X-Git-Url: https://git.madduck.net/etc/vim.git/blobdiff_plain/3f68af9813542a5e277b7a51b316644241c372d7..dc71922c768e543c9c3bbb1db5ea6d7fa801a814:/.vim/bundle/black/src/black/linegen.py?ds=sidebyside

diff --git a/.vim/bundle/black/src/black/linegen.py b/.vim/bundle/black/src/black/linegen.py
new file mode 100644
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+++ b/.vim/bundle/black/src/black/linegen.py
@@ -0,0 +1,1004 @@
+"""
+Generating lines of code.
+"""
+from functools import partial, wraps
+import sys
+from typing import Collection, Iterator, List, Optional, Set, Union
+
+from dataclasses import dataclass, field
+
+from black.nodes import WHITESPACE, RARROW, STATEMENT, STANDALONE_COMMENT
+from black.nodes import ASSIGNMENTS, OPENING_BRACKETS, CLOSING_BRACKETS
+from black.nodes import Visitor, syms, first_child_is_arith, ensure_visible
+from black.nodes import is_docstring, is_empty_tuple, is_one_tuple, is_one_tuple_between
+from black.nodes import is_walrus_assignment, is_yield, is_vararg, is_multiline_string
+from black.nodes import is_stub_suite, is_stub_body, is_atom_with_invisible_parens
+from black.nodes import wrap_in_parentheses
+from black.brackets import max_delimiter_priority_in_atom
+from black.brackets import DOT_PRIORITY, COMMA_PRIORITY
+from black.lines import Line, line_to_string, is_line_short_enough
+from black.lines import can_omit_invisible_parens, can_be_split, append_leaves
+from black.comments import generate_comments, list_comments, FMT_OFF
+from black.numerics import normalize_numeric_literal
+from black.strings import get_string_prefix, fix_docstring
+from black.strings import normalize_string_prefix, normalize_string_quotes
+from black.trans import Transformer, CannotTransform, StringMerger
+from black.trans import StringSplitter, StringParenWrapper, StringParenStripper
+from black.mode import Mode
+from black.mode import Feature
+
+from blib2to3.pytree import Node, Leaf
+from blib2to3.pgen2 import token
+
+
+# types
+LeafID = int
+LN = Union[Leaf, Node]
+
+
+class CannotSplit(CannotTransform):
+    """A readable split that fits the allotted line length is impossible."""
+
+
+@dataclass
+class LineGenerator(Visitor[Line]):
+    """Generates reformatted Line objects.  Empty lines are not emitted.
+
+    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.
+    """
+
+    mode: Mode
+    remove_u_prefix: bool = False
+    current_line: Line = field(init=False)
+
+    def line(self, indent: int = 0) -> Iterator[Line]:
+        """Generate a line.
+
+        If the line is empty, only emit if it makes sense.
+        If the line is too long, split it first and then generate.
+
+        If any lines were generated, set up a new current_line.
+        """
+        if not self.current_line:
+            self.current_line.depth += indent
+            return  # Line is empty, don't emit. Creating a new one unnecessary.
+
+        complete_line = self.current_line
+        self.current_line = Line(mode=self.mode, depth=complete_line.depth + indent)
+        yield complete_line
+
+    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()
+            for comment in generate_comments(node):
+                if any_open_brackets:
+                    # any comment within brackets is subject to splitting
+                    self.current_line.append(comment)
+                elif comment.type == token.COMMENT:
+                    # regular trailing comment
+                    self.current_line.append(comment)
+                    yield from self.line()
+
+                else:
+                    # regular standalone comment
+                    yield from self.line()
+
+                    self.current_line.append(comment)
+                    yield from self.line()
+
+            normalize_prefix(node, inside_brackets=any_open_brackets)
+            if self.mode.string_normalization and node.type == token.STRING:
+                node.value = normalize_string_prefix(
+                    node.value, remove_u_prefix=self.remove_u_prefix
+                )
+                node.value = normalize_string_quotes(node.value)
+            if node.type == token.NUMBER:
+                normalize_numeric_literal(node)
+            if node.type not in WHITESPACE:
+                self.current_line.append(node)
+        yield from super().visit_default(node)
+
+    def visit_INDENT(self, node: Leaf) -> Iterator[Line]:
+        """Increase indentation level, maybe yield a line."""
