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Fix unintentionally swapped words in index.md (#3809)
[etc/vim.git] / src / black / linegen.py
index 9c85e76d3e881c2a6afeda30285477a868d56a7a..5ef3bbd170578159249eb9f850676767a9bc1f56 100644 (file)
@@ -1,38 +1,80 @@
 """
 Generating lines of code.
 """
-from functools import partial, wraps
 import sys
-from typing import Collection, Iterator, List, Optional, Set, Union
+from dataclasses import replace
+from enum import Enum, auto
+from functools import partial, wraps
+from typing import Collection, Iterator, List, Optional, Set, Union, cast
 
-from black.nodes import WHITESPACE, RARROW, STATEMENT, STANDALONE_COMMENT
-from black.nodes import ASSIGNMENTS, OPENING_BRACKETS, CLOSING_BRACKETS
-from black.nodes import Visitor, syms, is_arith_like, ensure_visible
+from black.brackets import (
+    COMMA_PRIORITY,
+    DOT_PRIORITY,
+    get_leaves_inside_matching_brackets,
+    max_delimiter_priority_in_atom,
+)
+from black.comments import FMT_OFF, generate_comments, list_comments
+from black.lines import (
+    Line,
+    RHSResult,
+    append_leaves,
+    can_be_split,
+    can_omit_invisible_parens,
+    is_line_short_enough,
+    line_to_string,
+)
+from black.mode import Feature, Mode, Preview
 from black.nodes import (
+    ASSIGNMENTS,
+    BRACKETS,
+    CLOSING_BRACKETS,
+    OPENING_BRACKETS,
+    RARROW,
+    STANDALONE_COMMENT,
+    STATEMENT,
+    WHITESPACE,
+    Visitor,
+    ensure_visible,
+    is_arith_like,
+    is_async_stmt_or_funcdef,
+    is_atom_with_invisible_parens,
     is_docstring,
     is_empty_tuple,
-    is_one_tuple,
+    is_lpar_token,
+    is_multiline_string,
+    is_name_token,
     is_one_sequence_between,
+    is_one_tuple,
+    is_rpar_token,
+    is_stub_body,
+    is_stub_suite,
+    is_tuple_containing_walrus,
+    is_type_ignore_comment_string,
+    is_vararg,
+    is_walrus_assignment,
+    is_yield,
+    syms,
+    wrap_in_parentheses,
 )
-from black.nodes import is_name_token, is_lpar_token, is_rpar_token
-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, StringSplitter
-from black.trans import StringParenWrapper, StringParenStripper, hug_power_op
-from black.mode import Mode, Feature, Preview
-
-from blib2to3.pytree import Node, Leaf
+from black.strings import (
+    fix_docstring,
+    get_string_prefix,
+    normalize_string_prefix,
+    normalize_string_quotes,
+    normalize_unicode_escape_sequences,
+)
+from black.trans import (
+    CannotTransform,
+    StringMerger,
+    StringParenStripper,
+    StringParenWrapper,
+    StringSplitter,
+    Transformer,
+    hug_power_op,
+)
 from blib2to3.pgen2 import token
-
+from blib2to3.pytree import Leaf, Node
 
 # types
 LeafID = int
@@ -52,8 +94,9 @@ class LineGenerator(Visitor[Line]):
     in ways that will no longer stringify to valid Python code on the tree.
     """
 
-    def __init__(self, mode: Mode) -> None:
+    def __init__(self, mode: Mode, features: Collection[Feature]) -> None:
         self.mode = mode
+        self.features = features
         self.current_line: Line
         self.__post_init__()
 
@@ -69,6 +112,17 @@ class LineGenerator(Visitor[Line]):
             self.current_line.depth += indent
             return  # Line is empty, don't emit. Creating a new one unnecessary.
 
+        if (
+            Preview.improved_async_statements_handling in self.mode
+            and len(self.current_line.leaves) == 1
+            and is_async_stmt_or_funcdef(self.current_line.leaves[0])
+        ):
+            # Special case for async def/for/with statements. `visit_async_stmt`
+            # adds an `ASYNC` leaf then visits the child def/for/with statement
+            # nodes. Line yields from those nodes shouldn't treat the former
+            # `ASYNC` leaf as a complete line.
+            return
+
         complete_line = self.current_line
         self.current_line = Line(mode=self.mode, depth=complete_line.depth + indent)
         yield complete_line
@@ -77,7 +131,7 @@ class LineGenerator(Visitor[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, preview=self.mode.preview):
+            for comment in generate_comments(node):
                 if any_open_brackets:
                     # any comment within brackets is subject to splitting
                     self.current_line.append(comment)
@@ -103,6 +157,22 @@ class LineGenerator(Visitor[Line]):
                 self.current_line.append(node)
         yield from super().visit_default(node)
 
