ICE: index out of bounds `#[rustc_host]`

[matthiaskrgr]

Code

trait Fake {}
impl<T, #[rustc_host] const host: bool = true> Fake for T {}

Meta

rustc --version --verbose:

rustc 1.74.0-nightly (69e97df5c 2023-08-26)
binary: rustc
commit-hash: 69e97df5ce571a777acd654ec3697ae8d25962ea
commit-date: 2023-08-26
host: x86_64-unknown-linux-gnu
release: 1.74.0-nightly
LLVM version: 17.0.0

Error output

error[E0658]: #[rustc_host] annotates const generic parameters as the `host` effect param, and it is only intended for internal use and as a desugaring.
 --> icemaker_reduced/F468B92A11E7FFBD4CF8B971AE2AA2D6EC86BEE083B0F18C53B36FFBC97CD71B.rs:2:9
  |
2 | impl<T, #[rustc_host] const host: bool = true> Fake for T {}
  |         ^^^^^^^^^^^^^
  |
  = help: add `#![feature(rustc_attrs)]` to the crate attributes to enable

error[E0601]: `main` function not found in crate `F468B92A11E7FFBD4CF8B971AE2AA2D6EC86BEE083B0F18C53B36FFBC97CD71B`
 --> icemaker_reduced/F468B92A11E7FFBD4CF8B971AE2AA2D6EC86BEE083B0F18C53B36FFBC97CD71B.rs:2:61
  |
2 | impl<T, #[rustc_host] const host: bool = true> Fake for T {}
  |                                                             ^ consider adding a `main` function to `icemaker_reduced/F468B92A11E7FFBD4CF8B971AE2AA2D6EC86BEE083B0F18C53B36FFBC97CD71B.rs`

error: const `impl` for trait `Fake` which is not marked with `#[const_trait]`
 --> icemaker_reduced/F468B92A11E7FFBD4CF8B971AE2AA2D6EC86BEE083B0F18C53B36FFBC97CD71B.rs:2:48
  |
2 | impl<T, #[rustc_host] const host: bool = true> Fake for T {}
  |                                                ^^^^ help: mark `Fake` as const: `#[const_trait]`
  |
  = note: marking a trait with `#[const_trait]` ensures all default method bodies are `const`
  = note: adding a non-const method body in the future would be a breaking change

