Rust

Another meme answer: nu.

I never actually used nu for anything. But I've been thinking (unironically) that nu with its built-in from_json and to_json can be interesting.

The use-case I had in mind is not games or anything like that, but some system or dev tools that traditionally utilized shell scripts, but are moving towards better languages like python. So I thought a single binary that embeds nu, but also has a lot of sub-commands that implement a lot of sub-tasks in Rust directly, and with JSON used as an exchange format, the combination can be interesting.

Now that I think about it more, this can work in both directions, with main execution being in nu (what I had in mind), or in Rust.

nu even has an lsp server, so the development experience should theoretically be good.

There is a Python interpreter written in Rust. It's apparently intended to (besides being fast an all that) make Rust scriptable.

Would something like Steel work?

The Helix editor is working on adding it as a plugin scripting language. You could take a look at the in-progress fork to see how they're doing it.

Crates.io has tags like scripting. It suggests languages like rhai, dyon, or rune.

There's a list of good options on Are We Game Yet, hope one of these crates is useful. https://arewegameyet.rs/ecosystem/scripting/

One more vote for using WASM. Using WASM has the benefit of allowing the user to use almost whatever language they want, as long as it can compile to WASM. So the user doesn't have to learn some bespoke scripting-specific language.

Boa is a remarkably well-developed JS runtime written in Rust. Nice API, and well sandboxed. We’re considering adopting it for Biome as well.

Many languages can be compiled to wasm, and it's quite easy to load and run wasm from rust

That way you could give the user multiple options, they could write it in rust, c, c++, javascript, etc

The most battletested way is via bindings to other languages. Ex. mlua with luau sandboxing Or Javascript via v8 or deno_core

There are also a few languages implemented in rust like rhai

There is also the option of compiling the user code to wasm and using wasmtime to run it

You can embed Lua pretty easily using a few different libraries. One I liked in particular was mlua. Lua is tiny, usually sufficiently fast, and easy to learn.

Otherwise, there are some others like Rhai, but there may be fewer resources available for users if you go with a less popular language.