Document the future style changes introduced in #3489 and #3440 (#3541)

[etc/vim.git] / src / black / linegen.py

diff --git a/src/black/linegen.py b/src/black/linegen.py
index 8e8d41e239ae8e732e380ad08710c49f25156745..7afb1733939d6d0472663b371c88f8a5cc435bda 100644 (file)
--- a/src/black/linegen.py
+++ b/src/black/linegen.py
@@ -1,38 +1,77 @@
 """
 Generating lines of code.
 """
 """
 Generating lines of code.
 """

-from functools import partial, wraps

 import sys
 import sys

+from dataclasses import dataclass
+from enum import Enum, auto
+from functools import partial, wraps

 from typing import Collection, Iterator, List, Optional, Set, Union, cast
 
 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,
+    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 (
 from black.nodes import (

+    ASSIGNMENTS,
+    BRACKETS,
+    CLOSING_BRACKETS,
+    OPENING_BRACKETS,
+    RARROW,
+    STANDALONE_COMMENT,
+    STATEMENT,
+    WHITESPACE,
+    Visitor,
+    ensure_visible,
+    is_arith_like,
+    is_atom_with_invisible_parens,

     is_docstring,
     is_empty_tuple,
     is_docstring,
     is_empty_tuple,

-    is_one_tuple,
+    is_lpar_token,
+    is_multiline_string,
+    is_name_token,

     is_one_sequence_between,
     is_one_sequence_between,

+    is_one_tuple,
+    is_rpar_token,
+    is_stub_body,
+    is_stub_suite,
+    is_tuple_containing_walrus,
+    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.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.pgen2 import token

-
+from blib2to3.pytree import Leaf, Node

 
 # types
 LeafID = int
 
 # types
 LeafID = int


@@ -52,8 +91,9 @@ class LineGenerator(Visitor[Line]):
     in ways that will no longer stringify to valid Python code on the tree.
     """
 
     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.mode = mode

+        self.features = features

         self.current_line: Line
         self.__post_init__()
 
         self.current_line: Line
         self.__post_init__()
 


@@ -77,7 +117,7 @@ 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()
         """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)
                 if any_open_brackets:
                     # any comment within brackets is subject to splitting
                     self.current_line.append(comment)


@@ -103,6 +143,22 @@ class LineGenerator(Visitor[Line]):
                 self.current_line.append(node)
         yield from super().visit_default(node)
 
                 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.
     def visit_INDENT(self, node: Leaf) -> Iterator[Line]:
         """Increase indentation level, maybe yield a line."""
         # In blib2to3 INDENT never holds comments.


@@ -137,26 +193,21 @@ class LineGenerator(Visitor[Line]):
         `parens` holds a set of string leaf values immediately after which
         invisible parens should be put.
         """
         `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)
 
         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_funcdef(self, node: Node) -> Iterator[Line]:
-        """Visit function definition."""
-        if Preview.annotation_parens not in self.mode:
-            yield from self.visit_stmt(node, keywords={"def"}, parens=set())
-        else:
-            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:
+    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,
                     if child.type == syms.atom and child.children[0].type == token.LPAR:
                         if maybe_make_parens_invisible_in_atom(
                             child,


@@ -166,14 +217,37 @@ class LineGenerator(Visitor[Line]):
                             wrap_in_parentheses(node, child, visible=False)
                     else:
                         wrap_in_parentheses(node, child, visible=False)
                             wrap_in_parentheses(node, child, visible=False)
                     else:
                         wrap_in_parentheses(node, child, visible=False)

-                    is_return_annotation = 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)
+        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."""
 
