Macro s2 

macro_rules! s2 {
    ($(
        $(#$attr:tt)*
        $pub:vis $t:ident $i:ident { $($field:tt)* }
    )*) => { ... };
    (it: $(#$attr:tt)* $pub:vis union $i:ident { $($field:tt)* }) => { ... };
    (it: $(#$attr:tt)* $pub:vis struct $i:ident { $($field:tt)* }) => { ... };
}

Like s, but (1) generates a Default impl for every struct in the block, and (2) adds a private field to the struct to replicate the effects of the non_exhaustive attribute while rust-lang/rust#132699 gets sorted out.

To opt out of having the private field added, annotate the struct with an exhaustive attribute, as in:

s2! {
    #[exhaustive]
    struct Something {
        ...
    }
}

See [custom_struct] for details.