Fix unstable formatting on trailers omitted from line splitting with comments

Fixes #238

README.md

@@ -661,9 +661,13 @@ More details can be found in [CONTRIBUTING](CONTRIBUTING.md).
 
 * fixed optional parentheses being removed within `# fmt: off` sections (#224)
 
-* fixed invalid code produced when stars in very long imports were incorrectly 
+* fixed invalid code produced when stars in very long imports were incorrectly
   wrapped in optional parentheses (#234)
 
+* fixed unstable formatting when inline comments were moved around in
+  a trailer that was omitted from line splitting on a large expression
+  (#238) 
+
 ### 18.5b0
 
 * call chains are now formatted according to the

black.py

@@ -2599,7 +2599,8 @@ def generate_trailers_to_omit(line: Line, line_length: int) -> Iterator[Set[Leaf
         if length > line_length:
             break
 
-        if leaf.type == STANDALONE_COMMENT:
+        has_inline_comment = leaf_length > len(leaf.value) + len(leaf.prefix)
+        if leaf.type == STANDALONE_COMMENT or has_inline_comment:
             break
 
         optional_brackets.discard(id(leaf))
@@ -2940,9 +2941,6 @@ def enumerate_with_length(
 
         comment: Optional[Leaf]
         for comment in line.comments_after(leaf, index):
-            if "\n" in comment.prefix:
-                return  # Oops, standalone comment!
-
             length += len(comment.value)
 
         yield index, leaf, length

tests/expression.diff

@@ -116,7 +116,7 @@
  call(**self.screen_kwargs)
  call(b, **self.screen_kwargs)
  lukasz.langa.pl
-@@ -93,11 +114,11 @@
+@@ -93,23 +114,25 @@
  1.0 .real
  ....__class__
  list[str]
@@ -127,9 +127,27 @@
  very_long_variable_name_filters: t.List[
      t.Tuple[str, t.Union[str, t.List[t.Optional[str]]]],
  ]
+ xxxx_xxxxx_xxxx_xxx: Callable[..., List[SomeClass]] = classmethod(  # type: ignore
+     sync(async_xxxx_xxx_xxxx_xxxxx_xxxx_xxx.__func__)
+ )
+-xxxx_xxx_xxxx_xxxxx_xxxx_xxx: Callable[..., List[SomeClass]] = classmethod(  # type: ignore
+-    sync(async_xxxx_xxx_xxxx_xxxxx_xxxx_xxx.__func__)
+-)
+ xxxx_xxx_xxxx_xxxxx_xxxx_xxx: Callable[
+     ..., List[SomeClass]
+-] = classmethod(sync(async_xxxx_xxx_xxxx_xxxxx_xxxx_xxx.__func__))  # type: ignore
++] = classmethod(  # type: ignore
++    sync(async_xxxx_xxx_xxxx_xxxxx_xxxx_xxx.__func__)
++)
++xxxx_xxx_xxxx_xxxxx_xxxx_xxx: Callable[..., List[SomeClass]] = classmethod(
++    sync(async_xxxx_xxx_xxxx_xxxxx_xxxx_xxx.__func__)
++)  # type: ignore
  slice[0]
  slice[0:1]
-@@ -124,107 +145,159 @@
+ slice[0:1:2]
+ slice[:]
+ slice[:-1]
+@@ -133,107 +156,159 @@
  numpy[-(c + 1) :, d]
  numpy[:, l[-2]]
  numpy[:, ::-1]

tests/expression.py

@@ -99,6 +99,15 @@
 very_long_variable_name_filters: t.List[
     t.Tuple[str, t.Union[str, t.List[t.Optional[str]]]],
 ]
+xxxx_xxxxx_xxxx_xxx: Callable[..., List[SomeClass]] = classmethod(  # type: ignore
+    sync(async_xxxx_xxx_xxxx_xxxxx_xxxx_xxx.__func__)
+)
+xxxx_xxx_xxxx_xxxxx_xxxx_xxx: Callable[..., List[SomeClass]] = classmethod(  # type: ignore
+    sync(async_xxxx_xxx_xxxx_xxxxx_xxxx_xxx.__func__)
+)
+xxxx_xxx_xxxx_xxxxx_xxxx_xxx: Callable[
+    ..., List[SomeClass]
+] = classmethod(sync(async_xxxx_xxx_xxxx_xxxxx_xxxx_xxx.__func__))  # type: ignore
 slice[0]
 slice[0:1]
 slice[0:1:2]
@@ -354,6 +363,17 @@ async def f():
 very_long_variable_name_filters: t.List[
     t.Tuple[str, t.Union[str, t.List[t.Optional[str]]]],
 ]
+xxxx_xxxxx_xxxx_xxx: Callable[..., List[SomeClass]] = classmethod(  # type: ignore
+    sync(async_xxxx_xxx_xxxx_xxxxx_xxxx_xxx.__func__)
+)
+xxxx_xxx_xxxx_xxxxx_xxxx_xxx: Callable[
+    ..., List[SomeClass]
+] = classmethod(  # type: ignore
+    sync(async_xxxx_xxx_xxxx_xxxxx_xxxx_xxx.__func__)
+)
+xxxx_xxx_xxxx_xxxxx_xxxx_xxx: Callable[..., List[SomeClass]] = classmethod(
+    sync(async_xxxx_xxx_xxxx_xxxxx_xxxx_xxx.__func__)
+)  # type: ignore
 slice[0]
 slice[0:1]
 slice[0:1:2]