alias.rs

// use proc_macro2::TokenStream;
use quote::{ToTokens}; // 1.0.26;
use syn::{parse_quote, Ident, Item, ItemConst, ItemEnum, ItemFn, ItemStatic, Signature, Stmt}; // 2.0.11

    /// input:
    /// ```rs
    /// #[alias(B, C)]
    /// pub const A: u32 = 0;
    /// ```
    ///
    /// output:
    /// ```rs
    /// pub const A: u32 = 0;
    /// pub const B: u32 = 0;
    /// pub const C: u32 = 0;
    /// ```
pub fn main() {


    let names = vec!["B", "C"];
    let tokens: Stmt = parse_quote! { pub static A: u32 = 0; };

    let new = names
        .into_iter()
        .map(|name| match &tokens {
            Stmt::Item(i) => match i {
                Item::Const(c) => Some(Stmt::Item(Item::Const(ItemConst {
                    ident: syn::parse_str::<Ident>(name).unwrap(),
                    ..c.clone()
                }))),

                Item::Enum(c) => Some(Stmt::Item(Item::Enum(ItemEnum {
                    ident: syn::parse_str::<Ident>(name).unwrap(),
                    ..c.clone()
                }))),
                
                Item::Fn(c) => Some(Stmt::Item(Item::Fn(ItemFn {
                    sig: Signature {
                        ident: syn::parse_str::<Ident>(name).unwrap(),
                        ..c.sig.clone()
                    },
                    ..c.clone()
                }))),
                
                Item::Static(c) => Some(Stmt::Item(Item::Static(ItemStatic {
                    ident: syn::parse_str::<Ident>(name).unwrap(),
                    ..c.clone()
                }))),
                
                _ => None,
            },
            _ => None,
        }).map(|x| x.unwrap().into_token_stream().to_string())
        .collect::<Vec<_>>();
    println!("{}", tokens.into_token_stream());
    println!("{}", new.join("\n"));
}