I'd actually love to see a relatively high-performance (i.e., including a decent JIT) runtime for a dynamic language that's written in Rust. There's a lot of implementations like Rust Python, the Boa JS engine, etc. that are purely interpreted – and fun! – but I haven't seen a proper, high-performance VM yet.
I considered writing such a JVM in Rust, following writing one in C (https://github.com/anematode/b-jvm) that could JIT WebAssembly code and run in the browser, but decided it would be too time-consuming.
Obviously such a VM would involve a lot of unsafe, but I'm wondering if you could establish some proper, compile-time-checked invariants that make things a lot safer, without the complicated sandboxing that modern JS runtimes use to make it harder for JIT bugs to escalate into full blown RCE.
rust seems alergic to the un-safety required of "i dynamically built this executable code segment just now, please jump into it"
This is wrong, demonstrably. There are multiple OS kernels written in Rust (with small amounts of ASM glue, as is required in any kernel project).
wasmtime exists
yes i love to use a language runtime within another language runtime for a sweet sweet 30% performance penalty
Why the snark? wasmtime is a (pretty popular) Rust project which uses a JIT, demonstrating that it's not incompatible with Rust. Obviously a proper VM wouldn't depend on wasmtime, but implement its own JIT and paraphernalia.
fair. i guess i used “rust” in collective noun sense for “rust the ecosystem and community”; from my armchair experience there’s a big contingent of that community that abhors unsafe and software that uses it, and it’s that community/ecosystem aspect that prohibits unsafe since of course the language and compiler support it just fine.
The community does not abhor use of unsafe. The community abhors bad usage of unsafe: unsafe code should be used only when necessary, and ideally to build safe abstractions.