I can't say I'm familiar with Bun, but I've used a similar syntax to the example you provided of the current Bun syntax when working with Frida (https://frida.re). I agree it leaves something to be desired and indeed it would be cool if Aro could do this in the future.
LuaJIT spends about 2000 lines[1] on its C parser which even includes a limited expression evaluator, though not a preprocessor. My experience suggests explicit memory management could add half again that (LuaJIT’s piggybacks on its GC), and writing one is something like a month of work even if you know exactly what you’re doing (I didn’t), but in any case it’s not a monumental task.
