Mention fix for #59

[etc/vim.git] / black.py

diff --git a/black.py b/black.py
index 39f25d3eb73058a4b28cb14e48ede96266cc89fe..877b632f3a54c3a5893290c1447c6221f73c1f68 100644 (file)
--- a/black.py
+++ b/black.py
@@ -1,4 +1,5 @@
 #!/usr/bin/env python3
 #!/usr/bin/env python3

+

 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


@@ -12,7 +13,7 @@ from typing import (
     Dict, Generic, Iterable, Iterator, List, Optional, Set, Tuple, TypeVar, Union
 )
 
     Dict, Generic, Iterable, Iterator, List, Optional, Set, Tuple, TypeVar, Union
 )
 

-from attr import attrib, dataclass, Factory
+from attr import dataclass, Factory

 import click
 
 # lib2to3 fork
 import click
 
 # lib2to3 fork


@@ -21,7 +22,7 @@ from blib2to3 import pygram, pytree
 from blib2to3.pgen2 import driver, token
 from blib2to3.pgen2.parse import ParseError
 
 from blib2to3.pgen2 import driver, token
 from blib2to3.pgen2.parse import ParseError
 

-__version__ = "18.3a1"
+__version__ = "18.3a3"

 DEFAULT_LINE_LENGTH = 88
 # types
 syms = pygram.python_symbols
 DEFAULT_LINE_LENGTH = 88
 # types
 syms = pygram.python_symbols


@@ -74,7 +75,9 @@ class CannotSplit(Exception):
 @click.argument(
     'src',
     nargs=-1,
 @click.argument(
     'src',
     nargs=-1,

-    type=click.Path(exists=True, file_okay=True, dir_okay=True, readable=True),
+    type=click.Path(
+        exists=True, file_okay=True, dir_okay=True, readable=True, allow_dash=True
+    ),

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


@@ -89,6 +92,8 @@ def main(
         elif p.is_file():
             # if a file was explicitly given, we don't care about its extension
             sources.append(p)
         elif p.is_file():
             # if a file was explicitly given, we don't care about its extension
             sources.append(p)

+        elif s == '-':
+            sources.append(Path('-'))

         else:
             err(f'invalid path: {s}')
     if len(sources) == 0:
         else:
             err(f'invalid path: {s}')
     if len(sources) == 0:


@@ -97,9 +102,14 @@ def main(
         p = sources[0]
         report = Report()
         try:
         p = sources[0]
         report = Report()
         try:

-            changed = format_file_in_place(
-                p, line_length=line_length, fast=fast, write_back=not check
-            )
+            if not p.is_file() and str(p) == '-':
+                changed = format_stdin_to_stdout(
+                    line_length=line_length, fast=fast, write_back=not check
+                )
+            else:
+                changed = format_file_in_place(
+                    p, line_length=line_length, fast=fast, write_back=not check
+                )

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


@@ -156,41 +166,59 @@ 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."""
     src: Path, line_length: int, fast: bool, write_back: bool = False
 ) -> bool:
     """Format the file and rewrite if changed. Return True if changed."""

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

     try:
     try:

-        contents, encoding = format_file(src, line_length=line_length, fast=fast)
+        contents = format_file_contents(
+            src_contents, line_length=line_length, fast=fast
+        )

     except NothingChanged:
         return False
 
     if write_back:
     except NothingChanged:
         return False
 
     if write_back:

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

             f.write(contents)
     return True
 
 
             f.write(contents)
     return True
 
 

-def format_file(
-    src: Path, line_length: int, fast: bool
-) -> Tuple[FileContent, Encoding]:
+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."""
+    contents = sys.stdin.read()
+    try:
+        contents = format_file_contents(contents, line_length=line_length, fast=fast)
+        return True
+
+    except NothingChanged:
+        return False
+
+    finally:
+        if write_back:
+            sys.stdout.write(contents)
+
+
+def format_file_contents(
+    src_contents: str, line_length: int, fast: bool
+) -> FileContent:

     """Reformats a file and returns its contents and encoding."""
     """Reformats a file and returns its contents and encoding."""

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

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

-        raise NothingChanged(src)
+        raise NothingChanged

 
     dst_contents = format_str(src_contents, line_length=line_length)
     if src_contents == dst_contents:
 
     dst_contents = format_str(src_contents, line_length=line_length)
     if src_contents == dst_contents:

-        raise NothingChanged(src)
+        raise NothingChanged

 
     if not fast:
         assert_equivalent(src_contents, dst_contents)
         assert_stable(src_contents, dst_contents, line_length=line_length)
 
     if not fast:
         assert_equivalent(src_contents, dst_contents)
         assert_stable(src_contents, dst_contents, line_length=line_length)

-    return dst_contents, src_buffer.encoding
+    return dst_contents

 
 
 def format_str(src_contents: str, line_length: int) -> FileContent:
     """Reformats a string and returns new contents."""
     src_node = lib2to3_parse(src_contents)
     dst_contents = ""
 
 
 def format_str(src_contents: str, line_length: int) -> FileContent:
     """Reformats a string and returns new contents."""
     src_node = lib2to3_parse(src_contents)
     dst_contents = ""