+        # In blib2to3 INDENT never holds comments.
+        yield from self.line(+1)
+        yield from self.visit_default(node)
+
+    def visit_DEDENT(self, node: Leaf) -> Iterator[Line]:
+        """Decrease indentation level, maybe yield a line."""
+        # The current line might still wait for trailing comments.  At DEDENT time
+        # there won't be any (they would be prefixes on the preceding NEWLINE).
+        # Emit the line then.
+        yield from self.line()
+
+        # While DEDENT has no value, its prefix may contain standalone comments
+        # that belong to the current indentation level.  Get 'em.
+        yield from self.visit_default(node)
+
+        # Finally, emit the dedent.
+        yield from self.line(-1)
+
+    def visit_stmt(
+        self, node: Node, keywords: Set[str], parens: Set[str]
+    ) -> Iterator[Line]:
+        """Visit a statement.
+
+        This implementation is shared for `if`, `while`, `for`, `try`, `except`,
+        `def`, `with`, `class`, `assert` and assignments.
+
+        The relevant Python language `keywords` for a given statement will be
+        NAME leaves within it. This methods puts those on a separate line.
+
+        `parens` holds a set of string leaf values immediately after which
+        invisible parens should be put.
+        """
+        normalize_invisible_parens(node, parens_after=parens)
+        for child in node.children:
+            if child.type == token.NAME and child.value in keywords:  # type: ignore
+                yield from self.line()
+
+            yield from self.visit(child)
+
+    def visit_suite(self, node: Node) -> Iterator[Line]:
+        """Visit a suite."""
+        if self.mode.is_pyi and is_stub_suite(node):
+            yield from self.visit(node.children[2])
+        else:
+            yield from self.visit_default(node)
+
+    def visit_simple_stmt(self, node: Node) -> Iterator[Line]:
+        """Visit a statement without nested statements."""
+        if first_child_is_arith(node):
+            wrap_in_parentheses(node, node.children[0], visible=False)
+        is_suite_like = node.parent and node.parent.type in STATEMENT
+        if is_suite_like:
+            if self.mode.is_pyi and is_stub_body(node):
+                yield from self.visit_default(node)
+            else:
+                yield from self.line(+1)
+                yield from self.visit_default(node)
+                yield from self.line(-1)
+
+        else:
+            if (
+                not self.mode.is_pyi
+                or not node.parent
+                or not is_stub_suite(node.parent)
+            ):
+                yield from self.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)
+        for child in children:
+            yield from self.visit(child)
+
+            if child.type == token.ASYNC:
+                break
+
+        internal_stmt = next(children)
+        for child in internal_stmt.children:
+            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]:
+        """Remove a semicolon and put the other statement on a separate 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_STANDALONE_COMMENT(self, leaf: Leaf) -> Iterator[Line]:
+        if not self.current_line.bracket_tracker.any_open_brackets():
+            yield from self.line()
+        yield from self.visit_default(leaf)
+
+    def visit_factor(self, node: Node) -> Iterator[Line]:
+        """Force parentheses between a unary op and a binary power:
+
+        -2 ** 8 -> -(2 ** 8)
+        """
+        _operator, operand = node.children
+        if (
+            operand.type == syms.power
+            and len(operand.children) == 3
+            and operand.children[1].type == token.DOUBLESTAR
+        ):
+            lpar = Leaf(token.LPAR, "(")
+            rpar = Leaf(token.RPAR, ")")
+            index = operand.remove() or 0
+            node.insert_child(index, Node(syms.atom, [lpar, operand, rpar]))
+        yield from self.visit_default(node)
+
+    def visit_STRING(self, leaf: Leaf) -> Iterator[Line]:
+        if is_docstring(leaf) and "\\\n" not in leaf.value:
+            # We're ignoring docstrings with backslash newline escapes because changing
+            # indentation of those changes the AST representation of the code.
+            docstring = normalize_string_prefix(leaf.value, self.remove_u_prefix)
+            prefix = get_string_prefix(docstring)
+            docstring = docstring[len(prefix) :]  # Remove the prefix
+            quote_char = docstring[0]
+            # A natural way to remove the outer quotes is to do:
+            #   docstring = docstring.strip(quote_char)
+            # but that breaks on """""x""" (which is '""x').
