Document asyncio fixes

[etc/vim.git] / black.py

diff --git a/black.py b/black.py
index a61a40fe5995e7a41fc0b29e6d3fa052f86f9ace..82fe5d11cdc7f7551d999141fb21fe57c97e8255 100644 (file)
--- a/black.py
+++ b/black.py
@@ -3,14 +3,27 @@
 import asyncio
 from asyncio.base_events import BaseEventLoop
 from concurrent.futures import Executor, ProcessPoolExecutor
 import asyncio
 from asyncio.base_events import BaseEventLoop
 from concurrent.futures import Executor, ProcessPoolExecutor

-from functools import partial
+from functools import partial, wraps

 import keyword
 import keyword

+import logging

 import os
 from pathlib import Path
 import tokenize
 import os
 from pathlib import Path
 import tokenize

+import signal

 import sys
 from typing import (
 import sys
 from typing import (

-    Dict, Generic, Iterable, Iterator, List, Optional, Set, Tuple, Type, TypeVar, Union
+    Callable,
+    Dict,
+    Generic,
+    Iterable,
+    Iterator,
+    List,
+    Optional,
+    Set,
+    Tuple,
+    Type,
+    TypeVar,
+    Union,

 )
 
 from attr import dataclass, Factory
 )
 
 from attr import dataclass, Factory


@@ -32,19 +45,22 @@ Depth = int
 NodeType = int
 LeafID = int
 Priority = int
 NodeType = int
 LeafID = int
 Priority = int

+Index = int

 LN = Union[Leaf, Node]
 LN = Union[Leaf, Node]

+SplitFunc = Callable[['Line', bool], Iterator['Line']]

 out = partial(click.secho, bold=True, err=True)
 err = partial(click.secho, fg='red', err=True)
 
 
 class NothingChanged(UserWarning):
 out = partial(click.secho, bold=True, err=True)
 err = partial(click.secho, fg='red', err=True)
 
 
 class NothingChanged(UserWarning):

-    """Raised by `format_file` when the reformatted code is the same as source."""
+    """Raised by :func:`format_file` when reformatted code is the same as source."""

 
 
 class CannotSplit(Exception):
     """A readable split that fits the allotted line length is impossible.
 
 
 
 class CannotSplit(Exception):
     """A readable split that fits the allotted line length is impossible.
 

-    Raised by `left_hand_split()`, `right_hand_split()`, and `delimiter_split()`.
+    Raised by :func:`left_hand_split`, :func:`right_hand_split`, and
+    :func:`delimiter_split`.

     """
 
 
     """
 
 


@@ -153,7 +169,7 @@ def main(
                 )
             )
         finally:
                 )
             )
         finally:

-            loop.close()
+            shutdown(loop)

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


@@ -165,27 +181,40 @@ async def schedule_formatting(
     loop: BaseEventLoop,
     executor: Executor,
 ) -> int:
     loop: BaseEventLoop,
     executor: Executor,
 ) -> int:

+    """Run formatting of `sources` in parallel using the provided `executor`.
+
+    (Use ProcessPoolExecutors for actual parallelism.)
+
+    `line_length`, `write_back`, and `fast` options are passed to
+    :func:`format_file_in_place`.
+    """

     tasks = {
         src: loop.run_in_executor(
             executor, format_file_in_place, src, line_length, fast, write_back
         )
         for src in sources
     }
     tasks = {
         src: loop.run_in_executor(
             executor, format_file_in_place, src, line_length, fast, write_back
         )
         for src in sources
     }

+    _task_values = list(tasks.values())
+    loop.add_signal_handler(signal.SIGINT, cancel, _task_values)
+    loop.add_signal_handler(signal.SIGTERM, cancel, _task_values)

     await asyncio.wait(tasks.values())
     cancelled = []
     await asyncio.wait(tasks.values())
     cancelled = []

-    report = Report()
+    report = Report(check=not write_back)

     for src, task in tasks.items():
         if not task.done():
             report.failed(src, 'timed out, cancelling')
             task.cancel()
             cancelled.append(task)
     for src, task in tasks.items():
         if not task.done():
             report.failed(src, 'timed out, cancelling')
             task.cancel()
             cancelled.append(task)

+        elif task.cancelled():
+            cancelled.append(task)

         elif task.exception():
             report.failed(src, str(task.exception()))
         else:
             report.done(src, task.result())
     if cancelled:
         elif task.exception():
             report.failed(src, str(task.exception()))
         else:
             report.done(src, task.result())
     if cancelled:

-        await asyncio.wait(cancelled, timeout=2)
-    out('All done! ✨ 🍰 ✨')
+        await asyncio.gather(*cancelled, loop=loop, return_exceptions=True)
+    else:
+        out('All done! ✨ 🍰 ✨')

     click.echo(str(report))
     return report.return_code
 
     click.echo(str(report))
     return report.return_code
 


@@ -193,7 +222,11 @@ async def schedule_formatting(
 def format_file_in_place(
     src: Path, line_length: int, fast: bool, write_back: bool = False
 ) -> bool:
 def format_file_in_place(
     src: Path, line_length: int, fast: bool, write_back: bool = False
 ) -> bool:

-    """Format the file and rewrite if changed. Return True if changed."""
+    """Format file under `src` path. Return True if changed.
+
+    If `write_back` is True, write reformatted code back to stdout.
+    `line_length` and `fast` options are passed to :func:`format_file_contents`.
+    """

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


@@ -212,7 +245,11 @@ def format_file_in_place(
 def format_stdin_to_stdout(
     line_length: int, fast: bool, write_back: bool = False
 ) -> bool:
 def format_stdin_to_stdout(
     line_length: int, fast: bool, write_back: bool = False
 ) -> bool:

