> I start to see a lot of these re-writes that depend on tests to state that its working.
There's another way to validate the rewrite though. Just run both pgrust and postgres and compare the output. Know of an edge case? Run it too. Doesn't know? Use a fuzzer or some automated tool to find interesting inputs. Found an inconsistency? The input/output pair becomes a test case now
Not sure if there's tooling for that though. If there is, just give it to Claude so they will incorporate it in their development loop
> Just run both pgrust and postgres and compare the output.
The space of inputs and outputs is infinite. You can't prove programs are the same by "just" testing a bunch inputs.
Indeed. This approach is an improvement / augmentation over tests, not a panacea.
Neither postgres nor pgrust have their behavior specified using formal methods. (pgrust could write some contracts using something like kani or creusot, but having upstream postgres also write contracts is a tougher sell). If they had, one could write a giant proof that said the two software essentially do the same thing (at least in a subset of environments and some simplifying assumptions)
> Not sure if there's tooling for that though.
I can recommend proptest. What you're describing is a common pattern in property-based testing which basically boils down to "comparing against an oracle". In this case, postgres would be the oracle, pgrust is the system under test, and the idea is to generate strategies comprised of sequences of valid (and invalid) SQL statements and ensure the system under test behaves the same as the oracle in every case.
(I'm working with malisper on this) we built this too and are using it for a new version we're working on right now
Oh, that's cool!