Function fold_name_str 

pub fn fold_name_str<'new, 'src>(
    name: NameStr<'_, 'src>,
    arena: &'new Bump,
) -> NameStr<'new, 'src>

Moves a NameStr into the output arena of a fold: a string borrowed from the source stays borrowed, an arena string is copied into arena. Use it when overriding a fold method that rebuilds names, variables or strings.