment(comment):
         for leaf_id, comments in self.comments.items():
             for comment in comments:
                 if is_type_comment(comment):

-                    if leaf_id not in ignored_ids or comment_seen:
+                    if comment_seen or (
+                        not is_type_comment(comment, " ignore")
+                        and leaf_id not in ignored_ids
+                    ):

                         return True
 
                 comment_seen = True
                         return True
 
                 comment_seen = True


@@ -1413,16 +1479,13 @@ class Line:
         return False
 
     def contains_multiline_strings(self) -> bool:
         return False
 
     def contains_multiline_strings(self) -> bool:

-        for leaf in self.leaves:
-            if is_multiline_string(leaf):
-                return True
-
-        return False
+        return any(is_multiline_string(leaf) for leaf in self.leaves)

 
     def maybe_remove_trailing_comma(self, closing: Leaf) -> bool:
         """Remove trailing comma if there is one and it's safe."""
         if not (self.leaves and self.leaves[-1].type == token.COMMA):
             return False
 
     def maybe_remove_trailing_comma(self, closing: Leaf) -> bool:
         """Remove trailing comma if there is one and it's safe."""
         if not (self.leaves and self.leaves[-1].type == token.COMMA):
             return False

+

         # We remove trailing commas only in the case of importing a
         # single name from a module.
         if not (
         # We remove trailing commas only in the case of importing a
         # single name from a module.
         if not (


@@ -1487,6 +1550,7 @@ class Line:
                 comment.type = STANDALONE_COMMENT
                 comment.prefix = ""
                 return False
                 comment.type = STANDALONE_COMMENT
                 comment.prefix = ""
                 return False

+

             last_leaf = self.leaves[-2]
         self.comments.setdefault(id(last_leaf), []).append(comment)
         return True
             last_leaf = self.leaves[-2]
         self.comments.setdefault(id(last_leaf), []).append(comment)
         return True


@@ -1554,7 +1618,7 @@ class EmptyLineTracker:
     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

-    previous_defs: List[int] = Factory(list)
+    previous_defs: List[int] = field(default_factory=list)

 
     def maybe_empty_lines(self, current_line: Line) -> Tuple[int, int]:
         """Return the number of extra empty lines before and after the `current_line`.
 
     def maybe_empty_lines(self, current_line: Line) -> Tuple[int, int]:
         """Return the number of extra empty lines before and after the `current_line`.


@@ -1668,7 +1732,7 @@ class LineGenerator(Visitor[Line]):
 
     is_pyi: bool = False
     normalize_strings: bool = True
 
     is_pyi: bool = False
     normalize_strings: bool = True

-    current_line: Line = Factory(Line)
+    current_line: Line = field(default_factory=Line)

     remove_u_prefix: bool = False
 
     def line(self, indent: int = 0) -> Iterator[Line]:
     remove_u_prefix: bool = False
 
     def line(self, indent: int = 0) -> Iterator[Line]:


@@ -1717,26 +1781,13 @@ class LineGenerator(Visitor[Line]):
                 self.current_line.append(node)
         yield from super().visit_default(node)
 
                 self.current_line.append(node)
         yield from super().visit_default(node)
 

-    def visit_factor(self, node: Node) -> Iterator[Line]:
-        """Force parentheses between a unary op and a binary power:
-
-        -2 ** 8 -> -(2 ** 8)
-        """
-        child = node.children[1]
-        if child.type == syms.power and len(child.children) == 3:
-            lpar = Leaf(token.LPAR, "(")
-            rpar = Leaf(token.RPAR, ")")
-            index = child.remove() or 0
-            node.insert_child(index, Node(syms.atom, [lpar, child, rpar]))
-        yield from self.visit_default(node)
-
-    def visit_INDENT(self, node: Node) -> Iterator[Line]:
+    def visit_INDENT(self, node: Leaf) -> Iterator[Line]:

         """Increase indentation level, maybe yield a line."""
         # In blib2to3 INDENT never holds comments.
         yield from self.line(+1)
         yield from self.visit_default(node)
 
         """Increase indentation level, maybe yield a line."""
         # In blib2to3 INDENT never holds comments.
         yield from self.line(+1)
         yield from self.visit_default(node)
 

-    def visit_DEDENT(self, node: Node) -> Iterator[Line]:
+    def visit_DEDENT(self, node: Leaf) -> Iterator[Line]:

         """Decrease indentation level, maybe yield a line."""
         # The current line might still wait for trailing comments.  At DEDENT time
         # there won't be any (they would be prefixes on the preceding NEWLINE).
         """Decrease indentation level, maybe yield a line."""
         # The current line might still wait for trailing comments.  At DEDENT time
         # there won't be any (they would be prefixes on the preceding NEWLINE).