+            # So we actually need to remove the first character and the next two
+            # characters but only if they are the same as the first.
+            quote_len = 1 if docstring[1] != quote_char else 3
+            docstring = docstring[quote_len:-quote_len]
+            docstring_started_empty = not docstring
+
+            if is_multiline_string(leaf):
+                indent = " " * 4 * self.current_line.depth
+                docstring = fix_docstring(docstring, indent)
+            else:
+                docstring = docstring.strip()
+
+            if docstring:
+                # Add some padding if the docstring starts / ends with a quote mark.
+                if docstring[0] == quote_char:
+                    docstring = " " + docstring
+                if docstring[-1] == quote_char:
+                    docstring += " "
+                if docstring[-1] == "\\":
+                    backslash_count = len(docstring) - len(docstring.rstrip("\\"))
+                    if backslash_count % 2:
+                        # Odd number of tailing backslashes, add some padding to
+                        # avoid escaping the closing string quote.
+                        docstring += " "
+            elif not docstring_started_empty:
+                docstring = " "
+
+            # We could enforce triple quotes at this point.
+            quote = quote_char * quote_len
+            leaf.value = prefix + quote + docstring + quote
+
+        yield from self.visit_default(leaf)
+
+    def __post_init__(self) -> None:
+        """You are in a twisty little maze of passages."""
+        self.current_line = Line(mode=self.mode)
+
+        v = self.visit_stmt
+        Ø: Set[str] = set()
+        self.visit_assert_stmt = partial(v, keywords={"assert"}, parens={"assert", ","})
+        self.visit_if_stmt = partial(
+            v, keywords={"if", "else", "elif"}, parens={"if", "elif"}
+        )
+        self.visit_while_stmt = partial(v, keywords={"while", "else"}, parens={"while"})
+        self.visit_for_stmt = partial(v, keywords={"for", "else"}, parens={"for", "in"})
+        self.visit_try_stmt = partial(
+            v, keywords={"try", "except", "else", "finally"}, parens=Ø
+        )
+        self.visit_except_clause = partial(v, keywords={"except"}, parens=Ø)
+        self.visit_with_stmt = partial(v, keywords={"with"}, parens=Ø)
+        self.visit_funcdef = partial(v, keywords={"def"}, parens=Ø)
+        self.visit_classdef = partial(v, keywords={"class"}, parens=Ø)
+        self.visit_expr_stmt = partial(v, keywords=Ø, parens=ASSIGNMENTS)
+        self.visit_return_stmt = partial(v, keywords={"return"}, parens={"return"})
+        self.visit_import_from = partial(v, keywords=Ø, parens={"import"})
+        self.visit_del_stmt = partial(v, keywords=Ø, parens={"del"})
+        self.visit_async_funcdef = self.visit_async_stmt
+        self.visit_decorated = self.visit_decorators
+
+
+def transform_line(
+    line: Line, mode: Mode, features: Collection[Feature] = ()
+) -> Iterator[Line]:
+    """Transform a `line`, potentially splitting it into many lines.
+
+    They should fit in the allotted `line_length` but might not be able to.
+
+    `features` are syntactical features that may be used in the output.
+    """
+    if line.is_comment:
+        yield line
+        return
+
+    line_str = line_to_string(line)
+
+    ll = mode.line_length
+    sn = mode.string_normalization
+    string_merge = StringMerger(ll, sn)
+    string_paren_strip = StringParenStripper(ll, sn)
+    string_split = StringSplitter(ll, sn)
+    string_paren_wrap = StringParenWrapper(ll, sn)
+
+    transformers: List[Transformer]
+    if (
+        not line.contains_uncollapsable_type_comments()
+        and not line.should_split_rhs
+        and not line.magic_trailing_comma
+        and (
+            is_line_short_enough(line, line_length=mode.line_length, line_str=line_str)
+            or line.contains_unsplittable_type_ignore()
+        )
+        and not (line.inside_brackets and line.contains_standalone_comments())
+    ):
+        # Only apply basic string preprocessing, since lines shouldn't be split here.
+        if mode.experimental_string_processing:
+            transformers = [string_merge, string_paren_strip]
+        else:
+            transformers = []
+    elif line.is_def:
+        transformers = [left_hand_split]
+    else:
+
+        def rhs(line: Line, features: Collection[Feature]) -> Iterator[Line]:
+            """Wraps calls to `right_hand_split`.
