Specify the minimum click version (#284)

[etc/vim.git] / black.py

diff --git a/black.py b/black.py
index e8af3f05b944f5b9f50179ce6ae1186f3886f65a..4599bdd98a9ae536bb25c27d4b3d1511e0523f17 100644 (file)
--- a/black.py
+++ b/black.py
@@ -2,7 +2,7 @@ import asyncio
 import pickle
 from asyncio.base_events import BaseEventLoop
 from concurrent.futures import Executor, ProcessPoolExecutor
 import pickle
 from asyncio.base_events import BaseEventLoop
 from concurrent.futures import Executor, ProcessPoolExecutor

-from enum import Enum
+from enum import Enum, Flag

 from functools import partial, wraps
 import keyword
 import logging
 from functools import partial, wraps
 import keyword
 import logging


@@ -30,6 +30,7 @@ from typing import (
     Type,
     TypeVar,
     Union,
     Type,
     TypeVar,
     Union,

+    cast,

 )
 
 from appdirs import user_cache_dir
 )
 
 from appdirs import user_cache_dir


@@ -43,11 +44,12 @@ from blib2to3.pgen2 import driver, token
 from blib2to3.pgen2.parse import ParseError
 
 
 from blib2to3.pgen2.parse import ParseError
 
 

-__version__ = "18.4a6"
+__version__ = "18.5b1"

 DEFAULT_LINE_LENGTH = 88
 DEFAULT_LINE_LENGTH = 88

+CACHE_DIR = Path(user_cache_dir("black", version=__version__))
+

 
 # types
 
 # types

-syms = pygram.python_symbols

 FileContent = str
 Encoding = str
 Depth = int
 FileContent = str
 Encoding = str
 Depth = int


@@ -64,6 +66,9 @@ Cache = Dict[Path, CacheInfo]
 out = partial(click.secho, bold=True, err=True)
 err = partial(click.secho, fg="red", err=True)
 
 out = partial(click.secho, bold=True, err=True)
 err = partial(click.secho, fg="red", err=True)
 

+pygram.initialize(CACHE_DIR)
+syms = pygram.python_symbols
+

 
 class NothingChanged(UserWarning):
     """Raised by :func:`format_file` when reformatted code is the same as source."""
 
 class NothingChanged(UserWarning):
     """Raised by :func:`format_file` when reformatted code is the same as source."""


@@ -117,6 +122,13 @@ class Changed(Enum):
     YES = 2
 
 
     YES = 2
 
 

+class FileMode(Flag):
+    AUTO_DETECT = 0
+    PYTHON36 = 1
+    PYI = 2
+    NO_STRING_NORMALIZATION = 4
+
+

 @click.command()
 @click.option(
     "-l",
 @click.command()
 @click.option(
     "-l",


@@ -154,6 +166,29 @@ class Changed(Enum):
         "silence those with 2>/dev/null."
     ),
 )
         "silence those with 2>/dev/null."
     ),
 )

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

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


@@ -169,6 +204,9 @@ def main(
     check: bool,
     diff: bool,
     fast: bool,
     check: bool,
     diff: bool,
     fast: bool,

+    pyi: bool,
+    py36: bool,
+    skip_string_normalization: bool,

     quiet: bool,
     src: List[str],
 ) -> None:
     quiet: bool,
     src: List[str],
 ) -> None:


@@ -192,6 +230,13 @@ def main(
         write_back = WriteBack.DIFF
     else:
         write_back = WriteBack.YES
         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:
         out("No paths given. Nothing to do 😴")
     report = Report(check=check, quiet=quiet)
     if len(sources) == 0:
         out("No paths given. Nothing to do 😴")


@@ -199,14 +244,28 @@ def main(
         return
 
     elif len(sources) == 1:
         return
 
     elif len(sources) == 1:

-        reformat_one(sources[0], line_length, fast, write_back, report)
+        reformat_one(
+            src=sources[0],
+            line_length=line_length,
+            fast=fast,
+            write_back=write_back,
+            mode=mode,
+            report=report,
+        )

     else:
         loop = asyncio.get_event_loop()
         executor = ProcessPoolExecutor(max_workers=os.cpu_count())
         try:
             loop.run_until_complete(
                 schedule_formatting(
     else:
         loop = asyncio.get_event_loop()
         executor = ProcessPoolExecutor(max_workers=os.cpu_count())
         try:
             loop.run_until_complete(
                 schedule_formatting(

