Tally votes on conflicting block with no inactive votes (#2744)

Mostly applicable to tests, but consider this sequence of events:
- An election gets created for a processed block
- A vote arrives for a conflicting block; gets added to election, not inactive
- The conflicting block gets processed

Currently, `election::publish` calls `insert_inactive_votes_cache` but votes are not tallied since there was no inactive vote.

This fixes the above situation by calling `confirm_if_quorum` if no votes were cached when a new conflicting block is inserted.

nano/core_test/active_transactions.cpp

@@ -1088,4 +1088,32 @@ TEST (active_transactions, restart_dropped)
 	ASSERT_EQ (2, node.stats.count (nano::stat::type::election, nano::stat::detail::election_restart));
 	// Wait for the election to complete
 	ASSERT_TIMELY (5s, node.ledger.cache.cemented_count == 2);
-}
+}
+
+// Ensures votes are tallied on election::publish even if no vote is inserted through inactive_votes_cache
+TEST (active_transactions, conflicting_block_vote_existing_election)
+{
+	nano::system system;
+	nano::node_flags node_flags;
+	node_flags.disable_request_loop = true;
+	auto & node = *system.add_node (node_flags);
+	nano::genesis genesis;
+	nano::keypair key;
+	auto send (std::make_shared<nano::state_block> (nano::test_genesis_key.pub, genesis.hash (), nano::test_genesis_key.pub, nano::genesis_amount - 100, key.pub, nano::test_genesis_key.prv, nano::test_genesis_key.pub, *system.work.generate (genesis.hash ())));
+	auto fork (std::make_shared<nano::state_block> (nano::test_genesis_key.pub, genesis.hash (), nano::test_genesis_key.pub, nano::genesis_amount - 200, key.pub, nano::test_genesis_key.prv, nano::test_genesis_key.pub, *system.work.generate (genesis.hash ())));
+	auto vote_fork (std::make_shared<nano::vote> (nano::test_genesis_key.pub, nano::test_genesis_key.prv, 0, fork));
+
+	ASSERT_EQ (nano::process_result::progress, node.process_local (send).code);
+	ASSERT_EQ (1, node.active.size ());
+
+	// Vote for conflicting block, but the block does not yet exist in the ledger
+	node.active.vote (vote_fork);
+
+	// Block now gets processed
+	ASSERT_EQ (nano::process_result::fork, node.process_local (fork).code);
+
+	// Election must be confirmed
+	auto election (node.active.election (fork->qualified_root ()));
+	ASSERT_NE (nullptr, election);
+	ASSERT_TRUE (election->confirmed ());
+}

nano/node/election.cpp

@@ -481,7 +481,11 @@ bool nano::election::publish (std::shared_ptr<nano::block> block_a)
 		if (existing == blocks.end ())
 		{
 			blocks.emplace (std::make_pair (block_a->hash (), block_a));
-			insert_inactive_votes_cache (block_a->hash ());
+			if (!insert_inactive_votes_cache (block_a->hash ()))
+			{
+				// Even if no votes were in cache, they could be in the election
+				confirm_if_quorum ();
+			}
 			node.network.flood_block (block_a, nano::buffer_drop_policy::no_limiter_drop);
 		}
 		else
@@ -576,10 +580,10 @@ void nano::election::cleanup ()
 	}
 }
 
-void nano::election::insert_inactive_votes_cache (nano::block_hash const & hash_a)
+size_t nano::election::insert_inactive_votes_cache (nano::block_hash const & hash_a)
 {
 	auto cache (node.active.find_inactive_votes_cache (hash_a));
-	for (auto & rep : cache.voters)
+	for (auto const & rep : cache.voters)
 	{
 		auto inserted (last_votes.emplace (rep, nano::vote_info{ std::chrono::steady_clock::time_point::min (), 0, hash_a }));
 		if (inserted.second)
@@ -597,6 +601,7 @@ void nano::election::insert_inactive_votes_cache (nano::block_hash const & hash_
 		}
 		confirm_if_quorum ();
 	}
+	return cache.voters.size ();
 }
 
 bool nano::election::prioritized () const

nano/node/election.hpp

@@ -84,7 +84,7 @@ public:
 	size_t last_votes_size ();
 	void update_dependent ();
 	void adjust_dependent_difficulty ();
-	void insert_inactive_votes_cache (nano::block_hash const &);
+	size_t insert_inactive_votes_cache (nano::block_hash const &);
 	bool prioritized () const;
 	void prioritize_election (nano::vote_generator_session &);
 	// Erase all blocks from active and, if not confirmed, clear digests from network filters