Derive Macro medea_macro::JsCaused

#[derive(JsCaused)]
{
    // Attributes available to this derive:
    #[js]
}

Generate implementation of JsCaused trait for errors represented as enum.

How to use

1. Declare wrapper for JS error and enum for error variants.

The js_cause() method returns error if nested error has its type declared as an argument of the attribute #[js(error = "path::to::Error")] or the error type is assumed to be imported as JsError.

use medea_jason::utils::JsCaused;

struct JsError;

#[derive(JsCaused)]
enum FooError {
    Internal,
    Js(JsError),
}

let err = FooError::Internal;
assert_eq!(err.name(), "Internal");
assert!(err.js_cause().is_none());

let err = FooError::Js(JsError {});
assert_eq!(err.name(), "Js");
assert!(err.js_cause().is_some());

If enum variant has attribute #[js(cause)] it will call the js_cause() method on nested error.

#[derive(JsCaused)]
enum BarError {
    Foo(#[js(cause)] FooError),
}

let err = BarError::Foo(FooError::Internal);
assert_eq!(err.name(), "Foo");
assert!(err.js_cause().is_none());

let err = BarError::Foo(FooError::Js(JsError {}));
assert_eq!(err.name(), "Foo");
assert!(err.js_cause().is_some());