-    """Format file on stdin and pipe output to stdout. Return True if changed."""
+    """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`.
+    """

     contents = sys.stdin.read()
     try:
         contents = format_file_contents(contents, line_length=line_length, fast=fast)
     contents = sys.stdin.read()
     try:
         contents = format_file_contents(contents, line_length=line_length, fast=fast)


@@ -229,7 +266,12 @@ def format_stdin_to_stdout(
 def format_file_contents(
     src_contents: str, line_length: int, fast: bool
 ) -> FileContent:
 def format_file_contents(
     src_contents: str, line_length: int, fast: bool
 ) -> FileContent:

-    """Reformats a file and returns its contents and encoding."""
+    """Reformat contents a file and return new contents.
+
+    If `fast` is False, additionally confirm that the reformatted code is
+    valid by calling :func:`assert_equivalent` and :func:`assert_stable` on it.
+    `line_length` is passed to :func:`format_str`.
+    """

     if src_contents.strip() == '':
         raise NothingChanged
 
     if src_contents.strip() == '':
         raise NothingChanged
 


@@ -244,7 +286,10 @@ def format_file_contents(
 
 
 def format_str(src_contents: str, line_length: int) -> FileContent:
 
 
 def format_str(src_contents: str, line_length: int) -> FileContent:

-    """Reformats a string and returns new contents."""
+    """Reformat a string and return new contents.
+
+    `line_length` determines how many characters per line are allowed.
+    """

     src_node = lib2to3_parse(src_contents)
     dst_contents = ""
     lines = LineGenerator()
     src_node = lib2to3_parse(src_contents)
     dst_contents = ""
     lines = LineGenerator()


@@ -312,7 +357,7 @@ class Visitor(Generic[T]):
     """Basic lib2to3 visitor that yields things of type `T` on `visit()`."""
 
     def visit(self, node: LN) -> Iterator[T]:
     """Basic lib2to3 visitor that yields things of type `T` on `visit()`."""
 
     def visit(self, node: LN) -> Iterator[T]:

-        """Main method to start the visit process. Yields objects of type `T`.
+        """Main method to visit `node` and its children.

 
         It tries to find a `visit_*()` method for the given `node.type`, like
         `visit_simple_stmt` for Node objects or `visit_INDENT` for Leaf objects.
 
         It tries to find a `visit_*()` method for the given `node.type`, like
         `visit_simple_stmt` for Node objects or `visit_INDENT` for Leaf objects.


@@ -360,7 +405,7 @@ class DebugVisitor(Visitor[T]):
 
     @classmethod
     def show(cls, code: str) -> None:
 
     @classmethod
     def show(cls, code: str) -> None:

-        """Pretty-prints a given string of `code`.
+        """Pretty-print the lib2to3 AST of a given string of `code`.

 
         Convenience method for debugging.
         """
 
         Convenience method for debugging.
         """


@@ -418,17 +463,13 @@ MATH_PRIORITY = 1
 class BracketTracker:
     """Keeps track of brackets on a line."""
 
 class BracketTracker:
     """Keeps track of brackets on a line."""
 

-    #: Current bracket depth.

     depth: int = 0
     depth: int = 0

-    #: All currently unclosed brackets.

     bracket_match: Dict[Tuple[Depth, NodeType], Leaf] = Factory(dict)
     bracket_match: Dict[Tuple[Depth, NodeType], Leaf] = Factory(dict)

-    #: All current delimiters with their assigned priority.

     delimiters: Dict[LeafID, Priority] = Factory(dict)
     delimiters: Dict[LeafID, Priority] = Factory(dict)

-    #: Last processed leaf, if any.

     previous: Optional[Leaf] = None
 
     def mark(self, leaf: Leaf) -> None:
     previous: Optional[Leaf] = None
 
     def mark(self, leaf: Leaf) -> None:

-        """Marks `leaf` with bracket-related metadata. Keeps track of delimiters.
+        """Mark `leaf` with bracket-related metadata. Keep track of delimiters.

 
         All leaves receive an int `bracket_depth` field that stores how deep
         within brackets a given leaf is. 0 means there are no enclosing brackets
 
         All leaves receive an int `bracket_depth` field that stores how deep
         within brackets a given leaf is. 0 means there are no enclosing brackets


@@ -483,11 +524,11 @@ class BracketTracker:
         self.previous = leaf
 
     def any_open_brackets(self) -> bool:
         self.previous = leaf
 
     def any_open_brackets(self) -> bool:

-        """Returns True if there is an yet unmatched open bracket on the line."""
+        """Return True if there is an yet unmatched open bracket on the line."""

         return bool(self.bracket_match)
 
     def max_delimiter_priority(self, exclude: Iterable[LeafID] = ()) -> int:
         return bool(self.bracket_match)
 
     def max_delimiter_priority(self, exclude: Iterable[LeafID] = ()) -> int:

-        """Returns the highest priority of a delimiter found on the line.
+        """Return the highest priority of a delimiter found on the line.

 
         Values are consistent with what `is_delimiter()` returns.
         """
 
         Values are consistent with what `is_delimiter()` returns.
         """


@@ -498,12 +539,9 @@ class BracketTracker:
 class Line:
     """Holds leaves and comments. Can be printed with `str(line)`."""
 
 class Line:
     """Holds leaves and comments. Can be printed with `str(line)`."""
 