+
+            The calls increasingly `omit` right-hand trailers (bracket pairs with
+            content), meaning the trailers get glued together to split on another
+            bracket pair instead.
+            """
+            for omit in generate_trailers_to_omit(line, mode.line_length):
+                lines = list(
+                    right_hand_split(line, mode.line_length, features, omit=omit)
+                )
+                # Note: this check is only able to figure out if the first line of the
+                # *current* transformation fits in the line length.  This is true only
+                # for simple cases.  All others require running more transforms via
+                # `transform_line()`.  This check doesn't know if those would succeed.
+                if is_line_short_enough(lines[0], line_length=mode.line_length):
+                    yield from lines
+                    return
+
+            # All splits failed, best effort split with no omits.
+            # This mostly happens to multiline strings that are by definition
+            # reported as not fitting a single line, as well as lines that contain
+            # trailing commas (those have to be exploded).
+            yield from right_hand_split(
+                line, line_length=mode.line_length, features=features
+            )
+
+        if mode.experimental_string_processing:
+            if line.inside_brackets:
+                transformers = [
+                    string_merge,
+                    string_paren_strip,
+                    string_split,
+                    delimiter_split,
+                    standalone_comment_split,
+                    string_paren_wrap,
+                    rhs,
+                ]
+            else:
+                transformers = [
+                    string_merge,
+                    string_paren_strip,
+                    string_split,
+                    string_paren_wrap,
+                    rhs,
+                ]
+        else:
+            if line.inside_brackets:
+                transformers = [delimiter_split, standalone_comment_split, rhs]
+            else:
+                transformers = [rhs]
+
+    for transform in transformers:
+        # We are accumulating lines in `result` because we might want to abort
+        # mission and return the original line in the end, or attempt a different
+        # split altogether.
+        try:
+            result = run_transformer(line, transform, mode, features, line_str=line_str)
+        except CannotTransform:
+            continue
+        else:
+            yield from result
+            break
+
+    else:
+        yield line
+
+
+def left_hand_split(line: Line, _features: Collection[Feature] = ()) -> Iterator[Line]:
+    """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.  This is why this function is not symmetrical with
+    :func:`right_hand_split` which also handles optional parentheses.
+    """
+    tail_leaves: List[Leaf] = []
+    body_leaves: List[Leaf] = []
+    head_leaves: List[Leaf] = []
+    current_leaves = head_leaves
+    matching_bracket: Optional[Leaf] = 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 = tail_leaves if body_leaves else head_leaves
+        current_leaves.append(leaf)
+        if current_leaves is head_leaves:
+            if leaf.type in OPENING_BRACKETS:
+                matching_bracket = leaf
+                current_leaves = body_leaves
+    if not matching_bracket:
+        raise CannotSplit("No brackets found")
+
+    head = bracket_split_build_line(head_leaves, line, matching_bracket)
+    body = bracket_split_build_line(body_leaves, line, matching_bracket, is_body=True)
+    tail = bracket_split_build_line(tail_leaves, line, matching_bracket)
+    bracket_split_succeeded_or_raise(head, body, tail)
+    for result in (head, body, tail):
+        if result:
+            yield result
+
+
+def right_hand_split(
+    line: Line,
+    line_length: int,
+    features: Collection[Feature] = (),
+    omit: Collection[LeafID] = (),
+) -> Iterator[Line]:
+    """Split line into many lines, starting with the last matching bracket pair.
+
+    If the split was by optional parentheses, attempt splitting without them, too.
+    `omit` is a collection of closing bracket IDs that shouldn't be considered for
+    this split.
+
+    Note: running this function modifies `bracket_depth` on the leaves of `line`.
+    """
+    tail_leaves: List[Leaf] = []
+    body_leaves: List[Leaf] = []
+    head_leaves: List[Leaf] = []
+    current_leaves = tail_leaves
+    opening_bracket: Optional[Leaf] = None
+    closing_bracket: Optional[Leaf] = None
+    for leaf in reversed(line.leaves):
+        if current_leaves is body_leaves:
+            if leaf is opening_bracket:
+                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 and id(leaf) not in omit:
+                opening_bracket = leaf.opening_bracket
+                closing_bracket = leaf
+                current_leaves = body_leaves
+    if not (opening_bracket and closing_bracket and head_leaves):
+        # If there is no opening or closing_bracket that means the split failed and
+        # all content is in the tail.  Otherwise, if `head_leaves` are empty, it means
+        # the matching `opening_bracket` wasn't available on `line` anymore.