-                    sources, line_length, fast, write_back, report, loop, executor
+                    sources=sources,
+                    line_length=line_length,
+                    fast=fast,
+                    write_back=write_back,
+                    mode=mode,
+                    report=report,
+                    loop=loop,
+                    executor=executor,

                 )
             )
         finally:
                 )
             )
         finally:


@@ -218,33 +277,43 @@ def main(
 
 
 def reformat_one(
 
 
 def reformat_one(

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

 ) -> None:
     """Reformat a single file under `src` without spawning child processes.
 
     If `quiet` is True, non-error messages are not output. `line_length`,
 ) -> None:
     """Reformat a single file under `src` without spawning child processes.
 
     If `quiet` is True, non-error messages are not output. `line_length`,

-    `write_back`, and `fast` options are passed to :func:`format_file_in_place`.
+    `write_back`, `fast` and `pyi` options are passed to
+    :func:`format_file_in_place` or :func:`format_stdin_to_stdout`.

     """
     try:
         changed = Changed.NO
         if not src.is_file() and str(src) == "-":
             if format_stdin_to_stdout(
     """
     try:
         changed = Changed.NO
         if not src.is_file() and str(src) == "-":
             if format_stdin_to_stdout(

-                line_length=line_length, fast=fast, write_back=write_back
+                line_length=line_length, fast=fast, write_back=write_back, mode=mode

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

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

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

-                src, line_length=line_length, fast=fast, write_back=write_back
+                src,
+                line_length=line_length,
+                fast=fast,
+                write_back=write_back,
+                mode=mode,

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

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

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


@@ -255,6 +324,7 @@ async def schedule_formatting(
     line_length: int,
     fast: bool,
     write_back: WriteBack,
     line_length: int,
     fast: bool,
     write_back: WriteBack,

+    mode: FileMode,

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


@@ -263,12 +333,12 @@ async def schedule_formatting(
 
     (Use ProcessPoolExecutors for actual parallelism.)
 
 
     (Use ProcessPoolExecutors for actual parallelism.)
 

-    `line_length`, `write_back`, and `fast` options are passed to
+    `line_length`, `write_back`, `fast`, and `pyi` options are passed to

     :func:`format_file_in_place`.
     """
     cache: Cache = {}
     if write_back != WriteBack.DIFF:
     :func:`format_file_in_place`.
     """
     cache: Cache = {}
     if write_back != WriteBack.DIFF:

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

         sources, cached = filter_cached(cache, sources)
         for src in cached:
             report.done(src, Changed.CACHED)
         sources, cached = filter_cached(cache, sources)
         for src in cached:
             report.done(src, Changed.CACHED)


@@ -283,7 +353,14 @@ async def schedule_formatting(
             lock = manager.Lock()
         tasks = {
             loop.run_in_executor(
             lock = manager.Lock()
         tasks = {
             loop.run_in_executor(

-                executor, format_file_in_place, src, line_length, fast, write_back, lock
+                executor,
+                format_file_in_place,
+                src,
+                line_length,
+                fast,
+                write_back,
+                mode,
+                lock,

             ): src
             for src in sorted(sources)
         }
             ): src
             for src in sorted(sources)
         }


@@ -308,7 +385,7 @@ async def schedule_formatting(
     if cancelled:
         await asyncio.gather(*cancelled, loop=loop, return_exceptions=True)
     if write_back == WriteBack.YES and formatted:
     if cancelled:
         await asyncio.gather(*cancelled, loop=loop, return_exceptions=True)
     if write_back == WriteBack.YES and formatted:

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

 
 
 def format_file_in_place(
 
 
 def format_file_in_place(


@@ -316,6 +393,7 @@ def format_file_in_place(
     line_length: int,
     fast: bool,
     write_back: WriteBack = WriteBack.NO,
     line_length: int,
     fast: bool,
     write_back: WriteBack = WriteBack.NO,

