Avoid treating ellipsis as a dot delimiter

[etc/vim.git] / black.py

diff --git a/black.py b/black.py
index 913fe8dfefaf496e57373e94d96b272caebf486d..a1a34685fdadcbaf65982560831c73778de646b8 100644 (file)
--- a/black.py
+++ b/black.py
@@ -24,6 +24,7 @@ from typing import (
     List,
     Optional,
     Pattern,
     List,
     Optional,
     Pattern,

+    Sequence,

     Set,
     Tuple,
     Type,
     Set,
     Tuple,
     Type,


@@ -41,6 +42,7 @@ from blib2to3 import pygram, pytree
 from blib2to3.pgen2 import driver, token
 from blib2to3.pgen2.parse import ParseError
 
 from blib2to3.pgen2 import driver, token
 from blib2to3.pgen2.parse import ParseError
 

+

 __version__ = "18.4a6"
 DEFAULT_LINE_LENGTH = 88
 
 __version__ = "18.4a6"
 DEFAULT_LINE_LENGTH = 88
 


@@ -237,11 +239,8 @@ def reformat_one(
                 src = src.resolve()
                 if src in cache and cache[src] == get_cache_info(src):
                     changed = Changed.CACHED
                 src = src.resolve()
                 if src in cache and cache[src] == get_cache_info(src):
                     changed = Changed.CACHED

-            if (
-                changed is not Changed.CACHED
-                and format_file_in_place(
-                    src, line_length=line_length, fast=fast, write_back=write_back
-                )
+            if changed is not Changed.CACHED and format_file_in_place(
+                src, line_length=line_length, fast=fast, write_back=write_back

             ):
                 changed = Changed.YES
             if write_back == WriteBack.YES and changed is not Changed.NO:
             ):
                 changed = Changed.YES
             if write_back == WriteBack.YES and changed is not Changed.NO:


@@ -283,32 +282,29 @@ async def schedule_formatting(
             manager = Manager()
             lock = manager.Lock()
         tasks = {
             manager = Manager()
             lock = manager.Lock()
         tasks = {

-            src: loop.run_in_executor(
+            loop.run_in_executor(

                 executor, format_file_in_place, src, line_length, fast, write_back, lock
                 executor, format_file_in_place, src, line_length, fast, write_back, lock

-            )
-            for src in sources
+            ): src
+            for src in sorted(sources)

         }
         }

-        _task_values = list(tasks.values())
+        pending: Iterable[asyncio.Task] = tasks.keys()

         try:
         try:

-            loop.add_signal_handler(signal.SIGINT, cancel, _task_values)
-            loop.add_signal_handler(signal.SIGTERM, cancel, _task_values)
+            loop.add_signal_handler(signal.SIGINT, cancel, pending)
+            loop.add_signal_handler(signal.SIGTERM, cancel, pending)

         except NotImplementedError:
             # There are no good alternatives for these on Windows
             pass
         except NotImplementedError:
             # There are no good alternatives for these on Windows
             pass

-        await asyncio.wait(_task_values)
-        for src, task in tasks.items():
-            if not task.done():
-                report.failed(src, "timed out, cancelling")
-                task.cancel()
-                cancelled.append(task)
-            elif task.cancelled():
-                cancelled.append(task)
-            elif task.exception():
-                report.failed(src, str(task.exception()))
-            else:
-                formatted.append(src)
-                report.done(src, Changed.YES if task.result() else Changed.NO)
-
+        while pending:
+            done, _ = await asyncio.wait(pending, return_when=asyncio.FIRST_COMPLETED)
+            for task in done:
+                src = tasks.pop(task)
+                if task.cancelled():
+                    cancelled.append(task)
+                elif task.exception():
+                    report.failed(src, str(task.exception()))
+                else:
+                    formatted.append(src)
+                    report.done(src, Changed.YES if task.result() else Changed.NO)

     if cancelled:
         await asyncio.gather(*cancelled, loop=loop, return_exceptions=True)
     if write_back == WriteBack.YES and formatted:
     if cancelled:
         await asyncio.gather(*cancelled, loop=loop, return_exceptions=True)
     if write_back == WriteBack.YES and formatted:


@@ -327,12 +323,13 @@ def format_file_in_place(
     If `write_back` is True, write reformatted code back to stdout.
     `line_length` and `fast` options are passed to :func:`format_file_contents`.
     """
     If `write_back` is True, write reformatted code back to stdout.
     `line_length` and `fast` options are passed to :func:`format_file_contents`.
     """

+    is_pyi = src.suffix == ".pyi"

 
     with tokenize.open(src) as src_buffer:
         src_contents = src_buffer.read()
     try:
         dst_contents = format_file_contents(
 
     with tokenize.open(src) as src_buffer:
         src_contents = src_buffer.read()
     try:
         dst_contents = format_file_contents(

-            src_contents, line_length=line_length, fast=fast
+            src_contents, line_length=line_length, fast=fast, is_pyi=is_pyi

         )
     except NothingChanged:
         return False
         )
     except NothingChanged:
         return False


@@ -381,7 +378,7 @@ def format_stdin_to_stdout(
 
 
 def format_file_contents(
 
 
 def format_file_contents(

-    src_contents: str, line_length: int, fast: bool
+    src_contents: str, *, line_length: int, fast: bool, is_pyi: bool = False

 ) -> FileContent:
     """Reformat contents a file and return new contents.
 
