Remove the test-specific .flake8 file

[etc/vim.git] / black.py

diff --git a/black.py b/black.py
index dc02128313154690de62de810abf399efcdb3433..dab3f004ff3289711dc26006b533844ad2268bac 100644 (file)
--- a/black.py
+++ b/black.py
@@ -22,7 +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__ = "18.3a3"
+__version__ = "18.3a4"

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


@@ -38,18 +38,19 @@ err = partial(click.secho, fg='red', err=True)
 
 
 class NothingChanged(UserWarning):
 
 
 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`.

     """
 
 
 class FormatError(Exception):
     """
 
 
 class FormatError(Exception):

-    """Base fmt: on/off error.
+    """Base exception for `# fmt: on` and `# fmt: off` handling.

 
     It holds the number of bytes of the prefix consumed before the format
     control comment appeared.
 
     It holds the number of bytes of the prefix consumed before the format
     control comment appeared.


@@ -165,6 +166,13 @@ 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
     tasks = {
         src: loop.run_in_executor(
             executor, format_file_in_place, src, line_length, fast, write_back


@@ -173,7 +181,7 @@ async def schedule_formatting(
     }
     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')
     for src, task in tasks.items():
         if not task.done():
             report.failed(src, 'timed out, cancelling')


@@ -193,7 +201,11 @@ 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 +224,11 @@ 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 +245,12 @@ 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 +265,10 @@ 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()


@@ -309,9 +333,18 @@ T = TypeVar('T')
 
 
 class Visitor(Generic[T]):
 
 
 class Visitor(Generic[T]):

-    """Basic lib2to3 visitor that yields things on visiting."""
+    """Basic lib2to3 visitor that yields things of type `T` on `visit()`."""

 
     def visit(self, node: LN) -> Iterator[T]:
 
     def visit(self, node: LN) -> Iterator[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.
+        If no dedicated `visit_*()` method is found, chooses `visit_default()`
+        instead.
+
+        Then yields objects of type `T` from the selected visitor.
+        """

         if node.type < 256:
             name = token.tok_name[node.type]
         else:
         if node.type < 256:
             name = token.tok_name[node.type]
         else:


@@ -319,6 +352,7 @@ class Visitor(Generic[T]):
         yield from getattr(self, f'visit_{name}', self.visit_default)(node)
 
     def visit_default(self, node: LN) -> Iterator[T]:
         yield from getattr(self, f'visit_{name}', self.visit_default)(node)
 
     def visit_default(self, node: LN) -> Iterator[T]:

+        """Default `visit_*()` implementation. Recurses to children of `node`."""

         if isinstance(node, Node):
             for child in node.children:
                 yield from self.visit(child)
         if isinstance(node, Node):
             for child in node.children:
                 yield from self.visit(child)


@@ -350,7 +384,7 @@ 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.
         """


@@ -406,12 +440,28 @@ MATH_PRIORITY = 1
 
 @dataclass
 class BracketTracker:
 
 @dataclass
 class BracketTracker:

+    """Keeps track of brackets on a line."""
+

     depth: int = 0
     bracket_match: Dict[Tuple[Depth, NodeType], Leaf] = Factory(dict)
     delimiters: Dict[LeafID, Priority] = Factory(dict)
     previous: Optional[Leaf] = None
 
     def mark(self, leaf: Leaf) -> 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:

+        """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
+        that started on this line.
+
+        If a leaf is itself a closing bracket, it receives an `opening_bracket`
+        field that it forms a pair with. This is a one-directional link to
+        avoid reference cycles.
+
+        If a leaf is a delimiter (a token on which Black can split the line if
+        needed) and it's on depth 0, its `id()` is stored in the tracker's
+        `delimiters` field.
+        """

         if leaf.type == token.COMMENT:
             return
 
         if leaf.type == token.COMMENT:
             return
 


@@ -453,11 +503,11 @@ 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)
 
         return bool(self.bracket_match)
 

