[estebank]

In my experience parsing is pretty robust and fast already, to the point where optimizing that stage of the compiler isn't worth it. Regarding the discrepancy between the AST and the source code, I think that it is worth noting that although there's a relationship between the syntax and the semantics, there need not be a 1:1 mapping between these, both allowing different features look similar (because they are pedagogically similar, like in impl Trait in Rust in argument position and return position) or dissimilar. I could see leveraging ASTs for more accurate diffing algorithms and fancy tools, but none of these would require that the AST be the source of truth.

[Gibbon1]

If you have ABI stability you don't need to do any of that stuff either to code that hasn't changed.

The fastest way to compile code is to not constantly recompile it from scratch.