@@ -1829,7 +1880,24 @@ class LineGenerator(Visitor[Line]):
             yield from self.line()
         yield from self.visit_default(leaf)
 
             yield from self.line()
         yield from self.visit_default(leaf)
 

-    def __attrs_post_init__(self) -> None:
+    def visit_factor(self, node: Node) -> Iterator[Line]:
+        """Force parentheses between a unary op and a binary power:
+
+        -2 ** 8 -> -(2 ** 8)
+        """
+        _operator, operand = node.children
+        if (
+            operand.type == syms.power
+            and len(operand.children) == 3
+            and operand.children[1].type == token.DOUBLESTAR
+        ):
+            lpar = Leaf(token.LPAR, "(")
+            rpar = Leaf(token.RPAR, ")")
+            index = operand.remove() or 0
+            node.insert_child(index, Node(syms.atom, [lpar, operand, rpar]))
+        yield from self.visit_default(node)
+
+    def __post_init__(self) -> None:

         """You are in a twisty little maze of passages."""
         v = self.visit_stmt
         Ø: Set[str] = set()
         """You are in a twisty little maze of passages."""
         v = self.visit_stmt
         Ø: Set[str] = set()


@@ -2402,7 +2470,9 @@ def split_line(
             # All splits failed, best effort split with no omits.
             # This mostly happens to multiline strings that are by definition
             # reported as not fitting a single line.
             # All splits failed, best effort split with no omits.
             # This mostly happens to multiline strings that are by definition
             # reported as not fitting a single line.

-            yield from right_hand_split(line, line_length, features=features)
+            # line_length=1 here was historically a bug that somehow became a feature.
+            # See #762 and #781 for the full story.
+            yield from right_hand_split(line, line_length=1, features=features)

 
         if line.inside_brackets:
             split_funcs = [delimiter_split, standalone_comment_split, rhs]
 
         if line.inside_brackets:
             split_funcs = [delimiter_split, standalone_comment_split, rhs]


@@ -2445,7 +2515,7 @@ def left_hand_split(line: Line, features: Collection[Feature] = ()) -> Iterator[
     body_leaves: List[Leaf] = []
     head_leaves: List[Leaf] = []
     current_leaves = head_leaves
     body_leaves: List[Leaf] = []
     head_leaves: List[Leaf] = []
     current_leaves = head_leaves

-    matching_bracket = None
+    matching_bracket: Optional[Leaf] = None

     for leaf in line.leaves:
         if (
             current_leaves is body_leaves
     for leaf in line.leaves:
         if (
             current_leaves is body_leaves


@@ -2488,8 +2558,8 @@ def right_hand_split(
     body_leaves: List[Leaf] = []
     head_leaves: List[Leaf] = []
     current_leaves = tail_leaves
     body_leaves: List[Leaf] = []
     head_leaves: List[Leaf] = []
     current_leaves = tail_leaves

-    opening_bracket = None
-    closing_bracket = None
+    opening_bracket: Optional[Leaf] = None
+    closing_bracket: Optional[Leaf] = None

     for leaf in reversed(line.leaves):
         if current_leaves is body_leaves:
             if leaf is opening_bracket:
     for leaf in reversed(line.leaves):
         if current_leaves is body_leaves:
             if leaf is opening_bracket:


@@ -2612,11 +2682,11 @@ def bracket_split_build_line(
                 for i in range(len(leaves) - 1, -1, -1):
                     if leaves[i].type == STANDALONE_COMMENT:
                         continue
                 for i in range(len(leaves) - 1, -1, -1):
                     if leaves[i].type == STANDALONE_COMMENT:
                         continue

