Allow FRU syntax on non_exhaustive structs

3

There was an interesting macro in that thread:

Click to see 
#[doc(hidden)] pub use ::core;

#[macro_export]
macro_rules! FRU {(
    $Struct:path {
        $(
            $field_name:ident : $value:expr,
        )*
        .. $($initial:expr)?
    }
) => ({
    let it = $crate::core::default::Default::default();
    $(
        let () = it;
        let it = $initial;
    )?
    let mut it = it;
    let $Struct { $($field_name: _,)* .. } = it; // ensure any DerefMut shenanigans are shadowed
    $(
        it.$field_name = $value;
    )*
    it
})}

which allows writing:

// Crate 2
fn main ()
{
    let _options = FRU!(Options { bar: "baz".to_string(), .. /* default() */ });
}