Definition
This idiom is used to express to someone that they are experiencing good fortune or success.
你真幸运！
You found a great parking spot; your luck's in!
你找到了一个很棒的停车位，真是好运！
They gave you a free upgrade? Your luck's in!
他们给你免费升级？真是好运！
You won the lottery at the last minute; your luck's in!
你在最后一刻中了彩票，真是好运！