+    mode: FileMode = FileMode.AUTO_DETECT,

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


@@ -323,13 +401,13 @@ def format_file_in_place(
     If `write_back` is True, write reformatted code back to stdout.
     `line_length` and `fast` options are passed to :func:`format_file_contents`.
     """
     If `write_back` is True, write reformatted code back to stdout.
     `line_length` and `fast` options are passed to :func:`format_file_contents`.
     """

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

     with tokenize.open(src) as src_buffer:
         src_contents = src_buffer.read()
     try:
         dst_contents = format_file_contents(
     with tokenize.open(src) as src_buffer:
         src_contents = src_buffer.read()
     try:
         dst_contents = format_file_contents(

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

         )
     except NothingChanged:
         return False
         )
     except NothingChanged:
         return False


@@ -352,17 +430,21 @@ def format_file_in_place(
 
 
 def format_stdin_to_stdout(
 
 
 def format_stdin_to_stdout(

-    line_length: int, fast: bool, write_back: WriteBack = WriteBack.NO
+    line_length: int,
+    fast: bool,
+    write_back: WriteBack = WriteBack.NO,
+    mode: FileMode = FileMode.AUTO_DETECT,

 ) -> bool:
     """Format file on stdin. Return True if changed.
 
     If `write_back` is True, write reformatted code back to stdout.
 ) -> bool:
     """Format file on stdin. Return True if changed.
 
     If `write_back` is True, write reformatted code back to stdout.

-    `line_length` and `fast` 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()
     dst = src
     try:
     """
     src = sys.stdin.read()
     dst = src
     try:

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

         return True
 
     except NothingChanged:
         return True
 
     except NothingChanged:


@@ -378,7 +460,11 @@ def format_stdin_to_stdout(
 
 
 def format_file_contents(
 
 
 def format_file_contents(

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

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


@@ -389,20 +475,18 @@ def format_file_contents(
     if src_contents.strip() == "":
         raise NothingChanged
 
     if src_contents.strip() == "":
         raise NothingChanged
 

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

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

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

     return dst_contents
 
 
 def format_str(
     return dst_contents
 
 
 def format_str(

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

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


@@ -411,11 +495,15 @@ def format_str(
     src_node = lib2to3_parse(src_contents)
     dst_contents = ""
     future_imports = get_future_imports(src_node)
     src_node = lib2to3_parse(src_contents)
     dst_contents = ""
     future_imports = get_future_imports(src_node)

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

     lines = LineGenerator(
     lines = LineGenerator(

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

     )
     )

+    elt = EmptyLineTracker(is_pyi=is_pyi)

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


@@ -873,27 +961,6 @@ class Line:
             and second_leaf.value == "def"
         )
 
             and second_leaf.value == "def"
         )
 

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

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


@@ -910,6 +977,15 @@ class Line:
             and self.leaves[3].value == ")"
         )
 
             and self.leaves[3].value == ")"
         )
 

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

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


@@ -1117,6 +1193,7 @@ class EmptyLineTracker:
     the prefix of the first leaf consists of optional newlines.  Those newlines
     are consumed by `maybe_empty_lines()` and included in the computation.
     """
     the prefix of the first leaf consists of optional newlines.  Those newlines
     are consumed by `maybe_empty_lines()` and included in the computation.
     """

+

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


@@ -1126,8 +1203,7 @@ class EmptyLineTracker:
         """Return the number of extra empty lines before and after the `current_line`.
 
         This is for separating `def`, `async def` and `class` with extra empty
         """Return the number of extra empty lines before and after the `current_line`.
 
         This is for separating `def`, `async def` and `class` with extra empty

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

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


@@ -1168,6 +1244,11 @@ class EmptyLineTracker:
             if self.previous_line.is_decorator:
                 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
             if (
                 self.previous_line.is_comment
                 and self.previous_line.depth == current_line.depth


@@ -1199,6 +1280,13 @@ class EmptyLineTracker:
         ):
             return (before or 1), 0
 
         ):
             return (before or 1), 0
 

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

         return before, 0
 
 
         return before, 0
 
 


@@ -1209,7 +1297,9 @@ class LineGenerator(Visitor[Line]):
     Note: destroys the tree it's visiting by mutating prefixes of its leaves
     in ways that will no longer stringify to valid Python code on the tree.
     """
     Note: destroys the tree it's visiting by mutating prefixes of its leaves
     in ways that will no longer stringify to valid Python code on the tree.
     """

