Support ignore, using for enums?

[dhardy]

#31 mostly implemented #6 (support enums), but with a significant missing feature: lack of support for using and ignore keywords.

The reason is very simple: syntax.

Case study: ignore

I recently wanted to implement Debug on the following enum. The problem: kas::Window does not support Debug. This was not important for my debugging purposes, but prevented use of derive or autoimpl.

enum PendingAction<A: crate::AppData> {
    AddPopup(WindowId, WindowId, kas::PopupDescriptor),
    AddWindow(WindowId, kas::Window<A>),
    CloseWindow(WindowId),
    Action(kas::Action),
}

This enum's variants use tuple syntax, but ignore self.1 is not specific enough.

This is sufficient: ignore AddWindow::1. It is not correct Rust syntax since AddWindow is not a type (though there was a proposal in that direction) and ::1 is not a valid path element (tuples not needing this).

Alternatively: AddWindow.1. This is also not correct Rust syntax since AddWindow is not a value, but at least .1 is a valid field accessor, so this may be the better option.

Using multiple fields?

Unlike ignore, using normally only targets a single field. Implementing e.g. Deref on an enum would require a field for each variant. This should not be a problem, however:

#[autoimpl(Deref<Target = T> using A.0, B.0)]
enum Either<T> {
    A(T),
    B(T),
}

Summary

The above, using . field accessors, appears a reasonable proposition, despite not being true Rust syntax.

There is motivation for supporting at least ignore on enums, though given how long it took me to find a real example this appears limited.

I will leave this issue open for now. Comments welcome.