+        raise CannotSplit("No brackets found")
+
+    tail_leaves.reverse()
+    body_leaves.reverse()
+    head_leaves.reverse()
+    head = bracket_split_build_line(head_leaves, line, opening_bracket)
+    body = bracket_split_build_line(body_leaves, line, opening_bracket, is_body=True)
+    tail = bracket_split_build_line(tail_leaves, line, opening_bracket)
+    bracket_split_succeeded_or_raise(head, body, tail)
+    if (
+        Feature.FORCE_OPTIONAL_PARENTHESES not in features
+        # the opening bracket is an optional paren
+        and opening_bracket.type == token.LPAR
+        and not opening_bracket.value
+        # the closing bracket is an optional paren
+        and closing_bracket.type == token.RPAR
+        and not closing_bracket.value
+        # it's not an import (optional parens are the only thing we can split on
+        # in this case; attempting a split without them is a waste of time)
+        and not line.is_import
+        # there are no standalone comments in the body
+        and not body.contains_standalone_comments(0)
+        # and we can actually remove the parens
+        and can_omit_invisible_parens(body, line_length, omit_on_explode=omit)
+    ):
+        omit = {id(closing_bracket), *omit}
+        try:
+            yield from right_hand_split(line, line_length, features=features, omit=omit)
+            return
+
+        except CannotSplit as e:
+            if not (
+                can_be_split(body)
+                or is_line_short_enough(body, line_length=line_length)
+            ):
+                raise CannotSplit(
+                    "Splitting failed, body is still too long and can't be split."
+                ) from e
+
+            elif head.contains_multiline_strings() or tail.contains_multiline_strings():
+                raise CannotSplit(
+                    "The current optional pair of parentheses is bound to fail to"
+                    " satisfy the splitting algorithm because the head or the tail"
+                    " contains multiline strings which by definition never fit one"
+                    " line."
+                ) from e
+
+    ensure_visible(opening_bracket)
+    ensure_visible(closing_bracket)
+    for result in (head, body, tail):
+        if result:
+            yield result
+
+
+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:
+            raise CannotSplit("Splitting brackets produced the same line")
+
+        elif tail_len < 3:
+            raise CannotSplit(
+                f"Splitting brackets on an empty body to save {tail_len} characters is"
+                " not worth it"
+            )
+
+
+def bracket_split_build_line(
+    leaves: List[Leaf], original: Line, opening_bracket: Leaf, *, is_body: bool = False
+) -> Line:
+    """Return a new line with given `leaves` and respective comments from `original`.
+
+    If `is_body` is True, the result line is one-indented inside brackets and as such
+    has its first leaf's prefix normalized and a trailing comma added when expected.
+    """
+    result = Line(mode=original.mode, depth=original.depth)
+    if is_body:
+        result.inside_brackets = True
+        result.depth += 1
+        if leaves:
+            # Since body is a new indent level, remove spurious leading whitespace.
+            normalize_prefix(leaves[0], inside_brackets=True)
+            # Ensure a trailing comma for imports and standalone function arguments, but
+            # be careful not to add one after any comments or within type annotations.
+            no_commas = (
+                original.is_def
+                and opening_bracket.value == "("
+                and not any(leaf.type == token.COMMA for leaf in leaves)
+                # In particular, don't add one within a parenthesized return annotation.
+                # Unfortunately the indicator we're in a return annotation (RARROW) may
+                # be defined directly in the parent node, the parent of the parent ...
+                # and so on depending on how complex the return annotation is.
+                # This isn't perfect and there's some false negatives but they are in
+                # contexts were a comma is actually fine.