+

     is_pyi: bool = False
     is_pyi: bool = False

+    normalize_strings: bool = True

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


@@ -1278,7 +1368,7 @@ class LineGenerator(Visitor[Line]):
 
             else:
                 normalize_prefix(node, inside_brackets=any_open_brackets)
 
             else:
                 normalize_prefix(node, inside_brackets=any_open_brackets)

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

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


@@ -1370,32 +1460,6 @@ class LineGenerator(Visitor[Line]):
             yield from self.line()
             yield from self.visit(child)
 
             yield from self.line()
             yield from self.visit(child)
 

-    def visit_import_from(self, node: Node) -> Iterator[Line]:
-        """Visit import_from and maybe put invisible parentheses.
-
-        This is separate from `visit_stmt` because import statements don't
-        support arbitrary atoms and thus handling of parentheses is custom.
-        """
-        check_lpar = False
-        for index, child in enumerate(node.children):
-            if check_lpar:
-                if child.type == token.LPAR:
-                    # make parentheses invisible
-                    child.value = ""  # type: ignore
-                    node.children[-1].value = ""  # type: ignore
-                else:
-                    # insert invisible parentheses
-                    node.insert_child(index, Leaf(token.LPAR, ""))
-                    node.append_child(Leaf(token.RPAR, ""))
-                break
-
-            check_lpar = (
-                child.type == token.NAME and child.value == "import"  # type: ignore
-            )
-
-        for child in node.children:
-            yield from self.visit(child)
-

     def visit_SEMI(self, leaf: Leaf) -> Iterator[Line]:
         """Remove a semicolon and put the other statement on a separate line."""
         yield from self.line()
     def visit_SEMI(self, leaf: Leaf) -> Iterator[Line]:
         """Remove a semicolon and put the other statement on a separate line."""
         yield from self.line()


@@ -1442,6 +1506,7 @@ class LineGenerator(Visitor[Line]):
         self.visit_classdef = partial(v, keywords={"class"}, parens=Ø)
         self.visit_expr_stmt = partial(v, keywords=Ø, parens=ASSIGNMENTS)
         self.visit_return_stmt = partial(v, keywords={"return"}, parens={"return"})
         self.visit_classdef = partial(v, keywords={"class"}, parens=Ø)
         self.visit_expr_stmt = partial(v, keywords=Ø, parens=ASSIGNMENTS)
         self.visit_return_stmt = partial(v, keywords={"return"}, parens={"return"})

+        self.visit_import_from = partial(v, keywords=Ø, parens={"import"})

         self.visit_async_funcdef = self.visit_async_stmt
         self.visit_decorated = self.visit_decorators
 
         self.visit_async_funcdef = self.visit_async_stmt
         self.visit_decorated = self.visit_decorators
 


@@ -1815,7 +1880,7 @@ def is_split_before_delimiter(leaf: Leaf, previous: Leaf = None) -> int:
     return 0
 
 
     return 0
 
 

-def generate_comments(leaf: Leaf) -> Iterator[Leaf]:
+def generate_comments(leaf: LN) -> Iterator[Leaf]:

     """Clean the prefix of the `leaf` and generate comments from it, if any.
 
     Comments in lib2to3 are shoved into the whitespace prefix.  This happens
     """Clean the prefix of the `leaf` and generate comments from it, if any.
 
     Comments in lib2to3 are shoved into the whitespace prefix.  This happens


@@ -1922,12 +1987,14 @@ def split_line(
 
         def rhs(line: Line, py36: bool = False) -> Iterator[Line]:
             for omit in generate_trailers_to_omit(line, line_length):
 
         def rhs(line: Line, py36: bool = False) -> Iterator[Line]:
             for omit in generate_trailers_to_omit(line, line_length):

-                lines = list(right_hand_split(line, py36, omit=omit))
+                lines = list(right_hand_split(line, line_length, py36, omit=omit))

                 if is_line_short_enough(lines[0], line_length=line_length):
                     yield from lines
                     return
 