+    def visit_test(self, node: Node) -> Iterator[Line]:
+        """Visit an `x if y else z` test"""
+
+        if Preview.parenthesize_conditional_expressions in self.mode:
+            already_parenthesized = (
+                node.prev_sibling and node.prev_sibling.type == token.LPAR
+            )
+
+            if not already_parenthesized:
+                lpar = Leaf(token.LPAR, "")
+                rpar = Leaf(token.RPAR, "")
+                node.insert_child(0, lpar)
+                node.append_child(rpar)
+
+        yield from self.visit_default(node)
+
     def visit_INDENT(self, node: Leaf) -> Iterator[Line]:
         """Increase indentation level, maybe yield a line."""
         # In blib2to3 INDENT never holds comments.
@@ -137,16 +207,73 @@ class LineGenerator(Visitor[Line]):
         `parens` holds a set of string leaf values immediately after which
         invisible parens should be put.
         """
-        normalize_invisible_parens(node, parens_after=parens, preview=self.mode.preview)
+        normalize_invisible_parens(
+            node, parens_after=parens, mode=self.mode, features=self.features
+        )
         for child in node.children:
             if is_name_token(child) and child.value in keywords:
                 yield from self.line()
 
             yield from self.visit(child)
 
+    def visit_typeparams(self, node: Node) -> Iterator[Line]:
+        yield from self.visit_default(node)
+        node.children[0].prefix = ""
+
+    def visit_typevartuple(self, node: Node) -> Iterator[Line]:
+        yield from self.visit_default(node)
+        node.children[1].prefix = ""
+
+    def visit_paramspec(self, node: Node) -> Iterator[Line]:
+        yield from self.visit_default(node)
+        node.children[1].prefix = ""
+
+    def visit_dictsetmaker(self, node: Node) -> Iterator[Line]:
+        if Preview.wrap_long_dict_values_in_parens in self.mode:
+            for i, child in enumerate(node.children):
+                if i == 0:
+                    continue
+                if node.children[i - 1].type == token.COLON:
+                    if child.type == syms.atom and child.children[0].type == token.LPAR:
+                        if maybe_make_parens_invisible_in_atom(
+                            child,
+                            parent=node,
+                            remove_brackets_around_comma=False,
+                        ):
+                            wrap_in_parentheses(node, child, visible=False)
+                    else:
+                        wrap_in_parentheses(node, child, visible=False)
+        yield from self.visit_default(node)
+
+    def visit_funcdef(self, node: Node) -> Iterator[Line]:
+        """Visit function definition."""
+        yield from self.line()
+
+        # Remove redundant brackets around return type annotation.
+        is_return_annotation = False
+        for child in node.children:
+            if child.type == token.RARROW:
+                is_return_annotation = True
+            elif is_return_annotation:
+                if child.type == syms.atom and child.children[0].type == token.LPAR:
+                    if maybe_make_parens_invisible_in_atom(
+                        child,
+                        parent=node,
+                        remove_brackets_around_comma=False,
+                    ):
+                        wrap_in_parentheses(node, child, visible=False)
+                else:
+                    wrap_in_parentheses(node, child, visible=False)
+                is_return_annotation = False
+
+        for child in node.children:
+            yield from self.visit(child)
+
     def visit_match_case(self, node: Node) -> Iterator[Line]:
         """Visit either a match or case statement."""
-        normalize_invisible_parens(node, parens_after=set(), preview=self.mode.preview)
+        normalize_invisible_parens(
+            node, parens_after=set(), mode=self.mode, features=self.features
+        )
 
         yield from self.line()
         for child in node.children:
@@ -193,12 +320,17 @@ class LineGenerator(Visitor[Line]):
         for child in children:
             yield from self.visit(child)
 
-            if child.type == token.ASYNC:
+            if child.type == token.ASYNC or child.type == STANDALONE_COMMENT:
+                # STANDALONE_COMMENT happens when `# fmt: skip` is applied on the async
+                # line.
                 break
 
         internal_stmt = next(children)
-        for child in internal_stmt.children:
-            yield from self.visit(child)
+        if Preview.improved_async_statements_handling in self.mode:
+            yield from self.visit(internal_stmt)
+        else:
+            for child in internal_stmt.children:
+                yield from self.visit(child)
 
     def visit_decorators(self, node: Node) -> Iterator[Line]:
         """Visit decorators."""
@@ -226,6 +358,8 @@ class LineGenerator(Visitor[Line]):
             ):
                 wrap_in_parentheses(node, leaf)
 