-    #: indentation level

     depth: int = 0
     depth: int = 0

-    #: list of leaves

     leaves: List[Leaf] = Factory(list)
     leaves: List[Leaf] = Factory(list)

-    #: inline comments that belong on this line
-    comments: Dict[LeafID, Leaf] = Factory(dict)
+    comments: List[Tuple[Index, Leaf]] = Factory(list)

     bracket_tracker: BracketTracker = Factory(BracketTracker)
     inside_brackets: bool = False
     has_for: bool = False
     bracket_tracker: BracketTracker = Factory(BracketTracker)
     inside_brackets: bool = False
     has_for: bool = False


@@ -532,16 +570,31 @@ class Line:
             self.bracket_tracker.mark(leaf)
             self.maybe_remove_trailing_comma(leaf)
             self.maybe_increment_for_loop_variable(leaf)
             self.bracket_tracker.mark(leaf)
             self.maybe_remove_trailing_comma(leaf)
             self.maybe_increment_for_loop_variable(leaf)

-            if self.maybe_adapt_standalone_comment(leaf):
-                return

 
         if not self.append_comment(leaf):
             self.leaves.append(leaf)
 
 
         if not self.append_comment(leaf):
             self.leaves.append(leaf)
 

+    def append_safe(self, leaf: Leaf, preformatted: bool = False) -> None:
+        """Like :func:`append()` but disallow invalid standalone comment structure.
+
+        Raises ValueError when any `leaf` is appended after a standalone comment
+        or when a standalone comment is not the first leaf on the line.
+        """
+        if self.bracket_tracker.depth == 0:
+            if self.is_comment:
+                raise ValueError("cannot append to standalone comments")
+
+            if self.leaves and leaf.type == STANDALONE_COMMENT:
+                raise ValueError(
+                    "cannot append standalone comments to a populated line"
+                )
+
+        self.append(leaf, preformatted=preformatted)
+

     @property
     def is_comment(self) -> bool:
         """Is this line a standalone comment?"""
     @property
     def is_comment(self) -> bool:
         """Is this line a standalone comment?"""

-        return bool(self) and self.leaves[0].type == STANDALONE_COMMENT
+        return len(self.leaves) == 1 and self.leaves[0].type == STANDALONE_COMMENT

 
     @property
     def is_decorator(self) -> bool:
 
     @property
     def is_decorator(self) -> bool:


@@ -555,7 +608,7 @@ class Line:
 
     @property
     def is_class(self) -> bool:
 
     @property
     def is_class(self) -> bool:

-        """Is this a class definition?"""
+        """Is this line a class definition?"""

         return (
             bool(self)
             and self.leaves[0].type == token.NAME
         return (
             bool(self)
             and self.leaves[0].type == token.NAME


@@ -586,7 +639,7 @@ class Line:
 
     @property
     def is_flow_control(self) -> bool:
 
     @property
     def is_flow_control(self) -> bool:

-        """Is this a flow control statement?
+        """Is this line a flow control statement?

 
         Those are `return`, `raise`, `break`, and `continue`.
         """
 
         Those are `return`, `raise`, `break`, and `continue`.
         """


@@ -598,13 +651,22 @@ class Line:
 
     @property
     def is_yield(self) -> bool:
 
     @property
     def is_yield(self) -> bool:

-        """Is this a yield statement?"""
+        """Is this line a yield statement?"""

         return (
             bool(self)
             and self.leaves[0].type == token.NAME
             and self.leaves[0].value == 'yield'
         )
 
         return (
             bool(self)
             and self.leaves[0].type == token.NAME
             and self.leaves[0].value == 'yield'
         )
 

+    @property
+    def contains_standalone_comments(self) -> bool:
+        """If so, needs to be split before emitting."""
+        for leaf in self.leaves:
+            if leaf.type == STANDALONE_COMMENT:
+                return True
+
+        return False
+

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


@@ -615,13 +677,13 @@ class Line:
             return False
 
         if closing.type == token.RBRACE:
             return False
 
         if closing.type == token.RBRACE:

-            self.leaves.pop()
+            self.remove_trailing_comma()

             return True
 
         if closing.type == token.RSQB:
             comma = self.leaves[-1]
             if comma.parent and comma.parent.type == syms.listmaker:
             return True
 
         if closing.type == token.RSQB:
             comma = self.leaves[-1]
             if comma.parent and comma.parent.type == syms.listmaker:

-                self.leaves.pop()
+                self.remove_trailing_comma()

                 return True
 
         # For parens let's check if it's safe to remove the comma.  If the
                 return True
 
         # For parens let's check if it's safe to remove the comma.  If the


@@ -649,7 +711,7 @@ class Line:
                     break
 
         if commas > 1:
                     break
 
         if commas > 1:

-            self.leaves.pop()
+            self.remove_trailing_comma()

             return True
 
         return False
             return True
 
         return False


@@ -657,8 +719,8 @@ class Line:
     def maybe_increment_for_loop_variable(self, leaf: Leaf) -> bool:
         """In a for loop, or comprehension, the variables are often unpacks.
 
     def maybe_increment_for_loop_variable(self, leaf: Leaf) -> bool:
         """In a for loop, or comprehension, the variables are often unpacks.
 

-        To avoid splitting on the comma in this situation, we will increase
-        the depth of tokens between `for` and `in`.
+        To avoid splitting on the comma in this situation, increase the depth of
+        tokens between `for` and `in`.

         """
         if leaf.type == token.NAME and leaf.value == 'for':
             self.has_for = True
         """
         if leaf.type == token.NAME and leaf.value == 'for':
             self.has_for = True


@@ -677,52 +739,49 @@ class Line:
 
         return False
 
 
         return False
 

-    def maybe_adapt_standalone_comment(self, comment: Leaf) -> bool:
-        """Hack a standalone comment to act as a trailing comment for line splitting.
-
-        If this line has brackets and a standalone `comment`, we need to adapt
-        it to be able to still reformat the line.
-
-        This is not perfect, the line to which the standalone comment gets
-        appended will appear "too long" when splitting.
-        """
-        if not (
+    def append_comment(self, comment: Leaf) -> bool:
+        """Add an inline or standalone comment to the line."""
+        if (

             comment.type == STANDALONE_COMMENT
             and self.bracket_tracker.any_open_brackets()
         ):
             comment.type == STANDALONE_COMMENT
             and self.bracket_tracker.any_open_brackets()
         ):

+            comment.prefix = ''

             return False
 
             return False
 

-        comment.type = token.COMMENT
-        comment.prefix = '\n' + '    ' * (self.depth + 1)
-        return self.append_comment(comment)
-
-    def append_comment(self, comment: Leaf) -> bool:
-        """Add an inline comment to the line."""

         if comment.type != token.COMMENT:
             return False
 
         if comment.type != token.COMMENT:
             return False
 

-        try:
-            after = id(self.last_non_delimiter())
-        except LookupError:
+        after = len(self.leaves) - 1
+        if after == -1:

             comment.type = STANDALONE_COMMENT
             comment.prefix = ''
             return False
 
         else:
             comment.type = STANDALONE_COMMENT
             comment.prefix = ''
             return False
 
         else:

-            if after in self.comments:
-                self.comments[after].value += str(comment)
-            else:
-                self.comments[after] = comment
+            self.comments.append((after, comment))

             return True
 
             return True
 

-    def last_non_delimiter(self) -> Leaf:
-        """Returns the last non-delimiter on the line. Raises LookupError otherwise."""
-        for i in range(len(self.leaves)):
-            last = self.leaves[-i - 1]
-            if not is_delimiter(last):
-                return last
+    def comments_after(self, leaf: Leaf) -> Iterator[Leaf]:
+        """Generate comments that should appear directly after `leaf`."""
+        for _leaf_index, _leaf in enumerate(self.leaves):
+            if leaf is _leaf:
+                break
+
+        else:
+            return
+
+        for index, comment_after in self.comments:
+            if _leaf_index == index:
+                yield comment_after

 
 

-        raise LookupError("No non-delimiters found")
+    def remove_trailing_comma(self) -> None:
+        """Remove the trailing comma and moves the comments attached to it."""
+        comma_index = len(self.leaves) - 1
+        for i in range(len(self.comments)):
+            comment_index, comment = self.comments[i]
+            if comment_index == comma_index:
+                self.comments[i] = (comma_index - 1, comment)
+        self.leaves.pop()

 
     def __str__(self) -> str:
         """Render the line."""
 
     def __str__(self) -> str:
         """Render the line."""


@@ -735,12 +794,12 @@ class Line:
         res = f'{first.prefix}{indent}{first.value}'
         for leaf in leaves:
             res += str(leaf)
         res = f'{first.prefix}{indent}{first.value}'
         for leaf in leaves:
             res += str(leaf)

-        for comment in self.comments.values():
+        for _, comment in self.comments:

             res += str(comment)
         return res + '\n'
 
     def __bool__(self) -> bool:
             res += str(comment)
         return res + '\n'
 
     def __bool__(self) -> bool:

-        """Returns True if the line has leaves or comments."""
+        """Return True if the line has leaves or comments."""

         return bool(self.leaves or self.comments)
 
 
         return bool(self.leaves or self.comments)
 
 


@@ -767,24 +826,8 @@ class UnformattedLines(Line):
         elif leaf.type == token.DEDENT:
             self.depth -= 1
 
         elif leaf.type == token.DEDENT:
             self.depth -= 1
 

-    def append_comment(self, comment: Leaf) -> bool:
-        """Not implemented in this class."""
-        raise NotImplementedError("Unformatted lines don't store comments separately.")
-
-    def maybe_remove_trailing_comma(self, closing: Leaf) -> bool:
-        """Does nothing and returns False."""
-        return False
-
-    def maybe_increment_for_loop_variable(self, leaf: Leaf) -> bool:
-        """Does nothing and returns False."""
-        return False
-
-    def maybe_adapt_standalone_comment(self, comment: Leaf) -> bool:
-        """Does nothing and returns False."""
-        return False
-

     def __str__(self) -> str:
     def __str__(self) -> str:

-        """Renders unformatted lines from leaves which were added with `append()`.
+        """Render unformatted lines from leaves which were added with `append()`.

 
         `depth` is not used for indentation in this case.
         """
 
         `depth` is not used for indentation in this case.
         """


@@ -796,6 +839,18 @@ class UnformattedLines(Line):
             res += str(leaf)
         return res
 
             res += str(leaf)
         return res
 

+    def append_comment(self, comment: Leaf) -> bool:
+        """Not implemented in this class. Raises `NotImplementedError`."""
+        raise NotImplementedError("Unformatted lines don't store comments separately.")
+
+    def maybe_remove_trailing_comma(self, closing: Leaf) -> bool:
+        """Does nothing and returns False."""
+        return False
+
+    def maybe_increment_for_loop_variable(self, leaf: Leaf) -> bool:
+        """Does nothing and returns False."""
+        return False
+

 
 @dataclass
 class EmptyLineTracker:
 
 @dataclass
 class EmptyLineTracker:


@@ -811,11 +866,11 @@ class EmptyLineTracker:
     previous_defs: List[int] = Factory(list)
 
     def maybe_empty_lines(self, current_line: Line) -> Tuple[int, int]:
     previous_defs: List[int] = Factory(list)
 
     def maybe_empty_lines(self, current_line: Line) -> Tuple[int, int]:

-        """Returns the number of extra empty lines before and after the `current_line`.
+        """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.
+        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.

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


@@ -909,7 +964,10 @@ class LineGenerator(Visitor[Line]):
         yield complete_line
 
     def visit(self, node: LN) -> Iterator[Line]:
         yield complete_line
 
     def visit(self, node: LN) -> Iterator[Line]:

-        """Main method to start the visit process. Yields :class:`Line` objects."""
+        """Main method to visit `node` and its children.
+
+        Yields :class:`Line` objects.
+        """

         if isinstance(self.current_line, UnformattedLines):
             # File contained `# fmt: off`
             yield from self.visit_unformatted(node)
         if isinstance(self.current_line, UnformattedLines):
             # File contained `# fmt: off`
             yield from self.visit_unformatted(node)


@@ -956,18 +1014,18 @@ class LineGenerator(Visitor[Line]):
         yield from super().visit_default(node)
 
     def visit_INDENT(self, node: Node) -> Iterator[Line]:
         yield from super().visit_default(node)
 
     def visit_INDENT(self, node: Node) -> Iterator[Line]:

-        """Increases indentation level, maybe yields a 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)
 
     def visit_DEDENT(self, node: Node) -> Iterator[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]:

-        """Decreases indentation level, maybe yields a line."""
+        """Decrease indentation level, maybe yield a line."""

