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0001. Use Luau as the embedded scripting language ​

Date: 2026-05-03

Status ​

Accepted

Context ​

Need: embedded scripting language with tight host control, fine-grained sandboxing, no JIT requirement.

Candidates:

  • Lua 5.4 — small, widely embedded. Unsafe os/io/package/debug surface needs stripping.
  • Luau — Roblox's Lua dialect. Sandbox-aware by design, gradual typing, deterministic. Bindable from Rust via mlua luau feature.
  • JavaScript (Deno/Boa) — heavyweight, less amenable to fixed-resource embedding.
  • WebAssembly — capable but high tooling burden on script authors.
  • Custom DSL — too narrow for general-purpose scripts.

Host is Rust. Bindings story via mlua is load-bearing.

Decision ​

neoc uses Luau, bundled via mlua's vendored feature.

Consequences ​

  • Luau's gradual type system and sandbox-aware design reduce host-level stripping work.
  • Deterministic execution (no JIT) — predictable allocation behaviour.
  • Script authors use Luau syntax. Most Lua 5.1/5.4 libraries compatible with adaptation.
  • Gated on mlua upstream's continued Luau support.
  • vendored bundles Luau into binary — no system Lua dependency, larger binary.