refactor: return MmrPeaks from PartialMmr::peaks()

src/merkle/mmr/partial.rs

@@ -88,9 +88,11 @@ impl PartialMmr {
         self.forest
     }
 
-    // Returns a reference to the current peaks in the [PartialMmr]
-    pub fn peaks(&self) -> &[RpoDigest] {
-        &self.peaks
+    // Returns a reference to the current peaks in the [PartialMmr].
+    pub fn peaks(&self) -> MmrPeaks {
+        // expect() is OK here because the constructor ensures that MMR peaks can be constructed
+        // correctly
+        MmrPeaks::new(self.forest, self.peaks.clone()).expect("invalid MMR peaks")
     }
 
     /// Given a leaf position, returns the Merkle path to its corresponding peak. If the position

src/merkle/mmr/peaks.rs

@@ -36,6 +36,14 @@ pub struct MmrPeaks {
 }
 
 impl MmrPeaks {
+    // CONSTRUCTOR
+    // --------------------------------------------------------------------------------------------
+
+    /// Returns new [MmrPeaks] instantiated from the provided vector of peaks and the number of
+    /// leaves in the underlying MMR.
+    ///
+    /// # Errors
+    /// Returns an error if the number of leaves and the number of peaks are inconsistent.
     pub fn new(num_leaves: usize, peaks: Vec<RpoDigest>) -> Result<Self, MmrError> {
         if num_leaves.count_ones() as usize != peaks.len() {
             return Err(MmrError::InvalidPeaks);
@@ -47,17 +55,23 @@ impl MmrPeaks {
     // ACCESSORS
     // --------------------------------------------------------------------------------------------
 
-    /// Returns a count of the MMR's leaves.
+    /// Returns a count of leaves in the underlying MMR.
     pub fn num_leaves(&self) -> usize {
         self.num_leaves
     }
 
-    /// Returns the current peaks of the MMR.
+    /// Returns the number of peaks of the underlying MMR.
+    pub fn num_peaks(&self) -> usize {
+        self.peaks.len()
+    }
+
+    /// Returns the list of peaks of the underlying MMR.
     pub fn peaks(&self) -> &[RpoDigest] {
         &self.peaks
     }
 
-    /// Returns the current num_leaves and peaks of the MMR.
+    /// Converts this [MmrPeaks] into its components: number of leaves and a vector of peaks of
+    /// the underlying MMR.
     pub fn into_parts(self) -> (usize, Vec<RpoDigest>) {
         (self.num_leaves, self.peaks)
     }

src/merkle/mmr/tests.rs

@@ -755,14 +755,14 @@ fn test_mmr_delta_old_forest() {
 #[test]
 fn test_partial_mmr_simple() {
     let mmr: Mmr = LEAVES.into();
-    let acc = mmr.peaks(mmr.forest()).unwrap();
-    let mut partial: PartialMmr = acc.clone().into();
+    let peaks = mmr.peaks(mmr.forest()).unwrap();
+    let mut partial: PartialMmr = peaks.clone().into();
 
     // check initial state of the partial mmr
-    assert_eq!(partial.peaks(), acc.peaks());
-    assert_eq!(partial.forest(), acc.num_leaves());
+    assert_eq!(partial.peaks(), peaks);
+    assert_eq!(partial.forest(), peaks.num_leaves());
     assert_eq!(partial.forest(), LEAVES.len());
-    assert_eq!(partial.peaks().len(), 3);
+    assert_eq!(partial.peaks().num_peaks(), 3);
     assert_eq!(partial.nodes.len(), 0);
 
     // check state after adding tracking one element
@@ -808,7 +808,7 @@ fn test_partial_mmr_update_single() {
         partial.apply(delta).unwrap();
 
         assert_eq!(partial.forest(), full.forest());
-        assert_eq!(partial.peaks(), full.peaks(full.forest()).unwrap().peaks());
+        assert_eq!(partial.peaks(), full.peaks(full.forest()).unwrap());
 
         let proof1 = full.open(i as usize, full.forest()).unwrap();
         partial.add(proof1.position, node, &proof1.merkle_path).unwrap();