raft: Allow an election immediately after start with checkQuorum

Previously, the checkQuorum flag required an election timeout to
expire before a node could cast its first vote. This change permits
the node to cast a vote at any time when the leader is not known,
including immediately after startup.

raft/raft.go

@@ -598,7 +598,7 @@ func (r *raft) Step(m pb.Message) error {
 		lead := m.From
 		if m.Type == pb.MsgVote {
 			force := bytes.Equal(m.Context, []byte(campaignTransfer))
-			inLease := r.checkQuorum && r.state != StateCandidate && r.electionElapsed < r.electionTimeout
+			inLease := r.checkQuorum && r.lead != None && r.electionElapsed < r.electionTimeout
 			if !force && inLease {
 				// If a server receives a RequestVote request within the minimum election timeout
 				// of hearing from a current leader, it does not update its term or grant its vote

raft/raft_test.go

@@ -1281,10 +1281,8 @@ func TestLeaderElectionWithCheckQuorum(t *testing.T) {
 	setRandomizedElectionTimeout(a, a.electionTimeout+1)
 	setRandomizedElectionTimeout(b, b.electionTimeout+2)
 
-	// Letting b's electionElapsed reach to timeout so that it can vote for a
-	for i := 0; i < b.electionTimeout; i++ {
-		b.tick()
-	}
+	// Immediately after creation, votes are cast regardless of the
+	// election timeout.
 	nt.send(pb.Message{From: 1, To: 1, Type: pb.MsgHup})
 
 	if a.state != StateLeader {