[jroesch]

I'm pretty sure even when building a JIT Rust would provide advantages. The only unsafe part of JITing is allocating the underlying instruction buffer and marking the memory as executable to the OS. You could still leverage Rust in building compilers from IR -> Instructions.

[eslaught]

The point is that whenever you do "IR -> Instructions" you are opening the possibility for logic errors to become memory errors. E.g. emitting opcode 9 instead of opcode 8 might (on some system) allow an attacker to execute arbitrary code. And these sorts of bugs cannot be prevented by pure memory safety alone, once you have (intentionally) opened the door to writing executable memory. You would actually need a full theorem prover to check the correctness of your code for you (which obviously Rust does not provide).

[steveklabnik]

Yeah, it's only for part of it, maybe the SpiderMonkey people I was talking too are more focused on the unsafe part than the other parts.