         # DEDENT has no value. Additionally, in blib2to3 it never holds comments.
         yield from self.line(-1)
 
     def visit_stmt(self, node: Node, keywords: Set[str]) -> Iterator[Line]:
         # DEDENT has no value. Additionally, in blib2to3 it never holds comments.
         yield from self.line(-1)
 
     def visit_stmt(self, node: Node, keywords: Set[str]) -> Iterator[Line]:

-        """Visits a statement.
+        """Visit a statement.

 
         This implementation is shared for `if`, `while`, `for`, `try`, `except`,
         `def`, `with`, and `class`.
 
         This implementation is shared for `if`, `while`, `for`, `try`, `except`,
         `def`, `with`, and `class`.


@@ -982,7 +1040,7 @@ class LineGenerator(Visitor[Line]):
             yield from self.visit(child)
 
     def visit_simple_stmt(self, node: Node) -> Iterator[Line]:
             yield from self.visit(child)
 
     def visit_simple_stmt(self, node: Node) -> Iterator[Line]:

-        """Visits a statement without nested statements."""
+        """Visit a statement without nested statements."""

         is_suite_like = node.parent and node.parent.type in STATEMENT
         if is_suite_like:
             yield from self.line(+1)
         is_suite_like = node.parent and node.parent.type in STATEMENT
         if is_suite_like:
             yield from self.line(+1)


@@ -994,7 +1052,7 @@ class LineGenerator(Visitor[Line]):
             yield from self.visit_default(node)
 
     def visit_async_stmt(self, node: Node) -> Iterator[Line]:
             yield from self.visit_default(node)
 
     def visit_async_stmt(self, node: Node) -> Iterator[Line]:

-        """Visits `async def`, `async for`, `async with`."""
+        """Visit `async def`, `async for`, `async with`."""

         yield from self.line()
 
         children = iter(node.children)
         yield from self.line()
 
         children = iter(node.children)


@@ -1009,23 +1067,17 @@ class LineGenerator(Visitor[Line]):
             yield from self.visit(child)
 
     def visit_decorators(self, node: Node) -> Iterator[Line]:
             yield from self.visit(child)
 
     def visit_decorators(self, node: Node) -> Iterator[Line]:

-        """Visits decorators."""
+        """Visit decorators."""

         for child in node.children:
             yield from self.line()
             yield from self.visit(child)
 
     def visit_SEMI(self, leaf: Leaf) -> Iterator[Line]:
         for child in node.children:
             yield from self.line()
             yield from self.visit(child)
 
     def visit_SEMI(self, leaf: Leaf) -> Iterator[Line]:

-        """Semicolons are always removed.
-
-        Statements between them are put on separate lines.
-        """
+        """Remove a semicolon and put the other statement on a separate line."""

         yield from self.line()
 
     def visit_ENDMARKER(self, leaf: Leaf) -> Iterator[Line]:
         yield from self.line()
 
     def visit_ENDMARKER(self, leaf: Leaf) -> Iterator[Line]:

-        """End of file.
-
-        Process outstanding comments and end with a newline.
-        """
+        """End of file. Process outstanding comments and end with a newline."""

         yield from self.visit_default(leaf)
         yield from self.line()
 
         yield from self.visit_default(leaf)
         yield from self.line()
 


@@ -1303,7 +1355,7 @@ def whitespace(leaf: Leaf) -> str:  # noqa C901
 
 
 def preceding_leaf(node: Optional[LN]) -> Optional[Leaf]:
 
 
 def preceding_leaf(node: Optional[LN]) -> Optional[Leaf]:

-    """Returns the first leaf that precedes `node`, if any."""
+    """Return the first leaf that precedes `node`, if any."""

     while node:
         res = node.prev_sibling
         if res:
     while node:
         res = node.prev_sibling
         if res:


@@ -1321,7 +1373,7 @@ def preceding_leaf(node: Optional[LN]) -> Optional[Leaf]:
 
 
 def is_delimiter(leaf: Leaf) -> int:
 
 
 def is_delimiter(leaf: Leaf) -> int:

-    """Returns the priority of the `leaf` delimiter. Returns 0 if not delimiter.
+    """Return the priority of the `leaf` delimiter. Return 0 if not delimiter.

 
     Higher numbers are higher priority.
     """
 
     Higher numbers are higher priority.
     """


@@ -1342,7 +1394,7 @@ def is_delimiter(leaf: Leaf) -> int:
 
 
 def generate_comments(leaf: Leaf) -> Iterator[Leaf]:
 
 
 def generate_comments(leaf: Leaf) -> Iterator[Leaf]:

-    """Cleans the prefix of the `leaf` and generates comments from it, if any.
+    """Clean the prefix of the `leaf` and generate comments from it, if any.

 
     Comments in lib2to3 are shoved into the whitespace prefix.  This happens
     in `pgen2/driver.py:Driver.parse_tokens()`.  This was a brilliant implementation
 
     Comments in lib2to3 are shoved into the whitespace prefix.  This happens
     in `pgen2/driver.py:Driver.parse_tokens()`.  This was a brilliant implementation


@@ -1394,7 +1446,7 @@ def generate_comments(leaf: Leaf) -> Iterator[Leaf]:
 
 
 def make_comment(content: str) -> str:
 
 
 def make_comment(content: str) -> str:

-    """Returns a consistently formatted comment from the given `content` string.
+    """Return a consistently formatted comment from the given `content` string.