+                and not any(
+                    node.prev_sibling.type == RARROW
+                    for node in (
+                        leaves[0].parent,
+                        getattr(leaves[0].parent, "parent", None),
+                    )
+                    if isinstance(node, Node) and isinstance(node.prev_sibling, Leaf)
+                )
+            )
+
+            if original.is_import or no_commas:
+                for i in range(len(leaves) - 1, -1, -1):
+                    if leaves[i].type == STANDALONE_COMMENT:
+                        continue
+
+                    if leaves[i].type != token.COMMA:
+                        new_comma = Leaf(token.COMMA, ",")
+                        leaves.insert(i + 1, new_comma)
+                    break
+
+    # Populate the line
+    for leaf in leaves:
+        result.append(leaf, preformatted=True)
+        for comment_after in original.comments_after(leaf):
+            result.append(comment_after, preformatted=True)
+    if is_body and should_split_line(result, opening_bracket):
+        result.should_split_rhs = True
+    return result
+
+
+def dont_increase_indentation(split_func: Transformer) -> Transformer:
+    """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, features: Collection[Feature] = ()) -> Iterator[Line]:
+        for line in split_func(line, features):
+            normalize_prefix(line.leaves[0], inside_brackets=True)
+            yield line
+
+    return split_wrapper
+
+
+@dont_increase_indentation
+def delimiter_split(line: Line, features: Collection[Feature] = ()) -> Iterator[Line]:
+    """Split according to delimiters of the highest priority.
+
+    If the appropriate Features are given, the split will add trailing commas
+    also in function signatures and calls that contain `*` and `**`.
+    """
+    try:
+        last_leaf = line.leaves[-1]
+    except IndexError:
+        raise CannotSplit("Line empty") from None
+
+    bt = line.bracket_tracker
+    try:
+        delimiter_priority = bt.max_delimiter_priority(exclude={id(last_leaf)})
+    except ValueError:
+        raise CannotSplit("No delimiters found") from None
+
+    if delimiter_priority == DOT_PRIORITY:
+        if bt.delimiter_count_with_priority(delimiter_priority) == 1:
+            raise CannotSplit("Splitting a single attribute from its owner looks wrong")
+
+    current_line = Line(
+        mode=line.mode, 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:
+            yield current_line
+
+            current_line = Line(
+                mode=line.mode, 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)
+
+        lowest_depth = min(lowest_depth, leaf.bracket_depth)
+        if leaf.bracket_depth == lowest_depth:
+            if is_vararg(leaf, within={syms.typedargslist}):
+                trailing_comma_safe = (
+                    trailing_comma_safe and Feature.TRAILING_COMMA_IN_DEF in features
+                )
+            elif is_vararg(leaf, within={syms.arglist, syms.argument}):
+                trailing_comma_safe = (
+                    trailing_comma_safe and Feature.TRAILING_COMMA_IN_CALL in features
+                )
+
+        leaf_priority = bt.delimiters.get(id(leaf))
+        if leaf_priority == delimiter_priority:
+            yield current_line
+
+            current_line = Line(
+                mode=line.mode, depth=line.depth, inside_brackets=line.inside_brackets
+            )
+    if current_line:
+        if (
+            trailing_comma_safe
+            and delimiter_priority == COMMA_PRIORITY
+            and current_line.leaves[-1].type != token.COMMA
+            and current_line.leaves[-1].type != STANDALONE_COMMENT
+        ):
+            new_comma = Leaf(token.COMMA, ",")
+            current_line.append(new_comma)
+        yield current_line
+
+
+@dont_increase_indentation
+def standalone_comment_split(
+    line: Line, features: Collection[Feature] = ()
+) -> Iterator[Line]:
+    """Split standalone comments from the rest of the line."""
+    if not line.contains_standalone_comments(0):
+        raise CannotSplit("Line does not have any standalone comments")
+
+    current_line = Line(
+        mode=line.mode, 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:
+            yield current_line
+
+            current_line = Line(
+                line.mode, 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 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 = ""
+
+
+def normalize_invisible_parens(node: Node, parens_after: Set[str]) -> None:
+    """Make existing optional parentheses invisible or create new ones.
+
+    `parens_after` is a set of string leaf values immediately after which parens
+    should be put.
+
+    Standardizes on visible parentheses for single-element tuples, and keeps
+    existing visible parentheses for other tuples and generator expressions.
+    """
+    for pc in list_comments(node.prefix, is_endmarker=False):
+        if pc.value in FMT_OFF:
+            # This `node` has a prefix with `# fmt: off`, don't mess with parens.