-    comments: List[Line] = []

     lines = LineGenerator()
     elt = EmptyLineTracker()
     py36 = is_python36(src_node)
     lines = LineGenerator()
     elt = EmptyLineTracker()
     py36 = is_python36(src_node)


@@ -202,16 +230,8 @@ def format_str(src_contents: str, line_length: int) -> FileContent:
         before, after = elt.maybe_empty_lines(current_line)
         for _ in range(before):
             dst_contents += str(empty_line)
         before, after = elt.maybe_empty_lines(current_line)
         for _ in range(before):
             dst_contents += str(empty_line)

-        if not current_line.is_comment:
-            for comment in comments:
-                dst_contents += str(comment)
-            comments = []
-            for line in split_line(current_line, line_length=line_length, py36=py36):
-                dst_contents += str(line)
-        else:
-            comments.append(current_line)
-    for comment in comments:
-        dst_contents += str(comment)
+        for line in split_line(current_line, line_length=line_length, py36=py36):
+            dst_contents += str(line)

     return dst_contents
 
 
     return dst_contents
 
 


@@ -265,7 +285,7 @@ class Visitor(Generic[T]):
 
 @dataclass
 class DebugVisitor(Visitor[T]):
 
 @dataclass
 class DebugVisitor(Visitor[T]):

-    tree_depth: int = attrib(default=0)
+    tree_depth: int = 0

 
     def visit_default(self, node: LN) -> Iterator[T]:
         indent = ' ' * (2 * self.tree_depth)
 
     def visit_default(self, node: LN) -> Iterator[T]:
         indent = ' ' * (2 * self.tree_depth)


@@ -320,6 +340,7 @@ MATH_OPERATORS = {
     token.AMPER,
     token.PERCENT,
     token.CIRCUMFLEX,
     token.AMPER,
     token.PERCENT,
     token.CIRCUMFLEX,

+    token.TILDE,

     token.LEFTSHIFT,
     token.RIGHTSHIFT,
     token.DOUBLESTAR,
     token.LEFTSHIFT,
     token.RIGHTSHIFT,
     token.DOUBLESTAR,


@@ -335,10 +356,10 @@ MATH_PRIORITY = 1
 
 @dataclass
 class BracketTracker:
 
 @dataclass
 class BracketTracker:

-    depth: int = attrib(default=0)
-    bracket_match: Dict[Tuple[Depth, NodeType], Leaf] = attrib(default=Factory(dict))
-    delimiters: Dict[LeafID, Priority] = attrib(default=Factory(dict))
-    previous: Optional[Leaf] = attrib(default=None)
+    depth: int = 0
+    bracket_match: Dict[Tuple[Depth, NodeType], Leaf] = Factory(dict)
+    delimiters: Dict[LeafID, Priority] = Factory(dict)
+    previous: Optional[Leaf] = None

 
     def mark(self, leaf: Leaf) -> None:
         if leaf.type == token.COMMENT:
 
     def mark(self, leaf: Leaf) -> None:
         if leaf.type == token.COMMENT:


@@ -357,19 +378,25 @@ class BracketTracker:
                 if leaf.type == token.STRING and self.previous.type == token.STRING:
                     self.delimiters[id(self.previous)] = STRING_PRIORITY
                 elif (
                 if leaf.type == token.STRING and self.previous.type == token.STRING:
                     self.delimiters[id(self.previous)] = STRING_PRIORITY
                 elif (

-                    leaf.type == token.NAME and
-                    leaf.value == 'for' and
-                    leaf.parent and
-                    leaf.parent.type in {syms.comp_for, syms.old_comp_for}
+                    leaf.type == token.NAME
+                    and leaf.value == 'for'
+                    and leaf.parent
+                    and leaf.parent.type in {syms.comp_for, syms.old_comp_for}

                 ):
                     self.delimiters[id(self.previous)] = COMPREHENSION_PRIORITY
                 elif (
                 ):
                     self.delimiters[id(self.previous)] = COMPREHENSION_PRIORITY
                 elif (

-                    leaf.type == token.NAME and
-                    leaf.value == 'if' and
-                    leaf.parent and
-                    leaf.parent.type in {syms.comp_if, syms.old_comp_if}
+                    leaf.type == token.NAME
+                    and leaf.value == 'if'
+                    and leaf.parent
+                    and leaf.parent.type in {syms.comp_if, syms.old_comp_if}

                 ):
                     self.delimiters[id(self.previous)] = COMPREHENSION_PRIORITY
                 ):
                     self.delimiters[id(self.previous)] = COMPREHENSION_PRIORITY

+                elif (
+                    leaf.type == token.NAME
+                    and leaf.value in LOGIC_OPERATORS
+                    and leaf.parent
+                ):
+                    self.delimiters[id(self.previous)] = LOGIC_PRIORITY

         if leaf.type in OPENING_BRACKETS:
             self.bracket_match[self.depth, BRACKET[leaf.type]] = leaf
             self.depth += 1
         if leaf.type in OPENING_BRACKETS:
             self.bracket_match[self.depth, BRACKET[leaf.type]] = leaf
             self.depth += 1


