Traverse references held by operator callables (#9044)

Extract attrgetter, itemgetter and methodcaller GC traversal from #8954. Add four bounded reference-cycle cases to the existing operator snippet, including a non-dotted str subclass retained by attrgetter.

Assisted-by: OpenAI Codex:model identifier unavailable

crates/vm/src/stdlib/_operator.rs

@@ -351,7 +351,7 @@ mod _operator {
     }
 
     #[pyattr]
-    #[pyclass(name = "attrgetter", module = "operator")]
+    #[pyclass(name = "attrgetter", module = "operator", traverse)]
     #[derive(Debug, PyPayload)]
     struct PyAttrGetter {
         attrs: Vec<PyStrRef>,
@@ -470,7 +470,7 @@ mod _operator {
     }
 
     #[pyattr]
-    #[pyclass(name = "itemgetter", module = "operator")]
+    #[pyclass(name = "itemgetter", module = "operator", traverse)]
     #[derive(Debug, PyPayload)]
     struct PyItemGetter {
         items: Vec<PyObjectRef>,
@@ -556,7 +556,7 @@ mod _operator {
     }
 
     #[pyattr]
-    #[pyclass(name = "methodcaller", module = "operator")]
+    #[pyclass(name = "methodcaller", module = "operator", traverse)]
     #[derive(Debug, PyPayload)]
     struct PyMethodCaller {
         name: PyUtf8StrRef,

extra_tests/snippets/stdlib_operator.py

@@ -3,3 +3,31 @@ import _operator
 assert _operator._compare_digest("abcdef", "abcdef")
 assert not _operator._compare_digest("abcdef", "abc")
 assert not _operator._compare_digest("abc", "abcdef")
+
+
+def check_operator_reference_cycles():
+    import gc
+    import weakref
+
+    class Holder:
+        pass
+
+    class Name(str):
+        pass
+
+    for make, make_payload in (
+        (_operator.itemgetter, Holder),
+        (lambda value: _operator.methodcaller("method", value), Holder),
+        (lambda value: _operator.methodcaller("method", value=value), Holder),
+        (_operator.attrgetter, lambda: Name("attribute")),
+    ):
+        payload = make_payload()
+        wrapper = make(payload)
+        payload.wrapper = wrapper
+        reference = weakref.ref(payload)
+        del wrapper, payload
+        gc.collect()
+        assert reference() is None
+
+
+check_operator_reference_cycles()