Backtrace

thread 'rustc' panicked at compiler/rustc_hir_analysis/src/collect.rs:1376:34:
index out of bounds: the len is 0 but the index is 18446744073709551615
stack backtrace:
   0:     0x7ff416b62fac - std::backtrace_rs::backtrace::libunwind::trace::h7ead10aab469b9aa
                               at /rustc/69e97df5ce571a777acd654ec3697ae8d25962ea/library/std/src/../../backtrace/src/backtrace/libunwind.rs:93:5
   1:     0x7ff416b62fac - std::backtrace_rs::backtrace::trace_unsynchronized::hf548e9e8c1fe3e8d
                               at /rustc/69e97df5ce571a777acd654ec3697ae8d25962ea/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x7ff416b62fac - std::sys_common::backtrace::_print_fmt::h4f790d56eeca616b
                               at /rustc/69e97df5ce571a777acd654ec3697ae8d25962ea/library/std/src/sys_common/backtrace.rs:67:5
   3:     0x7ff416b62fac - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::h30e5bb3d4404f378
                               at /rustc/69e97df5ce571a777acd654ec3697ae8d25962ea/library/std/src/sys_common/backtrace.rs:44:22
   4:     0x7ff416bc91dc - core::fmt::rt::Argument::fmt::h35f06f2256f98b43
                               at /rustc/69e97df5ce571a777acd654ec3697ae8d25962ea/library/core/src/fmt/rt.rs:138:9
   5:     0x7ff416bc91dc - core::fmt::write::h5005ce68dd6774c4
                               at /rustc/69e97df5ce571a777acd654ec3697ae8d25962ea/library/core/src/fmt/mod.rs:1094:21
   6:     0x7ff416b55cae - std::io::Write::write_fmt::h8a7c95ddeefaf4be
                               at /rustc/69e97df5ce571a777acd654ec3697ae8d25962ea/library/std/src/io/mod.rs:1714:15
   7:     0x7ff416b62d94 - std::sys_common::backtrace::_print::hedccafa15bd98864
                               at /rustc/69e97df5ce571a777acd654ec3697ae8d25962ea/library/std/src/sys_common/backtrace.rs:47:5
   8:     0x7ff416b62d94 - std::sys_common::backtrace::print::h911d101d11c4e8b0
                               at /rustc/69e97df5ce571a777acd654ec3697ae8d25962ea/library/std/src/sys_common/backtrace.rs:34:9
   9:     0x7ff416b65e8a - std::panicking::panic_hook_with_disk_dump::{{closure}}::he8cf7cbd1dd11756
                               at /rustc/69e97df5ce571a777acd654ec3697ae8d25962ea/library/std/src/panicking.rs:278:22
  10:     0x7ff416b65b78 - std::panicking::panic_hook_with_disk_dump::h3baf172fecd393f6
                               at /rustc/69e97df5ce571a777acd654ec3697ae8d25962ea/library/std/src/panicking.rs:312:9
  11:     0x7ff419d4a279 - <rustc_driver_impl[98acc53e2d2f6ece]::install_ice_hook::{closure#0} as core[cb689c380e703cde]::ops::function::FnOnce<(&core[cb689c380e703cde]::panic::panic_info::PanicInfo,)>>::call_once::{shim:vtable#0}
  12:     0x7ff416b66731 - <alloc::boxed::Box<F,A> as core::ops::function::Fn<Args>>::call::h8e3b5b4f77120996
                               at /rustc/69e97df5ce571a777acd654ec3697ae8d25962ea/library/alloc/src/boxed.rs:2021:9
  13:     0x7ff416b66731 - std::panicking::rust_panic_with_hook::hcec56ff9d71a6f8a
                               at /rustc/69e97df5ce571a777acd654ec3697ae8d25962ea/library/std/src/panicking.rs:733:13
  14:     0x7ff416b664b7 - std::panicking::begin_panic_handler::{{closure}}::h080d65de76ce8958
                               at /rustc/69e97df5ce571a777acd654ec3697ae8d25962ea/library/std/src/panicking.rs:621:13
  15:     0x7ff416b634d6 - std::sys_common::backtrace::__rust_end_short_backtrace::had2be8eed332cfa1
                               at /rustc/69e97df5ce571a777acd654ec3697ae8d25962ea/library/std/src/sys_common/backtrace.rs:170:18
  16:     0x7ff416b66202 - rust_begin_unwind
                               at /rustc/69e97df5ce571a777acd654ec3697ae8d25962ea/library/std/src/panicking.rs:617:5
  17:     0x7ff416bc55c3 - core::panicking::panic_fmt::he0f6263a3bff06fd
                               at /rustc/69e97df5ce571a777acd654ec3697ae8d25962ea/library/core/src/panicking.rs:67:14
  18:     0x7ff416bc5719 - core::panicking::panic_bounds_check::h0b0bc4c77a041494
                               at /rustc/69e97df5ce571a777acd654ec3697ae8d25962ea/library/core/src/panicking.rs:162:5
  19:     0x7ff418fd5777 - rustc_hir_analysis[667fece327758e4f]::collect::impl_trait_ref
  20:     0x7ff417e72408 - rustc_query_impl[58a3c40f53c1e9dd]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[58a3c40f53c1e9dd]::query_impl::impl_trait_ref::dynamic_query::{closure#2}::{closure#0}, rustc_middle[464349d56e47250b]::query::erase::Erased<[u8; 16usize]>>
  21:     0x7ff417ebe8cb - rustc_query_system[771da89a8e6a97f0]::query::plumbing::try_execute_query::<rustc_query_impl[58a3c40f53c1e9dd]::DynamicConfig<rustc_query_system[771da89a8e6a97f0]::query::caches::DefaultCache<rustc_span[c92a35b362599b57]::def_id::DefId, rustc_middle[464349d56e47250b]::query::erase::Erased<[u8; 16usize]>>, false, false, false>, rustc_query_impl[58a3c40f53c1e9dd]::plumbing::QueryCtxt, false>
  22:     0x7ff417ebe564 - rustc_query_impl[58a3c40f53c1e9dd]::query_impl::impl_trait_ref::get_query_non_incr::__rust_end_short_backtrace
  23:     0x7ff4184080b9 - <rustc_hir_analysis[667fece327758e4f]::collect::CollectItemTypesVisitor as rustc_hir[3a72116ea74f2480]::intravisit::Visitor>::visit_item
  24:     0x7ff4184063f7 - <rustc_middle[464349d56e47250b]::hir::map::Map>::visit_item_likes_in_module::<rustc_hir_analysis[667fece327758e4f]::collect::CollectItemTypesVisitor>
