Remove unneeded mypy dependencies (#3783)

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

diff --git a/src/black/trans.py b/src/black/trans.py
index 74b932bb42256d041de728a012de1d3349197bbc..daed26427d79f2518cec3df0ff32f6e82025506e 100644 (file)
--- a/src/black/trans.py
+++ b/src/black/trans.py
@@ -2,7 +2,6 @@
 String transformers that can split and merge strings.
 """
 import re
 String transformers that can split and merge strings.
 """
 import re

-import sys

 from abc import ABC, abstractmethod
 from collections import defaultdict
 from dataclasses import dataclass
 from abc import ABC, abstractmethod
 from collections import defaultdict
 from dataclasses import dataclass


@@ -12,9 +11,11 @@ from typing import (
     ClassVar,
     Collection,
     Dict,
     ClassVar,
     Collection,
     Dict,

+    Final,

     Iterable,
     Iterator,
     List,
     Iterable,
     Iterator,
     List,

+    Literal,

     Optional,
     Sequence,
     Set,
     Optional,
     Sequence,
     Set,


@@ -23,17 +24,11 @@ from typing import (
     Union,
 )
 
     Union,
 )
 

-if sys.version_info < (3, 8):
-    from typing_extensions import Final, Literal
-else:
-    from typing import Literal, Final
-

 from mypy_extensions import trait
 
 from mypy_extensions import trait
 

-from black.brackets import BracketMatchError

 from black.comments import contains_pragma_comment
 from black.lines import Line, append_leaves
 from black.comments import contains_pragma_comment
 from black.lines import Line, append_leaves

-from black.mode import Feature
+from black.mode import Feature, Mode

 from black.nodes import (
     CLOSING_BRACKETS,
     OPENING_BRACKETS,
 from black.nodes import (
     CLOSING_BRACKETS,
     OPENING_BRACKETS,


@@ -41,6 +36,7 @@ from black.nodes import (
     is_empty_lpar,
     is_empty_par,
     is_empty_rpar,
     is_empty_lpar,
     is_empty_par,
     is_empty_rpar,

+    is_part_of_annotation,

     parent_type,
     replace_child,
     syms,
     parent_type,
     replace_child,
     syms,


@@ -48,9 +44,11 @@ from black.nodes import (
 from black.rusty import Err, Ok, Result
 from black.strings import (
     assert_is_leaf_string,
 from black.rusty import Err, Ok, Result
 from black.strings import (
     assert_is_leaf_string,

+    count_chars_in_width,

     get_string_prefix,
     has_triple_quotes,
     normalize_string_quotes,
     get_string_prefix,
     has_triple_quotes,
     normalize_string_quotes,

+    str_width,

 )
 from blib2to3.pgen2 import token
 from blib2to3.pytree import Leaf, Node
 )
 from blib2to3.pgen2 import token
 from blib2to3.pytree import Leaf, Node


@@ -63,13 +61,15 @@ class CannotTransform(Exception):
 # types
 T = TypeVar("T")
 LN = Union[Leaf, Node]
 # types
 T = TypeVar("T")
 LN = Union[Leaf, Node]

-Transformer = Callable[[Line, Collection[Feature]], Iterator[Line]]
+Transformer = Callable[[Line, Collection[Feature], Mode], Iterator[Line]]

 Index = int
 NodeType = int
 ParserState = int
 StringID = int
 TResult = Result[T, CannotTransform]  # (T)ransform Result
 Index = int
 NodeType = int
 ParserState = int
 StringID = int
 TResult = Result[T, CannotTransform]  # (T)ransform Result

-TMatchResult = TResult[Index]
+TMatchResult = TResult[List[Index]]
+
+SPLIT_SAFE_CHARS = frozenset(["\u3001", "\u3002", "\uff0c"])  # East Asian stops

 
 
 def TErr(err_msg: str) -> Err[CannotTransform]:
 
 
 def TErr(err_msg: str) -> Err[CannotTransform]:


@@ -81,7 +81,9 @@ def TErr(err_msg: str) -> Err[CannotTransform]:
     return Err(cant_transform)
 
 
     return Err(cant_transform)
 
 

-def hug_power_op(line: Line, features: Collection[Feature]) -> Iterator[Line]:
+def hug_power_op(
+    line: Line, features: Collection[Feature], mode: Mode
+) -> Iterator[Line]:

     """A transformer which normalizes spacing around power operators."""
 
     # Performance optimization to avoid unnecessary Leaf clones and other ops.
     """A transformer which normalizes spacing around power operators."""
 
     # Performance optimization to avoid unnecessary Leaf clones and other ops.


@@ -198,23 +200,28 @@ class StringTransformer(ABC):
     def do_match(self, line: Line) -> TMatchResult:
         """
         Returns:
     def do_match(self, line: Line) -> TMatchResult:
         """
         Returns:

-            * Ok(string_idx) such that `line.leaves[string_idx]` is our target
-            string, if a match was able to be made.
-                OR
-            * Err(CannotTransform), if a match was not able to be made.
+            * Ok(string_indices) such that for each index, `line.leaves[index]`
+              is our target string if a match was able to be made. For
+              transformers that don't result in more lines (e.g. StringMerger,
+              StringParenStripper), multiple matches and transforms are done at
+              once to reduce the complexity.
+              OR
+            * Err(CannotTransform), if no match could be made.

         """
 
     @abstractmethod
         """
 
     @abstractmethod

-    def do_transform(self, line: Line, string_idx: int) -> Iterator[TResult[Line]]:
+    def do_transform(
+        self, line: Line, string_indices: List[int]
+    ) -> Iterator[TResult[Line]]:

         """
         Yields:
             * Ok(new_line) where new_line is the new transformed line.
         """
         Yields:
             * Ok(new_line) where new_line is the new transformed line.

