mvcc/watcher_group.go
func (wg *watcherGroup) contains(key string) bool {
	_, ok := wg.keyWatchers[key]
	return ok || wg.ranges.Intersects(adt.NewStringAffinePoint(key))
}
func (wg *watcherGroup) contains(key string) bool {
	_, ok := wg.keyWatchers[key]
	return ok || wg.ranges.Intersects(adt.NewStringAffinePoint(key))
}
// contains is whether the given key has a watcher in the group.