-    def max_priority(self, exclude: Iterable[LeafID] = ()) -> int:
-        """Returns the highest priority of a delimiter found on the line.
+    def max_delimiter_priority(self, exclude: Iterable[LeafID] = ()) -> int:
+        """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.
         """


@@ -466,6 +516,8 @@ class BracketTracker:
 
 @dataclass
 class Line:
 
 @dataclass
 class Line:

+    """Holds leaves and comments. Can be printed with `str(line)`."""
+

     depth: int = 0
     leaves: List[Leaf] = Factory(list)
     comments: Dict[LeafID, Leaf] = Factory(dict)
     depth: int = 0
     leaves: List[Leaf] = Factory(list)
     comments: Dict[LeafID, Leaf] = Factory(dict)


@@ -475,6 +527,15 @@ class Line:
     _for_loop_variable: bool = False
 
     def append(self, leaf: Leaf, preformatted: bool = False) -> None:
     _for_loop_variable: bool = False
 
     def append(self, leaf: Leaf, preformatted: bool = False) -> None:

+        """Add a new `leaf` to the end of the line.
+
+        Unless `preformatted` is True, the `leaf` will receive a new consistent
+        whitespace prefix and metadata applied by :class:`BracketTracker`.
+        Trailing commas are maybe removed, unpacked for loop variables are
+        demoted from being delimiters.
+
+        Inline comments are put aside.
+        """

         has_value = leaf.value.strip()
         if not has_value:
             return
         has_value = leaf.value.strip()
         if not has_value:
             return


@@ -496,18 +557,22 @@ class Line:
 
     @property
     def is_comment(self) -> bool:
 
     @property
     def is_comment(self) -> bool:

+        """Is this line a standalone comment?"""

         return bool(self) and self.leaves[0].type == STANDALONE_COMMENT
 
     @property
     def is_decorator(self) -> bool:
         return bool(self) and self.leaves[0].type == STANDALONE_COMMENT
 
     @property
     def is_decorator(self) -> bool:

+        """Is this line a decorator?"""

         return bool(self) and self.leaves[0].type == token.AT
 
     @property
     def is_import(self) -> bool:
         return bool(self) and self.leaves[0].type == token.AT
 
     @property
     def is_import(self) -> bool:

+        """Is this an import line?"""

         return bool(self) and is_import(self.leaves[0])
 
     @property
     def is_class(self) -> bool:
         return bool(self) and is_import(self.leaves[0])
 
     @property
     def is_class(self) -> bool:

+        """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


@@ -516,7 +581,7 @@ class Line:
 
     @property
     def is_def(self) -> bool:
 
     @property
     def is_def(self) -> bool:

-        """Also returns True for async defs."""
+        """Is this a function definition? (Also returns True for async defs.)"""

         try:
             first_leaf = self.leaves[0]
         except IndexError:
         try:
             first_leaf = self.leaves[0]
         except IndexError:


@@ -538,6 +603,10 @@ class Line:
 
     @property
     def is_flow_control(self) -> bool:
 
     @property
     def is_flow_control(self) -> bool:

+        """Is this line a flow control statement?
+
+        Those are `return`, `raise`, `break`, and `continue`.
+        """

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


@@ -546,6 +615,7 @@ class Line:
 
     @property
     def is_yield(self) -> bool:
 
     @property
     def is_yield(self) -> bool:

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

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


@@ -553,6 +623,7 @@ class Line:
         )
 
     def maybe_remove_trailing_comma(self, closing: Leaf) -> bool:
         )
 
     def maybe_remove_trailing_comma(self, closing: Leaf) -> bool:

+        """Remove trailing comma if there is one and it's safe."""

         if not (
             self.leaves
             and self.leaves[-1].type == token.COMMA
         if not (
             self.leaves
             and self.leaves[-1].type == token.COMMA