-                OR
+              OR

             * Err(CannotTransform) if the transformation failed for some reason. The
             * Err(CannotTransform) if the transformation failed for some reason. The

-            `do_match(...)` template method should usually be used to reject
-            the form of the given Line, but in some cases it is difficult to
-            know whether or not a Line meets the StringTransformer's
-            requirements until the transformation is already midway.
+              `do_match(...)` template method should usually be used to reject
+              the form of the given Line, but in some cases it is difficult to
+              know whether or not a Line meets the StringTransformer's
+              requirements until the transformation is already midway.

 
         Side Effects:
             This method should NOT mutate @line directly, but it MAY mutate the
 
         Side Effects:
             This method should NOT mutate @line directly, but it MAY mutate the


@@ -223,7 +230,9 @@ class StringTransformer(ABC):
             yield an CannotTransform after that point.)
         """
 
             yield an CannotTransform after that point.)
         """
 

-    def __call__(self, line: Line, _features: Collection[Feature]) -> Iterator[Line]:
+    def __call__(
+        self, line: Line, _features: Collection[Feature], _mode: Mode
+    ) -> Iterator[Line]:

         """
         StringTransformer instances have a call signature that mirrors that of
         the Transformer type.
         """
         StringTransformer instances have a call signature that mirrors that of
         the Transformer type.


@@ -246,9 +255,9 @@ class StringTransformer(ABC):
                 " this line as one that it can transform."
             ) from cant_transform
 
                 " this line as one that it can transform."
             ) from cant_transform
 

-        string_idx = match_result.ok()
+        string_indices = match_result.ok()

 
 

-        for line_result in self.do_transform(line, string_idx):
+        for line_result in self.do_transform(line, string_indices):

             if isinstance(line_result, Err):
                 cant_transform = line_result.err()
                 raise CannotTransform(
             if isinstance(line_result, Err):
                 cant_transform = line_result.err()
                 raise CannotTransform(


@@ -322,8 +331,8 @@ class CustomSplitMapMixin:
 
         Returns:
             * A list of the custom splits that are mapped to @string, if any
 
         Returns:
             * A list of the custom splits that are mapped to @string, if any

-            exist.
-                OR
+              exist.
+              OR

             * [], otherwise.
 
         Side Effects:
             * [], otherwise.
 
         Side Effects:


@@ -351,15 +360,15 @@ class StringMerger(StringTransformer, CustomSplitMapMixin):
 
     Requirements:
         (A) The line contains adjacent strings such that ALL of the validation checks
 
     Requirements:
         (A) The line contains adjacent strings such that ALL of the validation checks

-        listed in StringMerger.__validate_msg(...)'s docstring pass.
-            OR
+        listed in StringMerger._validate_msg(...)'s docstring pass.
+        OR

         (B) The line contains a string which uses line continuation backslashes.
 
     Transformations:
         Depending on which of the two requirements above where met, either:
 
         (A) The string group associated with the target string is merged.
         (B) The line contains a string which uses line continuation backslashes.
 
     Transformations:
         Depending on which of the two requirements above where met, either:
 
         (A) The string group associated with the target string is merged.

-            OR
+        OR

         (B) All line-continuation backslashes are removed from the target string.
 
     Collaborations:
         (B) All line-continuation backslashes are removed from the target string.
 
     Collaborations:


@@ -371,28 +380,50 @@ class StringMerger(StringTransformer, CustomSplitMapMixin):
 
         is_valid_index = is_valid_index_factory(LL)
 
 
         is_valid_index = is_valid_index_factory(LL)
 

-        for i, leaf in enumerate(LL):
+        string_indices = []
+        idx = 0
+        while is_valid_index(idx):
+            leaf = LL[idx]

             if (
                 leaf.type == token.STRING
             if (
                 leaf.type == token.STRING

-                and is_valid_index(i + 1)
-                and LL[i + 1].type == token.STRING
+                and is_valid_index(idx + 1)
+                and LL[idx + 1].type == token.STRING

             ):
             ):

-                return Ok(i)
+                if not is_part_of_annotation(leaf):
+                    string_indices.append(idx)
+
+                # Advance to the next non-STRING leaf.
+                idx += 2
+                while is_valid_index(idx) and LL[idx].type == token.STRING:
+                    idx += 1

 
 

-            if leaf.type == token.STRING and "\\\n" in leaf.value:
-                return Ok(i)
+            elif leaf.type == token.STRING and "\\\n" in leaf.value:
+                string_indices.append(idx)
+                # Advance to the next non-STRING leaf.
+                idx += 1
+                while is_valid_index(idx) and LL[idx].type == token.STRING:
+                    idx += 1

 
 

-        return TErr("This line has no strings that need merging.")
+            else:
+                idx += 1
+
+        if string_indices:
+            return Ok(string_indices)
+        else:
+            return TErr("This line has no strings that need merging.")

 
 

-    def do_transform(self, line: Line, string_idx: int) -> Iterator[TResult[Line]]:
+    def do_transform(
+        self, line: Line, string_indices: List[int]
+    ) -> Iterator[TResult[Line]]:

         new_line = line
         new_line = line

+

         rblc_result = self._remove_backslash_line_continuation_chars(
         rblc_result = self._remove_backslash_line_continuation_chars(

-            new_line, string_idx
+            new_line, string_indices

         )
         if isinstance(rblc_result, Ok):
             new_line = rblc_result.ok()
 
         )
         if isinstance(rblc_result, Ok):
             new_line = rblc_result.ok()
 

-        msg_result = self._merge_string_group(new_line, string_idx)
+        msg_result = self._merge_string_group(new_line, string_indices)

         if isinstance(msg_result, Ok):
             new_line = msg_result.ok()
 
         if isinstance(msg_result, Ok):
             new_line = msg_result.ok()
 


@@ -413,7 +444,7 @@ class StringMerger(StringTransformer, CustomSplitMapMixin):
 
     @staticmethod
     def _remove_backslash_line_continuation_chars(
 
     @staticmethod
     def _remove_backslash_line_continuation_chars(

-        line: Line, string_idx: int
+        line: Line, string_indices: List[int]

     ) -> TResult[Line]:
         """
         Merge strings that were split across multiple lines using
     ) -> TResult[Line]:
         """
         Merge strings that were split across multiple lines using


