Fix wrong ref counting (#1358)

* Fix wrong ref counting

in case of multiple inserts at same height.

* More warn

---------

Co-authored-by: eskimor <eskimor@no-such-url.com>

polkadot/node/core/dispute-coordinator/src/initialized.rs

@@ -1271,7 +1271,7 @@ impl Initialized {
 		if import_result.has_fresh_byzantine_threshold_against() {
 			let blocks_including = self.scraper.get_blocks_including_candidate(&candidate_hash);
 			for (parent_block_number, parent_block_hash) in &blocks_including {
-				gum::trace!(
+				gum::warn!(
 					target: LOG_TARGET,
 					?candidate_hash,
 					?parent_block_number,
@@ -1282,7 +1282,7 @@ impl Initialized {
 			if blocks_including.len() > 0 {
 				ctx.send_message(ChainSelectionMessage::RevertBlocks(blocks_including)).await;
 			} else {
-				gum::debug!(
+				gum::warn!(
 					target: LOG_TARGET,
 					?candidate_hash,
 					?session,

polkadot/node/core/dispute-coordinator/src/scraping/candidates.rs

@@ -135,11 +135,14 @@ impl ScrapedCandidates {
 	}
 
 	pub fn insert(&mut self, block_number: BlockNumber, candidate_hash: CandidateHash) {
-		self.candidates.insert(candidate_hash);
-		self.candidates_by_block_number
+		if self
+			.candidates_by_block_number
 			.entry(block_number)
 			.or_default()
-			.insert(candidate_hash);
+			.insert(candidate_hash)
+		{
+			self.candidates.insert(candidate_hash);
+		}
 	}
 
 	// Used only for tests to verify the pruning doesn't leak data.
@@ -159,6 +162,8 @@ mod scraped_candidates_tests {
 		let mut candidates = ScrapedCandidates::new();
 		let target = CandidateHash(BlakeTwo256::hash(&vec![1, 2, 3]));
 		candidates.insert(1, target);
+		// Repeated inserts at same height should be fine:
+		candidates.insert(1, target);
 
 		assert!(candidates.contains(&target));