Attribute Macro derive

#[derive]

Like #[macro_rules_derive], but for allowing to be used to shadow the “built-in” #[derive] attribute (on Rust ≥ 1.57.0).

That is, it is made a bit more lenient to allow for things such as:

#[macro_use]
extern crate macro_rules_attribute;

derive_alias! {
   #[derive(Eq!)] = #[derive(PartialEq, Eq)];
}

#[derive(Debug, Eq!)]
struct Foo;

fn main ()
{
   assert_eq!(Foo, Foo);
}

This is achieved thanks to checking for the presence of a terminating ! (or lack thereof) to determine whether the given derive macro is a classic procedural macro one or a macro_rules! one.