+            return
+    check_lpar = False
+    for index, child in enumerate(list(node.children)):
+        # Fixes a bug where invisible parens are not properly stripped from
+        # assignment statements that contain type annotations.
+        if isinstance(child, Node) and child.type == syms.annassign:
+            normalize_invisible_parens(child, parens_after=parens_after)
+
+        # Add parentheses around long tuple unpacking in assignments.
+        if (
+            index == 0
+            and isinstance(child, Node)
+            and child.type == syms.testlist_star_expr
+        ):
+            check_lpar = True
+
+        if check_lpar:
+            if child.type == syms.atom:
+                if maybe_make_parens_invisible_in_atom(child, parent=node):
+                    wrap_in_parentheses(node, child, visible=False)
+            elif is_one_tuple(child):
+                wrap_in_parentheses(node, child, visible=True)
+            elif node.type == syms.import_from:
+                # "import from" nodes store parentheses directly as part of
+                # the statement
+                if child.type == token.LPAR:
+                    # make parentheses invisible
+                    child.value = ""  # type: ignore
+                    node.children[-1].value = ""  # type: ignore
+                elif child.type != token.STAR:
+                    # insert invisible parentheses
+                    node.insert_child(index, Leaf(token.LPAR, ""))
+                    node.append_child(Leaf(token.RPAR, ""))
+                break
+
+            elif not (isinstance(child, Leaf) and is_multiline_string(child)):
+                wrap_in_parentheses(node, child, visible=False)
+
+        check_lpar = isinstance(child, Leaf) and child.value in parens_after
+
+
+def maybe_make_parens_invisible_in_atom(node: LN, parent: LN) -> bool:
+    """If it's safe, make the parens in the atom `node` invisible, recursively.
+    Additionally, remove repeated, adjacent invisible parens from the atom `node`
+    as they are redundant.
+
+    Returns whether the node should itself be wrapped in invisible parentheses.
+
+    """
+
+    if (
+        node.type != syms.atom
+        or is_empty_tuple(node)
+        or is_one_tuple(node)
+        or (is_yield(node) and parent.type != syms.expr_stmt)
+        or max_delimiter_priority_in_atom(node) >= COMMA_PRIORITY
+    ):
+        return False
+
+    if is_walrus_assignment(node):
+        if parent.type in [
+            syms.annassign,
+            syms.expr_stmt,
+            syms.assert_stmt,
+            syms.return_stmt,
+            # these ones aren't useful to end users, but they do please fuzzers
+            syms.for_stmt,
+            syms.del_stmt,
+        ]:
+            return False
+
+    first = node.children[0]
+    last = node.children[-1]
+    if first.type == token.LPAR and last.type == token.RPAR:
+        middle = node.children[1]
+        # make parentheses invisible
+        first.value = ""  # type: ignore
+        last.value = ""  # type: ignore
+        maybe_make_parens_invisible_in_atom(middle, parent=parent)
+
+        if is_atom_with_invisible_parens(middle):
+            # Strip the invisible parens from `middle` by replacing
+            # it with the child in-between the invisible parens
+            middle.replace(middle.children[1])
+
+        return False
+
+    return True
+
+
+def should_split_line(line: Line, opening_bracket: Leaf) -> bool:
+    """Should `line` be immediately split with `delimiter_split()` after RHS?"""
+
+    if not (opening_bracket.parent and opening_bracket.value in "[{("):
+        return False
+
+    # We're essentially checking if the body is delimited by commas and there's more
+    # than one of them (we're excluding the trailing comma and if the delimiter priority
+    # is still commas, that means there's more).
+    exclude = set()
+    trailing_comma = False
+    try:
+        last_leaf = line.leaves[-1]
+        if last_leaf.type == token.COMMA:
+            trailing_comma = True
+            exclude.add(id(last_leaf))
+        max_priority = line.bracket_tracker.max_delimiter_priority(exclude=exclude)
+    except (IndexError, ValueError):
+        return False
+
+    return max_priority == COMMA_PRIORITY and (
+        (line.mode.magic_trailing_comma and trailing_comma)
+        # always explode imports
+        or opening_bracket.parent.type in {syms.atom, syms.import_from}
+    )
+
+
+def generate_trailers_to_omit(line: Line, line_length: int) -> Iterator[Set[LeafID]]:
+    """Generate sets of closing bracket IDs that should be omitted in a RHS.
