ICE: `Anonymous structs or unions cannot be type parameters`

[matthiaskrgr]

auto-reduced (treereduce-rust):

#[derive(Eq)]
#[repr(C)]
struct Bar {
    _: union {
        a: u8,
    },
}

original:

#![allow(incomplete_features)]
#![feature(unnamed_fields)]


#[derive(Eq)]
#[repr(C)]
struct Bar {
    _: union {
        a: u8,
    },
}

Version information

rustc 1.78.0-nightly (62fb0db9a 2024-02-15)
binary: rustc
commit-hash: 62fb0db9a5a2a381f81ce0474c9bbd9ad385dd88
commit-date: 2024-02-15
host: x86_64-unknown-linux-gnu
release: 1.78.0-nightly
LLVM version: 18.1.0

Command:
/home/matthias/.rustup/toolchains/master/bin/rustc

Program output

thread 'rustc' panicked at compiler/rustc_builtin_macros/src/deriving/mod.rs:127:5:
Anonymous structs or unions cannot be type parameters
stack backtrace:
   0:     0x7f0f7ef8ce46 - std::backtrace_rs::backtrace::libunwind::trace::h53163824e7303228
                               at /rustc/62fb0db9a5a2a381f81ce0474c9bbd9ad385dd88/library/std/src/../../backtrace/src/backtrace/libunwind.rs:104:5
   1:     0x7f0f7ef8ce46 - std::backtrace_rs::backtrace::trace_unsynchronized::hd2e35374a0eb2a80
                               at /rustc/62fb0db9a5a2a381f81ce0474c9bbd9ad385dd88/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x7f0f7ef8ce46 - std::sys_common::backtrace::_print_fmt::h22916166849b0f03
                               at /rustc/62fb0db9a5a2a381f81ce0474c9bbd9ad385dd88/library/std/src/sys_common/backtrace.rs:68:5
   3:     0x7f0f7ef8ce46 - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::h2879f5e85b0fff5f
                               at /rustc/62fb0db9a5a2a381f81ce0474c9bbd9ad385dd88/library/std/src/sys_common/backtrace.rs:44:22
   4:     0x7f0f7efdd46c - core::fmt::rt::Argument::fmt::h97dbf5cc12c408c7
                               at /rustc/62fb0db9a5a2a381f81ce0474c9bbd9ad385dd88/library/core/src/fmt/rt.rs:142:9
   5:     0x7f0f7efdd46c - core::fmt::write::h778946ec939e8793
                               at /rustc/62fb0db9a5a2a381f81ce0474c9bbd9ad385dd88/library/core/src/fmt/mod.rs:1120:17
   6:     0x7f0f7ef8087f - std::io::Write::write_fmt::h5c63578d080db7f3
                               at /rustc/62fb0db9a5a2a381f81ce0474c9bbd9ad385dd88/library/std/src/io/mod.rs:1854:15
   7:     0x7f0f7ef8cbf4 - std::sys_common::backtrace::_print::h0363c2f779186f3d
                               at /rustc/62fb0db9a5a2a381f81ce0474c9bbd9ad385dd88/library/std/src/sys_common/backtrace.rs:47:5
   8:     0x7f0f7ef8cbf4 - std::sys_common::backtrace::print::h25462c423434b7b1
                               at /rustc/62fb0db9a5a2a381f81ce0474c9bbd9ad385dd88/library/std/src/sys_common/backtrace.rs:34:9
   9:     0x7f0f7ef8f93b - std::panicking::default_hook::{{closure}}::h77a19008a0b97cd9
  10:     0x7f0f7ef8f689 - std::panicking::default_hook::hc24779731fadc8e1
                               at /rustc/62fb0db9a5a2a381f81ce0474c9bbd9ad385dd88/library/std/src/panicking.rs:292:9
  11:     0x7f0f81e073dc - std[520fd08387c28b7f]::panicking::update_hook::<alloc[91e232cd38241d97]::boxed::Box<rustc_driver_impl[2702a2e4e48d8624]::install_ice_hook::{closure#0}>>::{closure#0}
