Module probe 

Run a tiny probe binary that includes the user’s whisker.rs and emits the resulting Config as JSON on stdout.

Why a probe binary?

whisker.rs is regular Rust source — there’s no parser we could point at the file. The user’s configure function can do arbitrary computation (env lookups, conditional fields, etc.), so the only way to know what it means is to execute it.

The probe is a one-file cargo run that:

1. include!("path/to/whisker.rs") — splices the user’s configure fn into our tiny main.
2. Calls configure(&mut Config::default()).
3. Serializes the populated config to JSON and prints it.

Compile cost is single-digit seconds the first time (just whisker-config + serde_json), and the result is cached under target/.whisker/config-cache.json. The cache is invalidated by mtime: re-running the probe is a no-op unless whisker.rs was touched since the cache write.

Why not include the umbrella whisker crate?

whisker-config is intentionally a small, dependency-light crate so the probe build is cheap. Pulling in whisker (umbrella) would also pull whisker-runtime, whisker-driver, Lynx headers, etc. — turning the probe into a multi-minute build. The user crate’s whisker.rs therefore writes use whisker_config::Config directly, not use whisker::Config.

Functions

run

Run the probe and return the parsed config. Caches via mtime so the second call (and later) returns instantly until whisker.rs changes.