Reduce memory allocations in PMMR (#3328)

We have a pattern in the code - return Vec, turn it into an iterator, filter and collect to another Vec. The idea was to return iterator where possible to avoid allocating intermediate vecs.

core/tests/merkle_proof.rs

@@ -90,7 +90,7 @@ fn pmmr_merkle_proof() {
 	assert_eq!(pmmr.get_hash(3).unwrap(), pos_2);
 
 	assert_eq!(pmmr.root().unwrap(), pos_2);
-	assert_eq!(pmmr.peaks(), [pos_2]);
+	assert_eq!(pmmr.peaks().collect::<Vec<_>>(), [pos_2]);
 
 	// single peak, path with single sibling
 	let proof = pmmr.merkle_proof(1).unwrap();
@@ -107,7 +107,7 @@ fn pmmr_merkle_proof() {
 	assert_eq!(pmmr.get_hash(4).unwrap(), pos_3);
 
 	assert_eq!(pmmr.root().unwrap(), (pos_2, pos_3).hash_with_index(4));
-	assert_eq!(pmmr.peaks(), [pos_2, pos_3]);
+	assert_eq!(pmmr.peaks().collect::<Vec<_>>(), [pos_2, pos_3]);
 
 	let proof = pmmr.merkle_proof(1).unwrap();
 	assert_eq!(proof.path, vec![pos_1, pos_3]);

core/tests/pmmr.rs

@@ -150,10 +150,9 @@ fn various_families() {
 
 #[test]
 fn test_paths() {
-	assert_eq!(pmmr::path(1, 1), [1]);
-	assert_eq!(pmmr::path(1, 3), [1, 3]);
-	assert_eq!(pmmr::path(2, 3), [2, 3]);
-	assert_eq!(pmmr::path(4, 16), [4, 6, 7, 15]);
+	assert_eq!(pmmr::path(1, 3).collect::<Vec<_>>(), [1, 3]);
+	assert_eq!(pmmr::path(2, 3).collect::<Vec<_>>(), [2, 3]);
+	assert_eq!(pmmr::path(4, 16).collect::<Vec<_>>(), [4, 6, 7, 15]);
 }
 
 #[test]
@@ -279,7 +278,7 @@ fn pmmr_push_root() {
 	pmmr.push(&elems[0]).unwrap();
 	pmmr.dump(false);
 	let pos_0 = elems[0].hash_with_index(0);
-	assert_eq!(pmmr.peaks(), vec![pos_0]);
+	assert_eq!(pmmr.peaks().collect::<Vec<_>>(), vec![pos_0]);
 	assert_eq!(pmmr.root().unwrap(), pos_0);
 	assert_eq!(pmmr.unpruned_size(), 1);
 
@@ -288,7 +287,7 @@ fn pmmr_push_root() {
 	pmmr.dump(false);
 	let pos_1 = elems[1].hash_with_index(1);
 	let pos_2 = (pos_0, pos_1).hash_with_index(2);
-	assert_eq!(pmmr.peaks(), vec![pos_2]);
+	assert_eq!(pmmr.peaks().collect::<Vec<_>>(), vec![pos_2]);
 	assert_eq!(pmmr.root().unwrap(), pos_2);
 	assert_eq!(pmmr.unpruned_size(), 3);
 
@@ -296,7 +295,7 @@ fn pmmr_push_root() {
 	pmmr.push(&elems[2]).unwrap();
 	pmmr.dump(false);
 	let pos_3 = elems[2].hash_with_index(3);
-	assert_eq!(pmmr.peaks(), vec![pos_2, pos_3]);
+	assert_eq!(pmmr.peaks().collect::<Vec<_>>(), vec![pos_2, pos_3]);
 	assert_eq!(pmmr.root().unwrap(), (pos_2, pos_3).hash_with_index(4));
 	assert_eq!(pmmr.unpruned_size(), 4);
 
@@ -306,7 +305,7 @@ fn pmmr_push_root() {
 	let pos_4 = elems[3].hash_with_index(4);
 	let pos_5 = (pos_3, pos_4).hash_with_index(5);
 	let pos_6 = (pos_2, pos_5).hash_with_index(6);
-	assert_eq!(pmmr.peaks(), vec![pos_6]);
+	assert_eq!(pmmr.peaks().collect::<Vec<_>>(), vec![pos_6]);
 	assert_eq!(pmmr.root().unwrap(), pos_6);
 	assert_eq!(pmmr.unpruned_size(), 7);
 
@@ -314,7 +313,7 @@ fn pmmr_push_root() {
 	pmmr.push(&elems[4]).unwrap();
 	pmmr.dump(false);
 	let pos_7 = elems[4].hash_with_index(7);
-	assert_eq!(pmmr.peaks(), vec![pos_6, pos_7]);
+	assert_eq!(pmmr.peaks().collect::<Vec<_>>(), vec![pos_6, pos_7]);
 	assert_eq!(pmmr.root().unwrap(), (pos_6, pos_7).hash_with_index(8));
 	assert_eq!(pmmr.unpruned_size(), 8);
 
@@ -322,14 +321,14 @@ fn pmmr_push_root() {
 	pmmr.push(&elems[5]).unwrap();
 	let pos_8 = elems[5].hash_with_index(8);
 	let pos_9 = (pos_7, pos_8).hash_with_index(9);
-	assert_eq!(pmmr.peaks(), vec![pos_6, pos_9]);
+	assert_eq!(pmmr.peaks().collect::<Vec<_>>(), vec![pos_6, pos_9]);
 	assert_eq!(pmmr.root().unwrap(), (pos_6, pos_9).hash_with_index(10));
 	assert_eq!(pmmr.unpruned_size(), 10);
 
 	// seven elements
 	pmmr.push(&elems[6]).unwrap();
 	let pos_10 = elems[6].hash_with_index(10);
-	assert_eq!(pmmr.peaks(), vec![pos_6, pos_9, pos_10]);
+	assert_eq!(pmmr.peaks().collect::<Vec<_>>(), vec![pos_6, pos_9, pos_10]);
 	assert_eq!(
 		pmmr.root().unwrap(),
 		(pos_6, (pos_9, pos_10).hash_with_index(11)).hash_with_index(11)
@@ -343,14 +342,14 @@ fn pmmr_push_root() {
 	let pos_12 = (pos_10, pos_11).hash_with_index(12);
 	let pos_13 = (pos_9, pos_12).hash_with_index(13);
 	let pos_14 = (pos_6, pos_13).hash_with_index(14);
-	assert_eq!(pmmr.peaks(), vec![pos_14]);
+	assert_eq!(pmmr.peaks().collect::<Vec<_>>(), vec![pos_14]);
 	assert_eq!(pmmr.root().unwrap(), pos_14);
 	assert_eq!(pmmr.unpruned_size(), 15);
 
 	// nine elements
 	pmmr.push(&elems[8]).unwrap();
 	let pos_15 = elems[8].hash_with_index(15);
-	assert_eq!(pmmr.peaks(), vec![pos_14, pos_15]);
+	assert_eq!(pmmr.peaks().collect::<Vec<_>>(), vec![pos_14, pos_15]);
 	assert_eq!(pmmr.root().unwrap(), (pos_14, pos_15).hash_with_index(16));
 	assert_eq!(pmmr.unpruned_size(), 16);
 }