@@ -603,8 +674,8 @@ 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


@@ -615,7 +686,7 @@ class Line:
         return False
 
     def maybe_decrement_after_for_loop_variable(self, leaf: Leaf) -> bool:
         return False
 
     def maybe_decrement_after_for_loop_variable(self, leaf: Leaf) -> bool:

-        # See `maybe_increment_for_loop_variable` above for explanation.
+        """See `maybe_increment_for_loop_variable` above for explanation."""

         if self._for_loop_variable and leaf.type == token.NAME and leaf.value == 'in':
             self.bracket_tracker.depth -= 1
             self._for_loop_variable = False
         if self._for_loop_variable and leaf.type == token.NAME and leaf.value == 'in':
             self.bracket_tracker.depth -= 1
             self._for_loop_variable = False


@@ -643,6 +714,7 @@ class Line:
         return self.append_comment(comment)
 
     def append_comment(self, comment: Leaf) -> bool:
         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
 


@@ -661,6 +733,7 @@ class Line:
             return True
 
     def last_non_delimiter(self) -> Leaf:
             return True
 
     def last_non_delimiter(self) -> Leaf:

+        """Return the last non-delimiter on the line. Raise LookupError otherwise."""

         for i in range(len(self.leaves)):
             last = self.leaves[-i - 1]
             if not is_delimiter(last):
         for i in range(len(self.leaves)):
             last = self.leaves[-i - 1]
             if not is_delimiter(last):


@@ -669,6 +742,7 @@ class Line:
         raise LookupError("No non-delimiters found")
 
     def __str__(self) -> str:
         raise LookupError("No non-delimiters found")
 
     def __str__(self) -> str:

+        """Render the line."""

         if not self:
             return '\n'
 
         if not self:
             return '\n'
 


@@ -683,12 +757,21 @@ class Line:
         return res + '\n'
 
     def __bool__(self) -> bool:
         return res + '\n'
 
     def __bool__(self) -> bool:

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

         return bool(self.leaves or self.comments)
 
 
 class UnformattedLines(Line):
         return bool(self.leaves or self.comments)
 
 
 class UnformattedLines(Line):

+    """Just like :class:`Line` but stores lines which aren't reformatted."""

 
 

-    def append(self, leaf: Leaf, preformatted: bool = False) -> None:
+    def append(self, leaf: Leaf, preformatted: bool = True) -> None:
+        """Just add a new `leaf` to the end of the lines.
+
+        The `preformatted` argument is ignored.
+
+        Keeps track of indentation `depth`, which is useful when the user
+        says `# fmt: on`. Otherwise, doesn't do anything with the `leaf`.
+        """

         try:
             list(generate_comments(leaf))
         except FormatOn as f_on:
         try:
             list(generate_comments(leaf))
         except FormatOn as f_on:


@@ -701,27 +784,35 @@ class UnformattedLines(Line):
         elif leaf.type == token.DEDENT:
             self.depth -= 1
 
         elif leaf.type == token.DEDENT:
             self.depth -= 1
 

+    def __str__(self) -> str:
+        """Render unformatted lines from leaves which were added with `append()`.
+
+        `depth` is not used for indentation in this case.
+        """
+        if not self:
+            return '\n'
+
+        res = ''
+        for leaf in self.leaves:
+            res += str(leaf)
+        return res
+

     def append_comment(self, comment: Leaf) -> bool:
     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:
         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:
         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:
         return False
 
     def maybe_adapt_standalone_comment(self, comment: Leaf) -> bool:

+        """Does nothing and returns False."""

         return False
 
         return False
 

-    def __str__(self) -> str:
-        if not self:
-            return '\n'
-
-        res = ''
-        for leaf in self.leaves:
-            res += str(leaf)
-        return res
-

 
 @dataclass
 class EmptyLineTracker:
 
 @dataclass
 class EmptyLineTracker:


@@ -737,11 +828,11 @@ 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


@@ -754,13 +845,13 @@ class EmptyLineTracker:
 
     def _maybe_empty_lines(self, current_line: Line) -> Tuple[int, int]:
         max_allowed = 1
 
     def _maybe_empty_lines(self, current_line: Line) -> Tuple[int, int]:
         max_allowed = 1

-        if current_line.is_comment and current_line.depth == 0:
+        if 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')
             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))
+            before = min(before, max_allowed)

             first_leaf.prefix = ''
         else:
             before = 0
             first_leaf.prefix = ''
         else:
             before = 0


@@ -835,7 +926,10 @@ class LineGenerator(Visitor[Line]):
         yield complete_line
 
     def visit(self, node: LN) -> Iterator[Line]:
         yield complete_line
 
     def visit(self, node: LN) -> Iterator[Line]:

-        """High-level entry point to the visitor."""
+        """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)


@@ -844,6 +938,7 @@ class LineGenerator(Visitor[Line]):
             yield from super().visit(node)
 
     def visit_default(self, node: LN) -> Iterator[Line]:
             yield from super().visit(node)
 
     def visit_default(self, node: LN) -> Iterator[Line]:

+        """Default `visit_*()` implementation. Recurses to children of `node`."""

         if isinstance(node, Leaf):
             any_open_brackets = self.current_line.bracket_tracker.any_open_brackets()
             try:
         if isinstance(node, Leaf):
             any_open_brackets = self.current_line.bracket_tracker.any_open_brackets()
             try:


@@ -881,18 +976,24 @@ 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]:

+        """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]:
         yield from self.line(+1)
         yield from self.visit_default(node)
 
     def visit_DEDENT(self, node: Node) -> Iterator[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]:
         """Visit a statement.
 
         # 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]:
         """Visit a statement.
 

-        The relevant Python language keywords for this statement are NAME leaves
-        within it.
+        This implementation is shared for `if`, `while`, `for`, `try`, `except`,
+        `def`, `with`, and `class`.
+
+        The relevant Python language `keywords` for a given statement will be NAME
+        leaves within it. This methods puts those on a separate line.

         """
         for child in node.children:
             if child.type == token.NAME and child.value in keywords:  # type: ignore
         """
         for child in node.children:
             if child.type == token.NAME and child.value in keywords:  # type: ignore


@@ -901,7 +1002,7 @@ 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]:

-        """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)


@@ -913,6 +1014,7 @@ 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]:

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

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


@@ -927,18 +1029,22 @@ 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]:

+        """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]:

+        """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."""

         yield from self.visit_default(leaf)
         yield from self.line()
 
     def visit_unformatted(self, node: LN) -> Iterator[Line]:
         yield from self.visit_default(leaf)
         yield from self.line()
 
     def visit_unformatted(self, node: LN) -> Iterator[Line]:

+        """Used when file contained a `# fmt: off`."""

         if isinstance(node, Node):
             for child in node.children:
                 yield from self.visit(child)
         if isinstance(node, Node):
             for child in node.children:
                 yield from self.visit(child)


@@ -1211,7 +1317,7 @@ 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:


@@ -1229,7 +1335,7 @@ 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.
     """


@@ -1250,7 +1356,7 @@ 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


@@ -1302,6 +1408,13 @@ def generate_comments(leaf: Leaf) -> Iterator[Leaf]:
 
 
 def make_comment(content: str) -> str:
 
 
 def make_comment(content: str) -> str:

+    """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.
+
+    If `content` didn't start with a hash sign, one is provided.
+    """

     content = content.rstrip()
     if not content:
         return '#'
     content = content.rstrip()
     if not content:
         return '#'


@@ -1316,7 +1429,7 @@ 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


@@ -1407,7 +1520,7 @@ 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)

-    split_succeeded_or_raise(head, body, tail)
+    bracket_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


@@ -1447,13 +1560,26 @@ 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)

-    split_succeeded_or_raise(head, body, tail)
+    bracket_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
 
 