  25:     0x7ff4184062ac - rustc_hir_analysis[667fece327758e4f]::collect::collect_mod_item_types
  26:     0x7ff418a746fc - rustc_query_impl[58a3c40f53c1e9dd]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[58a3c40f53c1e9dd]::query_impl::collect_mod_item_types::dynamic_query::{closure#2}::{closure#0}, rustc_middle[464349d56e47250b]::query::erase::Erased<[u8; 0usize]>>
  27:     0x7ff418a746de - <rustc_query_impl[58a3c40f53c1e9dd]::query_impl::collect_mod_item_types::dynamic_query::{closure#2} as core[cb689c380e703cde]::ops::function::FnOnce<(rustc_middle[464349d56e47250b]::ty::context::TyCtxt, rustc_span[c92a35b362599b57]::def_id::LocalModDefId)>>::call_once
  28:     0x7ff418d74923 - rustc_query_system[771da89a8e6a97f0]::query::plumbing::try_execute_query::<rustc_query_impl[58a3c40f53c1e9dd]::DynamicConfig<rustc_query_system[771da89a8e6a97f0]::query::caches::DefaultCache<rustc_span[c92a35b362599b57]::def_id::LocalModDefId, rustc_middle[464349d56e47250b]::query::erase::Erased<[u8; 0usize]>>, false, false, false>, rustc_query_impl[58a3c40f53c1e9dd]::plumbing::QueryCtxt, false>
  29:     0x7ff4196cd374 - rustc_query_impl[58a3c40f53c1e9dd]::query_impl::collect_mod_item_types::get_query_non_incr::__rust_end_short_backtrace
  30:     0x7ff418c715d7 - <rustc_middle[464349d56e47250b]::hir::map::Map>::for_each_module::<rustc_hir_analysis[667fece327758e4f]::check_crate::{closure#0}::{closure#0}::{closure#0}>
  31:     0x7ff418c7018f - rustc_hir_analysis[667fece327758e4f]::check_crate
  32:     0x7ff418c69c4a - rustc_interface[b81038288d48d278]::passes::analysis
  33:     0x7ff41925ca4a - rustc_query_impl[58a3c40f53c1e9dd]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[58a3c40f53c1e9dd]::query_impl::analysis::dynamic_query::{closure#2}::{closure#0}, rustc_middle[464349d56e47250b]::query::erase::Erased<[u8; 1usize]>>
  34:     0x7ff41925ca39 - <rustc_query_impl[58a3c40f53c1e9dd]::query_impl::analysis::dynamic_query::{closure#2} as core[cb689c380e703cde]::ops::function::FnOnce<(rustc_middle[464349d56e47250b]::ty::context::TyCtxt, ())>>::call_once
  35:     0x7ff4193ecc18 - rustc_query_system[771da89a8e6a97f0]::query::plumbing::try_execute_query::<rustc_query_impl[58a3c40f53c1e9dd]::DynamicConfig<rustc_query_system[771da89a8e6a97f0]::query::caches::SingleCache<rustc_middle[464349d56e47250b]::query::erase::Erased<[u8; 1usize]>>, false, false, false>, rustc_query_impl[58a3c40f53c1e9dd]::plumbing::QueryCtxt, false>
  36:     0x7ff4193ec999 - rustc_query_impl[58a3c40f53c1e9dd]::query_impl::analysis::get_query_non_incr::__rust_end_short_backtrace
  37:     0x7ff419028da6 - <rustc_middle[464349d56e47250b]::ty::context::GlobalCtxt>::enter::<rustc_driver_impl[98acc53e2d2f6ece]::run_compiler::{closure#1}::{closure#2}::{closure#6}, core[cb689c380e703cde]::result::Result<(), rustc_span[c92a35b362599b57]::ErrorGuaranteed>>
  38:     0x7ff41902822c - <rustc_interface[b81038288d48d278]::interface::Compiler>::enter::<rustc_driver_impl[98acc53e2d2f6ece]::run_compiler::{closure#1}::{closure#2}, core[cb689c380e703cde]::result::Result<core[cb689c380e703cde]::option::Option<rustc_interface[b81038288d48d278]::queries::Linker>, rustc_span[c92a35b362599b57]::ErrorGuaranteed>>
  39:     0x7ff419025548 - std[ebccec195fc5e844]::sys_common::backtrace::__rust_begin_short_backtrace::<rustc_interface[b81038288d48d278]::util::run_in_thread_pool_with_globals<rustc_interface[b81038288d48d278]::interface::run_compiler<core[cb689c380e703cde]::result::Result<(), rustc_span[c92a35b362599b57]::ErrorGuaranteed>, rustc_driver_impl[98acc53e2d2f6ece]::run_compiler::{closure#1}>::{closure#0}, core[cb689c380e703cde]::result::Result<(), rustc_span[c92a35b362599b57]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[cb689c380e703cde]::result::Result<(), rustc_span[c92a35b362599b57]::ErrorGuaranteed>>
  40:     0x7ff4195c60f5 - <<std[ebccec195fc5e844]::thread::Builder>::spawn_unchecked_<rustc_interface[b81038288d48d278]::util::run_in_thread_pool_with_globals<rustc_interface[b81038288d48d278]::interface::run_compiler<core[cb689c380e703cde]::result::Result<(), rustc_span[c92a35b362599b57]::ErrorGuaranteed>, rustc_driver_impl[98acc53e2d2f6ece]::run_compiler::{closure#1}>::{closure#0}, core[cb689c380e703cde]::result::Result<(), rustc_span[c92a35b362599b57]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[cb689c380e703cde]::result::Result<(), rustc_span[c92a35b362599b57]::ErrorGuaranteed>>::{closure#1} as core[cb689c380e703cde]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  41:     0x7ff416b71195 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::hf6677bb1228f81ea
                               at /rustc/69e97df5ce571a777acd654ec3697ae8d25962ea/library/alloc/src/boxed.rs:2007:9
  42:     0x7ff416b71195 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h4f3130db7e13aaba
                               at /rustc/69e97df5ce571a777acd654ec3697ae8d25962ea/library/alloc/src/boxed.rs:2007:9
  43:     0x7ff416b71195 - std::sys::unix::thread::Thread::new::thread_start::h17fc5e491c7b31dd
                               at /rustc/69e97df5ce571a777acd654ec3697ae8d25962ea/library/std/src/sys/unix/thread.rs:108:17
  44:     0x7ff41688c9eb - <unknown>
  45:     0x7ff416910ebc - <unknown>
  46:                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: please attach the file at `/tmp/host/rustc-ice-2023-08-27T08:39:34.669355941Z-794436.txt` to your bug report

query stack during panic:
#0 [impl_trait_ref] computing trait implemented by `<impl at icemaker_reduced/F468B92A11E7FFBD4CF8B971AE2AA2D6EC86BEE083B0F18C53B36FFBC97CD71B.rs:2:1: 2:58>`
#1 [collect_mod_item_types] collecting item types in top-level module
#2 [analysis] running analysis passes on this crate
end of query stack
error: aborting due to 3 previous errors

Some errors have detailed explanations: E0601, E0658.
For more information about an error, try `rustc --explain E0601`.

[matthiaskrgr]

This crashes beta but not stable (yet) but will become a stable regression on the next bump.
It would be nice to prevent in-progress features leaking their crashes into the stable toolchain.

[matthiaskrgr]

Regression in nightly-2023-08-09
Regression in f88a8b7

#114545

[fmease]

It would be nice to prevent in-progress features leaking their crashes into the stable toolchain.

That would be very nice indeed¹ but in this specific case the probability of a real user being affected is 0% since there's no way anyone would actually use #[rustc_host], an internal feature.

@rustbot label -needs-triage F-effects F-rustc_attrs requires-internal-features

Footnotes

1. By having better quality control if we were to have more resources. Different branches (nightly vs. nightly-experiments) wouldn't make sense if that's what you are alluding to. ↩

[matthiaskrgr]

Shouldn't it trigger the internal_features lint then? 🤔

[fmease]

The lints incomplete_features and internal_features are only triggered if you explicitly use #![feature]. As you probably know, even if the user doesn't enable a specific feature with #![feature], in most cases the compiler resumes after emitting a feature gate error and still interprets said feature according to its semantics whose implementation might contain bugs that you discover.

Even without an explicit #![feature] to all intents and purposes such a bug was caused using the respective feature and therefore it warrants F-* and requires-*-features labels.

Edit: Here, #[rustc_host] requires F-rustc_attrs Internal rustc attributes gated on the `#[rustc_attrs]` feature gate. which is an internal feature, hence the requires-internal-features This issue requires the use of internal features. . Internal features come with next to no stability guarantees.

The error #[rustc_host] annotates const generic parameters as the host effect param, and it is only intended for internal use and as a desugaring. emitted before the ICE is the feature gate error that informs the user that they are attempting to use an internal feature and which implicitly signals that resulting ICEs are not necessarily bugs.