 
     All comments (except for "##", "#!", "#:") should have a single space between
     the hash sign and the content.
 
     All comments (except for "##", "#!", "#:") should have a single space between
     the hash sign and the content.


@@ -1415,7 +1467,7 @@ def make_comment(content: str) -> str:
 def split_line(
     line: Line, line_length: int, inner: bool = False, py36: bool = False
 ) -> Iterator[Line]:
 def split_line(
     line: Line, line_length: int, inner: bool = False, py36: bool = False
 ) -> Iterator[Line]:

-    """Splits a `line` into potentially many lines.
+    """Split a `line` into potentially many lines.

 
     They should fit in the allotted `line_length` but might not be able to.
     `inner` signifies that there were a pair of brackets somewhere around the
 
     They should fit in the allotted `line_length` but might not be able to.
     `inner` signifies that there were a pair of brackets somewhere around the


@@ -1425,23 +1477,24 @@ def split_line(
     If `py36` is True, splitting may generate syntax that is only compatible
     with Python 3.6 and later.
     """
     If `py36` is True, splitting may generate syntax that is only compatible
     with Python 3.6 and later.
     """

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

         yield line
         return
 
     line_str = str(line).strip('\n')
         yield line
         return
 
     line_str = str(line).strip('\n')

-    if len(line_str) <= line_length and '\n' not in line_str:
+    if (
+        len(line_str) <= line_length
+        and '\n' not in line_str  # multiline strings
+        and not line.contains_standalone_comments
+    ):

         yield line
         return
 
         yield line
         return
 

+    split_funcs: List[SplitFunc]

     if line.is_def:
         split_funcs = [left_hand_split]
     elif line.inside_brackets:
     if line.is_def:
         split_funcs = [left_hand_split]
     elif line.inside_brackets:

-        split_funcs = [delimiter_split]
-        if '\n' not in line_str:
-            # Only attempt RHS if we don't have multiline strings or comments
-            # on this line.
-            split_funcs.append(right_hand_split)
+        split_funcs = [delimiter_split, standalone_comment_split, right_hand_split]

     else:
         split_funcs = [right_hand_split]
     for split_func in split_funcs:
     else:
         split_funcs = [right_hand_split]
     for split_func in split_funcs:


@@ -1450,7 +1503,7 @@ def split_line(
         # split altogether.
         result: List[Line] = []
         try:
         # split altogether.
         result: List[Line] = []
         try:

-            for l in split_func(line, py36=py36):
+            for l in split_func(line, py36):

                 if str(l).strip('\n') == line_str:
                     raise CannotSplit("Split function returned an unchanged result")
 
                 if str(l).strip('\n') == line_str:
                     raise CannotSplit("Split function returned an unchanged result")
 


@@ -1469,7 +1522,7 @@ def split_line(
 
 
 def left_hand_split(line: Line, py36: bool = False) -> Iterator[Line]:
 
 
 def left_hand_split(line: Line, py36: bool = False) -> Iterator[Line]:

-    """Splits line into many lines, starting with the first matching bracket pair.
+    """Split line into many lines, starting with the first matching bracket pair.

 
     Note: this usually looks weird, only use this for function definitions.
     Prefer RHS otherwise.
 
     Note: this usually looks weird, only use this for function definitions.
     Prefer RHS otherwise.


@@ -1503,8 +1556,7 @@ def left_hand_split(line: Line, py36: bool = False) -> Iterator[Line]:
     ):
         for leaf in leaves:
             result.append(leaf, preformatted=True)
     ):
         for leaf in leaves:
             result.append(leaf, preformatted=True)

-            comment_after = line.comments.get(id(leaf))
-            if comment_after:
+            for comment_after in line.comments_after(leaf):

                 result.append(comment_after, preformatted=True)
     bracket_split_succeeded_or_raise(head, body, tail)
     for result in (head, body, tail):
                 result.append(comment_after, preformatted=True)
     bracket_split_succeeded_or_raise(head, body, tail)
     for result in (head, body, tail):


@@ -1513,7 +1565,7 @@ def left_hand_split(line: Line, py36: bool = False) -> Iterator[Line]:
 
 
 def right_hand_split(line: Line, py36: bool = False) -> Iterator[Line]:
 
 
 def right_hand_split(line: Line, py36: bool = False) -> Iterator[Line]:

-    """Splits line into many lines, starting with the last matching bracket pair."""
+    """Split line into many lines, starting with the last matching bracket pair."""

     head = Line(depth=line.depth)
     body = Line(depth=line.depth + 1, inside_brackets=True)
     tail = Line(depth=line.depth)
     head = Line(depth=line.depth)
     body = Line(depth=line.depth + 1, inside_brackets=True)
     tail = Line(depth=line.depth)


@@ -1543,8 +1595,7 @@ def right_hand_split(line: Line, py36: bool = False) -> Iterator[Line]:
     ):
         for leaf in leaves:
             result.append(leaf, preformatted=True)
     ):
         for leaf in leaves:
             result.append(leaf, preformatted=True)

-            comment_after = line.comments.get(id(leaf))
-            if comment_after:
+            for comment_after in line.comments_after(leaf):

                 result.append(comment_after, preformatted=True)
     bracket_split_succeeded_or_raise(head, body, tail)
     for result in (head, body, tail):
                 result.append(comment_after, preformatted=True)
     bracket_split_succeeded_or_raise(head, body, tail)
     for result in (head, body, tail):


@@ -1578,10 +1629,25 @@ def bracket_split_succeeded_or_raise(head: Line, body: Line, tail: Line) -> None
             )
 
 
             )
 
 

+def dont_increase_indentation(split_func: SplitFunc) -> SplitFunc:
+    """Normalize prefix of the first leaf in every line returned by `split_func`.
+
+    This is a decorator over relevant split functions.
+    """
+
+    @wraps(split_func)
+    def split_wrapper(line: Line, py36: bool = False) -> Iterator[Line]:
+        for l in split_func(line, py36):
+            normalize_prefix(l.leaves[0], inside_brackets=True)
+            yield l
+
+    return split_wrapper
+
+
+@dont_increase_indentation

 def delimiter_split(line: Line, py36: bool = False) -> Iterator[Line]:
 def delimiter_split(line: Line, py36: bool = False) -> Iterator[Line]:

-    """Splits according to delimiters of the highest priority.
+    """Split according to delimiters of the highest priority.

