Implement custom debug

[seppo0010]

Hi David!

I finally got around to continue with the workshop. Do you mind taking a look at my solution for custom debug? Thanks!

[dtolnay]

Nicely done!

Today I added the rest of the test cases for derive(CustomDebug) that get into more of the difficult cases around trait bounds. Check it out if you're interested: https://github.com/dtolnay/proc-macro-workshop/tree/master/debug/tests

[seppo0010]

Thanks for the feedback, it looks a lot better now!

[seppo0010]

I'm pretty sure at this point that there has to be a cleaner way of doing this, @dtolnay, but I'm not sure how to mix this destructuring of structs and arrays... https://github.com/dtolnay/proc-macro-workshop/pull/13/commits/f1f2384614f846b05a1a7854321812796bbe95cd#diff-fd4e0f3362d674b97a10b240e544747cR102

[dtolnay]

You may be able to write the same thing with less indentation and nested closures, like this:

fields
    .named
    .iter()
    .filter_map(|f| {
        let segment = match &f.ty {
            Type::Path(ty) => &ty.path.segments[0],
            _ => return None,
        };
        if segment.ident != "PhantomData" {
            return None;
        }
        let argument = match &segment.arguments {
            PathArguments::AngleBracketed(bracketed) => &bracketed.args[0],
            _ => return None,
        };
        match argument {
            GenericArgument::Type(Type::Path(arg)) => Some(arg.path.segments[0].ident.clone()),
            _ => None,
        }
    })
    .collect()