  12:     0x7f0f7ef900a0 - <alloc::boxed::Box<F,A> as core::ops::function::Fn<Args>>::call::hd2fc103bd8349bfb
                               at /rustc/62fb0db9a5a2a381f81ce0474c9bbd9ad385dd88/library/alloc/src/boxed.rs:2030:9
  13:     0x7f0f7ef900a0 - std::panicking::rust_panic_with_hook::h413c2c5969744120
                               at /rustc/62fb0db9a5a2a381f81ce0474c9bbd9ad385dd88/library/std/src/panicking.rs:785:13
  14:     0x7f0f7ef8fda9 - std::panicking::begin_panic_handler::{{closure}}::h1a6d4d7a04fe1759
                               at /rustc/62fb0db9a5a2a381f81ce0474c9bbd9ad385dd88/library/std/src/panicking.rs:651:13
  15:     0x7f0f7ef8d326 - std::sys_common::backtrace::__rust_end_short_backtrace::he707e3793b7e3c10
                               at /rustc/62fb0db9a5a2a381f81ce0474c9bbd9ad385dd88/library/std/src/sys_common/backtrace.rs:171:18
  16:     0x7f0f7ef8fb14 - rust_begin_unwind
                               at /rustc/62fb0db9a5a2a381f81ce0474c9bbd9ad385dd88/library/std/src/panicking.rs:647:5
  17:     0x7f0f7efd9975 - core::panicking::panic_fmt::he521a95bbefc6993
                               at /rustc/62fb0db9a5a2a381f81ce0474c9bbd9ad385dd88/library/core/src/panicking.rs:72:14
  18:     0x7f0f83bcfc1c - rustc_builtin_macros[c3e0db7c51eb1b0b]::deriving::assert_ty_bounds
  19:     0x7f0f83bce7ba - rustc_builtin_macros[c3e0db7c51eb1b0b]::deriving::eq::expand_deriving_eq::{closure#0}
  20:     0x7f0f838a3f8c - <rustc_builtin_macros[c3e0db7c51eb1b0b]::deriving::generic::TraitDef>::expand_struct_def
  21:     0x7f0f83bcaa51 - <rustc_builtin_macros[c3e0db7c51eb1b0b]::deriving::generic::TraitDef>::expand_ext
  22:     0x7f0f83cb1157 - rustc_builtin_macros[c3e0db7c51eb1b0b]::deriving::eq::expand_deriving_eq
  23:     0x7f0f838a1c92 - <rustc_builtin_macros[c3e0db7c51eb1b0b]::deriving::BuiltinDerive as rustc_expand[6d4d13d6cfdcaa99]::base::MultiItemModifier>::expand
  24:     0x7f0f8397ca07 - <rustc_expand[6d4d13d6cfdcaa99]::expand::MacroExpander>::fully_expand_fragment
  25:     0x7f0f8397a4b7 - <rustc_expand[6d4d13d6cfdcaa99]::expand::MacroExpander>::expand_crate
  26:     0x7f0f83edbd12 - rustc_interface[1a4459fc77d0f37b]::passes::resolver_for_lowering
  27:     0x7f0f83edb1e7 - rustc_query_impl[af4ac1f50c857cdc]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[af4ac1f50c857cdc]::query_impl::resolver_for_lowering::dynamic_query::{closure#2}::{closure#0}, rustc_middle[52734e1a61f3d33]::query::erase::Erased<[u8; 8usize]>>
  28:     0x7f0f83db790e - rustc_query_system[2a398b116e853220]::query::plumbing::try_execute_query::<rustc_query_impl[af4ac1f50c857cdc]::DynamicConfig<rustc_query_system[2a398b116e853220]::query::caches::SingleCache<rustc_middle[52734e1a61f3d33]::query::erase::Erased<[u8; 8usize]>>, false, false, false>, rustc_query_impl[af4ac1f50c857cdc]::plumbing::QueryCtxt, false>
  29:     0x7f0f83db708b - rustc_query_impl[af4ac1f50c857cdc]::query_impl::resolver_for_lowering::get_query_non_incr::__rust_end_short_backtrace
