Don't fold postscriptum standalone comment into last statement

[etc/vim.git] / black.py

diff --git a/black.py b/black.py
index 51b5b218889975090b41621c9e25ff0ae94c3a54..f305e8dd79e66d76168e16e06c3fc4302e6c61e1 100644 (file)
--- a/black.py
+++ b/black.py
@@ -12,7 +12,7 @@ from typing import (
     Dict, Generic, Iterable, Iterator, List, Optional, Set, Tuple, TypeVar, Union
 )
 
     Dict, Generic, Iterable, Iterator, List, Optional, Set, Tuple, TypeVar, Union
 )
 

-from attr import attrib, dataclass, Factory
+from attr import dataclass, Factory

 import click
 
 # lib2to3 fork
 import click
 
 # lib2to3 fork


@@ -21,7 +21,7 @@ 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__ = "18.3a1"
+__version__ = "18.3a2"

 DEFAULT_LINE_LENGTH = 88
 # types
 syms = pygram.python_symbols
 DEFAULT_LINE_LENGTH = 88
 # types
 syms = pygram.python_symbols


@@ -210,8 +210,13 @@ def format_str(src_contents: str, line_length: int) -> FileContent:
                 dst_contents += str(line)
         else:
             comments.append(current_line)
                 dst_contents += str(line)
         else:
             comments.append(current_line)

-    for comment in comments:
-        dst_contents += str(comment)
+    if comments:
+        if elt.previous_defs:
+            # Separate postscriptum comments from the last module-level def.
+            dst_contents += str(empty_line)
+            dst_contents += str(empty_line)
+        for comment in comments:
+            dst_contents += str(comment)

     return dst_contents
 
 
     return dst_contents
 
 


@@ -265,7 +270,7 @@ class Visitor(Generic[T]):
 
 @dataclass
 class DebugVisitor(Visitor[T]):
 
 @dataclass
 class DebugVisitor(Visitor[T]):

-    tree_depth: int = attrib(default=0)
+    tree_depth: int = 0

 
     def visit_default(self, node: LN) -> Iterator[T]:
         indent = ' ' * (2 * self.tree_depth)
 
     def visit_default(self, node: LN) -> Iterator[T]:
         indent = ' ' * (2 * self.tree_depth)


@@ -335,10 +340,10 @@ MATH_PRIORITY = 1
 
 @dataclass
 class BracketTracker:
 
 @dataclass
 class BracketTracker:

-    depth: int = attrib(default=0)
-    bracket_match: Dict[Tuple[Depth, NodeType], Leaf] = attrib(default=Factory(dict))
-    delimiters: Dict[LeafID, Priority] = attrib(default=Factory(dict))
-    previous: Optional[Leaf] = attrib(default=None)
+    depth: int = 0
+    bracket_match: Dict[Tuple[Depth, NodeType], Leaf] = Factory(dict)
+    delimiters: Dict[LeafID, Priority] = Factory(dict)
+    previous: Optional[Leaf] = None

 
     def mark(self, leaf: Leaf) -> None:
         if leaf.type == token.COMMENT:
 
     def mark(self, leaf: Leaf) -> None:
         if leaf.type == token.COMMENT:


@@ -357,19 +362,25 @@ class BracketTracker:
                 if leaf.type == token.STRING and self.previous.type == token.STRING:
                     self.delimiters[id(self.previous)] = STRING_PRIORITY
                 elif (
                 if leaf.type == token.STRING and self.previous.type == token.STRING:
                     self.delimiters[id(self.previous)] = STRING_PRIORITY
                 elif (

-                    leaf.type == token.NAME and
-                    leaf.value == 'for' and
-                    leaf.parent and
-                    leaf.parent.type in {syms.comp_for, syms.old_comp_for}
+                    leaf.type == token.NAME
+                    and leaf.value == 'for'
+                    and leaf.parent
+                    and leaf.parent.type in {syms.comp_for, syms.old_comp_for}

                 ):
                     self.delimiters[id(self.previous)] = COMPREHENSION_PRIORITY
                 elif (
                 ):
                     self.delimiters[id(self.previous)] = COMPREHENSION_PRIORITY
                 elif (

