> If you are depending on some behavior not covered in the regression tests, how do you know the next minor release won't break you?
Decades of intrinsic knowledge. Which a rewrite lacks.
imho the issue is the language used. AI rewrites are cheap and cheap exercises require a great deal of scrutiny and proof of correctness. Simply using regressions test lacks the intrinsic knowledge of a decades old codebase stuck in developers minds.
Claiming a rewrite is better because it passes all tests is a flex, a new version requires a boatload of evidence for people to accept it as an improvement and not just "passes tests, written in rust via LLM so it must be better". Run it in production for a year in a sufficiently large system and you might be somewhere.
>> Decades of intrinsic knowledge. Which a rewrite lacks.
You mean the ones encoded in the regression suite? I think your argument is valid in many medium-to-faang firms where the application is going to have encoded business logic that isn't explicitly tested for. If anything, projects like PG are the exact opposite: no business context and regression suites that test every possible scenario due to the accumulation of bug fixes and context over many years.
>> Run it in production for a year in a sufficiently large system and you might be somewhere.
How do you know every release of PG doesn't break in the setting of "a year in a sufficiently large system"?
> no business context and regression suites that test every possible scenario due to the accumulation of bug fixes and context over many years.
Spend time enough with a codebase and you’ll know stuff about its behavior that is not encoded in a test suite. Especially when you need to adjust an integration tests due to the modification of an invariant in a dependency.
> How do you know every release of PG doesn't break in the setting of "a year in a sufficiently large system"?
Because the postgres team is professional and will take care of publishing a changelog for what has been modified since the last version.