#[derive] seems to make rustc bypass #[repr] hint validation

[cloneable]

I have a 2-variant enum and was curious if I can use #[repr(bool)] maybe and got this error. Only works when there's some #[derive(...)], too.

Code

#[derive(Debug)]
#[repr(bool)]
pub enum Foo {
    Bar,
}

Meta

rustup check:

stable-aarch64-apple-darwin - Up to date : 1.75.0 (82e1608df 2023-12-21)
beta-aarch64-apple-darwin - Up to date : 1.76.0-beta.1 (0e09125c6 2023-12-21)
nightly-aarch64-apple-darwin - Up to date : 1.77.0-nightly (e51e98dde 2023-12-31)
rustup - Up to date : 1.26.0

Checked with stable, beta, and nightly via cargo.

Cargo's rustc execution:

${HOME}/.rustup/toolchains/nightly-aarch64-apple-darwin/bin/rustc \
--crate-name repr_bool \
--edition=2021 src/lib.rs \
--error-format=json \
--json=diagnostic-rendered-ansi,artifacts,future-incompat \
--diagnostic-width=97 \
--crate-type lib \
--emit=dep-info,metadata,link \
-C embed-bitcode=no \
-C debuginfo=2 \
-C split-debuginfo=unpacked \
-C metadata=9388f8b0ffb557cf \
-C extra-filename=-9388f8b0ffb557cf \
--out-dir ${CRATE}/target/debug/deps \
-L dependency=${CRATE}/target/debug/deps

Error output

warning: ignoring -C extra-filename flag due to -o flag

error: internal compiler error: no errors encountered even though `span_delayed_bug` issued

error: internal compiler error: unrecognized representation hint
 --> src/lib.rs:2:8
  |
2 | #[repr(bool)]
  |        ^^^^
  |

Backtrace

delayed span bug: unrecognized representation hint
   0: std::backtrace::Backtrace::create
   1: <rustc_errors::DiagCtxtInner>::emit_diagnostic_without_consuming
   2: <rustc_errors::DiagCtxt>::emit_diagnostic_without_consuming
   3: <rustc_errors::DiagCtxt>::span_delayed_bug::<rustc_span::span_encoding::Span, &str>
   4: rustc_attr::builtin::parse_repr_attr
   5: <rustc_builtin_macros::deriving::generic::TraitDef>::expand_ext
   6: rustc_builtin_macros::deriving::debug::expand_deriving_debug
   7: <rustc_builtin_macros::deriving::BuiltinDerive as rustc_expand::base::MultiItemModifier>::expand
   8: <rustc_expand::expand::MacroExpander>::fully_expand_fragment
   9: <rustc_expand::expand::MacroExpander>::expand_crate
  10: <rustc_session::session::Session>::time::<rustc_ast::ast::Crate, rustc_interface::passes::configure_and_expand::{closure#1}>
  11: rustc_interface::passes::resolver_for_lowering
  12: rustc_query_impl::plumbing::__rust_begin_short_backtrace::<rustc_query_impl::query_impl::resolver_for_lowering::dynamic_query::{closure#2}::{closure#0}, rustc_middle::query::erase::Erased<[u8; 8]>>
  13: <rustc_query_impl::query_impl::resolver_for_lowering::dynamic_query::{closure#2} as core::ops::function::FnOnce<(rustc_middle::ty::context::TyCtxt, ())>>::call_once
  14: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::DynamicConfig<rustc_query_system::query::caches::SingleCache<rustc_middle::query::erase::Erased<[u8; 8]>>, false, false, false>, rustc_query_impl::plumbing::QueryCtxt, false>
  15: rustc_query_impl::query_impl::resolver_for_lowering::get_query_non_incr::__rust_end_short_backtrace
  16: <rustc_middle::ty::context::GlobalCtxt>::enter::<rustc_driver_impl::run_compiler::{closure#0}::{closure#0}::{closure#2}, &rustc_data_structures::steal::Steal<(rustc_middle::ty::ResolverAstLowering, alloc::sync::Arc<rustc_ast::ast::Crate>)>>
  17: <rustc_interface::interface::Compiler>::enter::<rustc_driver_impl::run_compiler::{closure#0}::{closure#0}, core::result::Result<core::option::Option<rustc_interface::queries::Linker>, rustc_span::ErrorGuaranteed>>
  18: rustc_span::set_source_map::<core::result::Result<(), rustc_span::ErrorGuaranteed>, rustc_interface::interface::run_compiler<core::result::Result<(), rustc_span::ErrorGuaranteed>, rustc_driver_impl::run_compiler::{closure#0}>::{closure#0}::{closure#0}>
  19: <scoped_tls::ScopedKey<rustc_span::SessionGlobals>>::set::<rustc_interface::util::run_in_thread_pool_with_globals<rustc_interface::interface::run_compiler<core::result::Result<(), rustc_span::ErrorGuaranteed>, rustc_driver_impl::run_compiler::{closure#0}>::{closure#0}, core::result::Result<(), rustc_span::ErrorGuaranteed>>::{closure#0}, core::result::Result<(), rustc_span::ErrorGuaranteed>>
  20: std::sys_common::backtrace::__rust_begin_short_backtrace::<rustc_interface::util::run_in_thread_with_globals<rustc_interface::util::run_in_thread_pool_with_globals<rustc_interface::interface::run_compiler<core::result::Result<(), rustc_span::ErrorGuaranteed>, rustc_driver_impl::run_compiler::{closure#0}>::{closure#0}, core::result::Result<(), rustc_span::ErrorGuaranteed>>::{closure#0}, core::result::Result<(), rustc_span::ErrorGuaranteed>>::{closure#0}::{closure#0}, core::result::Result<(), rustc_span::ErrorGuaranteed>>
  21: <<std::thread::Builder>::spawn_unchecked_<rustc_interface::util::run_in_thread_with_globals<rustc_interface::util::run_in_thread_pool_with_globals<rustc_interface::interface::run_compiler<core::result::Result<(), rustc_span::ErrorGuaranteed>, rustc_driver_impl::run_compiler::{closure#0}>::{closure#0}, core::result::Result<(), rustc_span::ErrorGuaranteed>>::{closure#0}, core::result::Result<(), rustc_span::ErrorGuaranteed>>::{closure#0}::{closure#0}, core::result::Result<(), rustc_span::ErrorGuaranteed>>::{closure#1} as core::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  22: std::sys::unix::thread::Thread::new::thread_start
  23: __pthread_joiner_wake



rustc version: 1.77.0-nightly (e51e98dde 2023-12-31)
platform: aarch64-apple-darwin

[krtab]

Cannot reproduce on Linux x64, and does not reproduce on the playground either.

[cloneable]

Right, I'm sorry. I tracked this down to sccache. 🤦 It must have used an outdated artifact somehow, maybe from 1.74.1. After clearing its cache, everything is okay. Sorry about the noise!