@@ -427,34 +458,44 @@ class StringMerger(StringTransformer, CustomSplitMapMixin):
         """
         LL = line.leaves
 
         """
         LL = line.leaves
 

-        string_leaf = LL[string_idx]
-        if not (
-            string_leaf.type == token.STRING
-            and "\\\n" in string_leaf.value
-            and not has_triple_quotes(string_leaf.value)
-        ):
+        indices_to_transform = []
+        for string_idx in string_indices:
+            string_leaf = LL[string_idx]
+            if (
+                string_leaf.type == token.STRING
+                and "\\\n" in string_leaf.value
+                and not has_triple_quotes(string_leaf.value)
+            ):
+                indices_to_transform.append(string_idx)
+
+        if not indices_to_transform:

             return TErr(
             return TErr(

-                f"String leaf {string_leaf} does not contain any backslash line"
-                " continuation characters."
+                "Found no string leaves that contain backslash line continuation"
+                " characters."

             )
 
         new_line = line.clone()
         new_line.comments = line.comments.copy()
         append_leaves(new_line, line, LL)
 
             )
 
         new_line = line.clone()
         new_line.comments = line.comments.copy()
         append_leaves(new_line, line, LL)
 

-        new_string_leaf = new_line.leaves[string_idx]
-        new_string_leaf.value = new_string_leaf.value.replace("\\\n", "")
+        for string_idx in indices_to_transform:
+            new_string_leaf = new_line.leaves[string_idx]
+            new_string_leaf.value = new_string_leaf.value.replace("\\\n", "")

 
         return Ok(new_line)
 
 
         return Ok(new_line)
 

-    def _merge_string_group(self, line: Line, string_idx: int) -> TResult[Line]:
+    def _merge_string_group(
+        self, line: Line, string_indices: List[int]
+    ) -> TResult[Line]:

         """
         """

-        Merges string group (i.e. set of adjacent strings) where the first
-        string in the group is `line.leaves[string_idx]`.
+        Merges string groups (i.e. set of adjacent strings).
+
+        Each index from `string_indices` designates one string group's first
+        leaf in `line.leaves`.

 
         Returns:
             Ok(new_line), if ALL of the validation checks found in
 
         Returns:
             Ok(new_line), if ALL of the validation checks found in

-            __validate_msg(...) pass.
+            _validate_msg(...) pass.

                 OR
             Err(CannotTransform), otherwise.
         """
                 OR
             Err(CannotTransform), otherwise.
         """


@@ -462,10 +503,54 @@ class StringMerger(StringTransformer, CustomSplitMapMixin):
 
         is_valid_index = is_valid_index_factory(LL)
 
 
         is_valid_index = is_valid_index_factory(LL)
 

-        vresult = self._validate_msg(line, string_idx)
-        if isinstance(vresult, Err):
-            return vresult
+        # A dict of {string_idx: tuple[num_of_strings, string_leaf]}.
+        merged_string_idx_dict: Dict[int, Tuple[int, Leaf]] = {}
+        for string_idx in string_indices:
+            vresult = self._validate_msg(line, string_idx)
+            if isinstance(vresult, Err):
+                continue
+            merged_string_idx_dict[string_idx] = self._merge_one_string_group(
+                LL, string_idx, is_valid_index
+            )

 
 

+        if not merged_string_idx_dict:
+            return TErr("No string group is merged")
+
+        # Build the final line ('new_line') that this method will later return.
+        new_line = line.clone()
+        previous_merged_string_idx = -1
+        previous_merged_num_of_strings = -1
+        for i, leaf in enumerate(LL):
+            if i in merged_string_idx_dict:
+                previous_merged_string_idx = i
+                previous_merged_num_of_strings, string_leaf = merged_string_idx_dict[i]
+                new_line.append(string_leaf)
+
+            if (
+                previous_merged_string_idx
+                <= i
+                < previous_merged_string_idx + previous_merged_num_of_strings
+            ):
+                for comment_leaf in line.comments_after(LL[i]):
+                    new_line.append(comment_leaf, preformatted=True)
+                continue
+
+            append_leaves(new_line, line, [leaf])
+
+        return Ok(new_line)
+
+    def _merge_one_string_group(
+        self, LL: List[Leaf], string_idx: int, is_valid_index: Callable[[int], bool]
+    ) -> Tuple[int, Leaf]:
+        """
+        Merges one string group where the first string in the group is
+        `LL[string_idx]`.
+
+        Returns:
+            A tuple of `(num_of_strings, leaf)` where `num_of_strings` is the
+            number of strings merged and `leaf` is the newly merged string
+            to be replaced in the new line.
+        """

         # If the string group is wrapped inside an Atom node, we must make sure
         # to later replace that Atom with our new (merged) string leaf.
         atom_node = LL[string_idx].parent
         # If the string group is wrapped inside an Atom node, we must make sure
         # to later replace that Atom with our new (merged) string leaf.
         atom_node = LL[string_idx].parent


@@ -491,6 +576,12 @@ class StringMerger(StringTransformer, CustomSplitMapMixin):
                 characters have been escaped.
             """
             assert_is_leaf_string(string)
                 characters have been escaped.
             """
             assert_is_leaf_string(string)

+            if "f" in string_prefix:
+                string = _toggle_fexpr_quotes(string, QUOTE)
+                # After quotes toggling, quotes in expressions won't be escaped
+                # because quotes can't be reused in f-strings. So we can simply
+                # let the escaping logic below run without knowing f-string
+                # expressions.