@@ -389,13 +416,13 @@ class BracketTracker:
 
 @dataclass
 class Line:
 
 @dataclass
 class Line:

-    depth: int = attrib(default=0)
-    leaves: List[Leaf] = attrib(default=Factory(list))
-    comments: Dict[LeafID, Leaf] = attrib(default=Factory(dict))
-    bracket_tracker: BracketTracker = attrib(default=Factory(BracketTracker))
-    inside_brackets: bool = attrib(default=False)
-    has_for: bool = attrib(default=False)
-    _for_loop_variable: bool = attrib(default=False, init=False)
+    depth: int = 0
+    leaves: List[Leaf] = Factory(list)
+    comments: Dict[LeafID, Leaf] = Factory(dict)
+    bracket_tracker: BracketTracker = Factory(BracketTracker)
+    inside_brackets: bool = False
+    has_for: bool = False
+    _for_loop_variable: bool = False

 
     def append(self, leaf: Leaf, preformatted: bool = False) -> None:
         has_value = leaf.value.strip()
 
     def append(self, leaf: Leaf, preformatted: bool = False) -> None:
         has_value = leaf.value.strip()


@@ -432,9 +459,9 @@ class Line:
     @property
     def is_class(self) -> bool:
         return (
     @property
     def is_class(self) -> bool:
         return (

-            bool(self) and
-            self.leaves[0].type == token.NAME and
-            self.leaves[0].value == 'class'
+            bool(self)
+            and self.leaves[0].type == token.NAME
+            and self.leaves[0].value == 'class'

         )
 
     @property
         )
 
     @property


@@ -450,44 +477,49 @@ class Line:
         except IndexError:
             second_leaf = None
         return (
         except IndexError:
             second_leaf = None
         return (

-            (first_leaf.type == token.NAME and first_leaf.value == 'def') or
-            (
-                first_leaf.type == token.NAME and
-                first_leaf.value == 'async' and
-                second_leaf is not None and
-                second_leaf.type == token.NAME and
-                second_leaf.value == 'def'
+            (first_leaf.type == token.NAME and first_leaf.value == 'def')
+            or (
+                first_leaf.type == token.ASYNC
+                and second_leaf is not None
+                and second_leaf.type == token.NAME
+                and second_leaf.value == 'def'

             )
         )
 
     @property
     def is_flow_control(self) -> bool:
         return (
             )
         )
 
     @property
     def is_flow_control(self) -> bool:
         return (

-            bool(self) and
-            self.leaves[0].type == token.NAME and
-            self.leaves[0].value in FLOW_CONTROL
+            bool(self)
+            and self.leaves[0].type == token.NAME
+            and self.leaves[0].value in FLOW_CONTROL

         )
 
     @property
     def is_yield(self) -> bool:
         return (
         )
 
     @property
     def is_yield(self) -> bool:
         return (

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

         )
 
     def maybe_remove_trailing_comma(self, closing: Leaf) -> bool:
         if not (
         )
 
     def maybe_remove_trailing_comma(self, closing: Leaf) -> bool:
         if not (

-            self.leaves and
-            self.leaves[-1].type == token.COMMA and
-            closing.type in CLOSING_BRACKETS
+            self.leaves
+            and self.leaves[-1].type == token.COMMA
+            and closing.type in CLOSING_BRACKETS

         ):
             return False
 
         ):
             return False
 

-        if closing.type == token.RSQB or closing.type == token.RBRACE:
+        if closing.type == token.RBRACE:

             self.leaves.pop()
             return True
 
             self.leaves.pop()
             return True
 

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

         # For parens let's check if it's safe to remove the comma.  If the
         # trailing one is the only one, we might mistakenly change a tuple
         # into a different type by removing the comma.
         # For parens let's check if it's safe to remove the comma.  If the
         # trailing one is the only one, we might mistakenly change a tuple
         # into a different type by removing the comma.


@@ -508,6 +540,10 @@ class Line:
             bracket_depth = leaf.bracket_depth
             if bracket_depth == depth and leaf.type == token.COMMA:
                 commas += 1
             bracket_depth = leaf.bracket_depth
             if bracket_depth == depth and leaf.type == token.COMMA:
                 commas += 1

+                if leaf.parent and leaf.parent.type == syms.arglist:
+                    commas += 1
+                    break
+

         if commas > 1:
             self.leaves.pop()
             return True
         if commas > 1:
             self.leaves.pop()
             return True


@@ -547,8 +583,8 @@ class Line:
         appended will appear "too long" when splitting.
         """
         if not (
         appended will appear "too long" when splitting.
         """
         if not (

-            comment.type == STANDALONE_COMMENT and
-            self.bracket_tracker.any_open_brackets()
+            comment.type == STANDALONE_COMMENT
+            and self.bracket_tracker.any_open_brackets()

         ):
             return False
 
         ):
             return False
 


@@ -605,11 +641,13 @@ class EmptyLineTracker:
     """Provides a stateful method that returns the number of potential extra
     empty lines needed before and after the currently processed line.
 
     """Provides a stateful method that returns the number of potential extra
     empty lines needed before and after the currently processed line.
 

