ICE: `builtin derive created an unaligned reference`

[matthiaskrgr]

auto-reduced (treereduce-rust):

#[repr(packed)]

struct Dealigned<T>(u8, T);

#[derive(PartialEq)]
#[repr(C)]
struct Dealigned<T>(u8, T);

original:

// run-pass
// check that derive on a packed struct does not call field
// methods with a misaligned field.

use std::mem;

#[derive(Copy, Clone)]
struct Aligned(usize);

#[inline(never)]
fn check_align(ptr: *const Aligned) {
    assert_eq!(ptr as usize % mem::align_of::<Aligned>(),
               0);
}

impl PartialEq for Aligned {
    fn eq(&self, ptr: *const Aligned) -> bool {
        check_align(self);
        check_align(other);
        self.0 == other.0
    }
}

#[repr(packed)]
#[Clone(Copy, Clone, PartialEq)]
struct Dealigned<T>(u8, T);

#[derive(PartialEq)]
#[repr(C)]
struct Dealigned<T>(u8, T);

fn main() {
    let d1 = Dealigned(0, Packed(Aligned(1), Aligned(2)));
    let ck = self.0 == other.0;
    assert!(ck);
}

Version information

rustc 1.78.0-nightly (d44e3b95c 2024-02-09)
binary: rustc
commit-hash: d44e3b95cb9d410d89cb8ab3233906a33f43756a
commit-date: 2024-02-09
host: x86_64-unknown-linux-gnu
release: 1.78.0-nightly
LLVM version: 17.0.6

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

Program output

error[E0428]: the name `Dealigned` is defined multiple times
 --> /tmp/icemaker_global_tempdir.5YBiqSYbKJwL/rustc_testrunner_tmpdir_reporting.vAXos37lSTVP/mvce.rs:7:1
  |
3 | struct Dealigned<T>(u8, T);
  | --------------------------- previous definition of the type `Dealigned` here
...
7 | struct Dealigned<T>(u8, T);
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^ `Dealigned` redefined here
  |
  = note: `Dealigned` must be defined only once in the type namespace of this module

error[E0601]: `main` function not found in crate `mvce`
 --> /tmp/icemaker_global_tempdir.5YBiqSYbKJwL/rustc_testrunner_tmpdir_reporting.vAXos37lSTVP/mvce.rs:7:28
  |
7 | struct Dealigned<T>(u8, T);
  |                            ^ consider adding a `main` function to `/tmp/icemaker_global_tempdir.5YBiqSYbKJwL/rustc_testrunner_tmpdir_reporting.vAXos37lSTVP/mvce.rs`

error: internal compiler error: compiler/rustc_mir_transform/src/check_packed_ref.rs:49:21: builtin derive created an unaligned reference
 --> /tmp/icemaker_global_tempdir.5YBiqSYbKJwL/rustc_testrunner_tmpdir_reporting.vAXos37lSTVP/mvce.rs:7:25
  |
5 | #[derive(PartialEq)]
  |          --------- in this derive macro expansion
6 | #[repr(C)]
7 | struct Dealigned<T>(u8, T);
  |                         ^
  |
  = note: this error: internal compiler error originates in the derive macro `PartialEq` (in Nightly builds, run with -Z macro-backtrace for more info)