-def split_succeeded_or_raise(head: Line, body: Line, tail: Line) -> None:
+def bracket_split_succeeded_or_raise(head: Line, body: Line, tail: Line) -> None:
+    """Raise :exc:`CannotSplit` if the last left- or right-hand split failed.
+
+    Do nothing otherwise.
+
+    A left- or right-hand split is based on a pair of brackets. Content before
+    (and including) the opening bracket is left on one line, content inside the
+    brackets is put on a separate line, and finally content starting with and
+    following the closing bracket is put on a separate line.
+
+    Those are called `head`, `body`, and `tail`, respectively. If the split
+    produced the same line (all content in `head`) or ended up with an empty `body`
+    and the `tail` is just the closing bracket, then it's considered failed.
+    """

     tail_len = len(str(tail).strip())
     if not body:
         if tail_len == 0:
     tail_len = len(str(tail).strip())
     if not body:
         if tail_len == 0:


@@ -1471,7 +1597,7 @@ def delimiter_split(line: Line, py36: bool = False) -> Iterator[Line]:
 
     This kind of split doesn't increase indentation.
     If `py36` is True, the split will add trailing commas also in function
 
     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 **.
+    signatures that contain `*` and `**`.

     """
     try:
         last_leaf = line.leaves[-1]
     """
     try:
         last_leaf = line.leaves[-1]


@@ -1480,7 +1606,9 @@ def delimiter_split(line: Line, py36: bool = False) -> Iterator[Line]:
 
     delimiters = line.bracket_tracker.delimiters
     try:
 
     delimiters = line.bracket_tracker.delimiters
     try:

-        delimiter_priority = line.bracket_tracker.max_priority(exclude={id(last_leaf)})
+        delimiter_priority = line.bracket_tracker.max_delimiter_priority(
+            exclude={id(last_leaf)}
+        )

     except ValueError:
         raise CannotSplit("No delimiters found")
 
     except ValueError:
         raise CannotSplit("No delimiters found")
 


@@ -1517,7 +1645,7 @@ def delimiter_split(line: Line, py36: bool = False) -> Iterator[Line]:
 
 
 def is_import(leaf: Leaf) -> bool:
 
 
 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


@@ -1531,10 +1659,10 @@ def is_import(leaf: Leaf) -> bool:
 
 
 def normalize_prefix(leaf: Leaf, *, inside_brackets: bool) -> None:
 
 
 def normalize_prefix(leaf: Leaf, *, inside_brackets: bool) -> None:

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

 
 

-    Remove 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('#')


@@ -1549,7 +1677,7 @@ 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


@@ -1580,6 +1708,9 @@ BLACKLISTED_DIRECTORIES = {
 
 
 def gen_python_files_in_dir(path: Path) -> Iterator[Path]:
 
 
 def gen_python_files_in_dir(path: Path) -> Iterator[Path]:

+    """Generate all files under `path` which aren't under BLACKLISTED_DIRECTORIES
+    and have one of the PYTHON_EXTENSIONS.
+    """

     for child in path.iterdir():
         if child.is_dir():
             if child.name in BLACKLISTED_DIRECTORIES:
     for child in path.iterdir():
         if child.is_dir():
             if child.name in BLACKLISTED_DIRECTORIES:


@@ -1593,7 +1724,7 @@ def gen_python_files_in_dir(path: Path) -> Iterator[Path]:
 
 @dataclass
 class Report:
 
 @dataclass
 class Report:

-    """Provides a reformatting counter."""
+    """Provides a reformatting counter. Can be rendered with `str(report)`."""

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


@@ -1616,7 +1747,13 @@ 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:


@@ -1628,7 +1765,7 @@ 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.
         """


@@ -1658,10 +1795,7 @@ 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


@@ -1724,10 +1858,7 @@ 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(


@@ -1743,7 +1874,7 @@ 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(


@@ -1756,7 +1887,7 @@ 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')]