-    Note: this tracker works on lines that haven't been split yet.
+    Note: this tracker works on lines that haven't been split yet.  It assumes
+    the prefix of the first leaf consists of optional newlines.  Those newlines
+    are consumed by `maybe_empty_lines()` and included in the computation.

     """
     """

-    previous_line: Optional[Line] = attrib(default=None)
-    previous_after: int = attrib(default=0)
-    previous_defs: List[int] = attrib(default=Factory(list))
+    previous_line: Optional[Line] = None
+    previous_after: int = 0
+    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`.
 
     def maybe_empty_lines(self, current_line: Line) -> Tuple[int, int]:
         """Returns the number of extra empty lines before and after the `current_line`.


@@ -619,16 +657,27 @@ class EmptyLineTracker:
         control keywords to make them more prominent.
         """
         before, after = self._maybe_empty_lines(current_line)
         control keywords to make them more prominent.
         """
         before, after = self._maybe_empty_lines(current_line)

+        before -= self.previous_after

         self.previous_after = after
         self.previous_line = current_line
         return before, after
 
     def _maybe_empty_lines(self, current_line: Line) -> Tuple[int, int]:
         self.previous_after = after
         self.previous_line = current_line
         return before, after
 
     def _maybe_empty_lines(self, current_line: Line) -> Tuple[int, int]:

-        before = 0
+        max_allowed = 1
+        if current_line.is_comment and current_line.depth == 0:
+            max_allowed = 2
+        if current_line.leaves:
+            # Consume the first leaf's extra newlines.
+            first_leaf = current_line.leaves[0]
+            before = first_leaf.prefix.count('\n')
+            before = min(before, max(before, max_allowed))
+            first_leaf.prefix = ''
+        else:
+            before = 0

         depth = current_line.depth
         while self.previous_defs and self.previous_defs[-1] >= depth:
             self.previous_defs.pop()
         depth = current_line.depth
         while self.previous_defs and self.previous_defs[-1] >= depth:
             self.previous_defs.pop()

-            before = (1 if depth else 2) - self.previous_after
+            before = 1 if depth else 2

         is_decorator = current_line.is_decorator
         if is_decorator or current_line.is_def or current_line.is_class:
             if not is_decorator:
         is_decorator = current_line.is_decorator
         if is_decorator or current_line.is_def or current_line.is_class:
             if not is_decorator:


@@ -644,24 +693,23 @@ class EmptyLineTracker:
             newlines = 2
             if current_line.depth:
                 newlines -= 1
             newlines = 2
             if current_line.depth:
                 newlines -= 1

-            newlines -= self.previous_after

             return newlines, 0
 
         if current_line.is_flow_control:
             return before, 1
 
         if (
             return newlines, 0
 
         if current_line.is_flow_control:
             return before, 1
 
         if (

-            self.previous_line and
-            self.previous_line.is_import and
-            not current_line.is_import and
-            depth == self.previous_line.depth
+            self.previous_line
+            and self.previous_line.is_import
+            and not current_line.is_import
+            and depth == self.previous_line.depth

         ):
             return (before or 1), 0
 
         if (
         ):
             return (before or 1), 0
 
         if (

-            self.previous_line and
-            self.previous_line.is_yield and
-            (not current_line.is_yield or depth != self.previous_line.depth)
+            self.previous_line
+            and self.previous_line.is_yield
+            and (not current_line.is_yield or depth != self.previous_line.depth)

         ):
             return (before or 1), 0
 
         ):
             return (before or 1), 0
 


@@ -675,8 +723,7 @@ 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.
     """

-    current_line: Line = attrib(default=Factory(Line))
-    standalone_comments: List[Leaf] = attrib(default=Factory(list))
+    current_line: Line = Factory(Line)

 
     def line(self, indent: int = 0) -> Iterator[Line]:
         """Generate a line.
 
     def line(self, indent: int = 0) -> Iterator[Line]:
         """Generate a line.


@@ -696,8 +743,9 @@ class LineGenerator(Visitor[Line]):
 
     def visit_default(self, node: LN) -> Iterator[Line]:
         if isinstance(node, Leaf):
 
     def visit_default(self, node: LN) -> Iterator[Line]:
         if isinstance(node, Leaf):

+            any_open_brackets = self.current_line.bracket_tracker.any_open_brackets()

             for comment in generate_comments(node):
             for comment in generate_comments(node):

-                if self.current_line.bracket_tracker.any_open_brackets():
+                if any_open_brackets:

                     # any comment within brackets is subject to splitting
                     self.current_line.append(comment)
                 elif comment.type == token.COMMENT:
                     # any comment within brackets is subject to splitting
                     self.current_line.append(comment)
                 elif comment.type == token.COMMENT:


@@ -706,33 +754,22 @@ class LineGenerator(Visitor[Line]):
                     yield from self.line()
 
                 else:
                     yield from self.line()
 
                 else:

-                    # regular standalone comment, to be processed later (see
-                    # docstring in `generate_comments()`
-                    self.standalone_comments.append(comment)
-            normalize_prefix(node)
-            if node.type not in WHITESPACE:
-                for comment in self.standalone_comments:
+                    # regular standalone comment

                     yield from self.line()
 
                     self.current_line.append(comment)
                     yield from self.line()
 
                     yield from self.line()
 
                     self.current_line.append(comment)
                     yield from self.line()
 