     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:
 
         yield from self.line()
         for child in node.children:


@@ -255,8 +329,7 @@ class LineGenerator(Visitor[Line]):
             ):
                 wrap_in_parentheses(node, leaf)
 
             ):
                 wrap_in_parentheses(node, leaf)
 

-        if Preview.remove_redundant_parens in self.mode:
-            remove_await_parens(node)
+        remove_await_parens(node)

 
         yield from self.visit_default(node)
 
 
         yield from self.visit_default(node)
 


@@ -292,27 +365,23 @@ class LineGenerator(Visitor[Line]):
         yield from self.visit_default(node)
 
     def visit_STRING(self, leaf: Leaf) -> Iterator[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.
         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.

-            if Preview.normalize_docstring_quotes_and_prefixes_properly in self.mode:
-                # There was a bug where --skip-string-normalization wouldn't stop us
-                # from normalizing docstring prefixes. To maintain stability, we can
-                # only address this buggy behaviour while the preview style is enabled.
-                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
-            else:
-                # ... otherwise, we'll keep the buggy behaviour >.<
+            if self.mode.string_normalization:

                 docstring = normalize_string_prefix(leaf.value)
                 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]
             prefix = get_string_prefix(docstring)
             docstring = docstring[len(prefix) :]  # Remove the prefix
             quote_char = docstring[0]


@@ -331,6 +400,7 @@ class LineGenerator(Visitor[Line]):
             else:
                 docstring = docstring.strip()
 
             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:
             if docstring:
                 # Add some padding if the docstring starts / ends with a quote mark.
                 if docstring[0] == quote_char:


@@ -343,6 +413,7 @@ class LineGenerator(Visitor[Line]):
                         # Odd number of tailing backslashes, add some padding to
                         # avoid escaping the closing string quote.
                         docstring += " "
                         # 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 = " "
 
             elif not docstring_started_empty:
                 docstring = " "
 


@@ -350,23 +421,24 @@ class LineGenerator(Visitor[Line]):
             quote = quote_char * quote_len
 
             # It's invalid to put closing single-character quotes on a new line.
             quote = quote_char * quote_len
 
             # It's invalid to put closing single-character quotes on a new line.

-            if Preview.long_docstring_quotes_on_newline in self.mode and quote_len == 3:
+            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.
                 # 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, then we need to add the length
-                # of the indent, prefix, and starting quotes. Ending quotes are
-                # handled later.
+                # 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
 
                 lines = docstring.splitlines()
                 last_line_length = len(lines[-1]) if docstring else 0
 

-                if len(lines) == 1:
-                    last_line_length += len(indent) + len(prefix) + quote_len
-

                 # 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 adding closing quotes would cause the last line to exceed
                 # the maximum line length then put a line break before the
                 # closing quotes

-                if last_line_length + quote_len > self.mode.line_length:
+                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
                     leaf.value = prefix + quote + docstring + "\n" + indent + quote
                 else:
                     leaf.value = prefix + quote + docstring + quote


@@ -390,14 +462,8 @@ class LineGenerator(Visitor[Line]):
         self.visit_try_stmt = partial(
             v, keywords={"try", "except", "else", "finally"}, parens=Ø
         )
         self.visit_try_stmt = partial(
             v, keywords={"try", "except", "else", "finally"}, parens=Ø
         )

-        if self.mode.preview:
-            self.visit_except_clause = partial(
-                v, keywords={"except"}, parens={"except"}
-            )
-            self.visit_with_stmt = partial(v, keywords={"with"}, parens={"with"})
-        else:
-            self.visit_except_clause = partial(v, keywords={"except"}, parens=Ø)
-            self.visit_with_stmt = partial(v, keywords={"with"}, 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"})
         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"})


@@ -532,6 +598,12 @@ def transform_line(
         yield line
 
 
         yield line
 
 

+class _BracketSplitComponent(Enum):
+    head = auto()
+    body = auto()
+    tail = auto()
+
+

 def left_hand_split(line: Line, _features: Collection[Feature] = ()) -> Iterator[Line]:
     """Split line into many lines, starting with the first matching bracket pair.
 
 def left_hand_split(line: Line, _features: Collection[Feature] = ()) -> Iterator[Line]:
     """Split line into many lines, starting with the first matching bracket pair.
 


