Handle duplicated enum variants in the protocol

[kchibisov]

The enum in the wayland protocol could have duplicated items, advertising only different names.

Right now wayland scanner is not handling them, but I don't think there's a protocol in the wild using such a thing, so it's not an issue now, but it could be with the upcoming color management protocols.

The solution is simple and non-breaking, you should do something like:

#[repr(u32)]
#[derive(PartialEq, Eq)]
enum Foo {
  X = 1,
  B = 2,
}

impl Foo {
    // TODO: The same values should go into the `impl`.
    //
    // This is what should be emitted from the wayland-scanner.
    pub const C: Foo = Self::B;
}

fn main() {
    let z = Foo::C;
    match z {
        Foo::C => {}
        Foo::B => {}
        Foo::X => {}
    }
    println!("{}", Foo::X as u32);
}

[i509VCB]

One thing to consider (which sadly would be less ergonomic) would be to do enums like ash.

Another question, with the idea you proposed how do you determine which value name should be the variant name and which ones are associated constants?

fn main() {
    let z = Foo::C;
    match z {
        Foo::C => {}
        Foo::B => {}
        Foo::X => {}
    }
    println!("{}", Foo::X as u32);
}

This would lint in rustc since you'd have a redundant match statement branch.

[kchibisov]

@i509VCB by order? Since the goal simply to include all of them in some way. The point is not in matching in the first place, but having a value. The thing is that arbitrary wayland enum can look like that and what I propose is non-breaking change.