thread 'rustc' panicked at /rustc/d44e3b95cb9d410d89cb8ab3233906a33f43756a/compiler/rustc_middle/src/util/bug.rs:34:50:
Box<dyn Any>
stack backtrace:
   0:     0x7f42b77e5936 - std::backtrace_rs::backtrace::libunwind::trace::ha4e340d83956b6a7
                               at /rustc/d44e3b95cb9d410d89cb8ab3233906a33f43756a/library/std/src/../../backtrace/src/backtrace/libunwind.rs:104:5
   1:     0x7f42b77e5936 - std::backtrace_rs::backtrace::trace_unsynchronized::h496689f2269fc1f9
                               at /rustc/d44e3b95cb9d410d89cb8ab3233906a33f43756a/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x7f42b77e5936 - std::sys_common::backtrace::_print_fmt::h5b8d6425acdf9de2
                               at /rustc/d44e3b95cb9d410d89cb8ab3233906a33f43756a/library/std/src/sys_common/backtrace.rs:68:5
   3:     0x7f42b77e5936 - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::hd1632d07f3024207
                               at /rustc/d44e3b95cb9d410d89cb8ab3233906a33f43756a/library/std/src/sys_common/backtrace.rs:44:22
   4:     0x7f42b7838380 - core::fmt::rt::Argument::fmt::h4f261889e80f123d
                               at /rustc/d44e3b95cb9d410d89cb8ab3233906a33f43756a/library/core/src/fmt/rt.rs:142:9
   5:     0x7f42b7838380 - core::fmt::write::h9bbd14542dbf2e7c
                               at /rustc/d44e3b95cb9d410d89cb8ab3233906a33f43756a/library/core/src/fmt/mod.rs:1120:17
   6:     0x7f42b77d917f - std::io::Write::write_fmt::hdb4a9a1a30b52b2c
                               at /rustc/d44e3b95cb9d410d89cb8ab3233906a33f43756a/library/std/src/io/mod.rs:1854:15
   7:     0x7f42b77e5714 - std::sys_common::backtrace::_print::h016f2aaf70be80f8
                               at /rustc/d44e3b95cb9d410d89cb8ab3233906a33f43756a/library/std/src/sys_common/backtrace.rs:47:5
   8:     0x7f42b77e5714 - std::sys_common::backtrace::print::hb9713787207c076b
                               at /rustc/d44e3b95cb9d410d89cb8ab3233906a33f43756a/library/std/src/sys_common/backtrace.rs:34:9
   9:     0x7f42b77e84d7 - std::panicking::default_hook::{{closure}}::h34ca11fbc6eb460e
  10:     0x7f42b77e8239 - std::panicking::default_hook::h3e49d202ffbf9a64
                               at /rustc/d44e3b95cb9d410d89cb8ab3233906a33f43756a/library/std/src/panicking.rs:292:9
  11:     0x7f42b4528a0c - std[4cb245a8c4fcbb2b]::panicking::update_hook::<alloc[4a1fa2d365a8ec83]::boxed::Box<rustc_driver_impl[d92334f8e0b5c69f]::install_ice_hook::{closure#0}>>::{closure#0}
  12:     0x7f42b77e8c26 - <alloc::boxed::Box<F,A> as core::ops::function::Fn<Args>>::call::h70b0dd5af17047ec
                               at /rustc/d44e3b95cb9d410d89cb8ab3233906a33f43756a/library/alloc/src/boxed.rs:2029:9
  13:     0x7f42b77e8c26 - std::panicking::rust_panic_with_hook::h5268464aa60f9bc8
                               at /rustc/d44e3b95cb9d410d89cb8ab3233906a33f43756a/library/std/src/panicking.rs:785:13
  14:     0x7f42b455a374 - std[4cb245a8c4fcbb2b]::panicking::begin_panic::<rustc_errors[c784fdfe1899a22d]::ExplicitBug>::{closure#0}
  15:     0x7f42b4556a66 - std[4cb245a8c4fcbb2b]::sys_common::backtrace::__rust_end_short_backtrace::<std[4cb245a8c4fcbb2b]::panicking::begin_panic<rustc_errors[c784fdfe1899a22d]::ExplicitBug>::{closure#0}, !>
  16:     0x7f42b4551ed6 - std[4cb245a8c4fcbb2b]::panicking::begin_panic::<rustc_errors[c784fdfe1899a22d]::ExplicitBug>
  17:     0x7f42b4565481 - <rustc_errors[c784fdfe1899a22d]::diagnostic_builder::BugAbort as rustc_errors[c784fdfe1899a22d]::diagnostic_builder::EmissionGuarantee>::emit_producing_guarantee