             # All splits failed, best effort split with no omits.
                 if is_line_short_enough(lines[0], line_length=line_length):
                     yield from lines
                     return
 
             # 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, py36)
 
         if line.inside_brackets:
             yield from right_hand_split(line, py36)
 
         if line.inside_brackets:


@@ -2001,7 +2068,7 @@ def left_hand_split(line: Line, py36: bool = False) -> Iterator[Line]:
 
 
 def right_hand_split(
 
 
 def right_hand_split(

-    line: Line, py36: bool = False, omit: Collection[LeafID] = ()
+    line: Line, line_length: int, py36: bool = False, omit: Collection[LeafID] = ()

 ) -> Iterator[Line]:
     """Split line into many lines, starting with the last matching bracket pair.
 
 ) -> Iterator[Line]:
     """Split line into many lines, starting with the last matching bracket pair.
 


@@ -2063,27 +2130,9 @@ def right_hand_split(
         and not line.is_import
     ):
         omit = {id(closing_bracket), *omit}
         and not line.is_import
     ):
         omit = {id(closing_bracket), *omit}

-        delimiter_count = body.bracket_tracker.delimiter_count_with_priority()
-        first = body.leaves[0]
-        last = body.leaves[-1]
-        if (
-            delimiter_count == 0
-            or delimiter_count == 1
-            and (
-                first.type in OPENING_BRACKETS
-                or last.type == token.RPAR
-                or last.type == token.RBRACE
-                or (
-                    # don't use indexing for omitting optional parentheses;
-                    # it looks weird
-                    last.type == token.RSQB
-                    and last.parent
-                    and last.parent.type != syms.trailer
-                )
-            )
-        ):
+        if can_omit_invisible_parens(body, line_length):

             try:
             try:

-                yield from right_hand_split(line, py36=py36, omit=omit)
+                yield from right_hand_split(line, line_length, py36=py36, omit=omit)

                 return
             except CannotSplit:
                 pass
                 return
             except CannotSplit:
                 pass


@@ -2348,8 +2397,13 @@ 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.
+

     check_lpar = False
     check_lpar = False

-    for child in list(node.children):
+    for index, child in enumerate(list(node.children)):

         if check_lpar:
             if child.type == syms.atom:
                 maybe_make_parens_invisible_in_atom(child)
         if check_lpar:
             if child.type == syms.atom:
                 maybe_make_parens_invisible_in_atom(child)


@@ -2357,8 +2411,21 @@ def normalize_invisible_parens(node: Node, parens_after: Set[str]) -> None:
                 # wrap child in visible parentheses
                 lpar = Leaf(token.LPAR, "(")
                 rpar = Leaf(token.RPAR, ")")
                 # wrap child in visible parentheses
                 lpar = Leaf(token.LPAR, "(")
                 rpar = Leaf(token.RPAR, ")")

-                index = child.remove() or 0
+                child.remove()

                 node.insert_child(index, Node(syms.atom, [lpar, child, rpar]))
                 node.insert_child(index, Node(syms.atom, [lpar, child, rpar]))

+            elif node.type == syms.import_from:
+                # "import from" nodes store parentheses directly as part of
+                # the statement
+                if child.type == token.LPAR:
+                    # make parentheses invisible
+                    child.value = ""  # type: ignore
+                    node.children[-1].value = ""  # type: ignore
+                elif child.type != token.STAR:
+                    # insert invisible parentheses
+                    node.insert_child(index, Leaf(token.LPAR, ""))
+                    node.append_child(Leaf(token.RPAR, ""))
+                break
+

             elif not (isinstance(child, Leaf) and is_multiline_string(child)):
                 # wrap child in invisible parentheses
                 lpar = Leaf(token.LPAR, "")
             elif not (isinstance(child, Leaf) and is_multiline_string(child)):
                 # wrap child in invisible parentheses
                 lpar = Leaf(token.LPAR, "")


@@ -2547,13 +2614,21 @@ def ensure_visible(leaf: Leaf) -> None:
 
 def should_explode(line: Line, opening_bracket: Leaf) -> bool:
     """Should `line` immediately be split with `delimiter_split()` after RHS?"""
 
 def should_explode(line: Line, opening_bracket: Leaf) -> bool:
     """Should `line` immediately be split with `delimiter_split()` after RHS?"""

