ICE When Swapping Const Generic & Generic In Trait Method Impl

[danii]

Code

This is really as simple as ICEs get.

// No ICE here.
trait CrunchICE {
    fn crunch<const N: usize, T>(ice: T);
}

// Cold crunchy ICE here.
impl CrunchICE for () {
    // Note that the const generic and generic have swapped places here.
    fn crunch<T, const N: usize>(ice: T) {}
}

Meta

rustc --version --verbose:

rustc 1.62.0-nightly (69a5d2481 2022-04-27)
binary: rustc
commit-hash: 69a5d2481e856a5a18885390b8cf6950b9ff8dd3
commit-date: 2022-04-27
host: x86_64-unknown-linux-gnu
release: 1.62.0-nightly
LLVM version: 14.0.1

This also appears to work on stable from play.rust-lang.org.

note: rustc 1.61.0 (fe5b13d68 2022-05-18) running on x86_64-unknown-linux-gnu

Error output

Backtrace

error: internal compiler error: compiler/rustc_middle/src/ty/subst.rs:621:17: expected type for `W/#3` (W/3) but found Const(Const { ty: usize, val: Param(N/#3) }) when substituting, substs=[mode::Reader<T>, R, W, Const { ty: usize, val: Param(N/#3) }]

thread 'rustc' panicked at 'Box<dyn Any>', /rustc/69a5d2481e856a5a18885390b8cf6950b9ff8dd3/compiler/rustc_errors/src/lib.rs:1253:9
stack backtrace:
   0:     0x7f4f7a49dfed - std::backtrace_rs::backtrace::libunwind::trace::hc5abd1cb436aa528
                               at /rustc/69a5d2481e856a5a18885390b8cf6950b9ff8dd3/library/std/src/../../backtrace/src/backtrace/libunwind.rs:93:5
   1:     0x7f4f7a49dfed - std::backtrace_rs::backtrace::trace_unsynchronized::h16e652276c3c1a5f
                               at /rustc/69a5d2481e856a5a18885390b8cf6950b9ff8dd3/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x7f4f7a49dfed - std::sys_common::backtrace::_print_fmt::h866806c7f5375be1
                               at /rustc/69a5d2481e856a5a18885390b8cf6950b9ff8dd3/library/std/src/sys_common/backtrace.rs:66:5
   3:     0x7f4f7a49dfed - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::h7aeaa12c4281d2c8
                               at /rustc/69a5d2481e856a5a18885390b8cf6950b9ff8dd3/library/std/src/sys_common/backtrace.rs:45:22
   4:     0x7f4f7a4f9d6c - core::fmt::write::h03de7e659b82a590
                               at /rustc/69a5d2481e856a5a18885390b8cf6950b9ff8dd3/library/core/src/fmt/mod.rs:1194:17
   5:     0x7f4f7a48f6e1 - std::io::Write::write_fmt::h008eedacdce877e9
                               at /rustc/69a5d2481e856a5a18885390b8cf6950b9ff8dd3/library/std/src/io/mod.rs:1655:15
   6:     0x7f4f7a4a0d05 - std::sys_common::backtrace::_print::h4079f736a61c453b
                               at /rustc/69a5d2481e856a5a18885390b8cf6950b9ff8dd3/library/std/src/sys_common/backtrace.rs:48:5
   7:     0x7f4f7a4a0d05 - std::sys_common::backtrace::print::h610c7be10303d303
                               at /rustc/69a5d2481e856a5a18885390b8cf6950b9ff8dd3/library/std/src/sys_common/backtrace.rs:35:9
   8:     0x7f4f7a4a0d05 - std::panicking::default_hook::{{closure}}::hb2fea27db75549e4
                               at /rustc/69a5d2481e856a5a18885390b8cf6950b9ff8dd3/library/std/src/panicking.rs:295:22
   9:     0x7f4f7a4a0979 - std::panicking::default_hook::h6acb360d1343cfb8
