" I think you are confused because you have misunderstood how BEFORE is used in that sentence, and because THAT was omitted. If you just look at the part of the sentence that says "before they didn't use Clang", it does not sound right. The sentence is poorly worded.
New words, one handy idiom, and a 2-minute quiz — delivered to your inbox to keep your streak alive.
silak12do we use a negative sentence after beforeNo. We almost never do that when before introduces a clause, but Kris has already explained how this case is different.