+        remove_await_parens(node)
+
         yield from self.visit_default(node)
 
     def visit_SEMI(self, leaf: Leaf) -> Iterator[Line]:
@@ -260,10 +394,23 @@ class LineGenerator(Visitor[Line]):
         yield from self.visit_default(node)
 
     def visit_STRING(self, leaf: Leaf) -> Iterator[Line]:
+        if Preview.hex_codes_in_unicode_sequences in self.mode:
+            normalize_unicode_escape_sequences(leaf)
+
         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)
+            if self.mode.string_normalization:
+                docstring = normalize_string_prefix(leaf.value)
+                # visit_default() does handle string normalization for us, but
+                # since this method acts differently depending on quote style (ex.
+                # see padding logic below), there's a possibility for unstable
+                # formatting as visit_default() is called *after*. To avoid a
+                # situation where this function formats a docstring differently on
+                # the second pass, normalize it early.
+                docstring = normalize_string_quotes(docstring)
+            else:
+                docstring = leaf.value
             prefix = get_string_prefix(docstring)
             docstring = docstring[len(prefix) :]  # Remove the prefix
             quote_char = docstring[0]
@@ -275,13 +422,14 @@ class LineGenerator(Visitor[Line]):
             quote_len = 1 if docstring[1] != quote_char else 3
             docstring = docstring[quote_len:-quote_len]
             docstring_started_empty = not docstring
+            indent = " " * 4 * self.current_line.depth
 
             if is_multiline_string(leaf):
-                indent = " " * 4 * self.current_line.depth
                 docstring = fix_docstring(docstring, indent)
             else:
                 docstring = docstring.strip()
 
+            has_trailing_backslash = False
             if docstring:
                 # Add some padding if the docstring starts / ends with a quote mark.
                 if docstring[0] == quote_char:
@@ -294,12 +442,37 @@ class LineGenerator(Visitor[Line]):
                         # Odd number of tailing backslashes, add some padding to
                         # avoid escaping the closing string quote.
                         docstring += " "
+                        has_trailing_backslash = True
             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
+
+            # It's invalid to put closing single-character quotes on a new line.
+            if self.mode and quote_len == 3:
+                # We need to find the length of the last line of the docstring
+                # to find if we can add the closing quotes to the line without
+                # exceeding the maximum line length.
+                # If docstring is one line, we don't put the closing quotes on a
+                # separate line because it looks ugly (#3320).
+                lines = docstring.splitlines()
+                last_line_length = len(lines[-1]) if docstring else 0
+
+                # If adding closing quotes would cause the last line to exceed
+                # the maximum line length then put a line break before the
+                # closing quotes
+                if (
+                    len(lines) > 1
+                    and last_line_length + quote_len > self.mode.line_length
+                    and len(indent) + quote_len <= self.mode.line_length
+                    and not has_trailing_backslash
+                ):
+                    leaf.value = prefix + quote + docstring + "\n" + indent + quote
+                else:
+                    leaf.value = prefix + quote + docstring + quote
+            else:
+                leaf.value = prefix + quote + docstring + quote
 
         yield from self.visit_default(leaf)
 
@@ -318,9 +491,8 @@ class LineGenerator(Visitor[Line]):
         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_except_clause = partial(v, keywords={"except"}, parens={"except"})
+        self.visit_with_stmt = partial(v, keywords={"with"}, parens={"with"})
         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"})
@@ -362,7 +534,7 @@ def transform_line(
         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)
+            is_line_short_enough(line, mode=mode, line_str=line_str)
             or line.contains_unsplittable_type_ignore()
         )
         and not (line.inside_brackets and line.contains_standalone_comments())
@@ -377,7 +549,7 @@ def transform_line(
     else:
 
         def _rhs(
-            self: object, line: Line, features: Collection[Feature]
+            self: object, line: Line, features: Collection[Feature], mode: Mode
         ) -> Iterator[Line]:
             """Wraps calls to `right_hand_split`.
 
@@ -386,14 +558,12 @@ def transform_line(
             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)
-                )
+                lines = list(right_hand_split(line, mode, 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):
+                if is_line_short_enough(lines[0], mode=mode):
                     yield from lines
                     return
 
@@ -401,9 +571,7 @@ def transform_line(
             # 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
-            )
+            yield from right_hand_split(line, mode, features=features)
 
         # HACK: nested functions (like _rhs) compiled by mypyc don't retain their
         # __name__ attribute which is needed in `run_transformer` further down.
@@ -455,7 +623,15 @@ def transform_line(
         yield line
 