 
             RE_EVEN_BACKSLASHES = r"(?:(?<!\\)(?:\\\\)*)"
             naked_string = string[len(string_prefix) + 1 : -1]
 
             RE_EVEN_BACKSLASHES = r"(?:(?<!\\)(?:\\\\)*)"
             naked_string = string[len(string_prefix) + 1 : -1]


@@ -588,27 +679,14 @@ class StringMerger(StringTransformer, CustomSplitMapMixin):
                 # Else replace the atom node with the new string leaf.
                 replace_child(atom_node, string_leaf)
 
                 # Else replace the atom node with the new string leaf.
                 replace_child(atom_node, string_leaf)
 

-        # Build the final line ('new_line') that this method will later return.
-        new_line = line.clone()
-        for i, leaf in enumerate(LL):
-            if i == string_idx:
-                new_line.append(string_leaf)
-
-            if string_idx <= i < string_idx + num_of_strings:
-                for comment_leaf in line.comments_after(LL[i]):
-                    new_line.append(comment_leaf, preformatted=True)
-                continue
-
-            append_leaves(new_line, line, [leaf])
-

         self.add_custom_splits(string_leaf.value, custom_splits)
         self.add_custom_splits(string_leaf.value, custom_splits)

-        return Ok(new_line)
+        return num_of_strings, string_leaf

 
     @staticmethod
     def _validate_msg(line: Line, string_idx: int) -> TResult[None]:
         """Validate (M)erge (S)tring (G)roup
 
 
     @staticmethod
     def _validate_msg(line: Line, string_idx: int) -> TResult[None]:
         """Validate (M)erge (S)tring (G)roup
 

-        Transform-time string validation logic for __merge_string_group(...).
+        Transform-time string validation logic for _merge_string_group(...).

 
         Returns:
             * Ok(None), if ALL validation checks (listed below) pass.
 
         Returns:
             * Ok(None), if ALL validation checks (listed below) pass.


@@ -622,6 +700,11 @@ class StringMerger(StringTransformer, CustomSplitMapMixin):
                 - The set of all string prefixes in the string group is of
                   length greater than one and is not equal to {"", "f"}.
                 - The string group consists of raw strings.
                 - The set of all string prefixes in the string group is of
                   length greater than one and is not equal to {"", "f"}.
                 - The string group consists of raw strings.

+                - The string group is stringified type annotations. We don't want to
+                  process stringified type annotations since pyright doesn't support
+                  them spanning multiple string values. (NOTE: mypy, pytype, pyre do
+                  support them, so we can change if pyright also gains support in the
+                  future. See https://github.com/microsoft/pyright/issues/4359.)

         """
         # We first check for "inner" stand-alone comments (i.e. stand-alone
         # comments that have a string leaf before them AND after them).
         """
         # We first check for "inner" stand-alone comments (i.e. stand-alone
         # comments that have a string leaf before them AND after them).


@@ -711,7 +794,15 @@ class StringParenStripper(StringTransformer):
 
         is_valid_index = is_valid_index_factory(LL)
 
 
         is_valid_index = is_valid_index_factory(LL)
 

-        for idx, leaf in enumerate(LL):
+        string_indices = []
+
+        idx = -1
+        while True:
+            idx += 1
+            if idx >= len(LL):
+                break
+            leaf = LL[idx]
+

             # Should be a string...
             if leaf.type != token.STRING:
                 continue
             # Should be a string...
             if leaf.type != token.STRING:
                 continue


@@ -793,45 +884,73 @@ class StringParenStripper(StringTransformer):
                 }:
                     continue
 
                 }:
                     continue
 

-                return Ok(string_idx)
+                string_indices.append(string_idx)
+                idx = string_idx
+                while idx < len(LL) - 1 and LL[idx + 1].type == token.STRING:
+                    idx += 1

 
 

+        if string_indices:
+            return Ok(string_indices)

         return TErr("This line has no strings wrapped in parens.")
 
         return TErr("This line has no strings wrapped in parens.")
 

-    def do_transform(self, line: Line, string_idx: int) -> Iterator[TResult[Line]]:
+    def do_transform(
+        self, line: Line, string_indices: List[int]
+    ) -> Iterator[TResult[Line]]:

         LL = line.leaves
 
         LL = line.leaves
 

-        string_parser = StringParser()
-        rpar_idx = string_parser.parse(LL, string_idx)
+        string_and_rpar_indices: List[int] = []
+        for string_idx in string_indices:
+            string_parser = StringParser()
+            rpar_idx = string_parser.parse(LL, string_idx)
+
+            should_transform = True
+            for leaf in (LL[string_idx - 1], LL[rpar_idx]):
+                if line.comments_after(leaf):
+                    # Should not strip parentheses which have comments attached
+                    # to them.
+                    should_transform = False
+                    break
+            if should_transform:
+                string_and_rpar_indices.extend((string_idx, rpar_idx))

 
 

-        for leaf in (LL[string_idx - 1], LL[rpar_idx]):
-            if line.comments_after(leaf):
-                yield TErr(
-                    "Will not strip parentheses which have comments attached to them."
-                )
-                return
+        if string_and_rpar_indices:
+            yield Ok(self._transform_to_new_line(line, string_and_rpar_indices))
+        else:
+            yield Err(
+                CannotTransform("All string groups have comments attached to them.")
+            )
+
+    def _transform_to_new_line(
+        self, line: Line, string_and_rpar_indices: List[int]
+    ) -> Line:
+        LL = line.leaves

 
         new_line = line.clone()
         new_line.comments = line.comments.copy()
 
         new_line = line.clone()
         new_line.comments = line.comments.copy()

-        try:
-            append_leaves(new_line, line, LL[: string_idx - 1])
-        except BracketMatchError:
-            # HACK: I believe there is currently a bug somewhere in
-            # right_hand_split() that is causing brackets to not be tracked
-            # properly by a shared BracketTracker.
-            append_leaves(new_line, line, LL[: string_idx - 1], preformatted=True)
-
-        string_leaf = Leaf(token.STRING, LL[string_idx].value)
-        LL[string_idx - 1].remove()
-        replace_child(LL[string_idx], string_leaf)
-        new_line.append(string_leaf)
-
-        append_leaves(
-            new_line, line, LL[string_idx + 1 : rpar_idx] + LL[rpar_idx + 1 :]
-        )

 
 

