arora-module 2.0.0

Write an Arora module in Rust: the declaration macros and the traits they implement.
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arora-module

Write an Arora module in Rust: the crate that implements a module also carries its interface.

#[arora_module::module(id = "a1a6bb9a-…", name = "polly", version = "0.1.0")]
pub mod polly {
  #[export(id = "e1b4bda7-…")]
  pub fn say(#[param(id = "fb3787f2-…")] text: String) -> Status { … }
}

Ids are pinned in the attributes, in hex; a parameter is a plain Rust type, or &mut T when the function writes through it. From that one declaration come:
polly::ids the module id, and per function its id and parameter ids
polly::header(executor) the header a module.yaml is written from at export
polly::record(parent) the frozen module record a store serves
polly::exports() every export callable, for HostModule::of::<polly::Module>()
polly::client::say(&mut bridge, …) the typed stub a caller programs against
arora_function_<id> the entry point an executor looks up in the built artifact

The executor is not the declaration's to name. Only the step that builds the artifact knows whether it is native or wasm, so header takes it there. A module linked into the host has no header at all: it is registered from its exports and described by its record.

The two forms

#[module] goes on an inline Rust module and finds the #[export] functions itself. For a module in its own file, an attribute macro cannot see the items, so the file ends with the aggregate naming them:

use arora_module::{declare_module, export};

declare_module! {
  id = "a1a6bb9a-…", name = "polly", version = "0.1.0",
  exports = [hello_world, say]
}

Calling a module that is not a Rust declaration

module_from_header! reads a resolved header at expansion and produces the same ids and stubs from it:

arora_module::module_from_header!(
  "headers/polly.yaml",
  types = ["325a5767-e344-4532-860e-0749bcf2e428" => Status]
);
let status = say(&mut engine, "hello".to_string())?;

What a type must be

A parameter or return type is a primitive, a Vec<T> of one, an arora_types::value::Value (anything, as the dynamic key-value type), or a type deriving AroraType, which also gives it the Value conversions and the version a frozen signature pins it at. Maps are refused: the record vocabulary has no form for them.

An Option<T> of any of those but an array is an optional parameter or return. A caller may leave an optional argument out, or send Value::Option(None), and the function receives None. A present argument arrives wrapped in Value::Option, or as its bare element; either way the element's type is checked. Any other parameter is required: a call without it fails, naming the parameter.