Starlark — Rust runtime

Examples below assume this module is imported with an imports: entry under alias Starlark. If you import the module under a different name, substitute your alias accordingly.

The std/starlark module ships two controller implementations:

Implementation	Declared as	Backed by
nodejs	pkg:npm/@telorun/starlark	starlark-webasm
rust	pkg:cargo/telorun-starlark	Native Rust addon (N-API)

By default, importing std/starlark resolves to the kernel-native implementation — nodejs for the Node.js kernel today.

Opting into the Rust controller

The runtime: field selects the implementation. Use the object form of an imports: entry to set it:

kind: Telo.Application
metadata: { name: my-app, version: 1.0.0 }
imports:
  Starlark:
    source: std/starlark@0.6.0
    runtime: rust

The kernel will:

1. Probe rustc --version. Missing → fall back if the runtime spec allows it (e.g. runtime: [rust, any]); error if the spec is strict.
2. Run cargo build --release --features napi in modules/starlark/rust/.
3. Locate the produced dylib via cargo metadata and copy it to <libname>.node.
4. Load via Node's require and use it as the controller.

First-run cost is the cold cargo build (~30s). Subsequent runs hit Cargo's incremental cache and are sub-second.

Other runtime: forms

Form	Meaning
(omitted)	Same as runtime: auto — kernel-native first, fall through
runtime: auto	Best effort: kernel-native first, then any other available controller
runtime: native	Strict kernel-native (nodejs for the Node.js kernel)
runtime: nodejs	Strict — only the nodejs controller. Fails on miss
runtime: rust	Strict — only the rust controller. Fails on miss
runtime: [rust, nodejs]	Ordered fallback: try rust, then nodejs; fail if both miss
runtime: [rust, any]	Rust preferred; fall through to anything else available

Authoring a Rust controller

The Rust controller crate at modules/starlark/rust/ is a textbook Rust project — Cargo.toml + src/. The contributor never writes use napi::* or #[napi] attributes; the #[controller] macro from telorun-sdk generates all FFI plumbing.

See the SDK README for the controller-author contract.