alt Hacker NewsWhy does every build have the ability to run arbitrary code by default in the first place? That seems like something you should opt into only under very specific scenarios and even then it should probably be built around a WASM sandbox or microVM (as the parent suggested).
Because many many builds end up doing something just a little weird that the build system cannot handle by default. Ideally the build system would be fully property/dependency based and so it wouldn't have to run arbitrary code. In the real world everybody has something weird about their build that the build system cannot make work.
This is partially because for nearly every project the build system is something they need and don't care about. When they need something weird they hack just enough to make it work and never ask "how should the build system change so that this was a property instead of running code", and thus build systems are slow to improve. In a number of cases the build system did have a way to do that thing, but the person didn't know about it.
There are also a lot of code generators out there. I have yet to see a large project which didn't have their own code generator for something specific to their project (protobuf is an example from Google that has escaped and become useful elsewhere, but there are many others that are specific to one project. Yacc is from the 1970s, and stands for "yet another compiler compiler" - implying the idea was already common 50 years ago). You cannot have/use these useful tools without running arbitrary code.