 
-def left_hand_split(line: Line, _features: Collection[Feature] = ()) -> Iterator[Line]:
+class _BracketSplitComponent(Enum):
+    head = auto()
+    body = auto()
+    tail = auto()
+
+
+def left_hand_split(
+    line: Line, _features: Collection[Feature], mode: Mode
+) -> 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.
@@ -472,7 +648,10 @@ def left_hand_split(line: Line, _features: Collection[Feature] = ()) -> Iterator
             current_leaves is body_leaves
             and leaf.type in CLOSING_BRACKETS
             and leaf.opening_bracket is matching_bracket
+            and isinstance(matching_bracket, Leaf)
         ):
+            ensure_visible(leaf)
+            ensure_visible(matching_bracket)
             current_leaves = tail_leaves if body_leaves else head_leaves
         current_leaves.append(leaf)
         if current_leaves is head_leaves:
@@ -482,9 +661,15 @@ def left_hand_split(line: Line, _features: Collection[Feature] = ()) -> Iterator
     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)
+    head = bracket_split_build_line(
+        head_leaves, line, matching_bracket, component=_BracketSplitComponent.head
+    )
+    body = bracket_split_build_line(
+        body_leaves, line, matching_bracket, component=_BracketSplitComponent.body
+    )
+    tail = bracket_split_build_line(
+        tail_leaves, line, matching_bracket, component=_BracketSplitComponent.tail
+    )
     bracket_split_succeeded_or_raise(head, body, tail)
     for result in (head, body, tail):
         if result:
@@ -493,7 +678,7 @@ def left_hand_split(line: Line, _features: Collection[Feature] = ()) -> Iterator
 
 def right_hand_split(
     line: Line,
-    line_length: int,
+    mode: Mode,
     features: Collection[Feature] = (),
     omit: Collection[LeafID] = (),
 ) -> Iterator[Line]:
@@ -505,6 +690,22 @@ def right_hand_split(
 
     Note: running this function modifies `bracket_depth` on the leaves of `line`.
     """
+    rhs_result = _first_right_hand_split(line, omit=omit)
+    yield from _maybe_split_omitting_optional_parens(
+        rhs_result, line, mode, features=features, omit=omit
+    )
+
+
+def _first_right_hand_split(
+    line: Line,
+    omit: Collection[LeafID] = (),
+) -> RHSResult:
+    """Split the line into head, body, tail starting with the last bracket pair.
+
+    Note: this function should not have side effects. It's relied upon by
+    _maybe_split_omitting_optional_parens to get an opinion whether to prefer
+    splitting on the right side of an assignment statement.
+    """
     tail_leaves: List[Leaf] = []
     body_leaves: List[Leaf] = []
     head_leaves: List[Leaf] = []
@@ -530,41 +731,82 @@ def right_hand_split(
     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)
+    head = bracket_split_build_line(
+        head_leaves, line, opening_bracket, component=_BracketSplitComponent.head
+    )
+    body = bracket_split_build_line(
+        body_leaves, line, opening_bracket, component=_BracketSplitComponent.body
+    )
+    tail = bracket_split_build_line(
+        tail_leaves, line, opening_bracket, component=_BracketSplitComponent.tail
+    )
     bracket_split_succeeded_or_raise(head, body, tail)
+    return RHSResult(head, body, tail, opening_bracket, closing_bracket)
+
+
+def _maybe_split_omitting_optional_parens(
+    rhs: RHSResult,
+    line: Line,
+    mode: Mode,
+    features: Collection[Feature] = (),
+    omit: Collection[LeafID] = (),
+) -> Iterator[Line]:
     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
+        and rhs.opening_bracket.type == token.LPAR
+        and not rhs.opening_bracket.value
         # the closing bracket is an optional paren
-        and closing_bracket.type == token.RPAR
-        and not closing_bracket.value
+        and rhs.closing_bracket.type == token.RPAR
+        and not rhs.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 not rhs.body.contains_standalone_comments(0)
         # and we can actually remove the parens
-        and can_omit_invisible_parens(body, line_length)
+        and can_omit_invisible_parens(rhs, mode.line_length)
     ):
-        omit = {id(closing_bracket), *omit}
+        omit = {id(rhs.closing_bracket), *omit}
         try:
-            yield from right_hand_split(line, line_length, features=features, omit=omit)
-            return
+            # The RHSResult Omitting Optional Parens.
+            rhs_oop = _first_right_hand_split(line, omit=omit)
+            if not (
+                Preview.prefer_splitting_right_hand_side_of_assignments in line.mode
+                # the split is right after `=`
+                and len(rhs.head.leaves) >= 2
+                and rhs.head.leaves[-2].type == token.EQUAL
+                # the left side of assignment contains brackets
+                and any(leaf.type in BRACKETS for leaf in rhs.head.leaves[:-1])
+                # the left side of assignment is short enough (the -1 is for the ending
+                # optional paren)
+                and is_line_short_enough(
+                    rhs.head, mode=replace(mode, line_length=mode.line_length - 1)
+                )
+                # the left side of assignment won't explode further because of magic
+                # trailing comma
+                and rhs.head.magic_trailing_comma is None
+                # the split by omitting optional parens isn't preferred by some other
+                # reason
+                and not _prefer_split_rhs_oop(rhs_oop, mode)
+            ):
+                yield from _maybe_split_omitting_optional_parens(
+                    rhs_oop, line, mode, 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)
+                can_be_split(rhs.body) or is_line_short_enough(rhs.body, mode=mode)
             ):
                 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():
+            elif (
+                rhs.head.contains_multiline_strings()
+                or rhs.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"
@@ -572,13 +814,42 @@ def right_hand_split(
                     " line."
                 ) from e
 
