From 8f380911e0cd8057bd9a1f0c418d81195ce858a3 Mon Sep 17 00:00:00 2001
From: Zsolt Dollenstein <zsol.zsol@gmail.com>
Date: Sat, 15 Jun 2019 07:29:09 +0100
Subject: [PATCH] Pin comment to single leaf in invisible parens (#872)

---
 black.py                | 29 ++++++++++++++++++++++++-----
 tests/data/cantfit.py   |  4 ++--
 tests/data/comments6.py |  3 +++
 tests/data/comments7.py | 22 ++++++++++++++++++++++
 4 files changed, 51 insertions(+), 7 deletions(-)

diff --git a/black.py b/black.py
index 8318674..ce27653 100644
--- a/black.py
+++ b/black.py
@@ -1282,10 +1282,13 @@ class Line:
         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 @@ class Line:
             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]:
diff --git a/tests/data/cantfit.py b/tests/data/cantfit.py
index 0ab1575..317a38f 100644
--- a/tests/data/cantfit.py
+++ b/tests/data/cantfit.py
@@ -47,8 +47,8 @@ this_is_a_ridiculously_long_name_and_nobody_in_their_right_mind_would_use_one_li
     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,
diff --git a/tests/data/comments6.py b/tests/data/comments6.py
index ce17382..a2cd018 100644
--- a/tests/data/comments6.py
+++ b/tests/data/comments6.py
@@ -84,3 +84,6 @@ def func(
         0.0789,
         a[-1],  # type: ignore
     )
+
+
+result = "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"  # aaa
diff --git a/tests/data/comments7.py b/tests/data/comments7.py
index 4159d84..f69863e 100644
--- a/tests/data/comments7.py
+++ b/tests/data/comments7.py
@@ -23,6 +23,19 @@ from .config import (
     #  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 @@ from .config import (
     #  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
-- 
2.39.2