-                    leaf.type == token.NAME and
-                    leaf.value == 'if' and
-                    leaf.parent and
-                    leaf.parent.type in {syms.comp_if, syms.old_comp_if}
+                    leaf.type == token.NAME
+                    and leaf.value == 'if'
+                    and leaf.parent
+                    and leaf.parent.type in {syms.comp_if, syms.old_comp_if}

                 ):
                     self.delimiters[id(self.previous)] = COMPREHENSION_PRIORITY
                 ):
                     self.delimiters[id(self.previous)] = COMPREHENSION_PRIORITY

+                elif (
+                    leaf.type == token.NAME
+                    and leaf.value in LOGIC_OPERATORS
+                    and leaf.parent
+                ):
+                    self.delimiters[id(self.previous)] = LOGIC_PRIORITY

         if leaf.type in OPENING_BRACKETS:
             self.bracket_match[self.depth, BRACKET[leaf.type]] = leaf
             self.depth += 1
         if leaf.type in OPENING_BRACKETS:
             self.bracket_match[self.depth, BRACKET[leaf.type]] = leaf
             self.depth += 1


@@ -389,13 +400,13 @@ class BracketTracker:
 
 @dataclass
 class Line:
 
 @dataclass
 class Line:

-    depth: int = attrib(default=0)
-    leaves: List[Leaf] = attrib(default=Factory(list))
-    comments: Dict[LeafID, Leaf] = attrib(default=Factory(dict))
-    bracket_tracker: BracketTracker = attrib(default=Factory(BracketTracker))
-    inside_brackets: bool = attrib(default=False)
-    has_for: bool = attrib(default=False)
-    _for_loop_variable: bool = attrib(default=False, init=False)
+    depth: int = 0
+    leaves: List[Leaf] = Factory(list)
+    comments: Dict[LeafID, Leaf] = Factory(dict)
+    bracket_tracker: BracketTracker = Factory(BracketTracker)
+    inside_brackets: bool = False
+    has_for: bool = False
+    _for_loop_variable: bool = False

 
     def append(self, leaf: Leaf, preformatted: bool = False) -> None:
         has_value = leaf.value.strip()
 
     def append(self, leaf: Leaf, preformatted: bool = False) -> None:
         has_value = leaf.value.strip()


@@ -432,9 +443,9 @@ class Line:
     @property
     def is_class(self) -> bool:
         return (
     @property
     def is_class(self) -> bool:
         return (

-            bool(self) and
-            self.leaves[0].type == token.NAME and
-            self.leaves[0].value == 'class'
+            bool(self)
+            and self.leaves[0].type == token.NAME
+            and self.leaves[0].value == 'class'

         )
 
     @property
         )
 
     @property


@@ -450,37 +461,37 @@ class Line:
         except IndexError:
             second_leaf = None
         return (
         except IndexError:
             second_leaf = None
         return (

-            (first_leaf.type == token.NAME and first_leaf.value == 'def') or
-            (
-                first_leaf.type == token.NAME and
-                first_leaf.value == 'async' and
-                second_leaf is not None and
-                second_leaf.type == token.NAME and
-                second_leaf.value == 'def'
+            (first_leaf.type == token.NAME and first_leaf.value == 'def')
+            or (
+                first_leaf.type == token.NAME
+                and first_leaf.value == 'async'
+                and second_leaf is not None
+                and second_leaf.type == token.NAME
+                and second_leaf.value == 'def'

             )
         )
 
     @property
     def is_flow_control(self) -> bool:
         return (
             )
         )
 
     @property
     def is_flow_control(self) -> bool:
         return (

-            bool(self) and
-            self.leaves[0].type == token.NAME and
-            self.leaves[0].value in FLOW_CONTROL
+            bool(self)
+            and self.leaves[0].type == token.NAME
+            and self.leaves[0].value in FLOW_CONTROL

         )
 
     @property
     def is_yield(self) -> bool:
         return (
         )
 
     @property
     def is_yield(self) -> bool:
         return (

-            bool(self) and
-            self.leaves[0].type == token.NAME and
-            self.leaves[0].value == 'yield'
+            bool(self)
+            and self.leaves[0].type == token.NAME
+            and self.leaves[0].value == 'yield'