                               at /rustc/69a5d2481e856a5a18885390b8cf6950b9ff8dd3/library/std/src/panicking.rs:314:9
  10:     0x7f4f7acce781 - rustc_driver[a5dbbc9ca67f5eff]::DEFAULT_HOOK::{closure#0}::{closure#0}
  11:     0x7f4f7a4a14d6 - std::panicking::rust_panic_with_hook::h2c796f347414ce5b
                               at /rustc/69a5d2481e856a5a18885390b8cf6950b9ff8dd3/library/std/src/panicking.rs:702:17
  12:     0x7f4f7bc98e81 - std[1c075e4e42f0cfa5]::panicking::begin_panic::<rustc_errors[ee6c0c75111f4e19]::ExplicitBug>::{closure#0}
  13:     0x7f4f7bc987e6 - std[1c075e4e42f0cfa5]::sys_common::backtrace::__rust_end_short_backtrace::<std[1c075e4e42f0cfa5]::panicking::begin_panic<rustc_errors[ee6c0c75111f4e19]::ExplicitBug>::{closure#0}, !>
  14:     0x7f4f7bcceb1f - std[1c075e4e42f0cfa5]::panicking::begin_panic::<rustc_errors[ee6c0c75111f4e19]::ExplicitBug>
  15:     0x7f4f7bc87ff6 - std[1c075e4e42f0cfa5]::panic::panic_any::<rustc_errors[ee6c0c75111f4e19]::ExplicitBug>
  16:     0x7f4f7bc84441 - <rustc_errors[ee6c0c75111f4e19]::HandlerInner>::span_bug::<rustc_span[77ab89dfdf07db3a]::span_encoding::Span, &alloc[a937766a13aeb85d]::string::String>
  17:     0x7f4f7bc83fa0 - <rustc_errors[ee6c0c75111f4e19]::Handler>::span_bug::<rustc_span[77ab89dfdf07db3a]::span_encoding::Span, &alloc[a937766a13aeb85d]::string::String>
  18:     0x7f4f7bc9f698 - rustc_middle[37425aa7f7ab8925]::ty::context::tls::with_opt::<rustc_middle[37425aa7f7ab8925]::util::bug::opt_span_bug_fmt<rustc_span[77ab89dfdf07db3a]::span_encoding::Span>::{closure#0}, ()>
  19:     0x7f4f7bc9f856 - rustc_middle[37425aa7f7ab8925]::util::bug::opt_span_bug_fmt::<rustc_span[77ab89dfdf07db3a]::span_encoding::Span>
  20:     0x7f4f7bc9f817 - rustc_middle[37425aa7f7ab8925]::util::bug::span_bug_fmt::<rustc_span[77ab89dfdf07db3a]::span_encoding::Span>
  21:     0x7f4f7ccad8b9 - <rustc_middle[37425aa7f7ab8925]::ty::Predicate as rustc_middle[37425aa7f7ab8925]::ty::subst::Subst>::subst
  22:     0x7f4f7cbd7204 - <rustc_middle[37425aa7f7ab8925]::ty::generics::GenericPredicates>::instantiate_own
  23:     0x7f4f7d00d377 - rustc_typeck[44b08195efa16631]::check::compare_method::compare_impl_method
  24:     0x7f4f7c1b7e08 - rustc_typeck[44b08195efa16631]::check::check::check_item_type
  25:     0x7f4f7c2a77db - <rustc_middle[37425aa7f7ab8925]::hir::map::Map>::visit_item_likes_in_module::<rustc_typeck[44b08195efa16631]::check::CheckItemTypesVisitor>
  26:     0x7f4f7cfa4b3c - rustc_typeck[44b08195efa16631]::check::check::check_mod_item_types
  27:     0x7f4f7d2ba42f - <rustc_query_system[cf4e8b18efdea24]::dep_graph::graph::DepGraph<rustc_middle[37425aa7f7ab8925]::dep_graph::dep_node::DepKind>>::with_task::<rustc_middle[37425aa7f7ab8925]::ty::context::TyCtxt, rustc_span[77ab89dfdf07db3a]::def_id::LocalDefId, ()>
  28:     0x7f4f7c700fce - rustc_query_system[cf4e8b18efdea24]::query::plumbing::try_execute_query::<rustc_query_impl[613f3d57b9125cc2]::plumbing::QueryCtxt, rustc_query_system[cf4e8b18efdea24]::query::caches::DefaultCache<rustc_span[77ab89dfdf07db3a]::def_id::LocalDefId, ()>>
