xudong963 commented on code in PR #21749:
URL: https://github.com/apache/datafusion/pull/21749#discussion_r3115367445
##########
datafusion/common/src/tree_node.rs:
##########
@@ -2431,4 +2450,46 @@ pub(crate) mod tests {
item.visit(&mut visitor).unwrap();
}
+
+ #[test]
+ fn box_map_elements_reuses_allocation() {
+ let boxed = Box::new(TestTreeNode::new_leaf(42i32));
+ let before: *const TestTreeNode<i32> = &*boxed;
+ let out = boxed.map_elements(|n| Ok(Transformed::no(n))).unwrap();
+ let after: *const TestTreeNode<i32> = &*out.data;
+ assert_eq!(after, before);
+ }
+
+ #[test]
+ fn arc_map_elements_reuses_allocation_when_unique() {
+ let arc = Arc::new(TestTreeNode::new_leaf(42i32));
+ let before = Arc::as_ptr(&arc);
+ let out = arc.map_elements(|n| Ok(Transformed::no(n))).unwrap();
+ assert_eq!(Arc::as_ptr(&out.data), before);
+ }
+
+ #[test]
+ fn arc_map_elements_clones_when_shared() {
+ // When the input `Arc` is shared, `make_mut` clones into a fresh
+ // allocation, so the reuse optimization does not apply.
+ let arc = Arc::new(TestTreeNode::new_leaf(42i32));
+ let _keepalive = Arc::clone(&arc);
+ let before = Arc::as_ptr(&arc);
+ let out = arc.map_elements(|n| Ok(Transformed::no(n))).unwrap();
+ assert_ne!(Arc::as_ptr(&out.data), before);
+ }
+
+ #[test]
+ fn box_map_elements_panic() {
+ use std::panic::{AssertUnwindSafe, catch_unwind};
+ let boxed = Box::new(TestTreeNode::new_leaf(42i32));
+ let result = catch_unwind(AssertUnwindSafe(|| {
+ boxed
+ .map_elements(|_: TestTreeNode<i32>| -> Result<_> {
+ panic!("simulated panic during rewrite")
+ })
+ .ok()
+ }));
+ assert!(result.is_err());
Review Comment:
It doesn't verify the actual panic-safety invariant — that dropping an
unwound `Box` doesn't double-free or access garbage
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