playground.rs

#[proc_macro_derive(SomeTrait)]
pub fn derive_some_trait_from_def(item: TokenStream) -> TokenStream {
    let item: syn::DeriveInput = syn::parse(item).unwrap();
    ...
}

#[proc_macro_attribute]
pub fn derive_some_trait_from_impl(attr: TokenStream, item: TokenStream) -> TokenStream {
    let item: syn::ItemImpl = syn::parse(item).unwrap();
    ...
}

#[derive(SomeTrait)]
struct Foo {
    x: u32,
    y: u32,
}

#[derive_some_trait_from_impl]
impl Foo {
    fn cartesian(&self) -> f64 {
       let x = self.x as f64;
       let y = self.y as f64;
       (x*x + y*y).sqrt()
    }
}

trait SomeTrait {
    fn dump_schema(&self, w: &mut Write) -> fmt::Result;
}

playground2.rs

#[proc_macro]
pub fn derive_some_trait(tts: TokenStream) -> TokenStream {
    let CustomInput { def_, impl_ } = syn::parse(tts).unwrap();
    ...
}

derive_some_trait! {
    #[derive(Debug, SomeTrait)]
    struct Foo { x: u32, y: u32 }
  
    #[derive_some_trait_from_impl]
    impl Foo {
        fn cartesian(&self) -> f64 { ... }
    }
}