Great blog post ! One thing I wonder as a compiler head though is, what is the granularity of this stuff ? Is it per-file or per-function, or even per block ? If it's finer than per file, how do you do the tree diff ? Do you parse whole files and then do a node-by-node diff ? Do you have an incremental parser ?

If I was to implement incremental compilation, I'd start with per-module I guess, because it's the atomic unit for a compiler, so it would be a lot simpler. That's why I'm curious.