macro-attr-2018 2.1.2

// Copyright (c) 2015 macro-attr contributors.
// Copyright (c) 2020 Warlock <internalmike@gmail.com>.
//
// Licensed under the MIT license (see LICENSE or <http://opensource.org
// /licenses/MIT>) or the Apache License, Version 2.0 (see LICENSE of
// <http://www.apache.org/licenses/LICENSE-2.0>), at your option. All
// files in the project carrying such notice may not be copied, modified,
// or distributed except according to those terms.

#![deny(warnings)]

use macro_attr_2018::macro_attr;

macro_rules! TryFrom {
    (($prim:ty) $(pub)* enum $name:ident { $($body:tt)* }) => {
        TryFrom! {
            @collect_variants ($name, $prim),
            ($($body)*,) -> ()
        }
    };

    (
        @collect_variants ($name:ident, $prim:ty),
        ($(,)*) -> ($($var_names:ident,)*)
    ) => {
        impl TryFrom<$prim> for $name {
            type Error = $prim;
            fn try_from(src: $prim) -> Result<$name, $prim> {
                $(
                    if src == $name::$var_names as $prim {
                        return Ok($name::$var_names);
                    }
                )*
                Err(src)
            }
        }
    };

    (
        @collect_variants $fixed:tt,
        ($var:ident $(= $_val:expr)*, $($tail:tt)*) -> ($($var_names:tt)*)
    ) => {
        TryFrom! {
            @collect_variants $fixed,
            ($($tail)*) -> ($($var_names)* $var,)
        }
    };
}

macro_attr! {
    #[derive(Debug, PartialEq, TryFrom!(u8))]
    enum Get { Up, Down, AllAround }
}

#[test]
fn test_try_from() {
    assert_eq!(Get::try_from(0u8), Ok(Get::Up));
    assert_eq!(Get::try_from(1u8), Ok(Get::Down));
    assert_eq!(Get::try_from(2u8), Ok(Get::AllAround));
    assert_eq!(Get::try_from(3u8), Err(3u8));
}