@@ -562,15 +634,32 @@ def left_hand_split(line: Line, _features: Collection[Feature] = ()) -> Iterator
     if not matching_bracket:
         raise CannotSplit("No brackets found")
 
     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:
             yield result
 
 
     bracket_split_succeeded_or_raise(head, body, tail)
     for result in (head, body, tail):
         if result:
             yield result
 
 

+@dataclass
+class _RHSResult:
+    """Intermediate split result from a right hand split."""
+
+    head: Line
+    body: Line
+    tail: Line
+    opening_bracket: Leaf
+    closing_bracket: Leaf
+
+

 def right_hand_split(
     line: Line,
     line_length: int,
 def right_hand_split(
     line: Line,
     line_length: int,


@@ -585,6 +674,22 @@ def right_hand_split(
 
     Note: running this function modifies `bracket_depth` on the leaves of `line`.
     """
 
     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, line_length, 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] = []
     tail_leaves: List[Leaf] = []
     body_leaves: List[Leaf] = []
     head_leaves: List[Leaf] = []


@@ -610,41 +715,81 @@ def right_hand_split(
     tail_leaves.reverse()
     body_leaves.reverse()
     head_leaves.reverse()
     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)
     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,
+    line_length: int,
+    features: Collection[Feature] = (),
+    omit: Collection[LeafID] = (),
+) -> Iterator[Line]:

     if (
         Feature.FORCE_OPTIONAL_PARENTHESES not in features
         # the opening bracket is an optional paren
     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
         # 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
         # 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 we can actually remove the parens

-        and can_omit_invisible_parens(body, line_length)
+        and can_omit_invisible_parens(rhs.body, line_length)

     ):
     ):

-        omit = {id(closing_bracket), *omit}
+        omit = {id(rhs.closing_bracket), *omit}

         try:
         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 assignement 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, line_length=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, line_length=line_length)
+            ):
+                yield from _maybe_split_omitting_optional_parens(
+                    rhs_oop, line, line_length, features=features, omit=omit
+                )
+                return

 
         except CannotSplit as e:
             if not (
 
         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, line_length=line_length)

             ):
                 raise CannotSplit(
                     "Splitting failed, body is still too long and can't be split."
                 ) from e
 
             ):
                 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"
                 raise CannotSplit(
                     "The current optional pair of parentheses is bound to fail to"
                     " satisfy the splitting algorithm because the head or the tail"


@@ -652,13 +797,42 @@ def right_hand_split(
                     " line."
                 ) from e
 
                     " 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
 
 
         if result:
             yield result
 
 

+def _prefer_split_rhs_oop(rhs_oop: _RHSResult, line_length: int) -> 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, line_length=line_length)
+        )
+        # 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.
 
 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.
 


@@ -686,15 +860,23 @@ def bracket_split_succeeded_or_raise(head: Line, body: Line, tail: Line) -> None
 
 
 def bracket_split_build_line(
 
 
 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`.
 
 ) -> 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)
     """
     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:
         result.inside_brackets = True
         result.depth += 1
         if leaves:


@@ -732,12 +914,21 @@ def bracket_split_build_line(
                         leaves.insert(i + 1, new_comma)
                     break
 
                         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:
     # 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)
         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
 
         result.should_split_rhs = True
     return result
 


@@ -888,7 +1079,7 @@ def normalize_prefix(leaf: Leaf, *, inside_brackets: bool) -> None:
 
 
 def normalize_invisible_parens(
 
 
 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.
 
 ) -> None:
     """Make existing optional parentheses invisible or create new ones.
 