-                self.standalone_comments = []
+            normalize_prefix(node, inside_brackets=any_open_brackets)
+            if node.type not in WHITESPACE:

                 self.current_line.append(node)
         yield from super().visit_default(node)
 
                 self.current_line.append(node)
         yield from super().visit_default(node)
 

-    def visit_suite(self, node: Node) -> Iterator[Line]:
-        """Body of a statement after a colon."""
-        children = iter(node.children)
-        # Process newline before indenting.  It might contain an inline
-        # comment that should go right after the colon.
-        newline = next(children)
-        yield from self.visit(newline)
+    def visit_INDENT(self, node: Node) -> Iterator[Line]:

         yield from self.line(+1)
         yield from self.line(+1)

+        yield from self.visit_default(node)

 
 

-        for child in children:
-            yield from self.visit(child)
-
+    def visit_DEDENT(self, node: Node) -> Iterator[Line]:

         yield from self.line(-1)
 
     def visit_stmt(self, node: Node, keywords: Set[str]) -> Iterator[Line]:
         yield from self.line(-1)
 
     def visit_stmt(self, node: Node, keywords: Set[str]) -> Iterator[Line]:


@@ -766,7 +803,7 @@ class LineGenerator(Visitor[Line]):
         for child in children:
             yield from self.visit(child)
 
         for child in children:
             yield from self.visit(child)
 

-            if child.type == token.NAME and child.value == 'async':  # type: ignore
+            if child.type == token.ASYNC:

                 break
 
         internal_stmt = next(children)
                 break
 
         internal_stmt = next(children)


@@ -804,10 +841,10 @@ BRACKET = {token.LPAR: token.RPAR, token.LSQB: token.RSQB, token.LBRACE: token.R
 OPENING_BRACKETS = set(BRACKET.keys())
 CLOSING_BRACKETS = set(BRACKET.values())
 BRACKETS = OPENING_BRACKETS | CLOSING_BRACKETS
 OPENING_BRACKETS = set(BRACKET.keys())
 CLOSING_BRACKETS = set(BRACKET.values())
 BRACKETS = OPENING_BRACKETS | CLOSING_BRACKETS

-ALWAYS_NO_SPACE = CLOSING_BRACKETS | {token.COMMA, token.COLON, STANDALONE_COMMENT}
+ALWAYS_NO_SPACE = CLOSING_BRACKETS | {token.COMMA, STANDALONE_COMMENT}

 
 
 
 

-def whitespace(leaf: Leaf) -> str:
+def whitespace(leaf: Leaf) -> str:  # noqa C901

     """Return whitespace prefix if needed for the given `leaf`."""
     NO = ''
     SPACE = ' '
     """Return whitespace prefix if needed for the given `leaf`."""
     NO = ''
     SPACE = ' '


@@ -822,37 +859,48 @@ def whitespace(leaf: Leaf) -> str:
         return DOUBLESPACE
 
     assert p is not None, f"INTERNAL ERROR: hand-made leaf without parent: {leaf!r}"
         return DOUBLESPACE
 
     assert p is not None, f"INTERNAL ERROR: hand-made leaf without parent: {leaf!r}"

+    if t == token.COLON and p.type not in {syms.subscript, syms.subscriptlist}:
+        return NO
+

     prev = leaf.prev_sibling
     if not prev:
         prevp = preceding_leaf(p)
         if not prevp or prevp.type in OPENING_BRACKETS:
             return NO
 
     prev = leaf.prev_sibling
     if not prev:
         prevp = preceding_leaf(p)
         if not prevp or prevp.type in OPENING_BRACKETS:
             return NO
 

+        if t == token.COLON:
+            return SPACE if prevp.type == token.COMMA else NO
+

         if prevp.type == token.EQUAL:
             if prevp.parent and prevp.parent.type in {
         if prevp.type == token.EQUAL:
             if prevp.parent and prevp.parent.type in {

-                syms.typedargslist,
-                syms.varargslist,
-                syms.parameters,

                 syms.arglist,
                 syms.argument,
                 syms.arglist,
                 syms.argument,

+                syms.parameters,
+                syms.typedargslist,
+                syms.varargslist,

             }:
                 return NO
 
         elif prevp.type == token.DOUBLESTAR:
             if prevp.parent and prevp.parent.type in {
             }:
                 return NO
 
         elif prevp.type == token.DOUBLESTAR:
             if prevp.parent and prevp.parent.type in {

-                syms.typedargslist,
-                syms.varargslist,
-                syms.parameters,

                 syms.arglist,
                 syms.arglist,

+                syms.argument,

                 syms.dictsetmaker,
                 syms.dictsetmaker,

+                syms.parameters,
+                syms.typedargslist,
+                syms.varargslist,

             }:
                 return NO
 
         elif prevp.type == token.COLON:
             }:
                 return NO
 
         elif prevp.type == token.COLON:

-            if prevp.parent and prevp.parent.type == syms.subscript:
+            if prevp.parent and prevp.parent.type in {syms.subscript, syms.sliceop}:

                 return NO
 
                 return NO
 

-        elif prevp.parent and prevp.parent.type in {syms.factor, syms.star_expr}:
+        elif (
+            prevp.parent
+            and prevp.parent.type in {syms.factor, syms.star_expr}
+            and prevp.type in MATH_OPERATORS
+        ):

             return NO
 
     elif prev.type in OPENING_BRACKETS:
             return NO
 
     elif prev.type in OPENING_BRACKETS:


@@ -956,7 +1004,7 @@ def whitespace(leaf: Leaf) -> str:
 
             return NO
 
 
             return NO
 

-        elif prev.type == token.COLON:
+        else:

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


@@ -965,9 +1013,9 @@ def whitespace(leaf: Leaf) -> str:
             return NO
 
     elif (
             return NO
 
     elif (

-        p.type == syms.listmaker or
-        p.type == syms.testlist_gexp or
-        p.type == syms.subscriptlist
+        p.type == syms.listmaker
+        or p.type == syms.testlist_gexp
+        or p.type == syms.subscriptlist

     ):
         # list interior, including unpacking
         if not prev:
     ):
         # list interior, including unpacking
         if not prev:


@@ -1045,16 +1093,13 @@ def is_delimiter(leaf: Leaf) -> int:
     if leaf.type == token.COMMA:
         return COMMA_PRIORITY
 
     if leaf.type == token.COMMA:
         return COMMA_PRIORITY
 

-    if leaf.type == token.NAME and leaf.value in LOGIC_OPERATORS:
-        return LOGIC_PRIORITY
-

     if leaf.type in COMPARATORS:
         return COMPARATOR_PRIORITY
 
     if (
     if leaf.type in COMPARATORS:
         return COMPARATOR_PRIORITY
 
     if (

-        leaf.type in MATH_OPERATORS and
-        leaf.parent and
-        leaf.parent.type not in {syms.factor, syms.star_expr}
+        leaf.type in MATH_OPERATORS
+        and leaf.parent
+        and leaf.parent.type not in {syms.factor, syms.star_expr}

     ):
         return MATH_PRIORITY
 
     ):
         return MATH_PRIORITY
 


@@ -1080,30 +1125,40 @@ def generate_comments(leaf: Leaf) -> Iterator[Leaf]:
     Inline comments are emitted as regular token.COMMENT leaves.  Standalone
     are emitted with a fake STANDALONE_COMMENT token identifier.
     """
     Inline comments are emitted as regular token.COMMENT leaves.  Standalone
     are emitted with a fake STANDALONE_COMMENT token identifier.
     """

-    if not leaf.prefix:
-        return
-
-    if '#' not in leaf.prefix:
+    p = leaf.prefix
+    if not p:

         return
 
         return
 

-    before_comment, content = leaf.prefix.split('#', 1)
-    content = content.rstrip()
-    if content and (content[0] not in {' ', '!', '#'}):
-        content = ' ' + content
-    is_standalone_comment = (
-        '\n' in before_comment or '\n' in content or leaf.type == token.DEDENT
-    )
-    if not is_standalone_comment:
-        # simple trailing comment
-        yield Leaf(token.COMMENT, value='#' + content)
+    if '#' not in p:

         return
 
         return
 

-    for line in ('#' + content).split('\n'):
+    nlines = 0
+    for index, line in enumerate(p.split('\n')):

         line = line.lstrip()
         line = line.lstrip()

+        if not line:
+            nlines += 1

         if not line.startswith('#'):
             continue
 
         if not line.startswith('#'):
             continue
 

-        yield Leaf(STANDALONE_COMMENT, line)
+        if index == 0 and leaf.type != token.ENDMARKER:
+            comment_type = token.COMMENT  # simple trailing comment
+        else:
+            comment_type = STANDALONE_COMMENT
+        yield Leaf(comment_type, make_comment(line), prefix='\n' * nlines)
+
+        nlines = 0
+
+
+def make_comment(content: str) -> str:
+    content = content.rstrip()
+    if not content:
+        return '#'
+
+    if content[0] == '#':
+        content = content[1:]
+    if content and content[0] not in {' ', '!', '#'}:
+        content = ' ' + content
+    return '#' + content

 
 
 def split_line(
 
 
 def split_line(


@@ -1174,11 +1229,11 @@ def left_hand_split(line: Line, py36: bool = False) -> Iterator[Line]:
     matching_bracket = None
     for leaf in line.leaves:
         if (
     matching_bracket = None
     for leaf in line.leaves:
         if (

-            current_leaves is body_leaves and
-            leaf.type in CLOSING_BRACKETS and
-            leaf.opening_bracket is matching_bracket
+            current_leaves is body_leaves
+            and leaf.type in CLOSING_BRACKETS
+            and leaf.opening_bracket is matching_bracket

         ):
         ):

-            current_leaves = tail_leaves
+            current_leaves = tail_leaves if body_leaves else head_leaves

         current_leaves.append(leaf)
         if current_leaves is head_leaves:
             if leaf.type in OPENING_BRACKETS:
         current_leaves.append(leaf)
         if current_leaves is head_leaves:
             if leaf.type in OPENING_BRACKETS:


