Preserve parens when merging type: ignore with other comments to prevent AST errors

Author: Nikhil172913832

CHANGES.md

@@ -20,6 +20,8 @@
 - Fix crash when multiple `# fmt: skip` comments are used in a multi-part if-clause, on
   string literals, or on dictionary entries with long lines (#4872)
 - Fix possible crash when `fmt: ` directives aren't on the top level (#4856)
+- Preserve parentheses when `# type: ignore` comments would be merged with other
+  comments on the same line, preventing AST equivalence failures (#4880)
 
 ### Preview style
 

src/black/lines.py

@@ -974,6 +974,24 @@ def can_omit_invisible_parens(
     """
     line = rhs.body
 
+    # We can't omit parens if doing so would result in a type: ignore comment
+    # sharing a line with other comments, as that breaks type: ignore parsing.
+    # Check if there's a type: ignore comment in any part
+    has_type_ignore_comment = False
+    has_other_comment = False
+
+    for part in (rhs.head, rhs.body, rhs.tail):
+        for leaf in part.leaves:
+            for comment in part.comments.get(id(leaf), []):
+                if is_type_ignore_comment(comment, mode=part.mode):
+                    has_type_ignore_comment = True
+                else:
+                    has_other_comment = True
+
+    # If there's both a type: ignore comment and other comments, keep the parens
+    if has_type_ignore_comment and has_other_comment:
+        return False
+
     # We need optional parens in order to split standalone comments to their own lines
     # if there are no nested parens around the standalone comments
     closing_bracket: Leaf | None = None

tests/data/cases/type_ignore_with_other_comment.py

@@ -0,0 +1,27 @@
+import pandas as pd
+
+interval_td = pd.Interval(
+    pd.Timedelta("1 days"), pd.Timedelta("2 days"), closed="neither"
+)
+
+_td = (  # pyright: ignore[reportOperatorIssue,reportUnknownVariableType]
+    interval_td
+    - pd.Interval(  # type: ignore[operator]
+        pd.Timedelta(1, "ns"), pd.Timedelta(2, "ns")
+    )
+)
+
+# output
+
+import pandas as pd
+
+interval_td = pd.Interval(
+    pd.Timedelta("1 days"), pd.Timedelta("2 days"), closed="neither"
+)
+
+_td = (  # pyright: ignore[reportOperatorIssue,reportUnknownVariableType]
+    interval_td
+    - pd.Interval(  # type: ignore[operator]
+        pd.Timedelta(1, "ns"), pd.Timedelta(2, "ns")
+    )
+)