Intrinsics declared with wrong arg count ICE

[gurry]

An ICE occurs if you declare an intrinsic with the wrong number of args and then try to use it.

Code

#![feature(intrinsics)]

fn main() {
   unsafe { read_via_copy(); }
}

extern "rust-intrinsic" 
{
    fn read_via_copy();
}

Meta

rustc --version --verbose:

rustc 1.79.0-nightly (9d79cd5f7 2024-04-05)
binary: rustc
commit-hash: 9d79cd5f79e75bd0d2083260271307ce9acd9081
commit-date: 2024-04-05
host: x86_64-unknown-linux-gnu
release: 1.79.0-nightly
LLVM version: 18.1.2

Error output

  Compiling playground v0.0.1 (/playground)
warning: the feature `intrinsics` is internal to the compiler or standard library
 --> src/main.rs:1:12
  |
1 | #![feature(intrinsics)]
  |            ^^^^^^^^^^
  |
  = note: using it is strongly discouraged
  = note: `#[warn(internal_features)]` on by default

error[E0094]: intrinsic has wrong number of type parameters: found 0, expected 1
 --> src/main.rs:9:21
  |
9 |     fn read_via_copy();
  |                     ^ expected 1 type parameter

Backtrace

error: internal compiler error: compiler/rustc_mir_transform/src/lower_intrinsics.rs:177:29: Wrong number of arguments
 --> src/main.rs:4:13
  |
4 |    unsafe { read_via_copy(); }
  |             ^^^^^^^^^^^^^^^