-                    elif leaves[i].type == token.COMMA:
-                        break
-                    else:
+
+                    if leaves[i].type != token.COMMA:

                         leaves.insert(i + 1, Leaf(token.COMMA, ","))
                         leaves.insert(i + 1, Leaf(token.COMMA, ","))

-                        break
+                    break
+

     # Populate the line
     for leaf in leaves:
         result.append(leaf, preformatted=True)
     # Populate the line
     for leaf in leaves:
         result.append(leaf, preformatted=True)


@@ -2793,7 +2863,7 @@ def normalize_string_prefix(leaf: Leaf, remove_u_prefix: bool = False) -> None:
     match = re.match(r"^([furbFURB]*)(.*)$", leaf.value, re.DOTALL)
     assert match is not None, f"failed to match string {leaf.value!r}"
     orig_prefix = match.group(1)
     match = re.match(r"^([furbFURB]*)(.*)$", leaf.value, re.DOTALL)
     assert match is not None, f"failed to match string {leaf.value!r}"
     orig_prefix = match.group(1)

-    new_prefix = orig_prefix.lower()
+    new_prefix = orig_prefix.replace("F", "f").replace("B", "b").replace("U", "u")

     if remove_u_prefix:
         new_prefix = new_prefix.replace("u", "")
     leaf.value = f"{new_prefix}{match.group(2)}"
     if remove_u_prefix:
         new_prefix = new_prefix.replace("u", "")
     leaf.value = f"{new_prefix}{match.group(2)}"


@@ -2860,6 +2930,7 @@ def normalize_string_quotes(leaf: Leaf) -> None:
             if "\\" in str(m):
                 # Do not introduce backslashes in interpolated expressions
                 return
             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] + '\\"'
     if new_quote == '"""' and new_body[-1:] == '"':
         # edge case:
         new_body = new_body[:-1] + '\\"'


@@ -2932,7 +3003,6 @@ def normalize_invisible_parens(node: Node, parens_after: Set[str]) -> None:
         if pc.value in FMT_OFF:
             # This `node` has a prefix with `# fmt: off`, don't mess with parens.
             return
         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)):
         # Add parentheses around long tuple unpacking in assignments.
     check_lpar = False
     for index, child in enumerate(list(node.children)):
         # Add parentheses around long tuple unpacking in assignments.


@@ -2946,26 +3016,12 @@ def normalize_invisible_parens(node: Node, parens_after: Set[str]) -> None:
         if check_lpar:
             if is_walrus_assignment(child):
                 continue
         if check_lpar:
             if is_walrus_assignment(child):
                 continue

-            if child.type == syms.atom:
-                # Determines if the underlying atom should be surrounded with
-                # invisible params - also makes parens invisible recursively
-                # within the atom and removes repeated invisible parens within
-                # the atom
-                should_surround_with_parens = maybe_make_parens_invisible_in_atom(
-                    child, parent=node
-                )

 
 

-                if should_surround_with_parens:
-                    lpar = Leaf(token.LPAR, "")
-                    rpar = Leaf(token.RPAR, "")
-                    index = child.remove() or 0
-                    node.insert_child(index, Node(syms.atom, [lpar, child, rpar]))
+            if child.type == syms.atom:
+                if maybe_make_parens_invisible_in_atom(child, parent=node):
+                    wrap_in_parentheses(node, child, visible=False)

             elif is_one_tuple(child):
             elif is_one_tuple(child):

-                # wrap child in visible parentheses
-                lpar = Leaf(token.LPAR, "(")
-                rpar = Leaf(token.RPAR, ")")
-                child.remove()
-                node.insert_child(index, Node(syms.atom, [lpar, child, rpar]))
+                wrap_in_parentheses(node, child, visible=True)

             elif node.type == syms.import_from:
                 # "import from" nodes store parentheses directly as part of
                 # the statement
             elif node.type == syms.import_from:
                 # "import from" nodes store parentheses directly as part of
                 # the statement