-        LL[rpar_idx].remove()
+        previous_idx = -1
+        # We need to sort the indices, since string_idx and its matching
+        # rpar_idx may not come in order, e.g. in
+        # `("outer" % ("inner".join(items)))`, the "inner" string's
+        # string_idx is smaller than "outer" string's rpar_idx.
+        for idx in sorted(string_and_rpar_indices):
+            leaf = LL[idx]
+            lpar_or_rpar_idx = idx - 1 if leaf.type == token.STRING else idx
+            append_leaves(new_line, line, LL[previous_idx + 1 : lpar_or_rpar_idx])
+            if leaf.type == token.STRING:
+                string_leaf = Leaf(token.STRING, LL[idx].value)
+                LL[lpar_or_rpar_idx].remove()  # Remove lpar.
+                replace_child(LL[idx], string_leaf)
+                new_line.append(string_leaf)
+            else:
+                LL[lpar_or_rpar_idx].remove()  # This is a rpar.
+
+            previous_idx = idx
+
+        # Append the leaves after the last idx:
+        append_leaves(new_line, line, LL[idx + 1 :])

 
 

-        yield Ok(new_line)
+        return new_line

 
 
 class BaseStringSplitter(StringTransformer):
 
 
 class BaseStringSplitter(StringTransformer):


@@ -842,17 +961,20 @@ class BaseStringSplitter(StringTransformer):
 
     Requirements:
         * The target string value is responsible for the line going over the
 
     Requirements:
         * The target string value is responsible for the line going over the

-        line length limit. It follows that after all of black's other line
-        split methods have been exhausted, this line (or one of the resulting
-        lines after all line splits are performed) would still be over the
-        line_length limit unless we split this string.
-            AND
+          line length limit. It follows that after all of black's other line
+          split methods have been exhausted, this line (or one of the resulting
+          lines after all line splits are performed) would still be over the
+          line_length limit unless we split this string.
+          AND
+

         * The target string is NOT a "pointless" string (i.e. a string that has
         * The target string is NOT a "pointless" string (i.e. a string that has

-        no parent or siblings).
-            AND
+          no parent or siblings).
+          AND
+

         * The target string is not followed by an inline comment that appears
         * The target string is not followed by an inline comment that appears

-        to be a pragma.
-            AND
+          to be a pragma.
+          AND
+

         * The target string is not a multiline (i.e. triple-quote) string.
     """
 
         * The target string is not a multiline (i.e. triple-quote) string.
     """
 


@@ -884,7 +1006,12 @@ class BaseStringSplitter(StringTransformer):
         if isinstance(match_result, Err):
             return match_result
 
         if isinstance(match_result, Err):
             return match_result
 

-        string_idx = match_result.ok()
+        string_indices = match_result.ok()
+        assert len(string_indices) == 1, (
+            f"{self.__class__.__name__} should only find one match at a time, found"
+            f" {len(string_indices)}"
+        )
+        string_idx = string_indices[0]

         vresult = self._validate(line, string_idx)
         if isinstance(vresult, Err):
             return vresult
         vresult = self._validate(line, string_idx)
         if isinstance(vresult, Err):
             return vresult


@@ -899,7 +1026,7 @@ class BaseStringSplitter(StringTransformer):
 
         Returns:
             * Ok(None), if ALL of the requirements are met.
 
         Returns:
             * Ok(None), if ALL of the requirements are met.

-                OR
+              OR

             * Err(CannotTransform), if ANY of the requirements are NOT met.
         """
         LL = line.leaves
             * Err(CannotTransform), if ANY of the requirements are NOT met.
         """
         LL = line.leaves


@@ -1040,7 +1167,7 @@ class BaseStringSplitter(StringTransformer):
             # WMA4 the length of the inline comment.
             offset += len(comment_leaf.value)
 
             # WMA4 the length of the inline comment.
             offset += len(comment_leaf.value)
 

-        max_string_length = self.line_length - offset
+        max_string_length = count_chars_in_width(str(line), self.line_length - offset)

         return max_string_length
 
     @staticmethod
         return max_string_length
 
     @staticmethod


@@ -1140,6 +1267,30 @@ def fstring_contains_expr(s: str) -> bool:
     return any(iter_fexpr_spans(s))
 
 
     return any(iter_fexpr_spans(s))
 
 

+def _toggle_fexpr_quotes(fstring: str, old_quote: str) -> str:
+    """
+    Toggles quotes used in f-string expressions that are `old_quote`.
+
+    f-string expressions can't contain backslashes, so we need to toggle the
+    quotes if the f-string itself will end up using the same quote. We can
+    simply toggle without escaping because, quotes can't be reused in f-string
+    expressions. They will fail to parse.
+
+    NOTE: If PEP 701 is accepted, above statement will no longer be true.
+    Though if quotes can be reused, we can simply reuse them without updates or
+    escaping, once Black figures out how to parse the new grammar.
+    """
+    new_quote = "'" if old_quote == '"' else '"'
+    parts = []
+    previous_index = 0
+    for start, end in iter_fexpr_spans(fstring):
+        parts.append(fstring[previous_index:start])
+        parts.append(fstring[start:end].replace(old_quote, new_quote))
+        previous_index = end
+    parts.append(fstring[previous_index:])
+    return "".join(parts)
+
+

 class StringSplitter(BaseStringSplitter, CustomSplitMapMixin):
     """
     StringTransformer that splits "atom" strings (i.e. strings which exist on
 class StringSplitter(BaseStringSplitter, CustomSplitMapMixin):
     """
     StringTransformer that splits "atom" strings (i.e. strings which exist on


@@ -1147,9 +1298,9 @@ class StringSplitter(BaseStringSplitter, CustomSplitMapMixin):
 
     Requirements:
         * The line consists ONLY of a single string (possibly prefixed by a
 
     Requirements:
         * The line consists ONLY of a single string (possibly prefixed by a

-        string operator [e.g. '+' or '==']), MAYBE a string trailer, and MAYBE
-        a trailing comma.
-            AND
+          string operator [e.g. '+' or '==']), MAYBE a string trailer, and MAYBE
+          a trailing comma.
+          AND

         * All of the requirements listed in BaseStringSplitter's docstring.
 