         )
 
     def maybe_remove_trailing_comma(self, closing: Leaf) -> bool:
         if not (
         )
 
     def maybe_remove_trailing_comma(self, closing: Leaf) -> bool:
         if not (

-            self.leaves and
-            self.leaves[-1].type == token.COMMA and
-            closing.type in CLOSING_BRACKETS
+            self.leaves
+            and self.leaves[-1].type == token.COMMA
+            and closing.type in CLOSING_BRACKETS

         ):
             return False
 
         ):
             return False
 


@@ -508,6 +519,10 @@ class Line:
             bracket_depth = leaf.bracket_depth
             if bracket_depth == depth and leaf.type == token.COMMA:
                 commas += 1
             bracket_depth = leaf.bracket_depth
             if bracket_depth == depth and leaf.type == token.COMMA:
                 commas += 1

+                if leaf.parent and leaf.parent.type == syms.arglist:
+                    commas += 1
+                    break
+

         if commas > 1:
             self.leaves.pop()
             return True
         if commas > 1:
             self.leaves.pop()
             return True


@@ -547,8 +562,8 @@ class Line:
         appended will appear "too long" when splitting.
         """
         if not (
         appended will appear "too long" when splitting.
         """
         if not (

-            comment.type == STANDALONE_COMMENT and
-            self.bracket_tracker.any_open_brackets()
+            comment.type == STANDALONE_COMMENT
+            and self.bracket_tracker.any_open_brackets()

         ):
             return False
 
         ):
             return False
 


@@ -605,11 +620,13 @@ class EmptyLineTracker:
     """Provides a stateful method that returns the number of potential extra
     empty lines needed before and after the currently processed line.
 
     """Provides a stateful method that returns the number of potential extra
     empty lines needed before and after the currently processed line.
 

-    Note: this tracker works on lines that haven't been split yet.
+    Note: this tracker works on lines that haven't been split yet.  It assumes
+    the prefix of the first leaf consists of optional newlines.  Those newlines
+    are consumed by `maybe_empty_lines()` and included in the computation.

     """
     """

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

 
     def maybe_empty_lines(self, current_line: Line) -> Tuple[int, int]:
         """Returns the number of extra empty lines before and after the `current_line`.
 
     def maybe_empty_lines(self, current_line: Line) -> Tuple[int, int]:
         """Returns the number of extra empty lines before and after the `current_line`.


@@ -618,17 +635,28 @@ class EmptyLineTracker:
         (two on module-level), as well as providing an extra empty line after flow
         control keywords to make them more prominent.
         """
         (two on module-level), as well as providing an extra empty line after flow
         control keywords to make them more prominent.
         """

+        if current_line.is_comment:
+            # Don't count standalone comments towards previous empty lines.
+            return 0, 0
+

         before, after = self._maybe_empty_lines(current_line)
         before, after = self._maybe_empty_lines(current_line)

+        before -= self.previous_after

         self.previous_after = after
         self.previous_line = current_line
         return before, after
 
     def _maybe_empty_lines(self, current_line: Line) -> Tuple[int, int]:
         self.previous_after = after
         self.previous_line = current_line
         return before, after
 
     def _maybe_empty_lines(self, current_line: Line) -> Tuple[int, int]:

-        before = 0
+        if current_line.leaves:
+            # Consume the first leaf's extra newlines.
+            first_leaf = current_line.leaves[0]
+            before = int('\n' in first_leaf.prefix)
+            first_leaf.prefix = ''
+        else:
+            before = 0

         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) - self.previous_after
+            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:


@@ -644,24 +672,23 @@ class EmptyLineTracker:
             newlines = 2
             if current_line.depth:
                 newlines -= 1
             newlines = 2
             if current_line.depth:
                 newlines -= 1

-            newlines -= self.previous_after

             return newlines, 0
 
         if current_line.is_flow_control:
             return before, 1
 
         if (
             return newlines, 0
 
         if current_line.is_flow_control:
             return before, 1
 
         if (

-            self.previous_line and
-            self.previous_line.is_import and
-            not current_line.is_import and
-            depth == self.previous_line.depth
+            self.previous_line
+            and self.previous_line.is_import
+            and not current_line.is_import
+            and depth == self.previous_line.depth

         ):
             return (before or 1), 0
 
         if (
         ):
             return (before or 1), 0
 
         if (

-            self.previous_line and
-            self.previous_line.is_yield and
-            (not current_line.is_yield or depth != self.previous_line.depth)
+            self.previous_line
+            and self.previous_line.is_yield
+            and (not current_line.is_yield or depth != self.previous_line.depth)

         ):
             return (before or 1), 0
 
         ):
             return (before or 1), 0
 


@@ -675,8 +702,8 @@ 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.
     """

-    current_line: Line = attrib(default=Factory(Line))
-    standalone_comments: List[Leaf] = attrib(default=Factory(list))
+    current_line: Line = Factory(Line)
+    standalone_comments: List[Leaf] = Factory(list)

 
     def line(self, indent: int = 0) -> Iterator[Line]:
         """Generate a line.
 
     def line(self, indent: int = 0) -> Iterator[Line]:
         """Generate a line.


@@ -804,9 +831,10 @@ BRACKET = {token.LPAR: token.RPAR, token.LSQB: token.RSQB, token.LBRACE: token.R
 OPENING_BRACKETS = set(BRACKET.keys())
 CLOSING_BRACKETS = set(BRACKET.values())
 BRACKETS = OPENING_BRACKETS | CLOSING_BRACKETS
 OPENING_BRACKETS = set(BRACKET.keys())
 CLOSING_BRACKETS = set(BRACKET.values())
 BRACKETS = OPENING_BRACKETS | CLOSING_BRACKETS

+ALWAYS_NO_SPACE = CLOSING_BRACKETS | {token.COMMA, token.COLON, STANDALONE_COMMENT}

 
 
 
 

-def whitespace(leaf: Leaf) -> str:
+def whitespace(leaf: Leaf) -> str:  # noqa C901

     """Return whitespace prefix if needed for the given `leaf`."""
     NO = ''
     SPACE = ' '
     """Return whitespace prefix if needed for the given `leaf`."""
     NO = ''
     SPACE = ' '


@@ -814,24 +842,12 @@ def whitespace(leaf: Leaf) -> str:
     t = leaf.type
     p = leaf.parent
     v = leaf.value
     t = leaf.type
     p = leaf.parent
     v = leaf.value

-    if t == token.COLON:
-        return NO
-
-    if t == token.COMMA:
-        return NO
-
-    if t == token.RPAR:
+    if t in ALWAYS_NO_SPACE:

         return NO
 
     if t == token.COMMENT:
         return DOUBLESPACE
 
         return NO
 
     if t == token.COMMENT:
         return DOUBLESPACE
 

-    if t == STANDALONE_COMMENT:
-        return NO
-
-    if t in CLOSING_BRACKETS:
-        return NO
-

     assert p is not None, f"INTERNAL ERROR: hand-made leaf without parent: {leaf!r}"
     prev = leaf.prev_sibling
     if not prev:
     assert p is not None, f"INTERNAL ERROR: hand-made leaf without parent: {leaf!r}"
     prev = leaf.prev_sibling
     if not prev:


@@ -863,7 +879,7 @@ def whitespace(leaf: Leaf) -> str:
             if prevp.parent and prevp.parent.type == syms.subscript:
                 return NO
 
             if prevp.parent and prevp.parent.type == syms.subscript:
                 return NO
 

-        elif prevp.parent and prevp.parent.type == syms.factor:
+        elif prevp.parent and prevp.parent.type in {syms.factor, syms.star_expr}:

             return NO
 
     elif prev.type in OPENING_BRACKETS:
             return NO
 
     elif prev.type in OPENING_BRACKETS:


@@ -960,7 +976,14 @@ def whitespace(leaf: Leaf) -> str:
 
     elif p.type == syms.subscript:
         # indexing
 
     elif p.type == syms.subscript:
         # indexing

-        if not prev or prev.type == token.COLON:
+        if not prev:
+            assert p.parent is not None, "subscripts are always parented"
+            if p.parent.type == syms.subscriptlist:
+                return SPACE
+
+            return NO
+
+        elif prev.type == token.COLON:

             return NO
 
     elif p.type == syms.atom:
             return NO
 
     elif p.type == syms.atom:


@@ -969,9 +992,9 @@ def whitespace(leaf: Leaf) -> str:
             return NO
 
     elif (
             return NO
 
     elif (

-        p.type == syms.listmaker or
-        p.type == syms.testlist_gexp or
-        p.type == syms.subscriptlist
+        p.type == syms.listmaker
+        or p.type == syms.testlist_gexp
+        or p.type == syms.subscriptlist

     ):
         # list interior, including unpacking
         if not prev:
     ):
         # list interior, including unpacking
         if not prev:


@@ -985,7 +1008,7 @@ def whitespace(leaf: Leaf) -> str:
         if prev.type == token.DOUBLESTAR:
             return NO
 
         if prev.type == token.DOUBLESTAR:
             return NO
 

-    elif p.type == syms.factor or p.type == syms.star_expr:
+    elif p.type in {syms.factor, syms.star_expr}:

         # unary ops
         if not prev:
             prevp = preceding_leaf(p)
         # unary ops
         if not prev:
             prevp = preceding_leaf(p)


@@ -1049,16 +1072,13 @@ def is_delimiter(leaf: Leaf) -> int:
     if leaf.type == token.COMMA:
         return COMMA_PRIORITY
 
     if leaf.type == token.COMMA:
         return COMMA_PRIORITY
 

-    if leaf.type == token.NAME and leaf.value in LOGIC_OPERATORS:
-        return LOGIC_PRIORITY
-

     if leaf.type in COMPARATORS:
         return COMPARATOR_PRIORITY
 
     if (
     if leaf.type in COMPARATORS:
         return COMPARATOR_PRIORITY
 
     if (

-        leaf.type in MATH_OPERATORS and
-        leaf.parent and
-        leaf.parent.type not in {syms.factor, syms.star_expr}
+        leaf.type in MATH_OPERATORS
+        and leaf.parent
+        and leaf.parent.type not in {syms.factor, syms.star_expr}

     ):
         return MATH_PRIORITY
 
     ):
         return MATH_PRIORITY
 


@@ -1095,7 +1115,7 @@ def generate_comments(leaf: Leaf) -> Iterator[Leaf]:
     if content and (content[0] not in {' ', '!', '#'}):
         content = ' ' + content
     is_standalone_comment = (
     if content and (content[0] not in {' ', '!', '#'}):
         content = ' ' + content
     is_standalone_comment = (

-        '\n' in before_comment or '\n' in content or leaf.type == token.DEDENT
+        '\n' in before_comment or '\n' in content or leaf.type == token.ENDMARKER

     )
     if not is_standalone_comment:
         # simple trailing comment
     )
     if not is_standalone_comment:
         # simple trailing comment


@@ -1178,11 +1198,11 @@ def left_hand_split(line: Line, py36: bool = False) -> Iterator[Line]:
     matching_bracket = None
     for leaf in line.leaves:
         if (
     matching_bracket = None
     for leaf in line.leaves:
         if (

-            current_leaves is body_leaves and
-            leaf.type in CLOSING_BRACKETS and
-            leaf.opening_bracket is matching_bracket
+            current_leaves is body_leaves
+            and leaf.type in CLOSING_BRACKETS
+            and leaf.opening_bracket is matching_bracket

         ):
         ):

-            current_leaves = tail_leaves
+            current_leaves = tail_leaves if body_leaves else head_leaves

         current_leaves.append(leaf)
         if current_leaves is head_leaves:
             if leaf.type in OPENING_BRACKETS:
         current_leaves.append(leaf)
         if current_leaves is head_leaves:
             if leaf.type in OPENING_BRACKETS:


@@ -1200,18 +1220,7 @@ def left_hand_split(line: Line, py36: bool = False) -> Iterator[Line]:
             comment_after = line.comments.get(id(leaf))
             if comment_after:
                 result.append(comment_after, preformatted=True)
             comment_after = line.comments.get(id(leaf))
             if comment_after:
                 result.append(comment_after, preformatted=True)

-    # Check if the split succeeded.
-    tail_len = len(str(tail))
-    if not body:
-        if tail_len == 0:
-            raise CannotSplit("Splitting brackets produced the same line")
-
-        elif tail_len < 3:
-            raise CannotSplit(
-                f"Splitting brackets on an empty body to save "
-                f"{tail_len} characters is not worth it"
-            )
-
+    split_succeeded_or_raise(head, body, tail)

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


@@ -1230,7 +1239,7 @@ def right_hand_split(line: Line, py36: bool = False) -> Iterator[Line]:
     for leaf in reversed(line.leaves):
         if current_leaves is body_leaves:
             if leaf is opening_bracket:
     for leaf in reversed(line.leaves):
         if current_leaves is body_leaves:
             if leaf is opening_bracket:

-                current_leaves = head_leaves
+                current_leaves = head_leaves if body_leaves else tail_leaves

         current_leaves.append(leaf)
         if current_leaves is tail_leaves:
             if leaf.type in CLOSING_BRACKETS:
         current_leaves.append(leaf)
         if current_leaves is tail_leaves:
             if leaf.type in CLOSING_BRACKETS:


@@ -1251,8 +1260,14 @@ def right_hand_split(line: Line, py36: bool = False) -> Iterator[Line]:
             comment_after = line.comments.get(id(leaf))
             if comment_after:
                 result.append(comment_after, preformatted=True)
             comment_after = line.comments.get(id(leaf))
             if comment_after:
                 result.append(comment_after, preformatted=True)

-    # Check if the split succeeded.
-    tail_len = len(str(tail).strip('\n'))
+    split_succeeded_or_raise(head, body, tail)
+    for result in (head, body, tail):
+        if result:
+            yield result
+
+
+def split_succeeded_or_raise(head: Line, body: Line, tail: Line) -> None:
+    tail_len = len(str(tail).strip())

     if not body:
         if tail_len == 0:
             raise CannotSplit("Splitting brackets produced the same line")
     if not body:
         if tail_len == 0:
             raise CannotSplit("Splitting brackets produced the same line")


@@ -1263,10 +1278,6 @@ def right_hand_split(line: Line, py36: bool = False) -> Iterator[Line]:
                 f"{tail_len} characters is not worth it"
             )
 
                 f"{tail_len} characters is not worth it"
             )
 

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

 
 def delimiter_split(line: Line, py36: bool = False) -> Iterator[Line]:
     """Split according to delimiters of the highest priority.
 
 def delimiter_split(line: Line, py36: bool = False) -> Iterator[Line]:
     """Split according to delimiters of the highest priority.


@@ -1296,9 +1307,9 @@ def delimiter_split(line: Line, py36: bool = False) -> Iterator[Line]:
             current_line.append(comment_after, preformatted=True)
         lowest_depth = min(lowest_depth, leaf.bracket_depth)
         if (
             current_line.append(comment_after, preformatted=True)
         lowest_depth = min(lowest_depth, leaf.bracket_depth)
         if (

-            leaf.bracket_depth == lowest_depth and
-            leaf.type == token.STAR or
-            leaf.type == token.DOUBLESTAR
+            leaf.bracket_depth == lowest_depth
+            and leaf.type == token.STAR
+            or leaf.type == token.DOUBLESTAR

         ):
             trailing_comma_safe = trailing_comma_safe and py36
         leaf_priority = delimiters.get(id(leaf))
         ):
             trailing_comma_safe = trailing_comma_safe and py36
         leaf_priority = delimiters.get(id(leaf))


@@ -1309,9 +1320,9 @@ def delimiter_split(line: Line, py36: bool = False) -> Iterator[Line]:
             current_line = Line(depth=line.depth, inside_brackets=line.inside_brackets)
     if current_line:
         if (
             current_line = Line(depth=line.depth, inside_brackets=line.inside_brackets)
     if current_line:
         if (

-            delimiter_priority == COMMA_PRIORITY and
-            current_line.leaves[-1].type != token.COMMA and
-            trailing_comma_safe
+            delimiter_priority == COMMA_PRIORITY
+            and current_line.leaves[-1].type != token.COMMA
+            and trailing_comma_safe

         ):
             current_line.append(Leaf(token.COMMA, ','))
         normalize_prefix(current_line.leaves[0])
         ):
             current_line.append(Leaf(token.COMMA, ','))
         normalize_prefix(current_line.leaves[0])


@@ -1324,10 +1335,10 @@ def is_import(leaf: Leaf) -> bool:
     t = leaf.type
     v = leaf.value
     return bool(
     t = leaf.type
     v = leaf.value
     return bool(

