feat: filter empty values in Smt::with_entries (#383)

CHANGELOG.md

@@ -6,6 +6,7 @@
 - Implemented parallel leaf hashing in `Smt::process_sorted_pairs_to_leaves` (#365).
 - [BREAKING] Updated Winterfell dependency to v0.12 (#374).
 - Added debug-only duplicate column check in `build_subtree` (#378).
+- Filter out empty values in concurrent version of `Smt::with_entries` to fix a panic (#383).
 
 ## 0.13.3 (2025-02-18)
 

src/merkle/smt/full/concurrent/mod.rs

@@ -39,6 +39,8 @@ impl Smt {
         let mut seen_keys = BTreeSet::new();
         let entries: Vec<_> = entries
             .into_iter()
+            // Filter out key-value pairs whose value is empty.
+            .filter(|(_key, value)| *value != Self::EMPTY_VALUE)
             .map(|(key, value)| {
                 if seen_keys.insert(key) {
                     Ok((key, value))

src/merkle/smt/full/concurrent/tests.rs

@@ -375,7 +375,15 @@ fn test_multithreaded_subtrees() {
 #[test]
 fn test_with_entries_concurrent() {
     const PAIR_COUNT: u64 = COLS_PER_SUBTREE * 64;
-    let entries = generate_entries(PAIR_COUNT);
+    let mut entries = generate_entries(PAIR_COUNT);
+    let mut rng = rand::thread_rng();
+
+    // Set 10% of the entries to have empty words as their values.
+    for _ in 0..PAIR_COUNT / 10 {
+        let random_index = rng.gen_range(0..PAIR_COUNT);
+        entries[random_index as usize].1 = EMPTY_WORD;
+    }
+
     let control = Smt::with_entries_sequential(entries.clone()).unwrap();
     let smt = Smt::with_entries(entries.clone()).unwrap();
     assert_eq!(smt.root(), control.root());