-    return bool(
+    if not (

         opening_bracket.parent
         and opening_bracket.parent.type in {syms.atom, syms.import_from}
         and opening_bracket.value in "[{("
         opening_bracket.parent
         and opening_bracket.parent.type in {syms.atom, syms.import_from}
         and opening_bracket.value in "[{("

-        and line.bracket_tracker.delimiters
-        and line.bracket_tracker.max_delimiter_priority() == COMMA_PRIORITY
-    )
+    ):
+        return False
+
+    try:
+        last_leaf = line.leaves[-1]
+        exclude = {id(last_leaf)} if last_leaf.type == token.COMMA else set()
+        max_priority = line.bracket_tracker.max_delimiter_priority(exclude=exclude)
+    except (IndexError, ValueError):
+        return False
+
+    return max_priority == COMMA_PRIORITY

 
 
 def is_python36(node: Node) -> bool:
 
 
 def is_python36(node: Node) -> bool:


@@ -2604,21 +2679,14 @@ def generate_trailers_to_omit(line: Line, line_length: int) -> Iterator[Set[Leaf
     closing_bracket = None
     optional_brackets: Set[LeafID] = set()
     inner_brackets: Set[LeafID] = set()
     closing_bracket = None
     optional_brackets: Set[LeafID] = set()
     inner_brackets: Set[LeafID] = set()

-    for index, leaf in enumerate_reversed(line.leaves):
-        length += len(leaf.prefix) + len(leaf.value)
+    for index, leaf, leaf_length in enumerate_with_length(line, reversed=True):
+        length += leaf_length

         if length > line_length:
             break
 
         if length > line_length:
             break
 

-        comment: Optional[Leaf]
-        for comment in line.comments_after(leaf, index):
-            if "\n" in comment.prefix:
-                break  # Oops, standalone comment!
-
-            length += len(comment.value)
-        else:
-            comment = None
-        if comment is not None:
-            break  # There was a standalone comment, we can't continue.
+        has_inline_comment = leaf_length > len(leaf.value) + len(leaf.prefix)
+        if leaf.type == STANDALONE_COMMENT or has_inline_comment:
+            break

 
         optional_brackets.discard(id(leaf))
         if opening_bracket:
 
         optional_brackets.discard(id(leaf))
         if opening_bracket:


@@ -2714,6 +2782,7 @@ def gen_python_files_in_dir(path: Path) -> Iterator[Path]:
 @dataclass
 class Report:
     """Provides a reformatting counter. Can be rendered with `str(report)`."""
 @dataclass
 class Report:
     """Provides a reformatting counter. Can be rendered with `str(report)`."""

+

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


@@ -2853,9 +2922,11 @@ def assert_equivalent(src: str, dst: str) -> None:
         ) from None
 
 
         ) from None
 
 

-def assert_stable(src: str, dst: str, line_length: int, is_pyi: bool = False) -> None:
+def assert_stable(
+    src: str, dst: str, line_length: int, mode: FileMode = FileMode.AUTO_DETECT
+) -> None:

     """Raise AssertionError if `dst` reformats differently the second time."""
     """Raise AssertionError if `dst` reformats differently the second time."""

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

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


@@ -2940,6 +3011,29 @@ def enumerate_reversed(sequence: Sequence[T]) -> Iterator[Tuple[Index, T]]:
         index -= 1
 
 
         index -= 1
 
 

+def enumerate_with_length(
+    line: Line, reversed: bool = False
+) -> Iterator[Tuple[Index, Leaf, int]]:
+    """Return an enumeration of leaves with their length.
+
+    Stops prematurely on multiline strings and standalone comments.
+    """
+    op = cast(
+        Callable[[Sequence[Leaf]], Iterator[Tuple[Index, Leaf]]],
+        enumerate_reversed if reversed else enumerate,
+    )
+    for index, leaf in op(line.leaves):
+        length = len(leaf.prefix) + len(leaf.value)
+        if "\n" in leaf.value:
+            return  # Multiline strings, we can't continue.
+
+        comment: Optional[Leaf]
+        for comment in line.comments_after(leaf, index):
+            length += len(comment.value)
+
+        yield index, leaf, length
+
+

 def is_line_short_enough(line: Line, *, line_length: int, line_str: str = "") -> bool:
     """Return True if `line` is no longer than `line_length`.
 
 def is_line_short_enough(line: Line, *, line_length: int, line_str: str = "") -> bool:
     """Return True if `line` is no longer than `line_length`.
 