 ) -> FileContent:
     """Reformat contents a file and return new contents.
 


@@ -392,17 +389,21 @@ def format_file_contents(
     if src_contents.strip() == "":
         raise NothingChanged
 
     if src_contents.strip() == "":
         raise NothingChanged
 

-    dst_contents = format_str(src_contents, line_length=line_length)
+    dst_contents = format_str(src_contents, line_length=line_length, is_pyi=is_pyi)

     if src_contents == dst_contents:
         raise NothingChanged
 
     if not fast:
         assert_equivalent(src_contents, dst_contents)
     if src_contents == dst_contents:
         raise NothingChanged
 
     if not fast:
         assert_equivalent(src_contents, dst_contents)

-        assert_stable(src_contents, dst_contents, line_length=line_length)
+        assert_stable(
+            src_contents, dst_contents, line_length=line_length, is_pyi=is_pyi
+        )

     return dst_contents
 
 
     return dst_contents
 
 

-def format_str(src_contents: str, line_length: int) -> FileContent:
+def format_str(
+    src_contents: str, line_length: int, *, is_pyi: bool = False
+) -> FileContent:

     """Reformat a string and return new contents.
 
     `line_length` determines how many characters per line are allowed.
     """Reformat a string and return new contents.
 
     `line_length` determines how many characters per line are allowed.


@@ -410,9 +411,11 @@ def format_str(src_contents: str, line_length: int) -> FileContent:
     src_node = lib2to3_parse(src_contents)
     dst_contents = ""
     future_imports = get_future_imports(src_node)
     src_node = lib2to3_parse(src_contents)
     dst_contents = ""
     future_imports = get_future_imports(src_node)

+    elt = EmptyLineTracker(is_pyi=is_pyi)

     py36 = is_python36(src_node)
     py36 = is_python36(src_node)

-    lines = LineGenerator(remove_u_prefix=py36 or "unicode_literals" in future_imports)
-    elt = EmptyLineTracker()
+    lines = LineGenerator(
+        remove_u_prefix=py36 or "unicode_literals" in future_imports, is_pyi=is_pyi
+    )

     empty_line = Line()
     after = 0
     for current_line in lines.visit(src_node):
     empty_line = Line()
     after = 0
     for current_line in lines.visit(src_node):


@@ -623,21 +626,22 @@ LOGIC_PRIORITY = 14
 STRING_PRIORITY = 12
 COMPARATOR_PRIORITY = 10
 MATH_PRIORITIES = {
 STRING_PRIORITY = 12
 COMPARATOR_PRIORITY = 10
 MATH_PRIORITIES = {

-    token.VBAR: 8,
-    token.CIRCUMFLEX: 7,
-    token.AMPER: 6,
-    token.LEFTSHIFT: 5,
-    token.RIGHTSHIFT: 5,
-    token.PLUS: 4,
-    token.MINUS: 4,
-    token.STAR: 3,
-    token.SLASH: 3,
-    token.DOUBLESLASH: 3,
-    token.PERCENT: 3,
-    token.AT: 3,
-    token.TILDE: 2,
-    token.DOUBLESTAR: 1,
+    token.VBAR: 9,
+    token.CIRCUMFLEX: 8,
+    token.AMPER: 7,
+    token.LEFTSHIFT: 6,
+    token.RIGHTSHIFT: 6,
+    token.PLUS: 5,
+    token.MINUS: 5,
+    token.STAR: 4,
+    token.SLASH: 4,
+    token.DOUBLESLASH: 4,
+    token.PERCENT: 4,
+    token.AT: 4,
+    token.TILDE: 3,
+    token.DOUBLESTAR: 2,

 }
 }

+DOT_PRIORITY = 1

 
 
 @dataclass
 
 
 @dataclass


@@ -703,6 +707,17 @@ class BracketTracker:
         """
         return max(v for k, v in self.delimiters.items() if k not in exclude)
 
         """
         return max(v for k, v in self.delimiters.items() if k not in exclude)
 

+    def delimiter_count_with_priority(self, priority: int = 0) -> int:
+        """Return the number of delimiters with the given `priority`.
+
+        If no `priority` is passed, defaults to max priority on the line.
+        """
+        if not self.delimiters:
+            return 0
+
+        priority = priority or self.max_delimiter_priority()
+        return sum(1 for p in self.delimiters.values() if p == priority)
+

     def maybe_increment_for_loop_variable(self, leaf: Leaf) -> bool:
         """In a for loop, or comprehension, the variables are often unpacks.
 
     def maybe_increment_for_loop_variable(self, leaf: Leaf) -> bool:
         """In a for loop, or comprehension, the variables are often unpacks.
 


@@ -761,6 +776,7 @@ class Line:
     comments: List[Tuple[Index, Leaf]] = Factory(list)
     bracket_tracker: BracketTracker = Factory(BracketTracker)
     inside_brackets: bool = False
     comments: List[Tuple[Index, Leaf]] = Factory(list)
     bracket_tracker: BracketTracker = Factory(BracketTracker)
     inside_brackets: bool = False

+    should_explode: bool = False

 
     def append(self, leaf: Leaf, preformatted: bool = False) -> None:
         """Add a new `leaf` to the end of the line.
 
     def append(self, leaf: Leaf, preformatted: bool = False) -> None:
         """Add a new `leaf` to the end of the line.


@@ -831,6 +847,13 @@ class Line:
             and self.leaves[0].value == "class"
         )
 
             and self.leaves[0].value == "class"
         )
 

+    @property
+    def is_stub_class(self) -> bool:
+        """Is this line a class definition with a body consisting only of "..."?"""
+        return self.is_class and self.leaves[-3:] == [
+            Leaf(token.DOT, ".") for _ in range(3)
+        ]
+

     @property
     def is_def(self) -> bool:
         """Is this a function definition? (Also returns True for async defs.)"""
     @property
     def is_def(self) -> bool:
         """Is this a function definition? (Also returns True for async defs.)"""


@@ -843,14 +866,11 @@ class Line:
             second_leaf: Optional[Leaf] = self.leaves[1]
         except IndexError:
             second_leaf = None
             second_leaf: Optional[Leaf] = self.leaves[1]
         except IndexError:
             second_leaf = None

-        return (
-            (first_leaf.type == token.NAME and first_leaf.value == "def")
-            or (
-                first_leaf.type == token.ASYNC
-                and second_leaf is not None
-                and second_leaf.type == token.NAME
-                and second_leaf.value == "def"
-            )
+        return (first_leaf.type == token.NAME and first_leaf.value == "def") or (
+            first_leaf.type == token.ASYNC
+            and second_leaf is not None
+            and second_leaf.type == token.NAME
+            and second_leaf.value == "def"

         )
 
     @property
         )
 
     @property


@@ -975,17 +995,21 @@ class Line:
             self.comments.append((after, comment))
             return True
 
             self.comments.append((after, comment))
             return True
 

-    def comments_after(self, leaf: Leaf) -> Iterator[Leaf]:
-        """Generate comments that should appear directly after `leaf`."""
-        for _leaf_index, _leaf in enumerate(self.leaves):
-            if leaf is _leaf:
-                break
+    def comments_after(self, leaf: Leaf, _index: int = -1) -> Iterator[Leaf]:
+        """Generate comments that should appear directly after `leaf`.

 
 

-        else:
-            return
+        Provide a non-negative leaf `_index` to speed up the function.
+        """
+        if _index == -1:
+            for _index, _leaf in enumerate(self.leaves):
+                if leaf is _leaf:
+                    break
+
+            else:
+                return

 
         for index, comment_after in self.comments:
 
         for index, comment_after in self.comments:

-            if _leaf_index == index:
+            if _index == index:

                 yield comment_after
 
     def remove_trailing_comma(self) -> None:
                 yield comment_after
 
     def remove_trailing_comma(self) -> None:


@@ -1011,9 +1035,8 @@ class Line:
             and subscript_start.type == syms.subscriptlist
         ):
             subscript_start = child_towards(subscript_start, leaf)
             and subscript_start.type == syms.subscriptlist
         ):
             subscript_start = child_towards(subscript_start, leaf)

-        return (
-            subscript_start is not None
-            and any(n.type in TEST_DESCENDANTS for n in subscript_start.pre_order())
+        return subscript_start is not None and any(
+            n.type in TEST_DESCENDANTS for n in subscript_start.pre_order()

         )
 
     def __str__(self) -> str:
         )
 
     def __str__(self) -> str:


@@ -1094,6 +1117,7 @@ class EmptyLineTracker:
     the prefix of the first leaf consists of optional newlines.  Those newlines
     are consumed by `maybe_empty_lines()` and included in the computation.
     """
     the prefix of the first leaf consists of optional newlines.  Those newlines
     are consumed by `maybe_empty_lines()` and included in the computation.
     """

+    is_pyi: bool = False

     previous_line: Optional[Line] = None
     previous_after: int = 0
     previous_defs: List[int] = Factory(list)
     previous_line: Optional[Line] = None
     previous_after: int = 0
     previous_defs: List[int] = Factory(list)


@@ -1117,7 +1141,7 @@ class EmptyLineTracker:
     def _maybe_empty_lines(self, current_line: Line) -> Tuple[int, int]:
         max_allowed = 1
         if current_line.depth == 0:
     def _maybe_empty_lines(self, current_line: Line) -> Tuple[int, int]:
         max_allowed = 1
         if current_line.depth == 0:

-            max_allowed = 2
+            max_allowed = 1 if self.is_pyi else 2

         if current_line.leaves:
             # Consume the first leaf's extra newlines.
             first_leaf = current_line.leaves[0]
         if current_line.leaves:
             # Consume the first leaf's extra newlines.
             first_leaf = current_line.leaves[0]


@@ -1129,7 +1153,10 @@ class EmptyLineTracker:
         depth = current_line.depth
         while self.previous_defs and self.previous_defs[-1] >= depth:
             self.previous_defs.pop()
         depth = current_line.depth
         while self.previous_defs and self.previous_defs[-1] >= depth:
             self.previous_defs.pop()

-            before = 1 if depth else 2
+            if self.is_pyi:
+                before = 0 if depth else 1
+            else:
+                before = 1 if depth else 2

         is_decorator = current_line.is_decorator
         if is_decorator or current_line.is_def or current_line.is_class:
             if not is_decorator:
         is_decorator = current_line.is_decorator
         if is_decorator or current_line.is_def or current_line.is_class:
             if not is_decorator:


@@ -1148,8 +1175,19 @@ class EmptyLineTracker:
             ):
                 return 0, 0
 