 
 

-    This kind of split doesn't increase indentation.

     If `py36` is True, the split will add trailing commas also in function
     signatures that contain `*` and `**`.
     """
     If `py36` is True, the split will add trailing commas also in function
     signatures that contain `*` and `**`.
     """


@@ -1601,11 +1667,24 @@ def delimiter_split(line: Line, py36: bool = False) -> Iterator[Line]:
     current_line = Line(depth=line.depth, inside_brackets=line.inside_brackets)
     lowest_depth = sys.maxsize
     trailing_comma_safe = True
     current_line = Line(depth=line.depth, inside_brackets=line.inside_brackets)
     lowest_depth = sys.maxsize
     trailing_comma_safe = True

+
+    def append_to_line(leaf: Leaf) -> Iterator[Line]:
+        """Append `leaf` to current line or to new line if appending impossible."""
+        nonlocal current_line
+        try:
+            current_line.append_safe(leaf, preformatted=True)
+        except ValueError as ve:
+            yield current_line
+
+            current_line = Line(depth=line.depth, inside_brackets=line.inside_brackets)
+            current_line.append(leaf)
+

     for leaf in line.leaves:
     for leaf in line.leaves:

-        current_line.append(leaf, preformatted=True)
-        comment_after = line.comments.get(id(leaf))
-        if comment_after:
-            current_line.append(comment_after, preformatted=True)
+        yield from append_to_line(leaf)
+
+        for comment_after in line.comments_after(leaf):
+            yield from append_to_line(comment_after)
+

         lowest_depth = min(lowest_depth, leaf.bracket_depth)
         if (
             leaf.bracket_depth == lowest_depth
         lowest_depth = min(lowest_depth, leaf.bracket_depth)
         if (
             leaf.bracket_depth == lowest_depth


@@ -1615,7 +1694,6 @@ def delimiter_split(line: Line, py36: bool = False) -> Iterator[Line]:
             trailing_comma_safe = trailing_comma_safe and py36
         leaf_priority = delimiters.get(id(leaf))
         if leaf_priority == delimiter_priority:
             trailing_comma_safe = trailing_comma_safe and py36
         leaf_priority = delimiters.get(id(leaf))
         if leaf_priority == delimiter_priority:

-            normalize_prefix(current_line.leaves[0], inside_brackets=True)

             yield current_line
 
             current_line = Line(depth=line.depth, inside_brackets=line.inside_brackets)
             yield current_line
 
             current_line = Line(depth=line.depth, inside_brackets=line.inside_brackets)


@@ -1626,12 +1704,45 @@ def delimiter_split(line: Line, py36: bool = False) -> Iterator[Line]:
             and trailing_comma_safe
         ):
             current_line.append(Leaf(token.COMMA, ','))
             and trailing_comma_safe
         ):
             current_line.append(Leaf(token.COMMA, ','))

-        normalize_prefix(current_line.leaves[0], inside_brackets=True)
+        yield current_line
+
+
+@dont_increase_indentation
+def standalone_comment_split(line: Line, py36: bool = False) -> Iterator[Line]:
+    """Split standalone comments from the rest of the line."""
+    for leaf in line.leaves:
+        if leaf.type == STANDALONE_COMMENT:
+            if leaf.bracket_depth == 0:
+                break
+
+    else:
+        raise CannotSplit("Line does not have any standalone comments")
+
+    current_line = Line(depth=line.depth, inside_brackets=line.inside_brackets)
+
+    def append_to_line(leaf: Leaf) -> Iterator[Line]:
+        """Append `leaf` to current line or to new line if appending impossible."""
+        nonlocal current_line
+        try:
+            current_line.append_safe(leaf, preformatted=True)
+        except ValueError as ve:
+            yield current_line
+
+            current_line = Line(depth=line.depth, inside_brackets=line.inside_brackets)
+            current_line.append(leaf)
+
+    for leaf in line.leaves:
+        yield from append_to_line(leaf)
+
+        for comment_after in line.comments_after(leaf):
+            yield from append_to_line(comment_after)
+
+    if current_line:

         yield current_line
 
 
 def is_import(leaf: Leaf) -> bool:
         yield current_line
 
 
 def is_import(leaf: Leaf) -> bool:

-    """Returns True if the given leaf starts an import statement."""
+    """Return True if the given leaf starts an import statement."""

     p = leaf.parent
     t = leaf.type
     v = leaf.value
     p = leaf.parent
     t = leaf.type
     v = leaf.value


@@ -1645,10 +1756,10 @@ def is_import(leaf: Leaf) -> bool:
 
 
 def normalize_prefix(leaf: Leaf, *, inside_brackets: bool) -> None:
 
 
 def normalize_prefix(leaf: Leaf, *, inside_brackets: bool) -> None:

-    """Leaves existing extra newlines if not `inside_brackets`.
+    """Leave existing extra newlines if not `inside_brackets`. Remove everything
+    else.

 
 

-    Removes everything else.  Note: don't use backslashes for formatting or
-    you'll lose your voting rights.
+    Note: don't use backslashes for formatting or you'll lose your voting rights.

