raft/progress.go
func (in *inflights) add(inflight uint64) {
	if in.full() {
		panic("cannot add into a full inflights")
	}
	next := in.start + in.count
	size := in.size
	if next >= size {
		next -= size
	}
	if next >= len(in.buffer) {
		in.growBuf()
	}
	in.buffer[next] = inflight
	in.count++
}
func (in *inflights) add(inflight uint64) {
	if in.full() {
		panic("cannot add into a full inflights")
	}
	next := in.start + in.count
	size := in.size
	if next >= size {
		next -= size
	}
	if next >= len(in.buffer) {
		in.growBuf()
	}
	in.buffer[next] = inflight
	in.count++
}
// add adds an inflight into inflights