@@ -2980,15 +3036,7 @@ def normalize_invisible_parens(node: Node, parens_after: Set[str]) -> None:
                 break
 
             elif not (isinstance(child, Leaf) and is_multiline_string(child)):
                 break
 
             elif not (isinstance(child, Leaf) and is_multiline_string(child)):

-                # wrap child in invisible parentheses
-                lpar = Leaf(token.LPAR, "")
-                rpar = Leaf(token.RPAR, "")
-                index = child.remove() or 0
-                prefix = child.prefix
-                child.prefix = ""
-                new_child = Node(syms.atom, [lpar, child, rpar])
-                new_child.prefix = prefix
-                node.insert_child(index, new_child)
+                wrap_in_parentheses(node, child, visible=False)

 
         check_lpar = isinstance(child, Leaf) and child.value in parens_after
 
 
         check_lpar = isinstance(child, Leaf) and child.value in parens_after
 


@@ -3032,7 +3080,7 @@ def convert_one_fmt_off_pair(node: Node) -> bool:
                     # That happens when one of the `ignored_nodes` ended with a NEWLINE
                     # leaf (possibly followed by a DEDENT).
                     hidden_value = hidden_value[:-1]
                     # 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
+                first_idx: Optional[int] = None

                 for ignored in ignored_nodes:
                     index = ignored.remove()
                     if first_idx is None:
                 for ignored in ignored_nodes:
                     index = ignored.remove()
                     if first_idx is None:


@@ -3061,9 +3109,14 @@ def generate_ignored_nodes(leaf: Leaf) -> Iterator[LN]:
     """
     container: Optional[LN] = container_of(leaf)
     while container is not None and container.type != token.ENDMARKER:
     """
     container: Optional[LN] = container_of(leaf)
     while container is not None and container.type != token.ENDMARKER:

+        is_fmt_on = False

         for comment in list_comments(container.prefix, is_endmarker=False):
             if comment.value in FMT_ON:
         for comment in list_comments(container.prefix, is_endmarker=False):
             if comment.value in FMT_ON:

-                return
+                is_fmt_on = True
+            elif comment.value in FMT_OFF:
+                is_fmt_on = False
+        if is_fmt_on:
+            return

 
         yield container
 
 
         yield container
 


@@ -3140,6 +3193,7 @@ def unwrap_singleton_parenthesis(node: LN) -> Optional[LN]:
     Parenthesis can be optional. Returns None otherwise"""
     if len(node.children) != 3:
         return None
     Parenthesis can be optional. Returns None otherwise"""
     if len(node.children) != 3:
         return None

+

     lpar, wrapped, rpar = node.children
     if not (lpar.type == token.LPAR and rpar.type == token.RPAR):
         return None
     lpar, wrapped, rpar = node.children
     if not (lpar.type == token.LPAR and rpar.type == token.RPAR):
         return None


@@ -3147,6 +3201,24 @@ def unwrap_singleton_parenthesis(node: LN) -> Optional[LN]:
     return wrapped
 
 
     return wrapped
 
 

+def wrap_in_parentheses(parent: Node, child: LN, *, visible: bool = True) -> None:
+    """Wrap `child` in parentheses.
+
+    This replaces `child` with an atom holding the parentheses and the old
+    child.  That requires moving the prefix.
+
+    If `visible` is False, the leaves will be valueless (and thus invisible).
+    """
+    lpar = Leaf(token.LPAR, "(" if visible else "")
+    rpar = Leaf(token.RPAR, ")" if visible else "")
+    prefix = child.prefix
+    child.prefix = ""
+    index = child.remove() or 0
+    new_child = Node(syms.atom, [lpar, child, rpar])
+    new_child.prefix = prefix
+    parent.insert_child(index, new_child)
+
+

 def is_one_tuple(node: LN) -> bool:
     """Return True if `node` holds a tuple with one element, with or without parens."""
     if node.type == syms.atom:
 def is_one_tuple(node: LN) -> bool:
     """Return True if `node` holds a tuple with one element, with or without parens."""
     if node.type == syms.atom:


@@ -3379,8 +3451,8 @@ def generate_trailers_to_omit(line: Line, line_length: int) -> Iterator[Set[Leaf
     yield omit
 
     length = 4 * line.depth
     yield omit
 
     length = 4 * line.depth

-    opening_bracket = None
-    closing_bracket = None
+    opening_bracket: Optional[Leaf] = None
+    closing_bracket: Optional[Leaf] = None

     inner_brackets: Set[LeafID] = set()
     for index, leaf, leaf_length in enumerate_with_length(line, reversed=True):
         length += leaf_length
     inner_brackets: Set[LeafID] = set()
     for index, leaf, leaf_length in enumerate_with_length(line, reversed=True):
         length += leaf_length


@@ -3424,19 +3496,23 @@ def get_future_imports(node: Node) -> Set[str]:
             if isinstance(child, Leaf):
                 if child.type == token.NAME:
                     yield child.value
             if isinstance(child, Leaf):
                 if child.type == token.NAME:
                     yield child.value

+

             elif child.type == syms.import_as_name:
                 orig_name = child.children[0]
                 assert isinstance(orig_name, Leaf), "Invalid syntax parsing imports"
                 assert orig_name.type == token.NAME, "Invalid syntax parsing imports"
                 yield orig_name.value
             elif child.type == syms.import_as_name:
                 orig_name = child.children[0]
                 assert isinstance(orig_name, Leaf), "Invalid syntax parsing imports"
                 assert orig_name.type == token.NAME, "Invalid syntax parsing imports"
                 yield orig_name.value

+

             elif child.type == syms.import_as_names:
                 yield from get_imports_from_children(child.children)
             elif child.type == syms.import_as_names:
                 yield from get_imports_from_children(child.children)

+

             else:
                 raise AssertionError("Invalid syntax parsing imports")
 
     for child in node.children:
         if child.type != syms.simple_stmt:
             break
             else:
                 raise AssertionError("Invalid syntax parsing imports")
 
     for child in node.children:
         if child.type != syms.simple_stmt:
             break

+

         first_child = child.children[0]
         if isinstance(first_child, Leaf):
             # Continue looking if we see a docstring; otherwise stop.
         first_child = child.children[0]
         if isinstance(first_child, Leaf):
             # Continue looking if we see a docstring; otherwise stop.


@@ -3446,15 +3522,18 @@ def get_future_imports(node: Node) -> Set[str]:
                 and child.children[1].type == token.NEWLINE
             ):
                 continue
                 and child.children[1].type == token.NEWLINE
             ):
                 continue

-            else:
-                break
+
+            break
+

         elif first_child.type == syms.import_from:
             module_name = first_child.children[1]
             if not isinstance(module_name, Leaf) or module_name.value != "__future__":
                 break
         elif first_child.type == syms.import_from:
             module_name = first_child.children[1]
             if not isinstance(module_name, Leaf) or module_name.value != "__future__":
                 break

+

             imports |= set(get_imports_from_children(first_child.children[3:]))
         else:
             break
             imports |= set(get_imports_from_children(first_child.children[3:]))
         else:
             break

+

     return imports
 
 
     return imports
 
 


@@ -3462,10 +3541,11 @@ def get_future_imports(node: Node) -> Set[str]:
 def get_gitignore(root: Path) -> PathSpec:
     """ Return a PathSpec matching gitignore content if present."""
     gitignore = root / ".gitignore"
 def get_gitignore(root: Path) -> PathSpec:
     """ Return a PathSpec matching gitignore content if present."""
     gitignore = root / ".gitignore"

-    if not gitignore.is_file():
-        return PathSpec.from_lines("gitwildmatch", [])
-    else:
-        return PathSpec.from_lines("gitwildmatch", gitignore.open())
+    lines: List[str] = []
+    if gitignore.is_file():
+        with gitignore.open() as gf:
+            lines = gf.readlines()
+    return PathSpec.from_lines("gitwildmatch", lines)

 
 
 def gen_python_files_in_dir(
 
 
 def gen_python_files_in_dir(


@@ -3496,6 +3576,7 @@ def gen_python_files_in_dir(
         except OSError as e:
             report.path_ignored(child, f"cannot be read because {e}")
             continue
         except OSError as e:
             report.path_ignored(child, f"cannot be read because {e}")
             continue