-    ensure_visible(opening_bracket)
-    ensure_visible(closing_bracket)
-    for result in (head, body, tail):
+    ensure_visible(rhs.opening_bracket)
+    ensure_visible(rhs.closing_bracket)
+    for result in (rhs.head, rhs.body, rhs.tail):
         if result:
             yield result
 
 
+def _prefer_split_rhs_oop(rhs_oop: RHSResult, mode: Mode) -> bool:
+    """
+    Returns whether we should prefer the result from a split omitting optional parens.
+    """
+    has_closing_bracket_after_assign = False
+    for leaf in reversed(rhs_oop.head.leaves):
+        if leaf.type == token.EQUAL:
+            break
+        if leaf.type in CLOSING_BRACKETS:
+            has_closing_bracket_after_assign = True
+            break
+    return (
+        # contains matching brackets after the `=` (done by checking there is a
+        # closing bracket)
+        has_closing_bracket_after_assign
+        or (
+            # the split is actually from inside the optional parens (done by checking
+            # the first line still contains the `=`)
+            any(leaf.type == token.EQUAL for leaf in rhs_oop.head.leaves)
+            # the first line is short enough
+            and is_line_short_enough(rhs_oop.head, mode=mode)
+        )
+        # contains unsplittable type ignore
+        or rhs_oop.head.contains_unsplittable_type_ignore()
+        or rhs_oop.body.contains_unsplittable_type_ignore()
+        or rhs_oop.tail.contains_unsplittable_type_ignore()
+    )
+
+
 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.
 
@@ -606,15 +877,23 @@ def bracket_split_succeeded_or_raise(head: Line, body: Line, tail: Line) -> None
 
 
 def bracket_split_build_line(
-    leaves: List[Leaf], original: Line, opening_bracket: Leaf, *, is_body: bool = False
+    leaves: List[Leaf],
+    original: Line,
+    opening_bracket: Leaf,
+    *,
+    component: _BracketSplitComponent,
 ) -> 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.
+    If it's the head component, brackets will be tracked so trailing commas are
+    respected.
+
+    If it's the body component, 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:
+    if component is _BracketSplitComponent.body:
         result.inside_brackets = True
         result.depth += 1
         if leaves:
@@ -640,6 +919,13 @@ def bracket_split_build_line(
                     )
                     if isinstance(node, Node) and isinstance(node.prev_sibling, Leaf)
                 )
+                # Except the false negatives above for PEP 604 unions where we
+                # can't add the comma.
+                and not (
+                    leaves[0].parent
+                    and leaves[0].parent.next_sibling
+                    and leaves[0].parent.next_sibling.type == token.VBAR
+                )
             )
 
             if original.is_import or no_commas:
@@ -652,12 +938,21 @@ def bracket_split_build_line(
                         leaves.insert(i + 1, new_comma)
                     break
 
+    leaves_to_track: Set[LeafID] = set()
+    if component is _BracketSplitComponent.head:
+        leaves_to_track = get_leaves_inside_matching_brackets(leaves)
     # Populate the line
     for leaf in leaves:
-        result.append(leaf, preformatted=True)
+        result.append(
+            leaf,
+            preformatted=True,
+            track_bracket=id(leaf) in leaves_to_track,
+        )
         for comment_after in original.comments_after(leaf):
             result.append(comment_after, preformatted=True)
-    if is_body and should_split_line(result, opening_bracket):
+    if component is _BracketSplitComponent.body and should_split_line(
+        result, opening_bracket
+    ):
         result.should_split_rhs = True
     return result
 
@@ -669,16 +964,39 @@ def dont_increase_indentation(split_func: Transformer) -> Transformer:
     """
 
