codegen: prevent name duplication in Rust or Rhai

codegen/src/function.rs

@@ -18,6 +18,7 @@ pub(crate) struct ExportedFnParams {
     pub name: Option<String>,
     pub return_raw: bool,
     pub skip: bool,
+    pub span: Option<proc_macro2::Span>,
 }
 
 impl ExportedFnParams {
@@ -47,6 +48,7 @@ impl Parse for ExportedFnParams {
         let arg_list = args.call(
             syn::punctuated::Punctuated::<syn::Expr, syn::Token![,]>::parse_separated_nonempty,
         )?;
+        let span = arg_list.span();
 
         let mut attrs: HashMap<proc_macro2::Ident, Option<syn::LitStr>> = HashMap::new();
         for arg in arg_list {
@@ -125,6 +127,7 @@ impl Parse for ExportedFnParams {
             name,
             return_raw,
             skip,
+            span: Some(span),
             ..Default::default()
         })
     }