-        t == token.NAME and
-        (
-            (v == 'import' and p and p.type == syms.import_name) or
-            (v == 'from' and p and p.type == syms.import_from)
+        t == token.NAME
+        and (
+            (v == 'import' and p and p.type == syms.import_name)
+            or (v == 'from' and p and p.type == syms.import_from)

         )
     )
 
         )
     )
 


@@ -1337,9 +1348,6 @@ def normalize_prefix(leaf: Leaf) -> None:
     if is_import(leaf):
         spl = leaf.prefix.split('#', 1)
         nl_count = spl[0].count('\n')
     if is_import(leaf):
         spl = leaf.prefix.split('#', 1)
         nl_count = spl[0].count('\n')

-        if len(spl) > 1:
-            # Skip one newline since it was for a standalone comment.
-            nl_count -= 1

         leaf.prefix = '\n' * nl_count
         return
 
         leaf.prefix = '\n' * nl_count
         return
 


@@ -1360,9 +1368,9 @@ def is_python36(node: Node) -> bool:
                 return True
 
         elif (
                 return True
 
         elif (

-            n.type == syms.typedargslist and
-            n.children and
-            n.children[-1].type == token.COMMA
+            n.type == syms.typedargslist
+            and n.children
+            and n.children[-1].type == token.COMMA

         ):
             for ch in n.children:
                 if ch.type == token.STAR or ch.type == token.DOUBLESTAR:
         ):
             for ch in n.children:
                 if ch.type == token.STAR or ch.type == token.DOUBLESTAR:


@@ -1392,9 +1400,9 @@ def gen_python_files_in_dir(path: Path) -> Iterator[Path]:
 @dataclass
 class Report:
     """Provides a reformatting counter."""
 @dataclass
 class Report:
     """Provides a reformatting counter."""

-    change_count: int = attrib(default=0)
-    same_count: int = attrib(default=0)
-    failure_count: int = attrib(default=0)
+    change_count: int = 0
+    same_count: int = 0
+    failure_count: int = 0

 
     def done(self, src: Path, changed: bool) -> None:
         """Increment the counter for successful reformatting. Write out a message."""
 
     def done(self, src: Path, changed: bool) -> None:
         """Increment the counter for successful reformatting. Write out a message."""


@@ -1493,7 +1501,7 @@ def assert_equivalent(src: str, dst: str) -> None:
         raise AssertionError(
             f"INTERNAL ERROR: Black produced invalid code: {exc}. "
             f"Please report a bug on https://github.com/ambv/black/issues.  "
         raise AssertionError(
             f"INTERNAL ERROR: Black produced invalid code: {exc}. "
             f"Please report a bug on https://github.com/ambv/black/issues.  "

-            f"This invalid output might be helpful: {log}",
+            f"This invalid output might be helpful: {log}"

         ) from None
 
     src_ast_str = '\n'.join(_v(src_ast))
         ) from None
 
     src_ast_str = '\n'.join(_v(src_ast))


@@ -1504,7 +1512,7 @@ def assert_equivalent(src: str, dst: str) -> None:
             f"INTERNAL ERROR: Black produced code that is not equivalent to "
             f"the source.  "
             f"Please report a bug on https://github.com/ambv/black/issues.  "
             f"INTERNAL ERROR: Black produced code that is not equivalent to "
             f"the source.  "
             f"Please report a bug on https://github.com/ambv/black/issues.  "

-            f"This diff might be helpful: {log}",
+            f"This diff might be helpful: {log}"

         ) from None
 
 
         ) from None
 
 


@@ -1523,7 +1531,7 @@ def assert_stable(src: str, dst: str, line_length: int) -> None:
             f"INTERNAL ERROR: Black produced different code on the second pass "
             f"of the formatter.  "
             f"Please report a bug on https://github.com/ambv/black/issues.  "
             f"INTERNAL ERROR: Black produced different code on the second pass "
             f"of the formatter.  "
             f"Please report a bug on https://github.com/ambv/black/issues.  "

-            f"This diff might be helpful: {log}",
+            f"This diff might be helpful: {log}"

         ) from None
 
 
         ) from None