Completion in derive macro attributes

[mikatpt]

This might be a naive question/suggestion. Is it possible to have completion of derive attributes, and functional completion within their values?

For example, clap's derive macro has a huge list of undocumented attributes which are drawn from its builder API's public interface. If it weren't for the lack of completion, it would feel like an elegant, very well-designed API—as it is, devX is extremely lackluster compared to the builder API because rust-analyzer doesn't help you out.

#[command(
    name = "some-cli-program",   // suggest attribute titles?
    color = ColorChoice::Always, // auto-complete doesn't function here.
    styles = Styles::styled()
        .header(AnsiColor::Yellow.on_default())
        .usage(AnsiColor::Yellow.on_default())
        .literal(AnsiColor::Magenta.on_default())
        .placeholder(AnsiColor::Green.on_default())
)]

[lnicola]

Related: #15452.