     Transformations:
         * All of the requirements listed in BaseStringSplitter's docstring.
 
     Transformations:


@@ -1232,10 +1383,17 @@ class StringSplitter(BaseStringSplitter, CustomSplitMapMixin):
         if is_valid_index(idx):
             return TErr("This line does not end with a string.")
 
         if is_valid_index(idx):
             return TErr("This line does not end with a string.")
 

-        return Ok(string_idx)
+        return Ok([string_idx])

 
 

-    def do_transform(self, line: Line, string_idx: int) -> Iterator[TResult[Line]]:
+    def do_transform(
+        self, line: Line, string_indices: List[int]
+    ) -> Iterator[TResult[Line]]:

         LL = line.leaves
         LL = line.leaves

+        assert len(string_indices) == 1, (
+            f"{self.__class__.__name__} should only find one match at a time, found"
+            f" {len(string_indices)}"
+        )
+        string_idx = string_indices[0]

 
         QUOTE = LL[string_idx].value[-1]
 
 
         QUOTE = LL[string_idx].value[-1]
 


@@ -1256,7 +1414,7 @@ class StringSplitter(BaseStringSplitter, CustomSplitMapMixin):
 
         string_op_leaves = self._get_string_operator_leaves(LL)
         string_op_leaves_length = (
 
         string_op_leaves = self._get_string_operator_leaves(LL)
         string_op_leaves_length = (

-            sum([len(str(prefix_leaf)) for prefix_leaf in string_op_leaves]) + 1
+            sum(len(str(prefix_leaf)) for prefix_leaf in string_op_leaves) + 1

             if string_op_leaves
             else 0
         )
             if string_op_leaves
             else 0
         )


@@ -1278,11 +1436,13 @@ class StringSplitter(BaseStringSplitter, CustomSplitMapMixin):
             is_valid_index(string_idx + 1) and LL[string_idx + 1].type == token.COMMA
         )
 
             is_valid_index(string_idx + 1) and LL[string_idx + 1].type == token.COMMA
         )
 

-        def max_last_string() -> int:
+        def max_last_string_column() -> int:

             """
             Returns:
             """
             Returns:

-                The max allowed length of the string value used for the last
-                line we will construct.
+                The max allowed width of the string value used for the last
+                line we will construct.  Note that this value means the width
+                rather than the number of characters (e.g., many East Asian
+                characters expand to two columns).

             """
             result = self.line_length
             result -= line.depth * 4
             """
             result = self.line_length
             result -= line.depth * 4


@@ -1290,14 +1450,14 @@ class StringSplitter(BaseStringSplitter, CustomSplitMapMixin):
             result -= string_op_leaves_length
             return result
 
             result -= string_op_leaves_length
             return result
 

-        # --- Calculate Max Break Index (for string value)
+        # --- Calculate Max Break Width (for string value)

         # We start with the line length limit
         # We start with the line length limit

-        max_break_idx = self.line_length
+        max_break_width = self.line_length

         # The last index of a string of length N is N-1.
         # The last index of a string of length N is N-1.

-        max_break_idx -= 1
+        max_break_width -= 1

         # Leading whitespace is not present in the string value (e.g. Leaf.value).
         # Leading whitespace is not present in the string value (e.g. Leaf.value).

-        max_break_idx -= line.depth * 4
-        if max_break_idx < 0:
+        max_break_width -= line.depth * 4
+        if max_break_width < 0:

             yield TErr(
                 f"Unable to split {LL[string_idx].value} at such high of a line depth:"
                 f" {line.depth}"
             yield TErr(
                 f"Unable to split {LL[string_idx].value} at such high of a line depth:"
                 f" {line.depth}"


@@ -1310,7 +1470,7 @@ class StringSplitter(BaseStringSplitter, CustomSplitMapMixin):
         # line limit.
         use_custom_breakpoints = bool(
             custom_splits
         # line limit.
         use_custom_breakpoints = bool(
             custom_splits

-            and all(csplit.break_idx <= max_break_idx for csplit in custom_splits)
+            and all(csplit.break_idx <= max_break_width for csplit in custom_splits)

         )
 
         # Temporary storage for the remaining chunk of the string line that
         )
 
         # Temporary storage for the remaining chunk of the string line that


@@ -1326,7 +1486,7 @@ class StringSplitter(BaseStringSplitter, CustomSplitMapMixin):
             if use_custom_breakpoints:
                 return len(custom_splits) > 1
             else:
             if use_custom_breakpoints:
                 return len(custom_splits) > 1
             else:

-                return len(rest_value) > max_last_string()
+                return str_width(rest_value) > max_last_string_column()

 
         string_line_results: List[Ok[Line]] = []
         while more_splits_should_be_made():
 
         string_line_results: List[Ok[Line]] = []
         while more_splits_should_be_made():


@@ -1336,7 +1496,10 @@ class StringSplitter(BaseStringSplitter, CustomSplitMapMixin):
                 break_idx = csplit.break_idx
             else:
                 # Algorithmic Split (automatic)
                 break_idx = csplit.break_idx
             else:
                 # Algorithmic Split (automatic)

-                max_bidx = max_break_idx - string_op_leaves_length
+                max_bidx = (
+                    count_chars_in_width(rest_value, max_break_width)
+                    - string_op_leaves_length
+                )

                 maybe_break_idx = self._get_break_idx(rest_value, max_bidx)
                 if maybe_break_idx is None:
                     # If we are unable to algorithmically determine a good split
                 maybe_break_idx = self._get_break_idx(rest_value, max_bidx)
                 if maybe_break_idx is None:
                     # If we are unable to algorithmically determine a good split


@@ -1373,9 +1536,14 @@ class StringSplitter(BaseStringSplitter, CustomSplitMapMixin):
             # prefix, and the current custom split did NOT originally use a
             # prefix...
             if (
             # prefix, and the current custom split did NOT originally use a
             # prefix...
             if (

-                next_value != self._normalize_f_string(next_value, prefix)
-                and use_custom_breakpoints
+                use_custom_breakpoints

                 and not csplit.has_prefix
                 and not csplit.has_prefix

+                and (
+                    # `next_value == prefix + QUOTE` happens when the custom
+                    # split is an empty string.
+                    next_value == prefix + QUOTE
+                    or next_value != self._normalize_f_string(next_value, prefix)
+                )

             ):
                 # Then `csplit.break_idx` will be off by one after removing
                 # the 'f' prefix.
             ):
                 # Then `csplit.break_idx` will be off by one after removing
                 # the 'f' prefix.