     @wraps(split_func)
-    def split_wrapper(line: Line, features: Collection[Feature] = ()) -> Iterator[Line]:
-        for split_line in split_func(line, features):
+    def split_wrapper(
+        line: Line, features: Collection[Feature], mode: Mode
+    ) -> Iterator[Line]:
+        for split_line in split_func(line, features, mode):
             normalize_prefix(split_line.leaves[0], inside_brackets=True)
             yield split_line
 
     return split_wrapper
 
 
+def _get_last_non_comment_leaf(line: Line) -> Optional[int]:
+    for leaf_idx in range(len(line.leaves) - 1, 0, -1):
+        if line.leaves[leaf_idx].type != STANDALONE_COMMENT:
+            return leaf_idx
+    return None
+
+
+def _safe_add_trailing_comma(safe: bool, delimiter_priority: int, line: Line) -> Line:
+    if (
+        safe
+        and delimiter_priority == COMMA_PRIORITY
+        and line.leaves[-1].type != token.COMMA
+        and line.leaves[-1].type != STANDALONE_COMMENT
+    ):
+        new_comma = Leaf(token.COMMA, ",")
+        line.append(new_comma)
+    return line
+
+
 @dont_increase_indentation
-def delimiter_split(line: Line, features: Collection[Feature] = ()) -> Iterator[Line]:
+def delimiter_split(
+    line: Line, features: Collection[Feature], mode: Mode
+) -> Iterator[Line]:
     """Split according to delimiters of the highest priority.
 
     If the appropriate Features are given, the split will add trailing commas
@@ -718,7 +1036,8 @@ def delimiter_split(line: Line, features: Collection[Feature] = ()) -> Iterator[
             )
             current_line.append(leaf)
 
-    for leaf in line.leaves:
+    last_non_comment_leaf = _get_last_non_comment_leaf(line)
+    for leaf_idx, leaf in enumerate(line.leaves):
         yield from append_to_line(leaf)
 
         for comment_after in line.comments_after(leaf):
@@ -735,6 +1054,15 @@ def delimiter_split(line: Line, features: Collection[Feature] = ()) -> Iterator[
                     trailing_comma_safe and Feature.TRAILING_COMMA_IN_CALL in features
                 )
 
+        if (
+            Preview.add_trailing_comma_consistently in mode
+            and last_leaf.type == STANDALONE_COMMENT
+            and leaf_idx == last_non_comment_leaf
+        ):
+            current_line = _safe_add_trailing_comma(
+                trailing_comma_safe, delimiter_priority, current_line
+            )
+
         leaf_priority = bt.delimiters.get(id(leaf))
         if leaf_priority == delimiter_priority:
             yield current_line
@@ -743,20 +1071,15 @@ def delimiter_split(line: Line, features: Collection[Feature] = ()) -> Iterator[
                 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)
+        current_line = _safe_add_trailing_comma(
+            trailing_comma_safe, delimiter_priority, current_line
+        )
         yield current_line
 
 
 @dont_increase_indentation
 def standalone_comment_split(
-    line: Line, features: Collection[Feature] = ()
+    line: Line, features: Collection[Feature], mode: Mode
 ) -> Iterator[Line]:
     """Split standalone comments from the rest of the line."""
     if not line.contains_standalone_comments(0):
@@ -808,7 +1131,7 @@ def normalize_prefix(leaf: Leaf, *, inside_brackets: bool) -> None:
 
 
 def normalize_invisible_parens(
-    node: Node, parens_after: Set[str], *, preview: bool
+    node: Node, parens_after: Set[str], *, mode: Mode, features: Collection[Feature]
 ) -> None:
     """Make existing optional parentheses invisible or create new ones.
 
@@ -818,17 +1141,24 @@ def normalize_invisible_parens(
     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, preview=preview):
+    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
+
+    # The multiple context managers grammar has a different pattern, thus this is
+    # separate from the for-loop below. This possibly wraps them in invisible parens,
+    # and later will be removed in remove_with_parens when needed.
+    if node.type == syms.with_stmt:
+        _maybe_wrap_cms_in_parens(node, mode, features)
+
     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, preview=preview
+                child, parens_after=parens_after, mode=mode, features=features
             )
 
         # Add parentheses around long tuple unpacking in assignments.
@@ -840,64 +1170,212 @@ def normalize_invisible_parens(
             check_lpar = True
 
         if check_lpar:
-            if child.type == syms.atom:
+            if (
+                child.type == syms.atom
+                and node.type == syms.for_stmt
+                and isinstance(child.prev_sibling, Leaf)
+                and child.prev_sibling.type == token.NAME
+                and child.prev_sibling.value == "for"
+            ):
+                if maybe_make_parens_invisible_in_atom(
+                    child,
+                    parent=node,
+                    remove_brackets_around_comma=True,
+                ):
+                    wrap_in_parentheses(node, child, visible=False)
+            elif isinstance(child, Node) and node.type == syms.with_stmt:
+                remove_with_parens(child, node)
+            elif child.type == syms.atom:
                 if maybe_make_parens_invisible_in_atom(
                     child,
                     parent=node,
-                    preview=preview,
                 ):
                     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 is_lpar_token(child):
-                    assert is_rpar_token(node.children[-1])
-                    # make parentheses invisible
-                    child.value = ""
-                    node.children[-1].value = ""
-                elif child.type != token.STAR:
-                    # insert invisible parentheses
-                    node.insert_child(index, Leaf(token.LPAR, ""))
-                    node.append_child(Leaf(token.RPAR, ""))
+                _normalize_import_from(node, child, index)
                 break
+            elif (
+                index == 1
+                and child.type == token.STAR
+                and node.type == syms.except_clause
+            ):
+                # In except* (PEP 654), the star is actually part of
+                # of the keyword. So we need to skip the insertion of
+                # invisible parentheses to work more precisely.
+                continue
 
             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
+        comma_check = child.type == token.COMMA
+
+        check_lpar = isinstance(child, Leaf) and (
+            child.value in parens_after or comma_check
+        )
+
+
+def _normalize_import_from(parent: Node, child: LN, index: int) -> None:
+    # "import from" nodes store parentheses directly as part of
+    # the statement
+    if is_lpar_token(child):
+        assert is_rpar_token(parent.children[-1])
+        # make parentheses invisible
+        child.value = ""
+        parent.children[-1].value = ""
+    elif child.type != token.STAR:
+        # insert invisible parentheses
+        parent.insert_child(index, Leaf(token.LPAR, ""))
+        parent.append_child(Leaf(token.RPAR, ""))
+
+
+def remove_await_parens(node: Node) -> None:
+    if node.children[0].type == token.AWAIT and len(node.children) > 1:
+        if (
+            node.children[1].type == syms.atom
+            and node.children[1].children[0].type == token.LPAR
+        ):
+            if maybe_make_parens_invisible_in_atom(
+                node.children[1],
+                parent=node,
+                remove_brackets_around_comma=True,
+            ):
+                wrap_in_parentheses(node, node.children[1], visible=False)
+
+            # Since await is an expression we shouldn't remove
+            # brackets in cases where this would change
+            # the AST due to operator precedence.
+            # Therefore we only aim to remove brackets around
+            # power nodes that aren't also await expressions themselves.
+            # https://peps.python.org/pep-0492/#updated-operator-precedence-table
+            # N.B. We've still removed any redundant nested brackets though :)
+            opening_bracket = cast(Leaf, node.children[1].children[0])
+            closing_bracket = cast(Leaf, node.children[1].children[-1])
+            bracket_contents = node.children[1].children[1]
+            if isinstance(bracket_contents, Node):
+                if bracket_contents.type != syms.power:
+                    ensure_visible(opening_bracket)
+                    ensure_visible(closing_bracket)
+                elif (
+                    bracket_contents.type == syms.power
+                    and bracket_contents.children[0].type == token.AWAIT
+                ):
+                    ensure_visible(opening_bracket)
+                    ensure_visible(closing_bracket)
+                    # If we are in a nested await then recurse down.
+                    remove_await_parens(bracket_contents)
+
+
+def _maybe_wrap_cms_in_parens(
+    node: Node, mode: Mode, features: Collection[Feature]
+) -> None:
+    """When enabled and safe, wrap the multiple context managers in invisible parens.
+
+    It is only safe when `features` contain Feature.PARENTHESIZED_CONTEXT_MANAGERS.
+    """
+    if (
+        Feature.PARENTHESIZED_CONTEXT_MANAGERS not in features
+        or Preview.wrap_multiple_context_managers_in_parens not in mode
+        or len(node.children) <= 2
+        # If it's an atom, it's already wrapped in parens.
+        or node.children[1].type == syms.atom
+    ):
+        return
+    colon_index: Optional[int] = None
+    for i in range(2, len(node.children)):
+        if node.children[i].type == token.COLON:
+            colon_index = i
+            break
+    if colon_index is not None:
+        lpar = Leaf(token.LPAR, "")
+        rpar = Leaf(token.RPAR, "")
+        context_managers = node.children[1:colon_index]
+        for child in context_managers:
+            child.remove()
+        # After wrapping, the with_stmt will look like this:
+        #   with_stmt
+        #     NAME 'with'
+        #     atom
+        #       LPAR ''
+        #       testlist_gexp
+        #         ... <-- context_managers
+        #       /testlist_gexp
+        #       RPAR ''
+        #     /atom
+        #     COLON ':'
+        new_child = Node(
+            syms.atom, [lpar, Node(syms.testlist_gexp, context_managers), rpar]
+        )
+        node.insert_child(1, new_child)
+
+
+def remove_with_parens(node: Node, parent: Node) -> None:
+    """Recursively hide optional parens in `with` statements."""
+    # Removing all unnecessary parentheses in with statements in one pass is a tad
+    # complex as different variations of bracketed statements result in pretty
+    # different parse trees:
+    #
+    # with (open("file")) as f:                       # this is an asexpr_test
+    #     ...
+    #
+    # with (open("file") as f):                       # this is an atom containing an
+    #     ...                                         # asexpr_test
+    #
+    # with (open("file")) as f, (open("file")) as f:  # this is asexpr_test, COMMA,
+    #     ...                                         # asexpr_test
+    #
+    # with (open("file") as f, open("file") as f):    # an atom containing a
+    #     ...                                         # testlist_gexp which then
+    #                                                 # contains multiple asexpr_test(s)
+    if node.type == syms.atom:
+        if maybe_make_parens_invisible_in_atom(
+            node,
+            parent=parent,
+            remove_brackets_around_comma=True,
+        ):
+            wrap_in_parentheses(parent, node, visible=False)
+        if isinstance(node.children[1], Node):
+            remove_with_parens(node.children[1], node)
+    elif node.type == syms.testlist_gexp:
+        for child in node.children:
+            if isinstance(child, Node):
+                remove_with_parens(child, node)
+    elif node.type == syms.asexpr_test and not any(
+        leaf.type == token.COLONEQUAL for leaf in node.leaves()
+    ):
+        if maybe_make_parens_invisible_in_atom(
+            node.children[0],
+            parent=node,
+            remove_brackets_around_comma=True,
+        ):
+            wrap_in_parentheses(node, node.children[0], visible=False)
 
