Allow usage of enum variant name in Display format

[NightEule5]

I have an Displayed enum with a custom format on each variant, like this:

#[derive(Display)]
enum SomeEnum {
    #[display("valuea:{0}")]
    ValueA(String),
    #[display("valueb:{0}")]
    ValueB(String),
    #[display("valuec:{0}")]
    ValueC(String),
}

It'd be nice to make this more readable by using the lowercase term in the format, such as #[display("{lowercase}:{0}")] or #[display("{}:{0}", lowercase)]. A drawback of the former is ambiguity if the variant contains a lowercase field (positional format args don't appear to be accepted currently), so the latter is likely the preferred form.

Even better would be this:

#[derive(Display)]
#[display("{}:{0}", lowercase)]
enum SomeEnum {
    ValueA(String),
    ValueB(String),
    ValueC(String),
    #[display(lowercase)]
    Other // breaks above convention
}

[dr-orlovsky]

I see. Not sure what would be the best way not to make {lowercase} literal not to conflict with variable names which may come from associated enum data or structure fields.

I am planning improvements to Display derivation, like support for vectors/colection types with some separator etc, so will keep this in mind during the design.