segfault builtin_derive_item

[matthiaskrgr]

auto-reduced (treereduce-rust):

//@compile-flags: -frust-incomplete-and-experimental-compiler-do-not-use
#![no_core]
#[repr(C)]
#[derive(PartialEq, Eq, PartialOrd, Ord)]
union Value {
    a: u64,
    b: f64,
}

original:

#![feature(no_core)]
#![no_core]
#[repr(C)]
#[derive(PartialEq, Eq, PartialOrd, Ord)]
union Value {
    a: u64,
    b: f64,
}

Version information:

1a91028

Command:
/home/matthias/vcs/github/gccrs/gccrs-build/gcc/crab1 -frust-incomplete-and-experimental-compiler-do-not-use

Program output

/tmp/icemaker_global_tempdir.7cxs1UbUnTLY/rustc_testrunner_tmpdir_reporting.qLe7U24Ri4hh/mvce.rs:4:1: error: derive(PartialEq) cannot be used on unions
    4 | union Value {
      | ^~~~~
/tmp/icemaker_global_tempdir.7cxs1UbUnTLY/rustc_testrunner_tmpdir_reporting.qLe7U24Ri4hh/mvce.rs:4:1: error: derive(PartialOrd) cannot be used on unions
crab1: internal compiler error: Segmentation fault
0x3097ef9 internal_error(char const*, ...)
	../../gcc/diagnostic-global-context.cc:787
0x19c085f crash_signal
	../../gcc/toplev.cc:325
0xea7c30 builtin_derive_item
	../../gcc/rust/expand/rust-expand-visitor.cc:54
0xea7c30 Rust::ExpandVisitor::expand_inner_items(std::vector<std::unique_ptr<Rust::AST::Item, std::default_delete<Rust::AST::Item> >, std::allocator<std::unique_ptr<Rust::AST::Item, std::default_delete<Rust::AST::Item> > > >&)
	../../gcc/rust/expand/rust-expand-visitor.cc:201
0xe65cdb Rust::Session::expansion(Rust::AST::Crate&, Rust::Resolver2_0::NameResolutionContext&)
	../../gcc/rust/rust-session-manager.cc:1039
0xe73f9b Rust::Session::compile_crate(char const*)
	../../gcc/rust/rust-session-manager.cc:698
/home/matthias/vcs/github/gccrs/gccrs-build/gcc/crab1 /tmp/icemaker_global_tempdir.7cxs1UbUnTLY/rustc_testrunner_tmpdir_reporting.qLe7U24Ri4hh/mvce.rs -o/tmp/icemaker_global_tempdir.7cxs1UbUnTLY/rustc_testrunner_tmpdir_reporting.qLe7U24Ri4hh/binaryname -frust-incomplete-and-experimental-compiler-do-not-use
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.

[Eventidor]

This looks like an ICE in gccrs triggered during derive expansion on unions.

Steps to reproduce:

1. Compile the following code:

   #[repr(C)]
   #[derive(PartialEq)]
   union Value {
   a: u64,
   b: f64,
   }

2. The compiler correctly reports:
   error: derive(PartialEq) cannot be used on unions

3. However, after emitting the error, it crashes with a segmentation fault in:
   builtin_derive_item → DeriveVisitor::derive

Expected behavior:
The compiler should emit the error and terminate cleanly without crashing.

It seems the derive pipeline is still being executed even after detecting an invalid item (union), leading to a null/invalid AST state.

Possible fix:
Add an early return in builtin_derive_item when the item is a union, before calling DeriveVisitor::derive.

gcc version: