raft: add TODO for more safety checks

Signed-off-by: Pavel Kalinnikov <[email protected]>

raft.go

@@ -1785,6 +1785,11 @@ func (r *raft) handleAppendEntries(m pb.Message) {
 func (r *raft) handleHeartbeat(m pb.Message) {
 	// It is only safe to advance the commit index if our log is a prefix of the
 	// leader's log. Otherwise, entries at this index may mismatch.
+	//
+	// TODO(pav-kv): move this logic to r.raftLog, which is more appropriate for
+	// handling safety. The raftLog can use the logSynced flag for other safety
+	// checks. For example, unstable.truncateAndAppend currently may override a
+	// suffix of the log unconditionally, but it can only be done if !logSynced.
 	if r.logSynced {
 		r.raftLog.commitTo(min(m.Commit, r.raftLog.lastIndex()))
 	}