@@ -898,17 +1089,24 @@ def normalize_invisible_parens(
     Standardizes on visible parentheses for single-element tuples, and keeps
     existing visible parentheses for other tuples and generator expressions.
     """
     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
         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(
     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.
             )
 
         # Add parentheses around long tuple unpacking in assignments.


@@ -921,8 +1119,7 @@ def normalize_invisible_parens(
 
         if check_lpar:
             if (
 
         if check_lpar:
             if (

-                preview
-                and child.type == syms.atom
+                child.type == syms.atom

                 and node.type == syms.for_stmt
                 and isinstance(child.prev_sibling, Leaf)
                 and child.prev_sibling.type == token.NAME
                 and node.type == syms.for_stmt
                 and isinstance(child.prev_sibling, Leaf)
                 and child.prev_sibling.type == token.NAME


@@ -934,7 +1131,7 @@ def normalize_invisible_parens(
                     remove_brackets_around_comma=True,
                 ):
                     wrap_in_parentheses(node, child, visible=False)
                     remove_brackets_around_comma=True,
                 ):
                     wrap_in_parentheses(node, child, visible=False)

-            elif preview and isinstance(child, Node) and node.type == syms.with_stmt:
+            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(
                 remove_with_parens(child, node)
             elif child.type == syms.atom:
                 if maybe_make_parens_invisible_in_atom(


@@ -945,17 +1142,7 @@ def normalize_invisible_parens(
             elif is_one_tuple(child):
                 wrap_in_parentheses(node, child, visible=True)
             elif node.type == syms.import_from:
             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
                 break
             elif (
                 index == 1


@@ -970,13 +1157,27 @@ def normalize_invisible_parens(
             elif not (isinstance(child, Leaf) and is_multiline_string(child)):
                 wrap_in_parentheses(node, child, visible=False)
 
             elif not (isinstance(child, Leaf) and is_multiline_string(child)):
                 wrap_in_parentheses(node, child, visible=False)
 

-        comma_check = child.type == token.COMMA if preview else False
+        comma_check = child.type == token.COMMA

 
         check_lpar = isinstance(child, Leaf) and (
             child.value in parens_after or comma_check
         )
 
 
 
         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 (
 def remove_await_parens(node: Node) -> None:
     if node.children[0].type == token.AWAIT and len(node.children) > 1:
         if (


@@ -999,18 +1200,62 @@ def remove_await_parens(node: Node) -> None:
             # 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])
             # 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 = cast(Node, node.children[1].children[1])
-            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)
+            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:
 
 
 def remove_with_parens(node: Node, parent: Node) -> None:


@@ -1078,6 +1323,7 @@ def maybe_make_parens_invisible_in_atom(
             not remove_brackets_around_comma
             and max_delimiter_priority_in_atom(node) >= COMMA_PRIORITY
         )
             not remove_brackets_around_comma
             and max_delimiter_priority_in_atom(node) >= COMMA_PRIORITY
         )

+        or is_tuple_containing_walrus(node)

     ):
         return False
 
     ):
         return False
 


@@ -1087,9 +1333,13 @@ def maybe_make_parens_invisible_in_atom(
             syms.expr_stmt,
             syms.assert_stmt,
             syms.return_stmt,
             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,
             # these ones aren't useful to end users, but they do please fuzzers
             syms.for_stmt,
             syms.del_stmt,

+            syms.for_stmt,

         ]:
             return False
 
         ]:
             return False
 


@@ -1236,8 +1486,10 @@ def run_transformer(
 
         result.extend(transform_line(transformed_line, mode=mode, features=features))
 
 
         result.extend(transform_line(transformed_line, mode=mode, features=features))
 

+    features_set = set(features)

     if (
     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 not line.bracket_tracker.invisible
         or any(bracket.value for bracket in line.bracket_tracker.invisible)
         or line.contains_multiline_strings()


@@ -1254,7 +1506,7 @@ def run_transformer(
 
     line_copy = line.clone()
     append_leaves(line_copy, line, line.leaves)
 
     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
     )
     second_opinion = run_transformer(
         line_copy, transform, mode, features_fop, line_str=line_str
     )