             ):
                 return 0, 0
 

-            newlines = 2
-            if current_line.depth:
+            if self.is_pyi:
+                if self.previous_line.depth > current_line.depth:
+                    newlines = 1
+                elif current_line.is_class or self.previous_line.is_class:
+                    if current_line.is_stub_class and self.previous_line.is_stub_class:
+                        newlines = 0
+                    else:
+                        newlines = 1
+                else:
+                    newlines = 0
+            else:
+                newlines = 2
+            if current_line.depth and newlines:

                 newlines -= 1
             return newlines, 0
 
                 newlines -= 1
             return newlines, 0
 


@@ -1171,6 +1209,7 @@ class LineGenerator(Visitor[Line]):
     Note: destroys the tree it's visiting by mutating prefixes of its leaves
     in ways that will no longer stringify to valid Python code on the tree.
     """
     Note: destroys the tree it's visiting by mutating prefixes of its leaves
     in ways that will no longer stringify to valid Python code on the tree.
     """

+    is_pyi: bool = False

     current_line: Line = Factory(Line)
     remove_u_prefix: bool = False
 
     current_line: Line = Factory(Line)
     remove_u_prefix: bool = False
 


@@ -1277,7 +1316,7 @@ class LineGenerator(Visitor[Line]):
         The relevant Python language `keywords` for a given statement will be
         NAME leaves within it. This methods puts those on a separate line.
 
         The relevant Python language `keywords` for a given statement will be
         NAME leaves within it. This methods puts those on a separate line.
 

-        `parens` holds a set of string leaf values immeditely after which
+        `parens` holds a set of string leaf values immediately after which

         invisible parens should be put.
         """
         normalize_invisible_parens(node, parens_after=parens)
         invisible parens should be put.
         """
         normalize_invisible_parens(node, parens_after=parens)


@@ -1287,16 +1326,27 @@ class LineGenerator(Visitor[Line]):
 
             yield from self.visit(child)
 
 
             yield from self.visit(child)
 

+    def visit_suite(self, node: Node) -> Iterator[Line]:
+        """Visit a suite."""
+        if self.is_pyi and is_stub_suite(node):
+            yield from self.visit(node.children[2])
+        else:
+            yield from self.visit_default(node)
+

     def visit_simple_stmt(self, node: Node) -> Iterator[Line]:
         """Visit a statement without nested statements."""
         is_suite_like = node.parent and node.parent.type in STATEMENT
         if is_suite_like:
     def visit_simple_stmt(self, node: Node) -> Iterator[Line]:
         """Visit a statement without nested statements."""
         is_suite_like = node.parent and node.parent.type in STATEMENT
         if is_suite_like:

-            yield from self.line(+1)
-            yield from self.visit_default(node)
-            yield from self.line(-1)
+            if self.is_pyi and is_stub_body(node):
+                yield from self.visit_default(node)
+            else:
+                yield from self.line(+1)
+                yield from self.visit_default(node)
+                yield from self.line(-1)

 
         else:
 
         else:

-            yield from self.line()
+            if not self.is_pyi or not node.parent or not is_stub_suite(node.parent):
+                yield from self.line()

             yield from self.visit_default(node)
 
     def visit_async_stmt(self, node: Node) -> Iterator[Line]:
             yield from self.visit_default(node)
 
     def visit_async_stmt(self, node: Node) -> Iterator[Line]:


@@ -1423,10 +1473,11 @@ def whitespace(leaf: Leaf, *, complex_subscript: bool) -> str:  # noqa C901
         return DOUBLESPACE
 
     assert p is not None, f"INTERNAL ERROR: hand-made leaf without parent: {leaf!r}"
         return DOUBLESPACE
 
     assert p is not None, f"INTERNAL ERROR: hand-made leaf without parent: {leaf!r}"

-    if (
-        t == token.COLON
-        and p.type not in {syms.subscript, syms.subscriptlist, syms.sliceop}
-    ):
+    if t == token.COLON and p.type not in {
+        syms.subscript,
+        syms.subscriptlist,
+        syms.sliceop,
+    }:

         return NO
 
     prev = leaf.prev_sibling
         return NO
 
     prev = leaf.prev_sibling


@@ -1447,7 +1498,10 @@ def whitespace(leaf: Leaf, *, complex_subscript: bool) -> str:  # noqa C901
         if prevp.type == token.EQUAL:
             if prevp.parent:
                 if prevp.parent.type in {
         if prevp.type == token.EQUAL:
             if prevp.parent:
                 if prevp.parent.type in {

-                    syms.arglist, syms.argument, syms.parameters, syms.varargslist
+                    syms.arglist,
+                    syms.argument,
+                    syms.parameters,
+                    syms.varargslist,

                 }:
                     return NO
 
                 }:
                     return NO
 


@@ -1600,10 +1654,10 @@ def whitespace(leaf: Leaf, *, complex_subscript: bool) -> str:  # noqa C901
 
             prevp_parent = prevp.parent
             assert prevp_parent is not None
 
             prevp_parent = prevp.parent
             assert prevp_parent is not None

-            if (
-                prevp.type == token.COLON
-                and prevp_parent.type in {syms.subscript, syms.sliceop}
-            ):
+            if prevp.type == token.COLON and prevp_parent.type in {
+                syms.subscript,
+                syms.sliceop,
+            }:

                 return NO
 
             elif prevp.type == token.EQUAL and prevp_parent.type == syms.argument:
                 return NO
 
             elif prevp.type == token.EQUAL and prevp_parent.type == syms.argument:


@@ -1683,6 +1737,14 @@ def is_split_before_delimiter(leaf: Leaf, previous: Leaf = None) -> int:
         # Don't treat them as a delimiter.
         return 0
 
         # Don't treat them as a delimiter.
         return 0
 

+    if (
+        leaf.type == token.DOT
+        and leaf.parent
+        and leaf.parent.type not in {syms.import_from, syms.dotted_name}
+        and (previous is None or previous.type in CLOSING_BRACKETS)
+    ):
+        return DOT_PRIORITY
+

     if (
         leaf.type in MATH_OPERATORS
         and leaf.parent
     if (
         leaf.type in MATH_OPERATORS
         and leaf.parent


@@ -1700,31 +1762,54 @@ def is_split_before_delimiter(leaf: Leaf, previous: Leaf = None) -> int:
     ):
         return STRING_PRIORITY
 
     ):
         return STRING_PRIORITY
 

+    if leaf.type != token.NAME:
+        return 0
+

     if (
     if (

-        leaf.type == token.NAME
-        and leaf.value == "for"
+        leaf.value == "for"

         and leaf.parent
         and leaf.parent.type in {syms.comp_for, syms.old_comp_for}
     ):
         return COMPREHENSION_PRIORITY
 
     if (
         and leaf.parent
         and leaf.parent.type in {syms.comp_for, syms.old_comp_for}
     ):
         return COMPREHENSION_PRIORITY
 
     if (

-        leaf.type == token.NAME
-        and leaf.value == "if"
+        leaf.value == "if"

         and leaf.parent
         and leaf.parent.type in {syms.comp_if, syms.old_comp_if}
     ):
         return COMPREHENSION_PRIORITY
 
         and leaf.parent
         and leaf.parent.type in {syms.comp_if, syms.old_comp_if}
     ):
         return COMPREHENSION_PRIORITY
 

+    if leaf.value in {"if", "else"} and leaf.parent and leaf.parent.type == syms.test:
+        return TERNARY_PRIORITY
+
+    if leaf.value == "is":
+        return COMPARATOR_PRIORITY
+

     if (
     if (

-        leaf.type == token.NAME
-        and leaf.value in {"if", "else"}
+        leaf.value == "in"

         and leaf.parent
         and leaf.parent

-        and leaf.parent.type == syms.test
+        and leaf.parent.type in {syms.comp_op, syms.comparison}
+        and not (
+            previous is not None
+            and previous.type == token.NAME
+            and previous.value == "not"
+        )

     ):
     ):

-        return TERNARY_PRIORITY
+        return COMPARATOR_PRIORITY

 
 

-    if leaf.type == token.NAME and leaf.value in LOGIC_OPERATORS and leaf.parent:
+    if (
+        leaf.value == "not"
+        and leaf.parent
+        and leaf.parent.type == syms.comp_op
+        and not (
+            previous is not None
+            and previous.type == token.NAME
+            and previous.value == "is"
+        )
+    ):
+        return COMPARATOR_PRIORITY
+
+    if leaf.value in LOGIC_OPERATORS and leaf.parent:

         return LOGIC_PRIORITY
 
     return 0
         return LOGIC_PRIORITY
 
     return 0


@@ -1824,10 +1909,8 @@ def split_line(
         return
 
     line_str = str(line).strip("\n")
         return
 
     line_str = str(line).strip("\n")

-    if (
-        len(line_str) <= line_length
-        and "\n" not in line_str  # multiline strings
-        and not line.contains_standalone_comments()
+    if not line.should_explode and is_line_short_enough(
+        line, line_length=line_length, line_str=line_str

     ):
         yield line
         return
     ):
         yield line
         return


@@ -1835,12 +1918,22 @@ def split_line(
     split_funcs: List[SplitFunc]
     if line.is_def:
         split_funcs = [left_hand_split]
     split_funcs: List[SplitFunc]
     if line.is_def:
         split_funcs = [left_hand_split]

-    elif line.is_import:
-        split_funcs = [explode_split]
-    elif line.inside_brackets:
-        split_funcs = [delimiter_split, standalone_comment_split, right_hand_split]

     else:
     else:

-        split_funcs = [right_hand_split]
+
+        def rhs(line: Line, py36: bool = False) -> Iterator[Line]:
+            for omit in generate_trailers_to_omit(line, line_length):
+                lines = list(right_hand_split(line, py36, omit=omit))
+                if is_line_short_enough(lines[0], line_length=line_length):
+                    yield from lines
+                    return
+
+            # All splits failed, best effort split with no omits.
+            yield from right_hand_split(line, py36)
+
+        if line.inside_brackets:
+            split_funcs = [delimiter_split, standalone_comment_split, rhs]
+        else:
+            split_funcs = [rhs]

     for split_func in split_funcs:
         # We are accumulating lines in `result` because we might want to abort
         # mission and return the original line in the end, or attempt a different
     for split_func in split_funcs:
         # We are accumulating lines in `result` because we might want to abort
         # mission and return the original line in the end, or attempt a different


@@ -1913,6 +2006,10 @@ def right_hand_split(
     """Split line into many lines, starting with the last matching bracket pair.
 
     If the split was by optional parentheses, attempt splitting without them, too.
     """Split line into many lines, starting with the last matching bracket pair.
 
     If the split was by optional parentheses, attempt splitting without them, too.