  29:     0x7f4f7d243e13 - rustc_query_system[cf4e8b18efdea24]::query::plumbing::get_query::<rustc_query_impl[613f3d57b9125cc2]::queries::check_mod_item_types, rustc_query_impl[613f3d57b9125cc2]::plumbing::QueryCtxt>
  30:     0x7f4f7d0218bd - <rustc_middle[37425aa7f7ab8925]::hir::map::Map>::for_each_module::<rustc_typeck[44b08195efa16631]::check_crate::{closure#6}::{closure#0}>
  31:     0x7f4f7cfcd0e8 - <rustc_session[8d74270965aad24]::session::Session>::time::<(), rustc_typeck[44b08195efa16631]::check_crate::{closure#6}>
  32:     0x7f4f7cfbdee3 - rustc_typeck[44b08195efa16631]::check_crate
  33:     0x7f4f7cd4f427 - rustc_interface[4e7b840a6791346]::passes::analysis
  34:     0x7f4f7d2d1675 - <rustc_query_system[cf4e8b18efdea24]::dep_graph::graph::DepGraph<rustc_middle[37425aa7f7ab8925]::dep_graph::dep_node::DepKind>>::with_task::<rustc_middle[37425aa7f7ab8925]::ty::context::TyCtxt, (), core[8e7cf360a047e58a]::result::Result<(), rustc_errors[ee6c0c75111f4e19]::ErrorGuaranteed>>
  35:     0x7f4f7d212281 - rustc_query_system[cf4e8b18efdea24]::query::plumbing::try_execute_query::<rustc_query_impl[613f3d57b9125cc2]::plumbing::QueryCtxt, rustc_query_system[cf4e8b18efdea24]::query::caches::DefaultCache<(), core[8e7cf360a047e58a]::result::Result<(), rustc_errors[ee6c0c75111f4e19]::ErrorGuaranteed>>>
  36:     0x7f4f7d252e0e - rustc_query_system[cf4e8b18efdea24]::query::plumbing::get_query::<rustc_query_impl[613f3d57b9125cc2]::queries::analysis, rustc_query_impl[613f3d57b9125cc2]::plumbing::QueryCtxt>
  37:     0x7f4f7cd2ad07 - <rustc_interface[4e7b840a6791346]::passes::QueryContext>::enter::<rustc_driver[a5dbbc9ca67f5eff]::run_compiler::{closure#1}::{closure#2}::{closure#3}, core[8e7cf360a047e58a]::result::Result<(), rustc_errors[ee6c0c75111f4e19]::ErrorGuaranteed>>
  38:     0x7f4f7cd15af8 - <rustc_interface[4e7b840a6791346]::interface::Compiler>::enter::<rustc_driver[a5dbbc9ca67f5eff]::run_compiler::{closure#1}::{closure#2}, core[8e7cf360a047e58a]::result::Result<core[8e7cf360a047e58a]::option::Option<rustc_interface[4e7b840a6791346]::queries::Linker>, rustc_errors[ee6c0c75111f4e19]::ErrorGuaranteed>>
  39:     0x7f4f7cd3f2df - rustc_span[77ab89dfdf07db3a]::with_source_map::<core[8e7cf360a047e58a]::result::Result<(), rustc_errors[ee6c0c75111f4e19]::ErrorGuaranteed>, rustc_interface[4e7b840a6791346]::interface::create_compiler_and_run<core[8e7cf360a047e58a]::result::Result<(), rustc_errors[ee6c0c75111f4e19]::ErrorGuaranteed>, rustc_driver[a5dbbc9ca67f5eff]::run_compiler::{closure#1}>::{closure#1}>
  40:     0x7f4f7cd29de4 - rustc_interface[4e7b840a6791346]::interface::create_compiler_and_run::<core[8e7cf360a047e58a]::result::Result<(), rustc_errors[ee6c0c75111f4e19]::ErrorGuaranteed>, rustc_driver[a5dbbc9ca67f5eff]::run_compiler::{closure#1}>
  41:     0x7f4f7cd14592 - <scoped_tls[4941b86c876e991e]::ScopedKey<rustc_span[77ab89dfdf07db3a]::SessionGlobals>>::set::<rustc_interface[4e7b840a6791346]::interface::run_compiler<core[8e7cf360a047e58a]::result::Result<(), rustc_errors[ee6c0c75111f4e19]::ErrorGuaranteed>, rustc_driver[a5dbbc9ca67f5eff]::run_compiler::{closure#1}>::{closure#0}, core[8e7cf360a047e58a]::result::Result<(), rustc_errors[ee6c0c75111f4e19]::ErrorGuaranteed>>
  42:     0x7f4f7cd39c4f - std[1c075e4e42f0cfa5]::sys_common::backtrace::__rust_begin_short_backtrace::<rustc_interface[4e7b840a6791346]::util::run_in_thread_pool_with_globals<rustc_interface[4e7b840a6791346]::interface::run_compiler<core[8e7cf360a047e58a]::result::Result<(), rustc_errors[ee6c0c75111f4e19]::ErrorGuaranteed>, rustc_driver[a5dbbc9ca67f5eff]::run_compiler::{closure#1}>::{closure#0}, core[8e7cf360a047e58a]::result::Result<(), rustc_errors[ee6c0c75111f4e19]::ErrorGuaranteed>>::{closure#0}, core[8e7cf360a047e58a]::result::Result<(), rustc_errors[ee6c0c75111f4e19]::ErrorGuaranteed>>
  43:     0x7f4f7cd2c249 - <<std[1c075e4e42f0cfa5]::thread::Builder>::spawn_unchecked_<rustc_interface[4e7b840a6791346]::util::run_in_thread_pool_with_globals<rustc_interface[4e7b840a6791346]::interface::run_compiler<core[8e7cf360a047e58a]::result::Result<(), rustc_errors[ee6c0c75111f4e19]::ErrorGuaranteed>, rustc_driver[a5dbbc9ca67f5eff]::run_compiler::{closure#1}>::{closure#0}, core[8e7cf360a047e58a]::result::Result<(), rustc_errors[ee6c0c75111f4e19]::ErrorGuaranteed>>::{closure#0}, core[8e7cf360a047e58a]::result::Result<(), rustc_errors[ee6c0c75111f4e19]::ErrorGuaranteed>>::{closure#1} as core[8e7cf360a047e58a]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  44:     0x7f4f7a4ab423 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::hb45e490160efb1da
                               at /rustc/69a5d2481e856a5a18885390b8cf6950b9ff8dd3/library/alloc/src/boxed.rs:1866:9
  45:     0x7f4f7a4ab423 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h69d59fb5e559732f
                               at /rustc/69a5d2481e856a5a18885390b8cf6950b9ff8dd3/library/alloc/src/boxed.rs:1866:9
  46:     0x7f4f7a4ab423 - std::sys::unix::thread::Thread::new::thread_start::h93dc4d530899e0b7
                               at /rustc/69a5d2481e856a5a18885390b8cf6950b9ff8dd3/library/std/src/sys/unix/thread.rs:108:17
  47:     0x7f4f7a27f54d - <unknown>
  48:     0x7f4f7a304b14 - clone
  49:                0x0 - <unknown>

note: 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 1.62.0-nightly (69a5d2481 2022-04-27) running on x86_64-unknown-linux-gnu

note: compiler flags: --crate-type lib -C embed-bitcode=no -C debuginfo=2 -C incremental

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

query stack during panic:
#0 [check_mod_item_types] checking item types in module `mode`
#1 [analysis] running analysis passes on this crate
end of query stack

[matthiaskrgr]

can't reproduce with latest nightly rustc 1.63.0-nightly (ebbcbfc23 2022-05-27)

error[E0053]: method `crunch` has an incompatible generic parameter for trait `CrunchICE`
 --> 97541.rs:9:15
  |
2 | trait CrunchICE {
  |       ---------
3 |     fn crunch<const N: usize, T>(ice: T);
  |               -------------- expected const parameter of type `usize`
...
7 | impl CrunchICE for () {
  | ---------------------
8 |     // Note that the const generic and generic have swapped places here.
9 |     fn crunch<T, const N: usize>(ice: T) {}
  |               ^ found type parameter

error: aborting due to previous error

For more information about this error, try `rustc --explain E0053`.

[BoxyUwU]

#96717 fixed this