+

         except ValueError:
             if child.is_symlink():
                 report.path_ignored(
         except ValueError:
             if child.is_symlink():
                 report.path_ignored(


@@ -3542,7 +3623,7 @@ def find_project_root(srcs: Iterable[str]) -> Path:
         # Append a fake file so `parents` below returns `common_base_dir`, too.
         common_base /= "fake-file"
     for directory in common_base.parents:
         # 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():
+        if (directory / ".git").exists():

             return directory
 
         if (directory / ".hg").is_dir():
             return directory
 
         if (directory / ".hg").is_dir():


@@ -3559,6 +3640,7 @@ class Report:
     """Provides a reformatting counter. Can be rendered with `str(report)`."""
 
     check: bool = False
     """Provides a reformatting counter. Can be rendered with `str(report)`."""
 
     check: bool = False

+    diff: bool = False

     quiet: bool = False
     verbose: bool = False
     change_count: int = 0
     quiet: bool = False
     verbose: bool = False
     change_count: int = 0


@@ -3568,7 +3650,7 @@ class Report:
     def done(self, src: Path, changed: Changed) -> None:
         """Increment the counter for successful reformatting. Write out a message."""
         if changed is Changed.YES:
     def done(self, src: Path, changed: Changed) -> None:
         """Increment the counter for successful reformatting. Write out a message."""
         if changed is Changed.YES:

-            reformatted = "would reformat" if self.check else "reformatted"
+            reformatted = "would reformat" if self.check or self.diff else "reformatted"

             if self.verbose or not self.quiet:
                 out(f"{reformatted} {src}")
             self.change_count += 1
             if self.verbose or not self.quiet:
                 out(f"{reformatted} {src}")
             self.change_count += 1


@@ -3614,7 +3696,7 @@ class Report:
 
         Use `click.unstyle` to remove colors.
         """
 
         Use `click.unstyle` to remove colors.
         """

-        if self.check:
+        if self.check or self.diff:

             reformatted = "would be reformatted"
             unchanged = "would be left unchanged"
             failed = "would fail to reformat"
             reformatted = "would be reformatted"
             unchanged = "would be left unchanged"
             failed = "would fail to reformat"


@@ -3662,14 +3744,15 @@ def _fixup_ast_constants(
     node: Union[ast.AST, ast3.AST, ast27.AST]
 ) -> Union[ast.AST, ast3.AST, ast27.AST]:
     """Map ast nodes deprecated in 3.8 to Constant."""
     node: Union[ast.AST, ast3.AST, ast27.AST]
 ) -> Union[ast.AST, ast3.AST, ast27.AST]:
     """Map ast nodes deprecated in 3.8 to Constant."""

-    # casts are required until this is released:
-    # https://github.com/python/typeshed/pull/3142

     if isinstance(node, (ast.Str, ast3.Str, ast27.Str, ast.Bytes, ast3.Bytes)):
     if isinstance(node, (ast.Str, ast3.Str, ast27.Str, ast.Bytes, ast3.Bytes)):

-        return cast(ast.AST, ast.Constant(value=node.s))
-    elif isinstance(node, (ast.Num, ast3.Num, ast27.Num)):
-        return cast(ast.AST, ast.Constant(value=node.n))
-    elif isinstance(node, (ast.NameConstant, ast3.NameConstant)):
-        return cast(ast.AST, ast.Constant(value=node.value))
+        return ast.Constant(value=node.s)
+
+    if isinstance(node, (ast.Num, ast3.Num, ast27.Num)):
+        return ast.Constant(value=node.n)
+
+    if isinstance(node, (ast.NameConstant, ast3.NameConstant)):
+        return ast.Constant(value=node.value)
+

     return node
 
 
     return node
 
 


@@ -3683,7 +3766,7 @@ def assert_equivalent(src: str, dst: str) -> None:
 
         yield f"{'  ' * depth}{node.__class__.__name__}("
 
 
         yield f"{'  ' * depth}{node.__class__.__name__}("
 

-        for field in sorted(node._fields):
+        for field in sorted(node._fields):  # noqa: F402