+    `omit` is a collection of closing bracket IDs that shouldn't be considered for
+    this split.
+
+    Note: running this function modifies `bracket_depth` on the leaves of `line`.

     """
     head = Line(depth=line.depth)
     body = Line(depth=line.depth + 1, inside_brackets=True)
     """
     head = Line(depth=line.depth)
     body = Line(depth=line.depth + 1, inside_brackets=True)


@@ -1939,8 +2036,9 @@ def right_hand_split(
     # Since body is a new indent level, remove spurious leading whitespace.
     if body_leaves:
         normalize_prefix(body_leaves[0], inside_brackets=True)
     # Since body is a new indent level, remove spurious leading whitespace.
     if body_leaves:
         normalize_prefix(body_leaves[0], inside_brackets=True)

-    elif not head_leaves:
-        # No `head` and no `body` means the split failed. `tail` has all content.
+    if not head_leaves:
+        # No `head` means the split failed. Either `tail` has all content or
+        # the matching `opening_bracket` wasn't available on `line` anymore.

         raise CannotSplit("No brackets found")
 
     # Build the new lines.
         raise CannotSplit("No brackets found")
 
     # Build the new lines.


@@ -1958,22 +2056,31 @@ def right_hand_split(
         # the closing bracket is an optional paren
         and closing_bracket.type == token.RPAR
         and not closing_bracket.value
         # the closing bracket is an optional paren
         and closing_bracket.type == token.RPAR
         and not closing_bracket.value

-        # there are no delimiters or standalone comments in the body
-        and not body.bracket_tracker.delimiters
+        # there are no standalone comments in the body

         and not line.contains_standalone_comments(0)
         # and 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
     ):
         omit = {id(closing_bracket), *omit}
         and not line.contains_standalone_comments(0)
         # and 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
     ):
         omit = {id(closing_bracket), *omit}

-        try:
-            yield from right_hand_split(line, py36=py36, omit=omit)
-            return
-        except CannotSplit:
-            pass
+        delimiter_count = body.bracket_tracker.delimiter_count_with_priority()
+        if (
+            delimiter_count == 0
+            or delimiter_count == 1
+            and (
+                body.leaves[0].type in OPENING_BRACKETS
+                or body.leaves[-1].type in CLOSING_BRACKETS
+            )
+        ):
+            try:
+                yield from right_hand_split(line, py36=py36, omit=omit)
+                return
+            except CannotSplit:
+                pass

 
     ensure_visible(opening_bracket)
     ensure_visible(closing_bracket)
 
     ensure_visible(opening_bracket)
     ensure_visible(closing_bracket)

+    body.should_explode = should_explode(body, opening_bracket)

     for result in (head, body, tail):
         if result:
             yield result
     for result in (head, body, tail):
         if result:
             yield result


@@ -2032,14 +2139,16 @@ def delimiter_split(line: Line, py36: bool = False) -> Iterator[Line]:
     except IndexError:
         raise CannotSplit("Line empty")
 
     except IndexError:
         raise CannotSplit("Line empty")
 

-    delimiters = line.bracket_tracker.delimiters
+    bt = line.bracket_tracker

     try:
     try:

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

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

+    if delimiter_priority == DOT_PRIORITY:
+        if bt.delimiter_count_with_priority(delimiter_priority) == 1:
+            raise CannotSplit("Splitting a single attribute from its owner looks wrong")
+

     current_line = Line(depth=line.depth, inside_brackets=line.inside_brackets)
     lowest_depth = sys.maxsize
     trailing_comma_safe = True
     current_line = Line(depth=line.depth, inside_brackets=line.inside_brackets)
     lowest_depth = sys.maxsize
     trailing_comma_safe = True


@@ -2055,19 +2164,18 @@ def delimiter_split(line: Line, py36: bool = False) -> Iterator[Line]:
             current_line = Line(depth=line.depth, inside_brackets=line.inside_brackets)
             current_line.append(leaf)
 
             current_line = Line(depth=line.depth, inside_brackets=line.inside_brackets)
             current_line.append(leaf)
 

-    for leaf in line.leaves:
+    for index, leaf in enumerate(line.leaves):

         yield from append_to_line(leaf)
 
         yield from append_to_line(leaf)
 

-        for comment_after in line.comments_after(leaf):
+        for comment_after in line.comments_after(leaf, index):

             yield from append_to_line(comment_after)
 
         lowest_depth = min(lowest_depth, leaf.bracket_depth)
             yield from append_to_line(comment_after)
 
         lowest_depth = min(lowest_depth, leaf.bracket_depth)

-        if (
-            leaf.bracket_depth == lowest_depth
-            and is_vararg(leaf, within=VARARGS_PARENTS)
+        if leaf.bracket_depth == lowest_depth and is_vararg(
+            leaf, within=VARARGS_PARENTS

         ):
             trailing_comma_safe = trailing_comma_safe and py36
         ):
             trailing_comma_safe = trailing_comma_safe and py36

-        leaf_priority = delimiters.get(id(leaf))
+        leaf_priority = bt.delimiters.get(id(leaf))

         if leaf_priority == delimiter_priority:
             yield current_line
 
         if leaf_priority == delimiter_priority:
             yield current_line
 


@@ -2102,36 +2210,16 @@ def standalone_comment_split(line: Line, py36: bool = False) -> Iterator[Line]:
             current_line = Line(depth=line.depth, inside_brackets=line.inside_brackets)
             current_line.append(leaf)
 
             current_line = Line(depth=line.depth, inside_brackets=line.inside_brackets)
             current_line.append(leaf)
 

-    for leaf in line.leaves:
+    for index, leaf in enumerate(line.leaves):

         yield from append_to_line(leaf)
 
         yield from append_to_line(leaf)
 

-        for comment_after in line.comments_after(leaf):
+        for comment_after in line.comments_after(leaf, index):

             yield from append_to_line(comment_after)
 
     if current_line:
         yield current_line
 
 
             yield from append_to_line(comment_after)
 
     if current_line:
         yield current_line
 
 

-def explode_split(
-    line: Line, py36: bool = False, omit: Collection[LeafID] = ()
-) -> Iterator[Line]:
-    """Split by rightmost bracket and immediately split contents by a delimiter."""
-    new_lines = list(right_hand_split(line, py36, omit))
-    if len(new_lines) != 3:
-        yield from new_lines
-        return
-
-    yield new_lines[0]
-
-    try:
-        yield from delimiter_split(new_lines[1], py36)
-
-    except CannotSplit:
-        yield new_lines[1]
-
-    yield new_lines[2]
-
-

 def is_import(leaf: Leaf) -> bool:
     """Return True if the given leaf starts an import statement."""
     p = leaf.parent
 def is_import(leaf: Leaf) -> bool:
     """Return True if the given leaf starts an import statement."""
     p = leaf.parent


@@ -2261,7 +2349,7 @@ def normalize_invisible_parens(node: Node, parens_after: Set[str]) -> None:
                 rpar = Leaf(token.RPAR, ")")
                 index = child.remove() or 0
                 node.insert_child(index, Node(syms.atom, [lpar, child, rpar]))
                 rpar = Leaf(token.RPAR, ")")
                 index = child.remove() or 0
                 node.insert_child(index, Node(syms.atom, [lpar, child, rpar]))

-            else:
+            elif not (isinstance(child, Leaf) and is_multiline_string(child)):

                 # wrap child in invisible parentheses
                 lpar = Leaf(token.LPAR, "")
                 rpar = Leaf(token.RPAR, "")
                 # wrap child in invisible parentheses
                 lpar = Leaf(token.LPAR, "")
                 rpar = Leaf(token.RPAR, "")


@@ -2372,6 +2460,41 @@ def is_vararg(leaf: Leaf, within: Set[NodeType]) -> bool:
     return p.type in within
 
 
     return p.type in within
 
 

+def is_multiline_string(leaf: Leaf) -> bool:
+    """Return True if `leaf` is a multiline string that actually spans many lines."""
+    value = leaf.value.lstrip("furbFURB")
+    return value[:3] in {'"""', "'''"} and "\n" in value
+
+
+def is_stub_suite(node: Node) -> bool:
+    """Return True if `node` is a suite with a stub body."""
+    if (
+        len(node.children) != 4
+        or node.children[0].type != token.NEWLINE
+        or node.children[1].type != token.INDENT
+        or node.children[3].type != token.DEDENT
+    ):
+        return False
+
+    return is_stub_body(node.children[2])
+
+
+def is_stub_body(node: LN) -> bool:
+    """Return True if `node` is a simple statement containing an ellipsis."""
+    if not isinstance(node, Node) or node.type != syms.simple_stmt:
+        return False
+
+    if len(node.children) != 2:
+        return False
+
+    child = node.children[0]
+    return (
+        child.type == syms.atom
+        and len(child.children) == 3
+        and all(leaf == Leaf(token.DOT, ".") for leaf in child.children)
+    )
+
+

 def max_delimiter_priority_in_atom(node: LN) -> int:
     """Return maximum delimiter priority inside `node`.
 
 def max_delimiter_priority_in_atom(node: LN) -> int:
     """Return maximum delimiter priority inside `node`.
 


@@ -2412,6 +2535,17 @@ def ensure_visible(leaf: Leaf) -> None:
         leaf.value = ")"
 
 
         leaf.value = ")"
 
 

+def should_explode(line: Line, opening_bracket: Leaf) -> bool:
+    """Should `line` immediately be split with `delimiter_split()` after RHS?"""
+    return bool(
+        opening_bracket.parent
+        and opening_bracket.parent.type in {syms.atom, syms.import_from}
+        and opening_bracket.value in "[{("
+        and line.bracket_tracker.delimiters
+        and line.bracket_tracker.max_delimiter_priority() == COMMA_PRIORITY
+    )
+
+

 def is_python36(node: Node) -> bool:
     """Return True if the current file is using Python 3.6+ features.
 
 def is_python36(node: Node) -> bool:
     """Return True if the current file is using Python 3.6+ features.
 


@@ -2442,6 +2576,67 @@ def is_python36(node: Node) -> bool:
     return False
 
 
     return False
 
 

+def generate_trailers_to_omit(line: Line, line_length: int) -> Iterator[Set[LeafID]]:
+    """Generate sets of closing bracket IDs that should be omitted in a RHS.
+
+    Brackets can be omitted if the entire trailer up to and including
+    a preceding closing bracket fits in one line.
+
+    Yielded sets are cumulative (contain results of previous yields, too).  First
+    set is empty.
+    """
+
+    omit: Set[LeafID] = set()
+    yield omit
+
+    length = 4 * line.depth
+    opening_bracket = None
+    closing_bracket = None
+    optional_brackets: Set[LeafID] = set()
+    inner_brackets: Set[LeafID] = set()
+    for index, leaf in enumerate_reversed(line.leaves):
+        length += len(leaf.prefix) + len(leaf.value)
+        if length > line_length:
+            break
+
+        comment: Optional[Leaf]
+        for comment in line.comments_after(leaf, index):
+            if "\n" in comment.prefix:
+                break  # Oops, standalone comment!
+
+            length += len(comment.value)
+        else:
+            comment = None
+        if comment is not None:
+            break  # There was a standalone comment, we can't continue.
+
+        optional_brackets.discard(id(leaf))
+        if opening_bracket:
+            if leaf is opening_bracket:
+                opening_bracket = None
+            elif leaf.type in CLOSING_BRACKETS:
+                inner_brackets.add(id(leaf))
+        elif leaf.type in CLOSING_BRACKETS:
+            if not leaf.value:
+                optional_brackets.add(id(opening_bracket))
+                continue
+
+            if index > 0 and line.leaves[index - 1].type in OPENING_BRACKETS:
+                # Empty brackets would fail a split so treat them as "inner"
+                # brackets (e.g. only add them to the `omit` set if another
+                # pair of brackets was good enough.
+                inner_brackets.add(id(leaf))
+                continue
+
+            opening_bracket = leaf.opening_bracket
+            if closing_bracket:
+                omit.add(id(closing_bracket))
+                omit.update(inner_brackets)
+                inner_brackets.clear()
+                yield omit
+            closing_bracket = leaf
+
+

 def get_future_imports(node: Node) -> Set[str]:
     """Return a set of __future__ imports in the file."""
     imports = set()
 def get_future_imports(node: Node) -> Set[str]:
     """Return a set of __future__ imports in the file."""
     imports = set()


@@ -2477,9 +2672,17 @@ def get_future_imports(node: Node) -> Set[str]:
     return imports
 
 
     return imports
 
 

-PYTHON_EXTENSIONS = {".py"}
+PYTHON_EXTENSIONS = {".py", ".pyi"}

 BLACKLISTED_DIRECTORIES = {
 BLACKLISTED_DIRECTORIES = {

-    "build", "buck-out", "dist", "_build", ".git", ".hg", ".mypy_cache", ".tox", ".venv"
+    "build",
+    "buck-out",
+    "dist",
+    "_build",
+    ".git",
+    ".hg",
+    ".mypy_cache",
+    ".tox",
+    ".venv",

 }
 
 
 }
 
 


@@ -2494,7 +2697,7 @@ def gen_python_files_in_dir(path: Path) -> Iterator[Path]:
 
             yield from gen_python_files_in_dir(child)
 
 
             yield from gen_python_files_in_dir(child)
 

-        elif child.suffix in PYTHON_EXTENSIONS:
+        elif child.is_file() and child.suffix in PYTHON_EXTENSIONS:

             yield child
 
 
             yield child
 
 


@@ -2640,9 +2843,9 @@ def assert_equivalent(src: str, dst: str) -> None:
         ) from None
 
 
         ) from None
 
 

-def assert_stable(src: str, dst: str, line_length: int) -> None:
+def assert_stable(src: str, dst: str, line_length: int, is_pyi: bool = False) -> None:

     """Raise AssertionError if `dst` reformats differently the second time."""
     """Raise AssertionError if `dst` reformats differently the second time."""

-    newdst = format_str(dst, line_length=line_length)
+    newdst = format_str(dst, line_length=line_length, is_pyi=is_pyi)

     if dst != newdst:
         log = dump_to_file(
             diff(src, dst, "source", "first pass"),
     if dst != newdst:
         log = dump_to_file(
             diff(src, dst, "source", "first pass"),


@@ -2681,7 +2884,7 @@ def diff(a: str, b: str, a_name: str, b_name: str) -> str:
     )
 
 
     )
 
 

-def cancel(tasks: List[asyncio.Task]) -> None:
+def cancel(tasks: Iterable[asyncio.Task]) -> None:

     """asyncio signal handler that cancels all `tasks` and reports to stderr."""
     err("Aborted!")
     for task in tasks:
     """asyncio signal handler that cancels all `tasks` and reports to stderr."""
     err("Aborted!")
     for task in tasks:


@@ -2719,6 +2922,28 @@ def sub_twice(regex: Pattern[str], replacement: str, original: str) -> str:
     return regex.sub(replacement, regex.sub(replacement, original))
 
 
     return regex.sub(replacement, regex.sub(replacement, original))
 
 

+def enumerate_reversed(sequence: Sequence[T]) -> Iterator[Tuple[Index, T]]:
+    """Like `reversed(enumerate(sequence))` if that were possible."""
+    index = len(sequence) - 1
+    for element in reversed(sequence):
+        yield (index, element)
+        index -= 1
+
+
+def is_line_short_enough(line: Line, *, line_length: int, line_str: str = "") -> bool:
+    """Return True if `line` is no longer than `line_length`.
+
+    Uses the provided `line_str` rendering, if any, otherwise computes a new one.
+    """
+    if not line_str:
+        line_str = str(line).strip("\n")
+    return (
+        len(line_str) <= line_length
+        and "\n" not in line_str  # multiline strings
+        and not line.contains_standalone_comments()
+    )
+
+

 CACHE_DIR = Path(user_cache_dir("black", version=__version__))
 
 
 CACHE_DIR = Path(user_cache_dir("black", version=__version__))