@@ -1428,7 +1596,7 @@ class StringSplitter(BaseStringSplitter, CustomSplitMapMixin):
 
             # Try to fit them all on the same line with the last substring...
             if (
 
             # Try to fit them all on the same line with the last substring...
             if (

-                len(temp_value) <= max_last_string()
+                str_width(temp_value) <= max_last_string_column()

                 or LL[string_idx + 1].type == token.COMMA
             ):
                 last_line.append(rest_leaf)
                 or LL[string_idx + 1].type == token.COMMA
             ):
                 last_line.append(rest_leaf)


@@ -1548,6 +1716,7 @@ class StringSplitter(BaseStringSplitter, CustomSplitMapMixin):
                 section of this classes' docstring would be be met by returning @i.
             """
             is_space = string[i] == " "
                 section of this classes' docstring would be be met by returning @i.
             """
             is_space = string[i] == " "

+            is_split_safe = is_valid_index(i - 1) and string[i - 1] in SPLIT_SAFE_CHARS

 
             is_not_escaped = True
             j = i - 1
 
             is_not_escaped = True
             j = i - 1


@@ -1560,7 +1729,7 @@ class StringSplitter(BaseStringSplitter, CustomSplitMapMixin):
                 and len(string[:i]) >= self.MIN_SUBSTR_SIZE
             )
             return (
                 and len(string[:i]) >= self.MIN_SUBSTR_SIZE
             )
             return (

-                is_space
+                (is_space or is_split_safe)

                 and is_not_escaped
                 and is_big_enough
                 and not breaks_unsplittable_expression(i)
                 and is_not_escaped
                 and is_big_enough
                 and not breaks_unsplittable_expression(i)


@@ -1638,24 +1807,26 @@ class StringParenWrapper(BaseStringSplitter, CustomSplitMapMixin):
         addition to the requirements listed below:
 
         * The line is a return/yield statement, which returns/yields a string.
         addition to the requirements listed below:
 
         * The line is a return/yield statement, which returns/yields a string.

-            OR
+          OR

         * The line is part of a ternary expression (e.g. `x = y if cond else
         * The line is part of a ternary expression (e.g. `x = y if cond else

-        z`) such that the line starts with `else <string>`, where <string> is
-        some string.
-            OR
+          z`) such that the line starts with `else <string>`, where <string> is
+          some string.
+          OR

         * The line is an assert statement, which ends with a string.
         * The line is an assert statement, which ends with a string.

-            OR
+          OR

         * The line is an assignment statement (e.g. `x = <string>` or `x +=
         * The line is an assignment statement (e.g. `x = <string>` or `x +=

-        <string>`) such that the variable is being assigned the value of some
-        string.
-            OR
+          <string>`) such that the variable is being assigned the value of some
+          string.
+          OR

         * The line is a dictionary key assignment where some valid key is being
         * The line is a dictionary key assignment where some valid key is being

-        assigned the value of some string.
-            OR
+          assigned the value of some string.
+          OR
+        * The line is an lambda expression and the value is a string.
+          OR

         * The line starts with an "atom" string that prefers to be wrapped in
         * The line starts with an "atom" string that prefers to be wrapped in

-        parens. It's preferred to be wrapped when it's is an immediate child of
-        a list/set/tuple literal, AND the string is surrounded by commas (or is
-        the first/last child).
+          parens. It's preferred to be wrapped when it's is an immediate child of
+          a list/set/tuple literal, AND the string is surrounded by commas (or is
+          the first/last child).

 
     Transformations:
         The chosen string is wrapped in parentheses and then split at the LPAR.
 
     Transformations:
         The chosen string is wrapped in parentheses and then split at the LPAR.


@@ -1698,17 +1869,19 @@ class StringParenWrapper(BaseStringSplitter, CustomSplitMapMixin):
             or self._else_match(LL)
             or self._assert_match(LL)
             or self._assign_match(LL)
             or self._else_match(LL)
             or self._assert_match(LL)
             or self._assign_match(LL)

-            or self._dict_match(LL)
+            or self._dict_or_lambda_match(LL)

             or self._prefer_paren_wrap_match(LL)
         )
 
         if string_idx is not None:
             string_value = line.leaves[string_idx].value
             or self._prefer_paren_wrap_match(LL)
         )
 
         if string_idx is not None:
             string_value = line.leaves[string_idx].value

-            # If the string has no spaces...
-            if " " not in string_value:
+            # If the string has neither spaces nor East Asian stops...
+            if not any(
+                char == " " or char in SPLIT_SAFE_CHARS for char in string_value
+            ):

                 # And will still violate the line length limit when split...
                 # And will still violate the line length limit when split...

-                max_string_length = self.line_length - ((line.depth + 1) * 4)
-                if len(string_value) > max_string_length:
+                max_string_width = self.line_length - ((line.depth + 1) * 4)
+                if str_width(string_value) > max_string_width:

                     # And has no associated custom splits...
                     if not self.has_custom_splits(string_value):
                         # Then we should NOT put this string on its own line.
                     # And has no associated custom splits...
                     if not self.has_custom_splits(string_value):
                         # Then we should NOT put this string on its own line.