             # TypeIgnore has only one field 'lineno' which breaks this comparison
             type_ignore_classes = (ast3.TypeIgnore, ast27.TypeIgnore)
             if sys.version_info >= (3, 8):
             # TypeIgnore has only one field 'lineno' which breaks this comparison
             type_ignore_classes = (ast3.TypeIgnore, ast27.TypeIgnore)
             if sys.version_info >= (3, 8):


@@ -3709,6 +3792,7 @@ def assert_equivalent(src: str, dst: str) -> None:
                     ):
                         for item in item.elts:
                             yield from _v(item, depth + 2)
                     ):
                         for item in item.elts:
                             yield from _v(item, depth + 2)

+

                     elif isinstance(item, (ast.AST, ast3.AST, ast27.AST)):
                         yield from _v(item, depth + 2)
 
                     elif isinstance(item, (ast.AST, ast3.AST, ast27.AST)):
                         yield from _v(item, depth + 2)
 


@@ -3750,7 +3834,7 @@ def assert_equivalent(src: str, dst: str) -> None:
         ) from None
 
 
         ) from None
 
 

-def assert_stable(src: str, dst: str, mode: FileMode) -> None:
+def assert_stable(src: str, dst: str, mode: Mode) -> None:

     """Raise AssertionError if `dst` reformats differently the second time."""
     newdst = format_str(dst, mode=mode)
     if dst != newdst:
     """Raise AssertionError if `dst` reformats differently the second time."""
     newdst = format_str(dst, mode=mode)
     if dst != newdst:


@@ -3766,6 +3850,7 @@ def assert_stable(src: str, dst: str, mode: FileMode) -> None:
         ) from None
 
 
         ) from None
 
 

+@mypyc_attr(patchable=True)

 def dump_to_file(*output: str) -> str:
     """Dump `output` to a temporary file. Return path to the file."""
     with tempfile.NamedTemporaryFile(
 def dump_to_file(*output: str) -> str:
     """Dump `output` to a temporary file. Return path to the file."""
     with tempfile.NamedTemporaryFile(


@@ -3780,8 +3865,10 @@ def dump_to_file(*output: str) -> str:
 
 @contextmanager
 def nullcontext() -> Iterator[None]:
 
 @contextmanager
 def nullcontext() -> Iterator[None]:

-    """Return context manager that does nothing.
-    Similar to `nullcontext` from python 3.7"""
+    """Return an empty context manager.
+
+    To be used like `nullcontext` in Python 3.7.
+    """

     yield
 
 
     yield
 
 


@@ -3796,7 +3883,7 @@ def diff(a: str, b: str, a_name: str, b_name: str) -> str:
     )
 
 
     )
 
 

-def cancel(tasks: Iterable[asyncio.Task]) -> None:
+def cancel(tasks: Iterable["asyncio.Task[Any]"]) -> None:

     """asyncio signal handler that cancels all `tasks` and reports to stderr."""
     err("Aborted!")
     for task in tasks:
     """asyncio signal handler that cancels all `tasks` and reports to stderr."""
     err("Aborted!")
     for task in tasks:


@@ -4018,11 +4105,11 @@ def can_omit_invisible_parens(line: Line, line_length: int) -> bool:
     return False
 
 
     return False
 
 

-def get_cache_file(mode: FileMode) -> Path:
+def get_cache_file(mode: Mode) -> Path:

     return CACHE_DIR / f"cache.{mode.get_cache_key()}.pickle"
 
 
     return CACHE_DIR / f"cache.{mode.get_cache_key()}.pickle"
 
 

-def read_cache(mode: FileMode) -> Cache:
+def read_cache(mode: Mode) -> 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.


@@ -4062,7 +4149,7 @@ def filter_cached(cache: Cache, sources: Iterable[Path]) -> Tuple[Set[Path], Set
     return todo, done
 
 
     return todo, done
 
 

-def write_cache(cache: Cache, sources: Iterable[Path], mode: FileMode) -> None:
+def write_cache(cache: Cache, sources: Iterable[Path], mode: Mode) -> None:

     """Update the cache file."""
     cache_file = get_cache_file(mode)
     try:
     """Update the cache file."""
     cache_file = get_cache_file(mode)
     try: