Pin comment to single leaf in invisible parens (#872)

black.py

@@ -1282,10 +1282,13 @@ def contains_inner_type_comments(self) -> bool:
         try:
             last_leaf = self.leaves[-1]
             ignored_ids.add(id(last_leaf))
-            if last_leaf.type == token.COMMA:
-                # When trailing commas are inserted by Black for consistency, comments
-                # after the previous last element are not moved (they don't have to,
-                # rendering will still be correct).  So we ignore trailing commas.
+            if last_leaf.type == token.COMMA or (
+                last_leaf.type == token.RPAR and not last_leaf.value
+            ):
+                # When trailing commas or optional parens are inserted by Black for
+                # consistency, comments after the previous last element are not moved
+                # (they don't have to, rendering will still be correct).  So we ignore
+                # trailing commas and invisible.
                 last_leaf = self.leaves[-2]
                 ignored_ids.add(id(last_leaf))
         except IndexError:
@@ -1382,7 +1385,23 @@ def append_comment(self, comment: Leaf) -> bool:
             comment.prefix = ""
             return False
 
-        self.comments.setdefault(id(self.leaves[-1]), []).append(comment)
+        last_leaf = self.leaves[-1]
+        if (
+            last_leaf.type == token.RPAR
+            and not last_leaf.value
+            and last_leaf.parent
+            and len(list(last_leaf.parent.leaves())) <= 3
+            and not is_type_comment(comment)
+        ):
+            # Comments on an optional parens wrapping a single leaf should belong to
+            # the wrapped node except if it's a type comment. Pinning the comment like
+            # this avoids unstable formatting caused by comment migration.
+            if len(self.leaves) < 2:
+                comment.type = STANDALONE_COMMENT
+                comment.prefix = ""
+                return False
+            last_leaf = self.leaves[-2]
+        self.comments.setdefault(id(last_leaf), []).append(comment)
         return True
 
     def comments_after(self, leaf: Leaf) -> List[Leaf]:

tests/data/cantfit.py

@@ -47,8 +47,8 @@
     0
 )
 this_is_a_ridiculously_long_name_and_nobody_in_their_right_mind_would_use_one_like_it = (
-    1
-)  # with a comment
+    1  # with a comment
+)
 this_is_a_ridiculously_long_name_and_nobody_in_their_right_mind_would_use_one_like_it = [
     1,
     2,

tests/data/comments6.py

@@ -84,3 +84,6 @@ def func(
         0.0789,
         a[-1],  # type: ignore
     )
+
+
+result = "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"  # aaa

tests/data/comments7.py

@@ -23,6 +23,19 @@
     #  DEFAULT_TYPE_ATTRIBUTES,
 )
 
+
+result = 1  # look ma, no comment migration xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
+
+result = (
+    1  # look ma, no comment migration xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
+)
+
+result = (
+    "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"  # aaa
+)
+
+result = "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"  # aaa
+
 # output
 
 from .config import (
@@ -49,3 +62,12 @@
     #  resolve_to_config_type,
     #  DEFAULT_TYPE_ATTRIBUTES,
 )
+
+
+result = 1  # look ma, no comment migration xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
+
+result = 1  # look ma, no comment migration xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
+
+result = "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"  # aaa
+
+result = "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"  # aaa