ICE (Segmentation fault) when deriving Default on enum with multiple #[default] attributes

Summary

When compiling Rust code that contains an enum with multiple #[default] attributes using gccrs, the compiler crashes with a segmentation fault instead of emitting appropriate error messages. This behavior differs from rustc, which correctly reports "multiple declared defaults" and provides diagnostic suggestions.

Reproducer

I tried this code:

#[derive(Default)]
enum A {
    #[default]
    #[default]
    A,
    #[default]
    B,
}

#[derive(Default)]
enum E {
    #[default]
    A,
    #[default]
    A,
}

macro_rules! m {
    { $($id:ident)* } => {
        #[derive(Default)]
        enum F {
            $(
                #[default]
                $id,
            )*
        }
    }
}

m! { A B }

Does the code make use of any (1.49) nightly feature ?

• Nightly

Godbolt link

https://godbolt.org/z/WrPqvYc7G

Actual behavior

:1:3: sorry, unimplemented: uninmplemented builtin derive macro
1 | #[derive(Default)]
| ^~~~~~
:10:3: sorry, unimplemented: uninmplemented builtin derive macro
10 | #[derive(Default)]
| ^~~~~~
crab1: internal compiler error: Segmentation fault
0x2e9eb6c internal_error(char const*, ...)
???:0
0x1157677 void Rust::ExpandVisitor::expand_macro_children<std::vector<std::unique_ptr<Rust::AST::Item, std::default_deleteRust::AST::Item >, std::allocator<std::unique_ptr<Rust::AST::Item, std::default_deleteRust::AST::Item > > >, std::unique_ptr<Rust::AST::Item, std::default_deleteRust::AST::Item > >(std::vector<std::unique_ptr<Rust::AST::Item, std::default_deleteRust::AST::Item >, std::allocator<std::unique_ptr<Rust::AST::Item, std::default_deleteRust::AST::Item > > >&, std::function<std::unique_ptr<Rust::AST::Item, std::default_deleteRust::AST::Item > (Rust::AST::SingleASTNode)>)
???:0
0x1154628 Rust::ExpandVisitor::expand_inner_items(std::vector<std::unique_ptr<Rust::AST::Item, std::default_deleteRust::AST::Item >, std::allocator<std::unique_ptr<Rust::AST::Item, std::default_deleteRust::AST::Item > > >&)
???:0
0x1094f9d Rust::Session::expansion(Rust::AST::Crate&)
???:0
0x109a238 Rust::Session::compile_crate(char const*)
???:0
Please submit a full bug report, with preprocessed source (by using -freport-bug).
Please include the complete backtrace with any bug report.
See https://gcc.gnu.org/bugs/ for instructions.
Compiler returned: 1

Expected behavior

The compiler should emit errors for multiple #[default] attributes. No internal compiler errors or crashes should occur.

GCC Version

14.0.1

Start by reproducing the crash with the Rust enum and macro examples in the issue, then inspect the expansion path named in the backtrace: Rust::ExpandVisitor::expand_macro_children, expand_inner_items, and Session::expansion. Done means multiple #[default] attributes produce diagnostics like rustc without an internal compiler error or segmentation fault.