Improve Suggestion from the Compiler Specific Case?

Code

lib.rs

extern crate proc_macro;

use proc_macro::TokenStream;
use quote::quote;
use syn::{parse_macro_input, ItemStruct};


#[proc_macro_attribute]
pub fn foo_bar_attribute(_metadata: TokenStream, _input: TokenStream) -> TokenStream {
    let input = parse_macro_input!(_input as ItemStruct);
    let struct_name = &input.ident;`
    TokenStream::from(quote! {

        #[derive(Debug)]

        struct #struct_name {
            foo: i32,
            bar: i32
        }

        impl Default for #struct_name {
            fn default() -> Self {
                #struct_name { foo: 10. bar: 20 } <-- syntax error here '.'  instead of  ','
            }
        }

        impl #struct_name {
            fn double_foo(&self) -> i32 {
                self.foo * 2
            }
        }
    })
}

_main.rs_

use macro_demo::*;

#[foo_bar_attribute] <<----- error point to here
struct MyStruct {
    baz: i32,
}

fn main() {

    let demo = MyStruct::default();

    println!("struct is {:?}", demo);

    let double_foo = demo.double_foo();

    println!("double foo: {}", double_foo);
}

Current output

error: expected one of `,`, `.`, `?`, `}`, or an operator, found `bar`
 --> src/main.rs:3:1
  |
3 | #[foo_bar_attribute]
  | ^^^^^^^^^^^^^^^^^^^^- help: try adding a comma: `,`
  | |
  | expected one of `,`, `.`, `?`, `}`, or an operator
4 | #[derive(Debug, Default)]
5 | struct MyStruct {
  |        -------- while parsing this struct
  |
  = note: this error originates in the attribute macro `foo_bar_attribute` (in Nightly builds, run with -Z macro-backtrace for more info)

Desired output

Rationale and extra context

i created a custom macro attribute but made a syntax error in the method that creates the struct with it's attribute. the error message is unhelpful which is a bit of surprise from Rust. it should correctly locate the point at which the it occurs

Other cases

Rust Version

rustc --version --verbose
rustc 1.79.0 (129f3b996 2024-06-10)
binary: rustc
commit-hash: 129f3b9964af4d4a709d1383930ade12dfe7c081
commit-date: 2024-06-10
host: x86_64-unknown-linux-gnu
release: 1.79.0
LLVM version: 18.1.7

Anything else?

No response

Reproduce the example from lib.rs and main.rs, focusing on the syntax error inside the generated Default implementation and the resulting diagnostic at the attribute. Trace how the compiler reports errors from the procedural macro, then verify that the diagnostic points to the generated syntax error or otherwise gives a more useful location than the attribute invocation.