I have been trying to figure out this sentence “これまでにない上出来だ” looking it up it reads as “You have outdone yourself” however I’m confused because it seems like it says, “up until now you have not out done yourself”? the main reason it reads like this to me, is because of the ない part. ない usually means its not. so why is it in this sentence? can someone please break down the idea behind this sentence?
As for my interpretation of it, これまでに is like “before now”. In this context it refers to your past self.
無い can mean or “not had”, which applies to this sentence.
上出来 just means “good performance”
So its sorta like saying “Your past self had not had such a good performance”, implying that they have surpassed their past self. Its a weird translation, but thats the best I can explain it.