Rua: A blazingly fast, safe, Rust-based implementation of Lua

Warning: this is still both experimental and unstable. Any API provided is subject to change

You can try a live demo of the interpreter running as WASM here (according to a couple of benchmarks, it's about twice as slow as native compilation)

Goals

• Be mostly Lua 5.1 compatible
• No unnecessary unsafety. I'm still considering if some features can be implemented in safe rust, without absolutely trashing the performance of the entire interpreter (I'm looking at you, coroutines with upvalues)
• Achieve performance on par with the official PUC-Rio Lua implementation
• Offer a nice API for interacting between Rust and Lua

Non goals

• Be a 100% compatible, drop-in replacement for your favourite Lua implementation. This includes things like:
  • Having the same error messages
  • Bytecode compatibility
  • Having the same behaviour for thing like table iteration order
• Use JIT compilation, since that's impossible to implement within safe Rust

Currently working

• A rather complete single-pass compiler. Most of the Lua syntax is already supported (main exception being iterator-based for-loops)
• Some compile-time optimizations, like constant folding and specialized instructions
• A fast, register-based VM, with performance comparable with Lua 5.1 (see benchmarks)
• A memory safe garbage collector, that achieves a decent performance and memory usage by combining reference counting and a real tracing GC
• A table implementation similar to Lua's, that automatically optimizes itself depending on its usage (whether it's used as an array or as a dictionary)
• Proper tail calls
• Running on the browser as WASM
• Some proc macros to make the implementation of native functions incredibly simple
• Closures and lexical scoping
• Exceptions and stacktraces
• A somewhat decent test suite

TODOs

• Sandboxing
• Coroutines
• Varargs and multiple return values
• Switch to tail call based dispatch if/when explicit_tail_calls is stabilized
• Measure if incremental garbage collection is worth it, given that reference counting should make GC pauses quite infrequent

Credits

Some invaluable resources in the creation of this interpreter were:

• Writing an interpreter in Go, on which I based the original implementation of the interpreter
• Crafting interpreters, which helped me transform it into a bytecode interpreter, with a single-pass compiler
• The official PUC-Rio Lua implementation, on which I based my register-based compiler, the tables' implementation, and many other things
• The Rust performance book, which was extremely useful for optimizing the interpreter