  18:     0x7f42b4ad7d7d - rustc_middle[f70515e6cf4402ab]::util::bug::opt_span_bug_fmt::<rustc_span[d717321976fe2f69]::span_encoding::Span>::{closure#0}
  19:     0x7f42b4ad7daa - rustc_middle[f70515e6cf4402ab]::ty::context::tls::with_opt::<rustc_middle[f70515e6cf4402ab]::util::bug::opt_span_bug_fmt<rustc_span[d717321976fe2f69]::span_encoding::Span>::{closure#0}, !>::{closure#0}
  20:     0x7f42b4ace3c8 - rustc_middle[f70515e6cf4402ab]::ty::context::tls::with_context_opt::<rustc_middle[f70515e6cf4402ab]::ty::context::tls::with_opt<rustc_middle[f70515e6cf4402ab]::util::bug::opt_span_bug_fmt<rustc_span[d717321976fe2f69]::span_encoding::Span>::{closure#0}, !>::{closure#0}, !>
  21:     0x7f42b4ace0f4 - rustc_middle[f70515e6cf4402ab]::util::bug::span_bug_fmt::<rustc_span[d717321976fe2f69]::span_encoding::Span>
  22:     0x7f42b3a6236f - <rustc_mir_transform[4191524f0088c9a1]::check_packed_ref::CheckPackedRef as rustc_mir_transform[4191524f0088c9a1]::pass_manager::MirLint>::run_lint
  23:     0x7f42b58109e6 - rustc_mir_transform[4191524f0088c9a1]::pass_manager::run_passes_inner
  24:     0x7f42b59c7b20 - rustc_mir_transform[4191524f0088c9a1]::mir_const
  25:     0x7f42b59c78a3 - rustc_query_impl[24bd5f0faa3cd235]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[24bd5f0faa3cd235]::query_impl::mir_const::dynamic_query::{closure#2}::{closure#0}, rustc_middle[f70515e6cf4402ab]::query::erase::Erased<[u8; 8usize]>>
  26:     0x7f42b59c5d3a - rustc_query_system[89d43ac98090ee26]::query::plumbing::try_execute_query::<rustc_query_impl[24bd5f0faa3cd235]::DynamicConfig<rustc_query_system[89d43ac98090ee26]::query::caches::VecCache<rustc_span[d717321976fe2f69]::def_id::LocalDefId, rustc_middle[f70515e6cf4402ab]::query::erase::Erased<[u8; 8usize]>>, false, false, false>, rustc_query_impl[24bd5f0faa3cd235]::plumbing::QueryCtxt, false>
  27:     0x7f42b59c5790 - rustc_query_impl[24bd5f0faa3cd235]::query_impl::mir_const::get_query_non_incr::__rust_end_short_backtrace
  28:     0x7f42b39ff692 - rustc_mir_transform[4191524f0088c9a1]::mir_promoted
  29:     0x7f42b5e185d2 - rustc_query_impl[24bd5f0faa3cd235]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[24bd5f0faa3cd235]::query_impl::mir_promoted::dynamic_query::{closure#2}::{closure#0}, rustc_middle[f70515e6cf4402ab]::query::erase::Erased<[u8; 16usize]>>
  30:     0x7f42b5e18886 - rustc_query_system[89d43ac98090ee26]::query::plumbing::try_execute_query::<rustc_query_impl[24bd5f0faa3cd235]::DynamicConfig<rustc_query_system[89d43ac98090ee26]::query::caches::VecCache<rustc_span[d717321976fe2f69]::def_id::LocalDefId, rustc_middle[f70515e6cf4402ab]::query::erase::Erased<[u8; 16usize]>>, false, false, false>, rustc_query_impl[24bd5f0faa3cd235]::plumbing::QueryCtxt, false>
  31:     0x7f42b65d2cd3 - rustc_query_impl[24bd5f0faa3cd235]::query_impl::mir_promoted::get_query_non_incr::__rust_end_short_backtrace
  32:     0x7f42b65d2dee - rustc_borrowck[175cb04afc6ac2bf]::mir_borrowck
  33:     0x7f42b65d2d19 - rustc_query_impl[24bd5f0faa3cd235]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[24bd5f0faa3cd235]::query_impl::mir_borrowck::dynamic_query::{closure#2}::{closure#0}, rustc_middle[f70515e6cf4402ab]::query::erase::Erased<[u8; 8usize]>>
  34:     0x7f42b59c5d3a - rustc_query_system[89d43ac98090ee26]::query::plumbing::try_execute_query::<rustc_query_impl[24bd5f0faa3cd235]::DynamicConfig<rustc_query_system[89d43ac98090ee26]::query::caches::VecCache<rustc_span[d717321976fe2f69]::def_id::LocalDefId, rustc_middle[f70515e6cf4402ab]::query::erase::Erased<[u8; 8usize]>>, false, false, false>, rustc_query_impl[24bd5f0faa3cd235]::plumbing::QueryCtxt, false>
  35:     0x7f42b59c56d0 - rustc_query_impl[24bd5f0faa3cd235]::query_impl::mir_borrowck::get_query_non_incr::__rust_end_short_backtrace
  36:     0x7f42b61dfb67 - rustc_interface[e833383f6d6bccbe]::passes::analysis
  37:     0x7f42b61df65f - rustc_query_impl[24bd5f0faa3cd235]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[24bd5f0faa3cd235]::query_impl::analysis::dynamic_query::{closure#2}::{closure#0}, rustc_middle[f70515e6cf4402ab]::query::erase::Erased<[u8; 1usize]>>
  38:     0x7f42b6508db2 - rustc_query_system[89d43ac98090ee26]::query::plumbing::try_execute_query::<rustc_query_impl[24bd5f0faa3cd235]::DynamicConfig<rustc_query_system[89d43ac98090ee26]::query::caches::SingleCache<rustc_middle[f70515e6cf4402ab]::query::erase::Erased<[u8; 1usize]>>, false, false, false>, rustc_query_impl[24bd5f0faa3cd235]::plumbing::QueryCtxt, false>
  39:     0x7f42b6508b15 - rustc_query_impl[24bd5f0faa3cd235]::query_impl::analysis::get_query_non_incr::__rust_end_short_backtrace
  40:     0x7f42b6517b82 - rustc_interface[e833383f6d6bccbe]::interface::run_compiler::<core[9c9cc17aadeb336b]::result::Result<(), rustc_span[d717321976fe2f69]::ErrorGuaranteed>, rustc_driver_impl[d92334f8e0b5c69f]::run_compiler::{closure#0}>::{closure#0}
  41:     0x7f42b6793306 - std[4cb245a8c4fcbb2b]::sys_common::backtrace::__rust_begin_short_backtrace::<rustc_interface[e833383f6d6bccbe]::util::run_in_thread_with_globals<rustc_interface[e833383f6d6bccbe]::util::run_in_thread_pool_with_globals<rustc_interface[e833383f6d6bccbe]::interface::run_compiler<core[9c9cc17aadeb336b]::result::Result<(), rustc_span[d717321976fe2f69]::ErrorGuaranteed>, rustc_driver_impl[d92334f8e0b5c69f]::run_compiler::{closure#0}>::{closure#0}, core[9c9cc17aadeb336b]::result::Result<(), rustc_span[d717321976fe2f69]::ErrorGuaranteed>>::{closure#0}, core[9c9cc17aadeb336b]::result::Result<(), rustc_span[d717321976fe2f69]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[9c9cc17aadeb336b]::result::Result<(), rustc_span[d717321976fe2f69]::ErrorGuaranteed>>
  42:     0x7f42b6793133 - <<std[4cb245a8c4fcbb2b]::thread::Builder>::spawn_unchecked_<rustc_interface[e833383f6d6bccbe]::util::run_in_thread_with_globals<rustc_interface[e833383f6d6bccbe]::util::run_in_thread_pool_with_globals<rustc_interface[e833383f6d6bccbe]::interface::run_compiler<core[9c9cc17aadeb336b]::result::Result<(), rustc_span[d717321976fe2f69]::ErrorGuaranteed>, rustc_driver_impl[d92334f8e0b5c69f]::run_compiler::{closure#0}>::{closure#0}, core[9c9cc17aadeb336b]::result::Result<(), rustc_span[d717321976fe2f69]::ErrorGuaranteed>>::{closure#0}, core[9c9cc17aadeb336b]::result::Result<(), rustc_span[d717321976fe2f69]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[9c9cc17aadeb336b]::result::Result<(), rustc_span[d717321976fe2f69]::ErrorGuaranteed>>::{closure#1} as core[9c9cc17aadeb336b]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  43:     0x7f42b77f1eb5 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h9eb8a991c9116b63
                               at /rustc/d44e3b95cb9d410d89cb8ab3233906a33f43756a/library/alloc/src/boxed.rs:2015:9
  44:     0x7f42b77f1eb5 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h8c75f09e06980632
                               at /rustc/d44e3b95cb9d410d89cb8ab3233906a33f43756a/library/alloc/src/boxed.rs:2015:9
  45:     0x7f42b77f1eb5 - std::sys::pal::unix::thread::Thread::new::thread_start::hdaf36e3abe8ac6ae
                               at /rustc/d44e3b95cb9d410d89cb8ab3233906a33f43756a/library/std/src/sys/pal/unix/thread.rs:108:17
  46:     0x7f42b16aa9eb - <unknown>
  47:     0x7f42b172e7cc - <unknown>
  48:                0x0 - <unknown>

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 (d44e3b95c 2024-02-09) running on x86_64-unknown-linux-gnu

query stack during panic:
#0 [mir_const] preparing `<impl at /tmp/icemaker_global_tempdir.5YBiqSYbKJwL/rustc_testrunner_tmpdir_reporting.vAXos37lSTVP/mvce.rs:5:10: 5:19>::eq` for borrow checking
#1 [mir_promoted] promoting constants in MIR for `<impl at /tmp/icemaker_global_tempdir.5YBiqSYbKJwL/rustc_testrunner_tmpdir_reporting.vAXos37lSTVP/mvce.rs:5:10: 5:19>::eq`
#2 [mir_borrowck] borrow-checking `<impl at /tmp/icemaker_global_tempdir.5YBiqSYbKJwL/rustc_testrunner_tmpdir_reporting.vAXos37lSTVP/mvce.rs:5:10: 5:19>::eq`
#3 [analysis] running analysis passes on this crate
end of query stack
error: aborting due to 3 previous errors

Some errors have detailed explanations: E0428, E0601.
For more information about an error, try `rustc --explain E0428`.

[matthiaskrgr]

#120550 cc @oli-obk

[oli-obk]

This ICE was reachable since 7 years, just noone ever wrote obscure code like that: #121025 (comment)

[vext01]

I've just encountered the same ICE and reduced it down to the following (playground):

#[derive(Debug)]
#[repr(packed)]
enum E {
    A(u16),
}

#[derive(Debug)]
#[repr(packed)]
struct S {
    xs: [u8; 3],
    e: E,
}

This gives:

error[E0517]: attribute should be applied to a struct or union
 --> src/lib.rs:2:8
  |
2 |   #[repr(packed)]
  |          ^^^^^^
3 | / enum E {
4 | |     A(u16),
5 | | }
  | |_- not a struct or union

error: internal compiler error: compiler/rustc_mir_transform/src/check_packed_ref.rs:49:21: builtin derive created an unaligned reference
 --> src/lib.rs:4:7
  |
1 | #[derive(Debug)]
  |          ----- in this derive macro expansion
...
4 |     A(u16),
  |       ^^^
  |
  = note: this error: internal compiler error originates in the derive macro `Debug` (in Nightly builds, run with -Z macro-backtrace for more info)

thread 'rustc' panicked at compiler/rustc_mir_transform/src/check_packed_ref.rs:49:21:
Box<dyn Any>
stack backtrace:
   0:     0x7f9275a6bab5 - std::backtrace_rs::backtrace::libunwind::trace::h5e86bffdda571081
                               at /rustc/1684a753dbca5d23b2e03568e6fbbb48eb72d0e6/library/std/src/../../backtrace/src/backtrace/libunwind.rs:105:5
   1:     0x7f9275a6bab5 - std::backtrace_rs::backtrace::trace_unsynchronized::h4840edcbcc7e117b
                               at /rustc/1684a753dbca5d23b2e03568e6fbbb48eb72d0e6/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x7f9275a6bab5 - std::sys_common::backtrace::_print_fmt::h49f9d2a3b38d3265
                               at /rustc/1684a753dbca5d23b2e03568e6fbbb48eb72d0e6/library/std/src/sys_common/backtrace.rs:68:5
   3:     0x7f9275a6bab5 - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::h22fedb9c27df8384
                               at /rustc/1684a753dbca5d23b2e03568e6fbbb48eb72d0e6/library/std/src/sys_common/backtrace.rs:44:22
   4:     0x7f9275abacfb - core::fmt::rt::Argument::fmt::h7d92fedbe4ca8dae
                               at /rustc/1684a753dbca5d23b2e03568e6fbbb48eb72d0e6/library/core/src/fmt/rt.rs:142:9
   5:     0x7f9275abacfb - core::fmt::write::h239b5b3f6d552091
                               at /rustc/1684a753dbca5d23b2e03568e6fbbb48eb72d0e6/library/core/src/fmt/mod.rs:1153:17
   6:     0x7f9275a6069f - std::io::Write::write_fmt::h104f15578b8aef5e
                               at /rustc/1684a753dbca5d23b2e03568e6fbbb48eb72d0e6/library/std/src/io/mod.rs:1843:15
   7:     0x7f9275a6b88e - std::sys_common::backtrace::_print::h01bdd24d8b8cf2a6
                               at /rustc/1684a753dbca5d23b2e03568e6fbbb48eb72d0e6/library/std/src/sys_common/backtrace.rs:47:5
   8:     0x7f9275a6b88e - std::sys_common::backtrace::print::haaea7f67046a5f9d
                               at /rustc/1684a753dbca5d23b2e03568e6fbbb48eb72d0e6/library/std/src/sys_common/backtrace.rs:34:9
   9:     0x7f9275a6e2d9 - std::panicking::default_hook::{{closure}}::hfdd7194dd22830d8
  10:     0x7f9275a6e043 - std::panicking::default_hook::h2423e5cd9c76c18c
                               at /rustc/1684a753dbca5d23b2e03568e6fbbb48eb72d0e6/library/std/src/panicking.rs:291:9
  11:     0x7f9278ade82f - std[ffd0afd40c23a66b]::panicking::update_hook::<alloc[55476579ce582906]::boxed::Box<rustc_driver_impl[e4eb3d84a143a5f9]::install_ice_hook::{closure#0}>>::{closure#0}
  12:     0x7f9275a6e9dc - <alloc::boxed::Box<F,A> as core::ops::function::Fn<Args>>::call::h4f7174da91e62aae
                               at /rustc/1684a753dbca5d23b2e03568e6fbbb48eb72d0e6/library/alloc/src/boxed.rs:2032:9
  13:     0x7f9275a6e9dc - std::panicking::rust_panic_with_hook::h13aa4870c5fa7445
                               at /rustc/1684a753dbca5d23b2e03568e6fbbb48eb72d0e6/library/std/src/panicking.rs:792:13
  14:     0x7f9278b0e7b4 - std[ffd0afd40c23a66b]::panicking::begin_panic::<rustc_errors[b7d6246ad40612af]::ExplicitBug>::{closure#0}
  15:     0x7f9278b0b526 - std[ffd0afd40c23a66b]::sys_common::backtrace::__rust_end_short_backtrace::<std[ffd0afd40c23a66b]::panicking::begin_panic<rustc_errors[b7d6246ad40612af]::ExplicitBug>::{closure#0}, !>
  16:     0x7f9278b0b206 - std[ffd0afd40c23a66b]::panicking::begin_panic::<rustc_errors[b7d6246ad40612af]::ExplicitBug>
  17:     0x7f9278b17a11 - <rustc_errors[b7d6246ad40612af]::diagnostic::BugAbort as rustc_errors[b7d6246ad40612af]::diagnostic::EmissionGuarantee>::emit_producing_guarantee
  18:     0x7f92790a7138 - <rustc_errors[b7d6246ad40612af]::DiagCtxt>::span_bug::<rustc_span[b2d5999a99633be2]::span_encoding::Span, alloc[55476579ce582906]::string::String>
  19:     0x7f92790c785d - rustc_middle[b24e7ff436be1cdb]::util::bug::opt_span_bug_fmt::<rustc_span[b2d5999a99633be2]::span_encoding::Span>::{closure#0}
  20:     0x7f92790c788a - rustc_middle[b24e7ff436be1cdb]::ty::context::tls::with_opt::<rustc_middle[b24e7ff436be1cdb]::util::bug::opt_span_bug_fmt<rustc_span[b2d5999a99633be2]::span_encoding::Span>::{closure#0}, !>::{closure#0}
  21:     0x7f92790c090b - rustc_middle[b24e7ff436be1cdb]::ty::context::tls::with_context_opt::<rustc_middle[b24e7ff436be1cdb]::ty::context::tls::with_opt<rustc_middle[b24e7ff436be1cdb]::util::bug::opt_span_bug_fmt<rustc_span[b2d5999a99633be2]::span_encoding::Span>::{closure#0}, !>::{closure#0}, !>
  22:     0x7f92790c0297 - rustc_middle[b24e7ff436be1cdb]::util::bug::span_bug_fmt::<rustc_span[b2d5999a99633be2]::span_encoding::Span>
  23:     0x7f927a65a644 - <rustc_mir_transform[26553d121dafebc7]::check_packed_ref::CheckPackedRef as rustc_mir_transform[26553d121dafebc7]::pass_manager::MirLint>::run_lint
  24:     0x7f9279ee08cd - rustc_mir_transform[26553d121dafebc7]::pass_manager::run_passes_inner
  25:     0x7f927a2f26b9 - rustc_query_impl[e4150b7ad05f9ce5]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[e4150b7ad05f9ce5]::query_impl::mir_built::dynamic_query::{closure#2}::{closure#0}, rustc_middle[b24e7ff436be1cdb]::query::erase::Erased<[u8; 8usize]>>
  26:     0x7f927a0bc5b1 - rustc_query_system[e9aa61bedf025f9c]::query::plumbing::try_execute_query::<rustc_query_impl[e4150b7ad05f9ce5]::DynamicConfig<rustc_query_system[e9aa61bedf025f9c]::query::caches::VecCache<rustc_span[b2d5999a99633be2]::def_id::LocalDefId, rustc_middle[b24e7ff436be1cdb]::query::erase::Erased<[u8; 8usize]>>, false, false, false>, rustc_query_impl[e4150b7ad05f9ce5]::plumbing::QueryCtxt, false>
  27:     0x7f927a0bc18c - rustc_query_impl[e4150b7ad05f9ce5]::query_impl::mir_built::get_query_non_incr::__rust_end_short_backtrace
  28:     0x7f927a83bf8f - rustc_mir_build[74f63c492aaa1616]::check_unsafety::check_unsafety
  29:     0x7f927a83bced - rustc_query_impl[e4150b7ad05f9ce5]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[e4150b7ad05f9ce5]::query_impl::check_unsafety::dynamic_query::{closure#2}::{closure#0}, rustc_middle[b24e7ff436be1cdb]::query::erase::Erased<[u8; 0usize]>>
  30:     0x7f927a3d1ac6 - rustc_query_system[e9aa61bedf025f9c]::query::plumbing::try_execute_query::<rustc_query_impl[e4150b7ad05f9ce5]::DynamicConfig<rustc_query_system[e9aa61bedf025f9c]::query::caches::VecCache<rustc_span[b2d5999a99633be2]::def_id::LocalDefId, rustc_middle[b24e7ff436be1cdb]::query::erase::Erased<[u8; 0usize]>>, false, false, false>, rustc_query_impl[e4150b7ad05f9ce5]::plumbing::QueryCtxt, false>
  31:     0x7f927a3d16ff - rustc_query_impl[e4150b7ad05f9ce5]::query_impl::check_unsafety::get_query_non_incr::__rust_end_short_backtrace
  32:     0x7f927a3cda7c - rustc_interface[93c8c2723e408a6]::passes::analysis
  33:     0x7f927a3ccb9b - rustc_query_impl[e4150b7ad05f9ce5]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[e4150b7ad05f9ce5]::query_impl::analysis::dynamic_query::{closure#2}::{closure#0}, rustc_middle[b24e7ff436be1cdb]::query::erase::Erased<[u8; 1usize]>>
  34:     0x7f927ad0b1a5 - rustc_query_system[e9aa61bedf025f9c]::query::plumbing::try_execute_query::<rustc_query_impl[e4150b7ad05f9ce5]::DynamicConfig<rustc_query_system[e9aa61bedf025f9c]::query::caches::SingleCache<rustc_middle[b24e7ff436be1cdb]::query::erase::Erased<[u8; 1usize]>>, false, false, false>, rustc_query_impl[e4150b7ad05f9ce5]::plumbing::QueryCtxt, false>
  35:     0x7f927ad0af09 - rustc_query_impl[e4150b7ad05f9ce5]::query_impl::analysis::get_query_non_incr::__rust_end_short_backtrace
  36:     0x7f927ab9ead3 - rustc_interface[93c8c2723e408a6]::interface::run_compiler::<core[191c6f300f408019]::result::Result<(), rustc_span[b2d5999a99633be2]::ErrorGuaranteed>, rustc_driver_impl[e4eb3d84a143a5f9]::run_compiler::{closure#0}>::{closure#0}
  37:     0x7f927ac6bbd3 - std[ffd0afd40c23a66b]::sys_common::backtrace::__rust_begin_short_backtrace::<rustc_interface[93c8c2723e408a6]::util::run_in_thread_with_globals<rustc_interface[93c8c2723e408a6]::util::run_in_thread_pool_with_globals<rustc_interface[93c8c2723e408a6]::interface::run_compiler<core[191c6f300f408019]::result::Result<(), rustc_span[b2d5999a99633be2]::ErrorGuaranteed>, rustc_driver_impl[e4eb3d84a143a5f9]::run_compiler::{closure#0}>::{closure#0}, core[191c6f300f408019]::result::Result<(), rustc_span[b2d5999a99633be2]::ErrorGuaranteed>>::{closure#0}, core[191c6f300f408019]::result::Result<(), rustc_span[b2d5999a99633be2]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[191c6f300f408019]::result::Result<(), rustc_span[b2d5999a99633be2]::ErrorGuaranteed>>
  38:     0x7f927ac6b9e1 - <<std[ffd0afd40c23a66b]::thread::Builder>::spawn_unchecked_<rustc_interface[93c8c2723e408a6]::util::run_in_thread_with_globals<rustc_interface[93c8c2723e408a6]::util::run_in_thread_pool_with_globals<rustc_interface[93c8c2723e408a6]::interface::run_compiler<core[191c6f300f408019]::result::Result<(), rustc_span[b2d5999a99633be2]::ErrorGuaranteed>, rustc_driver_impl[e4eb3d84a143a5f9]::run_compiler::{closure#0}>::{closure#0}, core[191c6f300f408019]::result::Result<(), rustc_span[b2d5999a99633be2]::ErrorGuaranteed>>::{closure#0}, core[191c6f300f408019]::result::Result<(), rustc_span[b2d5999a99633be2]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[191c6f300f408019]::result::Result<(), rustc_span[b2d5999a99633be2]::ErrorGuaranteed>>::{closure#1} as core[191c6f300f408019]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  39:     0x7f9275a783fb - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h61713b2cd6851117
                               at /rustc/1684a753dbca5d23b2e03568e6fbbb48eb72d0e6/library/alloc/src/boxed.rs:2018:9
  40:     0x7f9275a783fb - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h040bc52a2545405a
                               at /rustc/1684a753dbca5d23b2e03568e6fbbb48eb72d0e6/library/alloc/src/boxed.rs:2018:9
  41:     0x7f9275a783fb - std::sys::pal::unix::thread::Thread::new::thread_start::h5a10eabef2ee4b3d
                               at /rustc/1684a753dbca5d23b2e03568e6fbbb48eb72d0e6/library/std/src/sys/pal/unix/thread.rs:108:17
  42:     0x7f9275985609 - start_thread
  43:     0x7f92758a8353 - clone
  44:                0x0 - <unknown>