@@ -1186,7 +1241,7 @@ def left_hand_split(line: Line, py36: bool = False) -> Iterator[Line]:
                 current_leaves = body_leaves
     # Since body is a new indent level, remove spurious leading whitespace.
     if body_leaves:
                 current_leaves = body_leaves
     # Since body is a new indent level, remove spurious leading whitespace.
     if body_leaves:

-        normalize_prefix(body_leaves[0])
+        normalize_prefix(body_leaves[0], inside_brackets=True)

     # Build the new lines.
     for result, leaves in (
         (head, head_leaves), (body, body_leaves), (tail, tail_leaves)
     # Build the new lines.
     for result, leaves in (
         (head, head_leaves), (body, body_leaves), (tail, tail_leaves)


@@ -1196,18 +1251,7 @@ def left_hand_split(line: Line, py36: bool = False) -> Iterator[Line]:
             comment_after = line.comments.get(id(leaf))
             if comment_after:
                 result.append(comment_after, preformatted=True)
             comment_after = line.comments.get(id(leaf))
             if comment_after:
                 result.append(comment_after, preformatted=True)

-    # Check if the split succeeded.
-    tail_len = len(str(tail))
-    if not body:
-        if tail_len == 0:
-            raise CannotSplit("Splitting brackets produced the same line")
-
-        elif tail_len < 3:
-            raise CannotSplit(
-                f"Splitting brackets on an empty body to save "
-                f"{tail_len} characters is not worth it"
-            )
-
+    split_succeeded_or_raise(head, body, tail)

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


@@ -1226,7 +1270,7 @@ def right_hand_split(line: Line, py36: bool = False) -> Iterator[Line]:
     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:

-                current_leaves = head_leaves
+                current_leaves = head_leaves if body_leaves else tail_leaves

         current_leaves.append(leaf)
         if current_leaves is tail_leaves:
             if leaf.type in CLOSING_BRACKETS:
         current_leaves.append(leaf)
         if current_leaves is tail_leaves:
             if leaf.type in CLOSING_BRACKETS:


@@ -1237,7 +1281,7 @@ def right_hand_split(line: Line, py36: bool = False) -> Iterator[Line]:
     head_leaves.reverse()
     # Since body is a new indent level, remove spurious leading whitespace.
     if body_leaves:
     head_leaves.reverse()
     # Since body is a new indent level, remove spurious leading whitespace.
     if body_leaves:

-        normalize_prefix(body_leaves[0])
+        normalize_prefix(body_leaves[0], inside_brackets=True)

     # Build the new lines.
     for result, leaves in (
         (head, head_leaves), (body, body_leaves), (tail, tail_leaves)
     # Build the new lines.
     for result, leaves in (
         (head, head_leaves), (body, body_leaves), (tail, tail_leaves)


@@ -1247,8 +1291,14 @@ def right_hand_split(line: Line, py36: bool = False) -> Iterator[Line]:
             comment_after = line.comments.get(id(leaf))
             if comment_after:
                 result.append(comment_after, preformatted=True)
             comment_after = line.comments.get(id(leaf))
             if comment_after:
                 result.append(comment_after, preformatted=True)

-    # Check if the split succeeded.
-    tail_len = len(str(tail).strip('\n'))
+    split_succeeded_or_raise(head, body, tail)
+    for result in (head, body, tail):
+        if result:
+            yield result
+
+
+def split_succeeded_or_raise(head: Line, body: Line, tail: Line) -> None:
+    tail_len = len(str(tail).strip())

     if not body:
         if tail_len == 0:
             raise CannotSplit("Splitting brackets produced the same line")
     if not body:
         if tail_len == 0:
             raise CannotSplit("Splitting brackets produced the same line")


@@ -1259,10 +1309,6 @@ def right_hand_split(line: Line, py36: bool = False) -> Iterator[Line]:
                 f"{tail_len} characters is not worth it"
             )
 
                 f"{tail_len} characters is not worth it"
             )
 

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

 
 def delimiter_split(line: Line, py36: bool = False) -> Iterator[Line]:
     """Split according to delimiters of the highest priority.
 
 def delimiter_split(line: Line, py36: bool = False) -> Iterator[Line]:
     """Split according to delimiters of the highest priority.


@@ -1292,25 +1338,25 @@ def delimiter_split(line: Line, py36: bool = False) -> Iterator[Line]:
             current_line.append(comment_after, preformatted=True)
         lowest_depth = min(lowest_depth, leaf.bracket_depth)
         if (
             current_line.append(comment_after, preformatted=True)
         lowest_depth = min(lowest_depth, leaf.bracket_depth)
         if (

-            leaf.bracket_depth == lowest_depth and
-            leaf.type == token.STAR or
-            leaf.type == token.DOUBLESTAR
+            leaf.bracket_depth == lowest_depth
+            and leaf.type == token.STAR
+            or leaf.type == token.DOUBLESTAR

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

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

-            delimiter_priority == COMMA_PRIORITY and
-            current_line.leaves[-1].type != token.COMMA and
-            trailing_comma_safe
+            delimiter_priority == COMMA_PRIORITY
+            and current_line.leaves[-1].type != token.COMMA
+            and trailing_comma_safe

         ):
             current_line.append(Leaf(token.COMMA, ','))
         ):
             current_line.append(Leaf(token.COMMA, ','))

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

         yield current_line
 
 
         yield current_line
 
 


@@ -1320,24 +1366,28 @@ def is_import(leaf: Leaf) -> bool:
     t = leaf.type
     v = leaf.value
     return bool(
     t = leaf.type
     v = leaf.value
     return bool(

-        t == token.NAME and
-        (
-            (v == 'import' and p and p.type == syms.import_name) or
-            (v == 'from' and p and p.type == syms.import_from)
+        t == token.NAME
+        and (
+            (v == 'import' and p and p.type == syms.import_name)
+            or (v == 'from' and p and p.type == syms.import_from)

         )
     )
 
 
         )
     )
 
 

-def normalize_prefix(leaf: Leaf) -> None:
-    """Leave existing extra newlines for imports.  Remove everything else."""
-    if is_import(leaf):
-        spl = leaf.prefix.split('#', 1)
-        nl_count = spl[0].count('\n')
-        if len(spl) > 1:
-            # Skip one newline since it was for a standalone comment.
-            nl_count -= 1
-        leaf.prefix = '\n' * nl_count
-        return
+def normalize_prefix(leaf: Leaf, *, inside_brackets: bool) -> None:
+    """Leave existing extra newlines if not `inside_brackets`.
+
+    Remove everything else.  Note: don't use backslashes for formatting or
+    you'll lose your voting rights.
+    """
+    if not inside_brackets:
+        spl = leaf.prefix.split('#')
+        if '\\' not in spl[0]:
+            nl_count = spl[-1].count('\n')
+            if len(spl) > 1:
+                nl_count -= 1
+            leaf.prefix = '\n' * nl_count
+            return

 
     leaf.prefix = ''
 
 
     leaf.prefix = ''
 


@@ -1356,9 +1406,9 @@ def is_python36(node: Node) -> bool:
                 return True
 
         elif (
                 return True
 
         elif (

-            n.type == syms.typedargslist and
-            n.children and
-            n.children[-1].type == token.COMMA
+            n.type == syms.typedargslist
+            and n.children
+            and n.children[-1].type == token.COMMA

         ):
             for ch in n.children:
                 if ch.type == token.STAR or ch.type == token.DOUBLESTAR:
         ):
             for ch in n.children:
                 if ch.type == token.STAR or ch.type == token.DOUBLESTAR:


@@ -1388,9 +1438,9 @@ def gen_python_files_in_dir(path: Path) -> Iterator[Path]:
 @dataclass
 class Report:
     """Provides a reformatting counter."""
 @dataclass
 class Report:
     """Provides a reformatting counter."""

-    change_count: int = attrib(default=0)
-    same_count: int = attrib(default=0)
-    failure_count: int = attrib(default=0)
+    change_count: int = 0
+    same_count: int = 0
+    failure_count: int = 0

 
     def done(self, src: Path, changed: bool) -> None:
         """Increment the counter for successful reformatting. Write out a message."""
 
     def done(self, src: Path, changed: bool) -> None:
         """Increment the counter for successful reformatting. Write out a message."""


@@ -1489,7 +1539,7 @@ def assert_equivalent(src: str, dst: str) -> None:
         raise AssertionError(
             f"INTERNAL ERROR: Black produced invalid code: {exc}. "
             f"Please report a bug on https://github.com/ambv/black/issues.  "
         raise AssertionError(
             f"INTERNAL ERROR: Black produced invalid code: {exc}. "
             f"Please report a bug on https://github.com/ambv/black/issues.  "

-            f"This invalid output might be helpful: {log}",
+            f"This invalid output might be helpful: {log}"

         ) from None
 
     src_ast_str = '\n'.join(_v(src_ast))
         ) from None
 
     src_ast_str = '\n'.join(_v(src_ast))


@@ -1500,7 +1550,7 @@ def assert_equivalent(src: str, dst: str) -> None:
             f"INTERNAL ERROR: Black produced code that is not equivalent to "
             f"the source.  "
             f"Please report a bug on https://github.com/ambv/black/issues.  "
             f"INTERNAL ERROR: Black produced code that is not equivalent to "
             f"the source.  "
             f"Please report a bug on https://github.com/ambv/black/issues.  "

-            f"This diff might be helpful: {log}",
+            f"This diff might be helpful: {log}"

         ) from None
 
 
         ) from None
 
 


@@ -1519,7 +1569,7 @@ def assert_stable(src: str, dst: str, line_length: int) -> None:
             f"INTERNAL ERROR: Black produced different code on the second pass "
             f"of the formatter.  "
             f"Please report a bug on https://github.com/ambv/black/issues.  "
             f"INTERNAL ERROR: Black produced different code on the second pass "
             f"of the formatter.  "
             f"Please report a bug on https://github.com/ambv/black/issues.  "

-            f"This diff might be helpful: {log}",
+            f"This diff might be helpful: {log}"

         ) from None
 
 
         ) from None