+
+    Brackets can be omitted if the entire trailer up to and including
+    a preceding closing bracket fits in one line.
+
+    Yielded sets are cumulative (contain results of previous yields, too).  First
+    set is empty, unless the line should explode, in which case bracket pairs until
+    the one that needs to explode are omitted.
+    """
+
+    omit: Set[LeafID] = set()
+    if not line.magic_trailing_comma:
+        yield omit
+
+    length = 4 * line.depth
+    opening_bracket: Optional[Leaf] = None
+    closing_bracket: Optional[Leaf] = None
+    inner_brackets: Set[LeafID] = set()
+    for index, leaf, leaf_length in line.enumerate_with_length(reversed=True):
+        length += leaf_length
+        if length > line_length:
+            break
+
+        has_inline_comment = leaf_length > len(leaf.value) + len(leaf.prefix)
+        if leaf.type == STANDALONE_COMMENT or has_inline_comment:
+            break
+
+        if opening_bracket:
+            if leaf is opening_bracket:
+                opening_bracket = None
+            elif leaf.type in CLOSING_BRACKETS:
+                prev = line.leaves[index - 1] if index > 0 else None
+                if (
+                    prev
+                    and prev.type == token.COMMA
+                    and not is_one_tuple_between(
+                        leaf.opening_bracket, leaf, line.leaves
+                    )
+                ):
+                    # Never omit bracket pairs with trailing commas.
+                    # We need to explode on those.
+                    break
+
+                inner_brackets.add(id(leaf))
+        elif leaf.type in CLOSING_BRACKETS:
+            prev = line.leaves[index - 1] if index > 0 else None
+            if prev and prev.type in OPENING_BRACKETS:
+                # Empty brackets would fail a split so treat them as "inner"
+                # brackets (e.g. only add them to the `omit` set if another
+                # pair of brackets was good enough.
+                inner_brackets.add(id(leaf))
+                continue
+
+            if closing_bracket:
+                omit.add(id(closing_bracket))
+                omit.update(inner_brackets)
+                inner_brackets.clear()
+                yield omit
+
+            if (
+                prev
+                and prev.type == token.COMMA
+                and not is_one_tuple_between(leaf.opening_bracket, leaf, line.leaves)
+            ):
+                # Never omit bracket pairs with trailing commas.
+                # We need to explode on those.
+                break
+
+            if leaf.value:
+                opening_bracket = leaf.opening_bracket
+                closing_bracket = leaf
+
+
+def run_transformer(
+    line: Line,
+    transform: Transformer,
+    mode: Mode,
+    features: Collection[Feature],
+    *,
+    line_str: str = "",
+) -> List[Line]:
+    if not line_str:
+        line_str = line_to_string(line)
+    result: List[Line] = []
+    for transformed_line in transform(line, features):
+        if str(transformed_line).strip("\n") == line_str:
+            raise CannotTransform("Line transformer returned an unchanged result")
+
+        result.extend(transform_line(transformed_line, mode=mode, features=features))
+
+    if (
+        transform.__name__ != "rhs"
+        or not line.bracket_tracker.invisible
+        or any(bracket.value for bracket in line.bracket_tracker.invisible)
+        or line.contains_multiline_strings()
+        or result[0].contains_uncollapsable_type_comments()
+        or result[0].contains_unsplittable_type_ignore()
+        or is_line_short_enough(result[0], line_length=mode.line_length)
+        # If any leaves have no parents (which _can_ occur since
+        # `transform(line)` potentially destroys the line's underlying node
+        # structure), then we can't proceed. Doing so would cause the below
+        # call to `append_leaves()` to fail.
+        or any(leaf.parent is None for leaf in line.leaves)
+    ):
+        return result
+
+    line_copy = line.clone()
+    append_leaves(line_copy, line, line.leaves)
+    features_fop = set(features) | {Feature.FORCE_OPTIONAL_PARENTHESES}
+    second_opinion = run_transformer(
+        line_copy, transform, mode, features_fop, line_str=line_str
+    )
+    if all(
+        is_line_short_enough(ln, line_length=mode.line_length) for ln in second_opinion
+    ):
+        result = second_opinion
+    return result