Attribute Macro starlark_module::starlark_module[−][src]

#[starlark_module]

Write Starlark modules concisely in Rust syntax.

For example:

ⓘ
#[starlark_module]
fn global(registry: &mut GlobalsBuilder) {
    fn cc_binary(name: &str, srcs: Vec<&str>) -> String {
        Ok(format!("{:?} {:?}", name, srcs))
    }
}

Parameters operate as named parameters of a given type, with five possible tweaks:

  • args means the argument is the *args.
  • kwargs means the argument is the **kwargs.
  • ref name means the argument must be passed by position, not by name.
  • A type of Option means the argument is optional.
  • A pattern x @ foo : bool means the argument defaults to foo if not specified.

During execution there are two local variables injected into scope:

  • ctx is the Evaluator.
  • heap is the Heap, obtained from ctx.heap().

A function with the #[starlark_module] attribute can be added to a GlobalsBuilder value using the with function. Those Globals can be passed to Evaluator to provide global functions. Alternatively, you can return Globals from get_members to attach functions to a specific type (e.g. the string type).

  • When unattached, you can define constants with const. We define True, False and None that way.
  • When attached, you can annotate the functions with #[attribute] to turn the name into an attribute on the value. Such a function must take exactly one argument, namely a value of the type you have attached it to.
  • The attribute #[starlark_type("test")] causes f.type to return "test".

All these functions interoperate properly with dir(), getattr() and hasattr().

If a desired function name is also a Rust keyword, use the r# prefix, e.g. r#type.