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Maintain cursor stack's position correctly when ascending the tree (#2795)

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This fixes a bug that could cause the cursor to incorrectly report its
start when using `slice` or `seek_forward`, and then calling `prev`. We
didn't notice this because we were not testing those three methods
together.

I suppose this could explain some of the panics we've observed because
we do use `slice`/`seek_forward` followed by `prev` calls in production.
This commit is contained in:
Antonio Scandurra 2023-07-27 13:51:09 +02:00
parent badc2ec0e9
commit a166f0b56a
2 changed files with 6 additions and 3 deletions
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1
crates/sum_tree/src/cursor.rs
View file

@ -438,6 +438,7 @@ where
} => { } => {
if ascending { if ascending {
entry.index += 1; entry.index += 1;
entry.position = self.position.clone();
} }
for (child_tree, child_summary) in child_trees[entry.index..] for (child_tree, child_summary) in child_trees[entry.index..]

8
crates/sum_tree/src/sum_tree.rs
View file

@ -738,7 +738,7 @@ mod tests {
for _ in 0..num_operations { for _ in 0..num_operations {
let splice_end = rng.gen_range(0..tree.extent::<Count>(&()).0 + 1); let splice_end = rng.gen_range(0..tree.extent::<Count>(&()).0 + 1);
let splice_start = rng.gen_range(0..splice_end + 1); let splice_start = rng.gen_range(0..splice_end + 1);
let count = rng.gen_range(0..3); let count = rng.gen_range(0..10);
let tree_end = tree.extent::<Count>(&()); let tree_end = tree.extent::<Count>(&());
let new_items = rng let new_items = rng
.sample_iter(distributions::Standard) .sample_iter(distributions::Standard)
@ -805,10 +805,12 @@ mod tests {
} }
assert_eq!(filter_cursor.item(), None); assert_eq!(filter_cursor.item(), None);
let mut pos = rng.gen_range(0..tree.extent::<Count>(&()).0 + 1);
let mut before_start = false; let mut before_start = false;
let mut cursor = tree.cursor::<Count>(); let mut cursor = tree.cursor::<Count>();
cursor.seek(&Count(pos), Bias::Right, &()); let start_pos = rng.gen_range(0..=reference_items.len());
cursor.seek(&Count(start_pos), Bias::Right, &());
let mut pos = rng.gen_range(start_pos..=reference_items.len());
cursor.seek_forward(&Count(pos), Bias::Right, &());
for i in 0..10 { for i in 0..10 {
assert_eq!(cursor.start().0, pos); assert_eq!(cursor.start().0, pos);