@@ -1717,7 +1890,7 @@ class StringParenWrapper(BaseStringSplitter, CustomSplitMapMixin):
                             " resultant line would still be over the specified line"
                             " length and can't be split further by StringSplitter."
                         )
                             " resultant line would still be over the specified line"
                             " length and can't be split further by StringSplitter."
                         )

-            return Ok(string_idx)
+            return Ok([string_idx])

 
         return TErr("This line does not contain any non-atomic strings.")
 
 
         return TErr("This line does not contain any non-atomic strings.")
 


@@ -1856,23 +2029,24 @@ class StringParenWrapper(BaseStringSplitter, CustomSplitMapMixin):
         return None
 
     @staticmethod
         return None
 
     @staticmethod

-    def _dict_match(LL: List[Leaf]) -> Optional[int]:
+    def _dict_or_lambda_match(LL: List[Leaf]) -> Optional[int]:

         """
         Returns:
             string_idx such that @LL[string_idx] is equal to our target (i.e.
             matched) string, if this line matches the dictionary key assignment
         """
         Returns:
             string_idx such that @LL[string_idx] is equal to our target (i.e.
             matched) string, if this line matches the dictionary key assignment

-            statement requirements listed in the 'Requirements' section of this
-            classes' docstring.
+            statement or lambda expression requirements listed in the
+            'Requirements' section of this classes' docstring.

                 OR
             None, otherwise.
         """
                 OR
             None, otherwise.
         """

-        # If this line is apart of a dictionary key assignment...
-        if syms.dictsetmaker in [parent_type(LL[0]), parent_type(LL[0].parent)]:
+        # If this line is a part of a dictionary key assignment or lambda expression...
+        parent_types = [parent_type(LL[0]), parent_type(LL[0].parent)]
+        if syms.dictsetmaker in parent_types or syms.lambdef in parent_types:

             is_valid_index = is_valid_index_factory(LL)
 
             for i, leaf in enumerate(LL):
             is_valid_index = is_valid_index_factory(LL)
 
             for i, leaf in enumerate(LL):

-                # We MUST find a colon...
-                if leaf.type == token.COLON:
+                # We MUST find a colon, it can either be dict's or lambda's colon...
+                if leaf.type == token.COLON and i < len(LL) - 1:

                     idx = i + 2 if is_empty_par(LL[i + 1]) else i + 1
 
                     # That colon MUST be followed by a string...
                     idx = i + 2 if is_empty_par(LL[i + 1]) else i + 1
 
                     # That colon MUST be followed by a string...


@@ -1893,8 +2067,15 @@ class StringParenWrapper(BaseStringSplitter, CustomSplitMapMixin):
 
         return None
 
 
         return None
 

-    def do_transform(self, line: Line, string_idx: int) -> Iterator[TResult[Line]]:
+    def do_transform(
+        self, line: Line, string_indices: List[int]
+    ) -> Iterator[TResult[Line]]:

         LL = line.leaves
         LL = line.leaves

+        assert len(string_indices) == 1, (
+            f"{self.__class__.__name__} should only find one match at a time, found"
+            f" {len(string_indices)}"
+        )
+        string_idx = string_indices[0]

 
         is_valid_index = is_valid_index_factory(LL)
         insert_str_child = insert_str_child_factory(LL[string_idx])
 
         is_valid_index = is_valid_index_factory(LL)
         insert_str_child = insert_str_child_factory(LL[string_idx])


@@ -1966,6 +2147,25 @@ class StringParenWrapper(BaseStringSplitter, CustomSplitMapMixin):
                     f" (left_leaves={left_leaves}, right_leaves={right_leaves})"
                 )
                 old_rpar_leaf = right_leaves.pop()
                     f" (left_leaves={left_leaves}, right_leaves={right_leaves})"
                 )
                 old_rpar_leaf = right_leaves.pop()

+            elif right_leaves and right_leaves[-1].type == token.RPAR:
+                # Special case for lambda expressions as dict's value, e.g.:
+                #     my_dict = {
+                #        "key": lambda x: f"formatted: {x},
+                #     }
+                # After wrapping the dict's value with parentheses, the string is
+                # followed by a RPAR but its opening bracket is lambda's, not
+                # the string's:
+                #        "key": (lambda x: f"formatted: {x}),
+                opening_bracket = right_leaves[-1].opening_bracket
+                if opening_bracket is not None and opening_bracket in left_leaves:
+                    index = left_leaves.index(opening_bracket)
+                    if (
+                        index > 0
+                        and index < len(left_leaves) - 1
+                        and left_leaves[index - 1].type == token.COLON
+                        and left_leaves[index + 1].value == "lambda"
+                    ):
+                        right_leaves.pop()

 
             append_leaves(string_line, line, right_leaves)
 
 
             append_leaves(string_line, line, right_leaves)
 


@@ -2072,7 +2272,7 @@ class StringParser:
         Returns:
             The index directly after the last leaf which is apart of the string
             trailer, if a "trailer" exists.
         Returns:
             The index directly after the last leaf which is apart of the string
             trailer, if a "trailer" exists.

-                OR
+            OR

             @string_idx + 1, if no string "trailer" exists.
         """
         assert leaves[string_idx].type == token.STRING
             @string_idx + 1, if no string "trailer" exists.
         """
         assert leaves[string_idx].type == token.STRING


@@ -2086,11 +2286,11 @@ class StringParser:
         """
         Pre-conditions:
             * On the first call to this function, @leaf MUST be the leaf that
         """
         Pre-conditions:
             * On the first call to this function, @leaf MUST be the leaf that

-            was directly after the string leaf in question (e.g. if our target
-            string is `line.leaves[i]` then the first call to this method must
-            be `line.leaves[i + 1]`).
+              was directly after the string leaf in question (e.g. if our target
+              string is `line.leaves[i]` then the first call to this method must
+              be `line.leaves[i + 1]`).

             * On the next call to this function, the leaf parameter passed in
             * On the next call to this function, the leaf parameter passed in

-            MUST be the leaf directly following @leaf.
+              MUST be the leaf directly following @leaf.

 
         Returns:
             True iff @leaf is apart of the string's trailer.
 
         Returns:
             True iff @leaf is apart of the string's trailer.