@@ -2954,19 +3048,110 @@ def is_line_short_enough(line: Line, *, line_length: int, line_str: str = "") ->
     )
 
 
     )
 
 

-CACHE_DIR = Path(user_cache_dir("black", version=__version__))
+def can_omit_invisible_parens(line: Line, line_length: int) -> bool:
+    """Does `line` have a shape safe to reformat without optional parens around it?
+
+    Returns True for only a subset of potentially nice looking formattings but
+    the point is to not return false positives that end up producing lines that
+    are too long.
+    """
+    bt = line.bracket_tracker
+    if not bt.delimiters:
+        # Without delimiters the optional parentheses are useless.
+        return True
+
+    max_priority = bt.max_delimiter_priority()
+    if bt.delimiter_count_with_priority(max_priority) > 1:
+        # With more than one delimiter of a kind the optional parentheses read better.
+        return False
+
+    if max_priority == DOT_PRIORITY:
+        # A single stranded method call doesn't require optional parentheses.
+        return True
+
+    assert len(line.leaves) >= 2, "Stranded delimiter"
+
+    first = line.leaves[0]
+    second = line.leaves[1]
+    penultimate = line.leaves[-2]
+    last = line.leaves[-1]
+
+    # With a single delimiter, omit if the expression starts or ends with
+    # a bracket.
+    if first.type in OPENING_BRACKETS and second.type not in CLOSING_BRACKETS:
+        remainder = False
+        length = 4 * line.depth
+        for _index, leaf, leaf_length in enumerate_with_length(line):
+            if leaf.type in CLOSING_BRACKETS and leaf.opening_bracket is first:
+                remainder = True
+            if remainder:
+                length += leaf_length
+                if length > line_length:
+                    break
+
+                if leaf.type in OPENING_BRACKETS:
+                    # There are brackets we can further split on.
+                    remainder = False

 
 

+        else:
+            # checked the entire string and line length wasn't exceeded
+            if len(line.leaves) == _index + 1:
+                return True
+
+        # Note: we are not returning False here because a line might have *both*
+        # a leading opening bracket and a trailing closing bracket.  If the
+        # opening bracket doesn't match our rule, maybe the closing will.
+
+    if (
+        last.type == token.RPAR
+        or last.type == token.RBRACE
+        or (
+            # don't use indexing for omitting optional parentheses;
+            # it looks weird
+            last.type == token.RSQB
+            and last.parent
+            and last.parent.type != syms.trailer
+        )
+    ):
+        if penultimate.type in OPENING_BRACKETS:
+            # Empty brackets don't help.
+            return False

 
 

-def get_cache_file(line_length: int) -> Path:
-    return CACHE_DIR / f"cache.{line_length}.pickle"
+        if is_multiline_string(first):
+            # Additional wrapping of a multiline string in this situation is
+            # unnecessary.
+            return True

 
 

+        length = 4 * line.depth
+        seen_other_brackets = False
+        for _index, leaf, leaf_length in enumerate_with_length(line):
+            length += leaf_length
+            if leaf is last.opening_bracket:
+                if seen_other_brackets or length <= line_length:
+                    return True

 
 

-def read_cache(line_length: int) -> Cache:
+            elif leaf.type in OPENING_BRACKETS:
+                # There are brackets we can further split on.
+                seen_other_brackets = True
+
+    return False
+
+
+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"
+    )
+
+
+def read_cache(line_length: int, mode: FileMode) -> Cache:

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

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

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


@@ -3003,9 +3188,11 @@ def filter_cached(
     return todo, done
 
 
     return todo, done
 
 

-def write_cache(cache: Cache, sources: List[Path], line_length: int) -> None:
+def write_cache(
+    cache: Cache, sources: List[Path], line_length: int, mode: FileMode
+) -> None:

     """Update the cache file."""
     """Update the cache file."""

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

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