thread 'rustc' panicked at compiler/rustc_mir_transform/src/lower_intrinsics.rs:177:29:
Box<dyn Any>
stack backtrace:
   0:     0x7f5e62c0b885 - std::backtrace_rs::backtrace::libunwind::trace::h2ac23be513f598d8
                               at /rustc/aa1c45908df252a5b0c14e1bcb38c6c55ae02efe/library/std/src/../../backtrace/src/backtrace/libunwind.rs:105:5
   1:     0x7f5e62c0b885 - std::backtrace_rs::backtrace::trace_unsynchronized::h714851d0c638595f
                               at /rustc/aa1c45908df252a5b0c14e1bcb38c6c55ae02efe/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x7f5e62c0b885 - std::sys_common::backtrace::_print_fmt::hde31106e881318f4
                               at /rustc/aa1c45908df252a5b0c14e1bcb38c6c55ae02efe/library/std/src/sys_common/backtrace.rs:68:5
   3:     0x7f5e62c0b885 - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::h5e44711e8e3e9bff
                               at /rustc/aa1c45908df252a5b0c14e1bcb38c6c55ae02efe/library/std/src/sys_common/backtrace.rs:44:22
   4:     0x7f5e62c5ab9b - core::fmt::rt::Argument::fmt::h9965750ec07aa88a
                               at /rustc/aa1c45908df252a5b0c14e1bcb38c6c55ae02efe/library/core/src/fmt/rt.rs:142:9
   5:     0x7f5e62c5ab9b - core::fmt::write::hc2ec2e3627fd006a
                               at /rustc/aa1c45908df252a5b0c14e1bcb38c6c55ae02efe/library/core/src/fmt/mod.rs:1153:17
   6:     0x7f5e62c003ff - std::io::Write::write_fmt::h1f82f51174f3abb0
                               at /rustc/aa1c45908df252a5b0c14e1bcb38c6c55ae02efe/library/std/src/io/mod.rs:1843:15
   7:     0x7f5e62c0b65e - std::sys_common::backtrace::_print::h003159894b30f46f
                               at /rustc/aa1c45908df252a5b0c14e1bcb38c6c55ae02efe/library/std/src/sys_common/backtrace.rs:47:5
   8:     0x7f5e62c0b65e - std::sys_common::backtrace::print::h787b5c1503f03df7
                               at /rustc/aa1c45908df252a5b0c14e1bcb38c6c55ae02efe/library/std/src/sys_common/backtrace.rs:34:9
   9:     0x7f5e62c0e159 - std::panicking::default_hook::{{closure}}::h5939a448f377040a
  10:     0x7f5e62c0de75 - std::panicking::default_hook::h3651e83a5c639e04
                               at /rustc/aa1c45908df252a5b0c14e1bcb38c6c55ae02efe/library/std/src/panicking.rs:291:9
  11:     0x7f5e65cb7aff - std[f2945facf614d202]::panicking::update_hook::<alloc[406fac374097d7f1]::boxed::Box<rustc_driver_impl[3d4f9373b5a704b5]::install_ice_hook::{closure#0}>>::{closure#0}
  12:     0x7f5e62c0e85c - <alloc::boxed::Box<F,A> as core::ops::function::Fn<Args>>::call::h53e9ce019f51ba71
                               at /rustc/aa1c45908df252a5b0c14e1bcb38c6c55ae02efe/library/alloc/src/boxed.rs:2032:9
  13:     0x7f5e62c0e85c - std::panicking::rust_panic_with_hook::h71ac878b54cf8b64
                               at /rustc/aa1c45908df252a5b0c14e1bcb38c6c55ae02efe/library/std/src/panicking.rs:792:13
  14:     0x7f5e65ce73c4 - std[f2945facf614d202]::panicking::begin_panic::<rustc_errors[39c86ef847bc51a8]::ExplicitBug>::{closure#0}
  15:     0x7f5e65ce3e66 - std[f2945facf614d202]::sys_common::backtrace::__rust_end_short_backtrace::<std[f2945facf614d202]::panicking::begin_panic<rustc_errors[39c86ef847bc51a8]::ExplicitBug>::{closure#0}, !>
  16:     0x7f5e65cdf486 - std[f2945facf614d202]::panicking::begin_panic::<rustc_errors[39c86ef847bc51a8]::ExplicitBug>
  17:     0x7f5e65cf1101 - <rustc_errors[39c86ef847bc51a8]::diagnostic::BugAbort as rustc_errors[39c86ef847bc51a8]::diagnostic::EmissionGuarantee>::emit_producing_guarantee
  18:     0x7f5e66288628 - <rustc_errors[39c86ef847bc51a8]::DiagCtxt>::span_bug::<rustc_span[a0270aa614b2185f]::span_encoding::Span, alloc[406fac374097d7f1]::string::String>
  19:     0x7f5e662a788d - rustc_middle[ed380b410dad9775]::util::bug::opt_span_bug_fmt::<rustc_span[a0270aa614b2185f]::span_encoding::Span>::{closure#0}
  20:     0x7f5e662a78ba - rustc_middle[ed380b410dad9775]::ty::context::tls::with_opt::<rustc_middle[ed380b410dad9775]::util::bug::opt_span_bug_fmt<rustc_span[a0270aa614b2185f]::span_encoding::Span>::{closure#0}, !>::{closure#0}
  21:     0x7f5e662a082b - rustc_middle[ed380b410dad9775]::ty::context::tls::with_context_opt::<rustc_middle[ed380b410dad9775]::ty::context::tls::with_opt<rustc_middle[ed380b410dad9775]::util::bug::opt_span_bug_fmt<rustc_span[a0270aa614b2185f]::span_encoding::Span>::{closure#0}, !>::{closure#0}, !>
  22:     0x7f5e6629fa77 - rustc_middle[ed380b410dad9775]::util::bug::span_bug_fmt::<rustc_span[a0270aa614b2185f]::span_encoding::Span>
  23:     0x7f5e67763b16 - <rustc_mir_transform[aadc44431e968acb]::lower_intrinsics::LowerIntrinsics as rustc_middle[ed380b410dad9775]::mir::MirPass>::run_pass
  24:     0x7f5e6708088d - rustc_mir_transform[aadc44431e968acb]::pass_manager::run_passes_inner
  25:     0x7f5e67782242 - rustc_mir_transform[aadc44431e968acb]::mir_drops_elaborated_and_const_checked
  26:     0x7f5e67781b13 - rustc_query_impl[f28317b5059654ba]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[f28317b5059654ba]::query_impl::mir_drops_elaborated_and_const_checked::dynamic_query::{closure#2}::{closure#0}, rustc_middle[ed380b410dad9775]::query::erase::Erased<[u8; 8usize]>>
  27:     0x7f5e673550f1 - rustc_query_system[4cc60357b0579df9]::query::plumbing::try_execute_query::<rustc_query_impl[f28317b5059654ba]::DynamicConfig<rustc_query_system[4cc60357b0579df9]::query::caches::VecCache<rustc_span[a0270aa614b2185f]::def_id::LocalDefId, rustc_middle[ed380b410dad9775]::query::erase::Erased<[u8; 8usize]>>, false, false, false>, rustc_query_impl[f28317b5059654ba]::plumbing::QueryCtxt, false>
  28:     0x7f5e67354aa4 - rustc_query_impl[f28317b5059654ba]::query_impl::mir_drops_elaborated_and_const_checked::get_query_non_incr::__rust_end_short_backtrace
  29:     0x7f5e679414f2 - rustc_interface[54c6bd1de51731e6]::passes::analysis
  30:     0x7f5e679402d5 - rustc_query_impl[f28317b5059654ba]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[f28317b5059654ba]::query_impl::analysis::dynamic_query::{closure#2}::{closure#0}, rustc_middle[ed380b410dad9775]::query::erase::Erased<[u8; 1usize]>>
  31:     0x7f5e67e9f6e5 - rustc_query_system[4cc60357b0579df9]::query::plumbing::try_execute_query::<rustc_query_impl[f28317b5059654ba]::DynamicConfig<rustc_query_system[4cc60357b0579df9]::query::caches::SingleCache<rustc_middle[ed380b410dad9775]::query::erase::Erased<[u8; 1usize]>>, false, false, false>, rustc_query_impl[f28317b5059654ba]::plumbing::QueryCtxt, false>
  32:     0x7f5e67e9f449 - rustc_query_impl[f28317b5059654ba]::query_impl::analysis::get_query_non_incr::__rust_end_short_backtrace
  33:     0x7f5e67c4f914 - rustc_interface[54c6bd1de51731e6]::interface::run_compiler::<core[faf3c98050982095]::result::Result<(), rustc_span[a0270aa614b2185f]::ErrorGuaranteed>, rustc_driver_impl[3d4f9373b5a704b5]::run_compiler::{closure#0}>::{closure#0}
  34:     0x7f5e67e2c41d - std[f2945facf614d202]::sys_common::backtrace::__rust_begin_short_backtrace::<rustc_interface[54c6bd1de51731e6]::util::run_in_thread_with_globals<rustc_interface[54c6bd1de51731e6]::util::run_in_thread_pool_with_globals<rustc_interface[54c6bd1de51731e6]::interface::run_compiler<core[faf3c98050982095]::result::Result<(), rustc_span[a0270aa614b2185f]::ErrorGuaranteed>, rustc_driver_impl[3d4f9373b5a704b5]::run_compiler::{closure#0}>::{closure#0}, core[faf3c98050982095]::result::Result<(), rustc_span[a0270aa614b2185f]::ErrorGuaranteed>>::{closure#0}, core[faf3c98050982095]::result::Result<(), rustc_span[a0270aa614b2185f]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[faf3c98050982095]::result::Result<(), rustc_span[a0270aa614b2185f]::ErrorGuaranteed>>
  35:     0x7f5e67e2c22a - <<std[f2945facf614d202]::thread::Builder>::spawn_unchecked_<rustc_interface[54c6bd1de51731e6]::util::run_in_thread_with_globals<rustc_interface[54c6bd1de51731e6]::util::run_in_thread_pool_with_globals<rustc_interface[54c6bd1de51731e6]::interface::run_compiler<core[faf3c98050982095]::result::Result<(), rustc_span[a0270aa614b2185f]::ErrorGuaranteed>, rustc_driver_impl[3d4f9373b5a704b5]::run_compiler::{closure#0}>::{closure#0}, core[faf3c98050982095]::result::Result<(), rustc_span[a0270aa614b2185f]::ErrorGuaranteed>>::{closure#0}, core[faf3c98050982095]::result::Result<(), rustc_span[a0270aa614b2185f]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[faf3c98050982095]::result::Result<(), rustc_span[a0270aa614b2185f]::ErrorGuaranteed>>::{closure#1} as core[faf3c98050982095]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  36:     0x7f5e62c1828b - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h63394803e5a3b584
                               at /rustc/aa1c45908df252a5b0c14e1bcb38c6c55ae02efe/library/alloc/src/boxed.rs:2018:9
  37:     0x7f5e62c1828b - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::hbe514eade38645bb
                               at /rustc/aa1c45908df252a5b0c14e1bcb38c6c55ae02efe/library/alloc/src/boxed.rs:2018:9
  38:     0x7f5e62c1828b - std::sys::pal::unix::thread::Thread::new::thread_start::hb4be61ed23447ea6
                               at /rustc/aa1c45908df252a5b0c14e1bcb38c6c55ae02efe/library/std/src/sys/pal/unix/thread.rs:108:17
  39:     0x7f5e62b25609 - start_thread
  40:     0x7f5e62a48353 - clone
  41:                0x0 - <unknown>

