Fix 4399 ASTSafetyError on comment in return type annotation

CHANGES.md

@@ -12,6 +12,9 @@
 
 <!-- Changes that affect Black's stable style -->
 
+Fix `ASTSafetyError` crash when return type contains one element and comments spanning
+multiple lines. (#4444)
+
 ### Preview style
 
 <!-- Changes that affect Black's preview style -->

src/black/linegen.py

@@ -1116,6 +1116,14 @@ def bracket_split_build_line(
                 )
                 # Don't add one inside parenthesized return annotations
                 and get_annotation_type(leaves[0]) != "return"
+                # Don't add comment for single element return type with comments
+                and not (
+                    sum(leaf.type is not STANDALONE_COMMENT for leaf in leaves) < 2
+                    and any(
+                        leaf.parent is not None and leaf.parent.type != syms.parameters
+                        for leaf in leaves
+                    )
+                )
                 # Don't add one inside PEP 604 unions
                 and not (
                     leaves[0].parent

tests/data/cases/single_element_parametized_return_type.py

@@ -0,0 +1,50 @@
+def MyClass():
+    pass
+
+
+def create_my_nested_class() -> (
+    # test asnkdasldnsalkdnaskldnaklsdnsakln
+    int
+):
+    class MyNestedClass(MyClass):
+        pass
+    return MyNestedClass
+
+
+def create_my_nested_class() -> (
+    # test asnkdasldnsalkdnaskldnaklsdnsakln
+    # test asnkdasldnsalkdnaskldnaklsdnsakln
+    int
+    # test asnkdasldnsalkdnaskldnaklsdnsakln
+):
+    class MyNestedClass(MyClass):
+        pass
+    return MyNestedClass
+
+# output
+
+
+def MyClass():
+    pass
+
+
+def create_my_nested_class() -> (
+    # test asnkdasldnsalkdnaskldnaklsdnsakln
+    int
+):
+    class MyNestedClass(MyClass):
+        pass
+
+    return MyNestedClass
+
+
+def create_my_nested_class() -> (
+    # test asnkdasldnsalkdnaskldnaklsdnsakln
+    # test asnkdasldnsalkdnaskldnaklsdnsakln
+    int
+    # test asnkdasldnsalkdnaskldnaklsdnsakln
+):
+    class MyNestedClass(MyClass):
+        pass
+
+    return MyNestedClass