Lua Component Demo

This repository is a demo of compiling Lua to a WebAssembly component. The tools used here are:

• Lua - either 5.{1,2,3,4} through the lua-src crate
• mlua - Rust bindings to the Lua C API
• wasi-sdk - C toolchain to compile Lua
• wasm-tools wit-dylib - hooks up components to the Lua interpreter
• wasm-tools component link - assembles libraries into a single component.

The end result is that you're able to do something like this:

$ cat test.wit
package my:test;

world test {
  export run: func(x: string);
}
$ cat main.lua
function run(s)
  print('Hello ' .. s .. '!')
end
$ cargo run ./test.wit -o lua.wasm
...
$ wasmtime run -Wexceptions --invoke 'run("World")' --dir . ./lua.wasm
Hello World!
()

Disclaimer

I am not a Lua programmer. I don't know Lua, nor do I know idiomatic Lua. I'm aware it's a common choice as an embedding language and I wanted to use it to test out the creation of wit-dylib. I do not plan to maintain this project to become a production-ready embedding of Lua nor is it complete as-is (there's a number of todo!() throughout the codebase). The purpose of this repository is to provide a road map to how componentizing Lua might work, but it'll require someone more invested than I to take this over the finish line.

What works and what doesn't

The state of things can be seen in crates/runtime/src/lib.rs and the amount of todo!() there. Implemented features are:

• Type conversions for integers
• Type conversions for floats
• Type conversions for bools
• Type conversions for chars
• Type conversions for strings
• Type conversions for lists
• Type conversions for tuples
• Type conversions for option<T>
• WIT variant and result types.
• WIT record type.
• WIT flags type.
• WIT enum type.
• WIT option<option<T>> type.
• Invoking world-exported functions
• Raw bindings to call imported functions
• Defining imports under an appropriate name (they're just import1 right now).
• WIT imported resources

Unimplemented features are:

• Exported functions of interfaces aren't supported.
• WIT exported resources