Grandpa justifications: Avoid duplicate vote ancestries (#2634) (#2635)

* Grandpa justifications: Avoid duplicate vote ancestries

bridges/primitives/header-chain/tests/implementation_match.rs

@@ -42,7 +42,7 @@ struct AncestryChain(bp_header_chain::justification::AncestryChain<TestHeader>);
 
 impl AncestryChain {
 	fn new(justification: &GrandpaJustification<TestHeader>) -> Self {
-		Self(bp_header_chain::justification::AncestryChain::new(justification))
+		Self(bp_header_chain::justification::AncestryChain::new(justification).0)
 	}
 }
 
@@ -58,7 +58,7 @@ impl finality_grandpa::Chain<TestHash, TestNumber> for AncestryChain {
 			if current_hash == base {
 				break
 			}
-			match self.0.parents.get(&current_hash) {
+			match self.0.parent_hash_of(&current_hash) {
 				Some(parent_hash) => {
 					current_hash = *parent_hash;
 					route.push(current_hash);

bridges/primitives/header-chain/tests/justification/optimizer.rs

@@ -158,6 +158,26 @@ fn unrelated_ancestry_votes_are_removed_by_optimizer() {
 	assert_eq!(num_precommits_before - 1, num_precommits_after);
 }
 
+#[test]
+fn duplicate_votes_ancestries_are_removed_by_optimizer() {
+	let mut justification = make_default_justification::<TestHeader>(&test_header(1));
+	let optimized_votes_ancestries = justification.votes_ancestries.clone();
+	justification.votes_ancestries = justification
+		.votes_ancestries
+		.into_iter()
+		.flat_map(|item| std::iter::repeat(item).take(3))
+		.collect();
+
+	verify_and_optimize_justification::<TestHeader>(
+		header_id::<TestHeader>(1),
+		&verification_context(TEST_GRANDPA_SET_ID),
+		&mut justification,
+	)
+	.unwrap();
+
+	assert_eq!(justification.votes_ancestries, optimized_votes_ancestries);
+}
+
 #[test]
 fn redundant_votes_ancestries_are_removed_by_optimizer() {
 	let mut justification = make_default_justification::<TestHeader>(&test_header(1));

bridges/primitives/header-chain/tests/justification/strict.rs

@@ -149,7 +149,21 @@ fn justification_with_invalid_authority_signature_rejected() {
 }
 
 #[test]
-fn justification_with_invalid_precommit_ancestry() {
+fn justification_with_duplicate_votes_ancestry() {
+	let mut justification = make_default_justification::<TestHeader>(&test_header(1));
+	justification.votes_ancestries.push(justification.votes_ancestries[0].clone());
+
+	assert_eq!(
+		verify_justification::<TestHeader>(
+			header_id::<TestHeader>(1),
+			&verification_context(TEST_GRANDPA_SET_ID),
+			&justification,
+		),
+		Err(JustificationVerificationError::DuplicateVotesAncestries),
+	);
+}
+#[test]
+fn justification_with_redundant_votes_ancestry() {
 	let mut justification = make_default_justification::<TestHeader>(&test_header(1));
 	justification.votes_ancestries.push(test_header(10));