Don't allow type comments to be merged behind regular comments (#1027)

Type comments only apply if they are the first comment on the line,
which means that allowing them to be pushed behind a regular comment
when joining lines is a semantic change (and, indeed, one that black
catches and fails on).

diff --git a/black.py b/black.py
index 71f42ef307194f3febbd336c2c70597b25eafe5c..a4f36887aecc3630136cb4ed040b3768b814564a 100644 (file)
--- a/black.py
+++ b/black.py
@@ -1296,7 +1296,7 @@ class Line:
                     return True
         return False
 
-    def contains_inner_type_comments(self) -> bool:
+    def contains_uncollapsable_type_comments(self) -> bool:
         ignored_ids = set()
         try:
             last_leaf = self.leaves[-1]
@@ -1313,13 +1313,19 @@ class Line:
         except IndexError:
             return False
 
+        # A type comment is uncollapsable if it is attached to a leaf
+        # that isn't at the end of the line (since that could cause it
+        # to get associated to a different argument) or if there are
+        # comments before it (since that could cause it to get hidden
+        # behind a comment.
+        comment_seen = False
         for leaf_id, comments in self.comments.items():
-            if leaf_id in ignored_ids:
-                continue
-
             for comment in comments:
                 if is_type_comment(comment):
-                    return True
+                    if leaf_id not in ignored_ids or comment_seen:
+                        return True
+
+            comment_seen = True
 
         return False
 
@@ -2328,7 +2334,7 @@ def split_line(
     line_str = str(line).strip("\n")
 
     if (
-        not line.contains_inner_type_comments()
+        not line.contains_uncollapsable_type_comments()
         and not line.should_explode
         and is_line_short_enough(line, line_length=line_length, line_str=line_str)
     ):

diff --git a/tests/data/comments6.py b/tests/data/comments6.py
index a2cd018adcb77cea5859184cfc3220a0abb45c3f..6e34b74f9e75c42360374aacef593158b11cbe49 100644 (file)
--- a/tests/data/comments6.py
+++ b/tests/data/comments6.py
@@ -69,6 +69,20 @@ def f(
     )  # type: int
 
 
+def f(
+    x,  # not a type comment
+    y,  # type: int
+):
+    # type: (...) -> None
+    pass
+
+
+def f(
+    x,  # not a type comment
+):  # type: (int) -> None
+    pass
+
+
 def func(
     a=some_list[0],  # type: int
 ):  # type: () -> int