     """
     if not inside_brackets:
         spl = leaf.prefix.split('#')
     """
     if not inside_brackets:
         spl = leaf.prefix.split('#')


@@ -1663,7 +1774,7 @@ def normalize_prefix(leaf: Leaf, *, inside_brackets: bool) -> None:
 
 
 def is_python36(node: Node) -> bool:
 
 
 def is_python36(node: Node) -> bool:

-    """Returns True if the current file is using Python 3.6+ features.
+    """Return True if the current file is using Python 3.6+ features.

 
     Currently looking for:
     - f-strings; and
 
     Currently looking for:
     - f-strings; and


@@ -1694,7 +1805,7 @@ BLACKLISTED_DIRECTORIES = {
 
 
 def gen_python_files_in_dir(path: Path) -> Iterator[Path]:
 
 
 def gen_python_files_in_dir(path: Path) -> Iterator[Path]:

-    """Generates all files under `path` which aren't under BLACKLISTED_DIRECTORIES
+    """Generate all files under `path` which aren't under BLACKLISTED_DIRECTORIES

     and have one of the PYTHON_EXTENSIONS.
     """
     for child in path.iterdir():
     and have one of the PYTHON_EXTENSIONS.
     """
     for child in path.iterdir():


@@ -1733,7 +1844,13 @@ class Report:
 
     @property
     def return_code(self) -> int:
 
     @property
     def return_code(self) -> int:

-        """Which return code should the app use considering the current state."""
+        """Return the exit code that the app should use.
+
+        This considers the current state of changed files and failures:
+        - if there were any failures, return 123;
+        - if any files were changed and --check is being used, return 1;
+        - otherwise return 0.
+        """

         # According to http://tldp.org/LDP/abs/html/exitcodes.html starting with
         # 126 we have special returncodes reserved by the shell.
         if self.failure_count:
         # According to http://tldp.org/LDP/abs/html/exitcodes.html starting with
         # 126 we have special returncodes reserved by the shell.
         if self.failure_count:


@@ -1745,7 +1862,7 @@ class Report:
         return 0
 
     def __str__(self) -> str:
         return 0
 
     def __str__(self) -> str:

-        """A color report of the current state.
+        """Render a color report of the current state.

 
         Use `click.unstyle` to remove colors.
         """
 
         Use `click.unstyle` to remove colors.
         """


@@ -1775,10 +1892,7 @@ class Report:
 
 
 def assert_equivalent(src: str, dst: str) -> None:
 
 
 def assert_equivalent(src: str, dst: str) -> None:

-    """Raises AssertionError if `src` and `dst` aren't equivalent.
-
-    This is a temporary sanity check until Black becomes stable.
-    """
+    """Raise AssertionError if `src` and `dst` aren't equivalent."""

 
     import ast
     import traceback
 
     import ast
     import traceback


@@ -1841,10 +1955,7 @@ def assert_equivalent(src: str, dst: str) -> None:
 
 
 def assert_stable(src: str, dst: str, line_length: int) -> None:
 
 
 def assert_stable(src: str, dst: str, line_length: int) -> None:

-    """Raises AssertionError if `dst` reformats differently the second time.
-
-    This is a temporary sanity check until Black becomes stable.
-    """
+    """Raise AssertionError if `dst` reformats differently the second time."""

     newdst = format_str(dst, line_length=line_length)
     if dst != newdst:
         log = dump_to_file(
     newdst = format_str(dst, line_length=line_length)
     if dst != newdst:
         log = dump_to_file(


@@ -1860,7 +1971,7 @@ def assert_stable(src: str, dst: str, line_length: int) -> None:
 
 
 def dump_to_file(*output: str) -> str:
 
 
 def dump_to_file(*output: str) -> str:

-    """Dumps `output` to a temporary file. Returns path to the file."""
+    """Dump `output` to a temporary file. Return path to the file."""

     import tempfile
 
     with tempfile.NamedTemporaryFile(
     import tempfile
 
     with tempfile.NamedTemporaryFile(


@@ -1873,7 +1984,7 @@ def dump_to_file(*output: str) -> str:
 
 
 def diff(a: str, b: str, a_name: str, b_name: str) -> str:
 
 
 def diff(a: str, b: str, a_name: str, b_name: str) -> str:

-    """Returns a udiff string between strings `a` and `b`."""
+    """Return a unified diff string between strings `a` and `b`."""

     import difflib
 
     a_lines = [line + '\n' for line in a.split('\n')]
     import difflib
 
     a_lines = [line + '\n' for line in a.split('\n')]


@@ -1883,5 +1994,34 @@ def diff(a: str, b: str, a_name: str, b_name: str) -> str:
     )
 
 
     )
 
 

+def cancel(tasks: List[asyncio.Task]) -> None:
+    """asyncio signal handler that cancels all `tasks` and reports to stderr."""
+    err("Aborted!")
+    for task in tasks:
+        task.cancel()
+
+
+def shutdown(loop: BaseEventLoop) -> None:
+    """Cancel all pending tasks on `loop`, wait for them, and close the loop."""
+    try:
+        # This part is borrowed from asyncio/runners.py in Python 3.7b2.
+        to_cancel = [task for task in asyncio.Task.all_tasks(loop) if not task.done()]
+        if not to_cancel:
+            return
+
+        for task in to_cancel:
+            task.cancel()
+        loop.run_until_complete(
+            asyncio.gather(*to_cancel, loop=loop, return_exceptions=True)
+        )
+    finally:
+        # `concurrent.futures.Future` objects cannot be cancelled once they
+        # are already running. There might be some when the `shutdown()` happened.
+        # Silence their logger's spew about the event loop being closed.
+        cf_logger = logging.getLogger("concurrent.futures")
+        cf_logger.setLevel(logging.CRITICAL)
+        loop.close()
+
+

 if __name__ == '__main__':
     main()
 if __name__ == '__main__':
     main()