Hahaha, I'm amazed that the Rust developers were able to do that.

Saying it was "quite a pain" is the understatement of the year.

Yup. I really think it was worth it though, it taught us a lot about how to make the language.

Mind, are you not worried at all that it may have taught you a lot... about how to make a language for writing compilers in? (paraphrasing Chris Lattner)

That is indeed a concern, I agree with Chris here.

The solution we had, though, is Servo. It being developed alongside as well meant we had another significant, non-compiler project, which guided us out of that trap.