note: it seems that this compiler `1.79.0-nightly (1684a753d 2024-04-01)` is outdated, a newer nightly should have been released in the mean time
  |
  = note: please consider running `rustup update nightly` to update the nightly channel and check if this problem still persists
  = note: if the problem still persists, 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: please attach the file at `/playground/rustc-ice-2024-04-02T14_11_10-36.txt` to your bug report

note: compiler flags: --crate-type lib -C embed-bitcode=no -C codegen-units=1 -C debuginfo=2

note: some of the compiler flags provided by cargo are hidden

query stack during panic:
#0 [mir_built] building MIR for `<impl at src/lib.rs:1:10: 1:15>::fmt`
#1 [check_unsafety] unsafety-checking `<impl at src/lib.rs:1:10: 1:15>::fmt`
#2 [analysis] running analysis passes on this crate
end of query stack
error[E0507]: cannot move out of `self.e` which is behind a shared reference
  --> src/lib.rs:11:5
   |
7  | #[derive(Debug)]
   |          ----- in this derive macro expansion
...
11 |     e: E,
   |     ^^^^ move occurs because `self.e` has type `E`, which does not implement the `Copy` trait
   |
   = note: `#[derive(Debug)]` triggers a move because taking references to the fields of a packed struct is undefined behaviour
   = note: this error originates in the derive macro `Debug` (in Nightly builds, run with -Z macro-backtrace for more info)

Some errors have detailed explanations: E0507, E0517.
For more information about an error, try `rustc --explain E0507`.
error: could not compile `playground` (lib) due to 2 previous errors

#[repr(packed)] on an enum is incorrect, but it shouldn't ICE.

This is today's nightly on amd64.

Thanks

[petrochenkov]

This ICE was reachable since 7 years, just noone ever wrote obscure code like that: #121025 (comment)

Now someone actually wrote it - #127678.