 
 def maybe_make_parens_invisible_in_atom(
     node: LN,
     parent: LN,
-    preview: bool = False,
+    remove_brackets_around_comma: bool = False,
 ) -> 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 (
-        preview
-        and parent.type == syms.for_stmt
-        and isinstance(node.prev_sibling, Leaf)
-        and node.prev_sibling.type == token.NAME
-        and node.prev_sibling.value == "for"
-    ):
-        for_stmt_check = False
-    else:
-        for_stmt_check = True
-
     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 and for_stmt_check)
+        or (
+            # This condition tries to prevent removing non-optional brackets
+            # around a tuple, however, can be a bit overzealous so we provide
+            # and option to skip this check for `for` and `with` statements.
+            not remove_brackets_around_comma
+            and max_delimiter_priority_in_atom(node) >= COMMA_PRIORITY
+        )
+        or is_tuple_containing_walrus(node)
     ):
         return False
 
@@ -907,9 +1385,13 @@ def maybe_make_parens_invisible_in_atom(
             syms.expr_stmt,
             syms.assert_stmt,
             syms.return_stmt,
+            syms.except_clause,
+            syms.funcdef,
+            syms.with_stmt,
             # these ones aren't useful to end users, but they do please fuzzers
             syms.for_stmt,
             syms.del_stmt,
+            syms.for_stmt,
         ]:
             return False
 
@@ -918,9 +1400,18 @@ def maybe_make_parens_invisible_in_atom(
     if is_lpar_token(first) and is_rpar_token(last):
         middle = node.children[1]
         # make parentheses invisible
-        first.value = ""
-        last.value = ""
-        maybe_make_parens_invisible_in_atom(middle, parent=parent, preview=preview)
+        if (
+            # If the prefix of `middle` includes a type comment with
+            # ignore annotation, then we do not remove the parentheses
+            not is_type_ignore_comment_string(middle.prefix.strip())
+        ):
+            first.value = ""
+            last.value = ""
+        maybe_make_parens_invisible_in_atom(
+            middle,
+            parent=parent,
+            remove_brackets_around_comma=remove_brackets_around_comma,
+        )
 
         if is_atom_with_invisible_parens(middle):
             # Strip the invisible parens from `middle` by replacing
@@ -1046,20 +1537,22 @@ def run_transformer(
     if not line_str:
         line_str = line_to_string(line)
     result: List[Line] = []
-    for transformed_line in transform(line, features):
+    for transformed_line in transform(line, features, mode):
         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))
 
+    features_set = set(features)
     if (
-        transform.__class__.__name__ != "rhs"
+        Feature.FORCE_OPTIONAL_PARENTHESES in features_set
+        or transform.__class__.__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)
+        or is_line_short_enough(result[0], mode=mode)
         # 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
@@ -1070,12 +1563,10 @@ def run_transformer(
 
     line_copy = line.clone()
     append_leaves(line_copy, line, line.leaves)
-    features_fop = set(features) | {Feature.FORCE_OPTIONAL_PARENTHESES}
+    features_fop = features_set | {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
-    ):
+    if all(is_line_short_enough(ln, mode=mode) for ln in second_opinion):
         result = second_opinion
     return result