note: using internal features is not supported and expected to cause internal compiler errors when used incorrectly

note: please attach the file at `/playground/rustc-ice-2024-04-07T07_42_23-24.txt` to your bug report

note: compiler flags: --crate-type bin -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_drops_elaborated_and_const_checked] elaborating drops for `main`
#1 [analysis] running analysis passes on this crate
end of query stack

The ICE originates in lower_intrinsics.rs e.g. over here for read_via_copy:

rust/compiler/rustc_mir_transform/src/lower_intrinsics.rs

Lines 176 to 178 in af25253

	let [arg] = args.as_slice() else {
	span_bug!(terminator.source_info.span, "Wrong number of arguments");
	};

Since there are a lot of occurrences of span_bug!(..., "Wrong number of arguments...") in this file, many other intrinsics will also ICE under the given conditions.

Related issue: #123442 which is a special case of this issue for the transmute intrinsic.

[Noratrieb]

note: using internal features is not supported and expected to cause internal compiler errors when used incorrectly

It's a bit hidden in the ICE message, understandable that you've missed it.

[gurry]

Oh. I should've seen that. Thanks :)

[estebank]

Copying from #123526 (comment):

we [should] introduce a new, separate, version of panicking that doesn't "look" like an ICE but rather a generic "invalid language state" error that stops the compilation, with no stack trace.

I think this ticket is a good example of a case where having a distinction between "the compiler made a mistake" and "the user modifiable language state is incorrect" in the panic output would be useful. It'd be already great if it only applied to the "expect" methods (like "assume the Sized trait is available" methods). If those weren't an automatic ICE, I think we could clean up rustc code a bunch.

[Noratrieb]

You could replace all of the bugs with that but you can't replace things like indexing with it without making the compiler code uglier. I am not sure where rustc could be cleaned up by making this code less panicky... if there's anything that would be cleaner in the compiler code without panicking then please just do that today!

[Noratrieb]

i think we should just make the ICE message here a bit clearer
keep the stack trace or whatever but mention way more clearly that internal features are not supported and that if the ICE is related to that, that we don't want a bug report.