  30:     0x7f0f83d60954 - rustc_interface[1a4459fc77d0f37b]::interface::run_compiler::<core[f365f26a3905eec5]::result::Result<(), rustc_span[f91837123c8497a4]::ErrorGuaranteed>, rustc_driver_impl[2702a2e4e48d8624]::run_compiler::{closure#0}>::{closure#0}
  31:     0x7f0f83fcd686 - std[520fd08387c28b7f]::sys_common::backtrace::__rust_begin_short_backtrace::<rustc_interface[1a4459fc77d0f37b]::util::run_in_thread_with_globals<rustc_interface[1a4459fc77d0f37b]::util::run_in_thread_pool_with_globals<rustc_interface[1a4459fc77d0f37b]::interface::run_compiler<core[f365f26a3905eec5]::result::Result<(), rustc_span[f91837123c8497a4]::ErrorGuaranteed>, rustc_driver_impl[2702a2e4e48d8624]::run_compiler::{closure#0}>::{closure#0}, core[f365f26a3905eec5]::result::Result<(), rustc_span[f91837123c8497a4]::ErrorGuaranteed>>::{closure#0}, core[f365f26a3905eec5]::result::Result<(), rustc_span[f91837123c8497a4]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[f365f26a3905eec5]::result::Result<(), rustc_span[f91837123c8497a4]::ErrorGuaranteed>>
  32:     0x7f0f83fcd4b2 - <<std[520fd08387c28b7f]::thread::Builder>::spawn_unchecked_<rustc_interface[1a4459fc77d0f37b]::util::run_in_thread_with_globals<rustc_interface[1a4459fc77d0f37b]::util::run_in_thread_pool_with_globals<rustc_interface[1a4459fc77d0f37b]::interface::run_compiler<core[f365f26a3905eec5]::result::Result<(), rustc_span[f91837123c8497a4]::ErrorGuaranteed>, rustc_driver_impl[2702a2e4e48d8624]::run_compiler::{closure#0}>::{closure#0}, core[f365f26a3905eec5]::result::Result<(), rustc_span[f91837123c8497a4]::ErrorGuaranteed>>::{closure#0}, core[f365f26a3905eec5]::result::Result<(), rustc_span[f91837123c8497a4]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[f365f26a3905eec5]::result::Result<(), rustc_span[f91837123c8497a4]::ErrorGuaranteed>>::{closure#1} as core[f365f26a3905eec5]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  33:     0x7f0f7ef991e5 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::hcab8919dd66e63e8
                               at /rustc/62fb0db9a5a2a381f81ce0474c9bbd9ad385dd88/library/alloc/src/boxed.rs:2016:9
  34:     0x7f0f7ef991e5 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h7fcf03bbae47bb99
                               at /rustc/62fb0db9a5a2a381f81ce0474c9bbd9ad385dd88/library/alloc/src/boxed.rs:2016:9
  35:     0x7f0f7ef991e5 - std::sys::pal::unix::thread::Thread::new::thread_start::hdab999c156b6bbcb
                               at /rustc/62fb0db9a5a2a381f81ce0474c9bbd9ad385dd88/library/std/src/sys/pal/unix/thread.rs:108:17
  36:     0x7f0f7ed809eb - <unknown>
  37:     0x7f0f7ee047cc - <unknown>
  38:                0x0 - <unknown>

error: the compiler unexpectedly panicked. this is a bug.

note: we would appreciate a bug report: https://github.com/rust-lang/rust/issues/new?labels=C-bug%2C+I-ICE%2C+T-compiler&template=ice.md

note: rustc 1.78.0-nightly (62fb0db9a 2024-02-15) running on x86_64-unknown-linux-gnu

query stack during panic:
#0 [resolver_for_lowering] getting the resolver for lowering
end of query stack

[clubby789]

Should be fixed by #121270