Bizarre higher-ranked type mismatch causes ICE on stable

[Radbuglet]

Code

pub trait Sig<'a> {
    type Input;
    type Output;
}

fn a<C, F>(_: F)
where
    C: Sig<'static>,
    F: FnMut(<C as Sig<'static>>::Input) -> C::Output,
{
}

pub fn b<C>()
where
    C: Sig<'static>,
{
    a::<C, _>(move |input: &'_ <C as Sig<'_>>::Input| unimplemented!());
}

Thanks to Talchas (whose Github username I do not know) for help minimizing this ICE.

Meta

rustc --version --verbose:

rustc 1.68.2 (9eb3afe9e 2023-03-27)
binary: rustc
commit-hash: 9eb3afe9ebe9c7d2b84b71002d44f4a0edac95e0
commit-date: 2023-03-27
host: x86_64-pc-windows-msvc
release: 1.68.2
LLVM version: 15.0.6

Error output

    Checking cool-ice v0.1.0 (C:\path\to\cool-ice)
error: internal compiler error: compiler\rustc_infer\src\infer\region_constraints\mod.rs:568:17: cannot relate bound region: ReLateBound(DebruijnIndex(0), BoundRegion { var: 
1, kind: BrNamed(DefId(0:14 ~ cool_ice[5d71]::b::'_#1), '_) }) <= ReStatic

thread 'rustc' panicked at 'Box<dyn Any>', /rustc/9eb3afe9ebe9c7d2b84b71002d44f4a0edac95e0\compiler\rustc_errors\src\lib.rs:987:33
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

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 1.68.2 (9eb3afe9e 2023-03-27) running on x86_64-pc-windows-msvc

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

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

query stack during panic:
#0 [typeck] type-checking `b`
#1 [typeck_item_bodies] type-checking all item bodies
end of query stack
error: could not compile `cool-ice`

Backtrace

    Checking cool-ice v0.1.0 (C:\path\to\cool-ice)
error: internal compiler error: compiler\rustc_infer\src\infer\region_constraints\mod.rs:568:17: cannot relate bound region: ReLateBound(DebruijnIndex(0), BoundRegion { var: 
1, kind: BrNamed(DefId(0:14 ~ cool_ice[5d71]::b::'_#1), '_) }) <= ReStatic

thread 'rustc' panicked at 'Box<dyn Any>', /rustc/9eb3afe9ebe9c7d2b84b71002d44f4a0edac95e0\compiler\rustc_errors\src\lib.rs:987:33
stack backtrace:
   0:     0x7ff946f39d02 - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::hbb6eec21cb8e3d1b
   1:     0x7ff946f7570b - core::fmt::write::h3f34d6e08b5a11e8
   2:     0x7ff946f2cdfa - <std::io::IoSlice as core::fmt::Debug>::fmt::h1d8b4e60e4c9e548
   3:     0x7ff946f39a4b - std::sys::common::alloc::realloc_fallback::h258dcd65da5985d2
   4:     0x7ff946f3d3f9 - std::panicking::default_hook::h90b70b966050cb60
   5:     0x7ff946f3d07b - std::panicking::default_hook::h90b70b966050cb60
   6:     0x7ff9264f9425 - rustc_driver[fbeb20e0897b27eb]::describe_lints
   7:     0x7ff946f3dd5f - std::panicking::rust_panic_with_hook::h1d50ae3462f62f01
   8:     0x7ff9287ba703 - <<rustc_infer[e1f2f17455595243]::infer::error_reporting::TypeErrCtxt>::construct_generic_bound_failure::SubOrigin as core[15ae0b8045847941]::fmt::Debug>::fmt
   9:     0x7ff9287b8c19 - <<rustc_infer[e1f2f17455595243]::infer::error_reporting::TypeErrCtxt>::construct_generic_bound_failure::SubOrigin as core[15ae0b8045847941]::fmt::Debug>::fmt
  10:     0x7ff9287b8bb9 - <<rustc_infer[e1f2f17455595243]::infer::error_reporting::TypeErrCtxt>::construct_generic_bound_failure::SubOrigin as core[15ae0b8045847941]::fmt::Debug>::fmt
  11:     0x7ff9287b8ba9 - <<rustc_infer[e1f2f17455595243]::infer::error_reporting::TypeErrCtxt>::construct_generic_bound_failure::SubOrigin as core[15ae0b8045847941]::fmt::Debug>::fmt
  12:     0x7ff9287b8220 - <<rustc_infer[e1f2f17455595243]::infer::error_reporting::TypeErrCtxt>::construct_generic_bound_failure::SubOrigin as core[15ae0b8045847941]::fmt::Debug>::fmt
  13:     0x7ff9287b8079 - <<rustc_infer[e1f2f17455595243]::infer::error_reporting::TypeErrCtxt>::construct_generic_bound_failure::SubOrigin as core[15ae0b8045847941]::fmt::Debug>::fmt
  14:     0x7ff9287c04c9 - <rustc_infer[e1f2f17455595243]::infer::opaque_types::table::OpaqueTypeStorage as core[15ae0b8045847941]::fmt::Debug>::fmt
  15:     0x7ff9287c052d - <rustc_infer[e1f2f17455595243]::infer::opaque_types::table::OpaqueTypeStorage as core[15ae0b8045847941]::fmt::Debug>::fmt
  16:     0x7ff9287bf73a - <rustc_infer[e1f2f17455595243]::infer::opaque_types::table::OpaqueTypeStorage as core[15ae0b8045847941]::fmt::Debug>::fmt
  17:     0x7ff9287bf678 - <rustc_infer[e1f2f17455595243]::infer::opaque_types::table::OpaqueTypeStorage as core[15ae0b8045847941]::fmt::Debug>::fmt
  18:     0x7ff9287bf636 - <rustc_infer[e1f2f17455595243]::infer::opaque_types::table::OpaqueTypeStorage as core[15ae0b8045847941]::fmt::Debug>::fmt
  19:     0x7ff92632776a - <rustc_infer[e1f2f17455595243]::infer::combine::ConstInferUnifier as rustc_middle[1d4803ea9c08b419]::ty::relate::TypeRelation>::consts
  20:     0x7ff92631f90a - <rustc_infer[e1f2f17455595243]::infer::combine::ConstInferUnifier as rustc_middle[1d4803ea9c08b419]::ty::relate::TypeRelation>::consts
  21:     0x7ff924aee9f1 - <rustc_infer[e1f2f17455595243]::infer::combine::Generalizer as rustc_middle[1d4803ea9c08b419]::ty::relate::TypeRelation>::regions
  22:     0x7ff92633698e - <rustc_middle[1d4803ea9c08b419]::ty::sty::AliasTy as rustc_infer[e1f2f17455595243]::infer::at::ToTrace>::to_trace
  23:     0x7ff9262f1909 - <rustc_infer[e1f2f17455595243]::infer::equate::Equate as rustc_middle[1d4803ea9c08b419]::ty::relate::TypeRelation>::tys
  24:     0x7ff924abd78a - <rustc_middle[1d4803ea9c08b419]::traits::specialization_graph::Children as rustc_trait_selection[5f0f54a03cd0c301]::traits::specialize::specialization_graph::ChildrenExt>::insert_blindly
  25:     0x7ff924aab10b - <rustc_trait_selection[5f0f54a03cd0c301]::traits::project::AssocTypeNormalizer as rustc_middle[1d4803ea9c08b419]::ty::fold::TypeFolder>::fold_const  26:     0x7ff928709218 - <rustc_trait_selection[5f0f54a03cd0c301]::solve::search_graph::StackDepth as core[15ae0b8045847941]::fmt::Debug>::fmt
  27:     0x7ff9286a7a09 - <rustc_trait_selection[5f0f54a03cd0c301]::traits::error_reporting::method_chain::CollectAllMismatches as rustc_middle[1d4803ea9c08b419]::ty::relate::TypeRelation>::consts
  28:     0x7ff9287216c3 - <rustc_infer[e1f2f17455595243]::infer::error_reporting::TypeErrCtxt as rustc_trait_selection[5f0f54a03cd0c301]::traits::error_reporting::suggestions::TypeErrCtxtExt>::report_closure_arg_mismatch
  29:     0x7ff928734bdb - <rustc_infer[e1f2f17455595243]::infer::error_reporting::TypeErrCtxt as rustc_trait_selection[5f0f54a03cd0c301]::traits::error_reporting::TypeErrCtxtExt>::report_selection_error
  30:     0x7ff928741805 - <rustc_infer[e1f2f17455595243]::infer::error_reporting::TypeErrCtxt as rustc_trait_selection[5f0f54a03cd0c301]::traits::error_reporting::InferCtxtPrivExt>::report_fulfillment_error
  31:     0x7ff928731569 - <rustc_infer[e1f2f17455595243]::infer::error_reporting::TypeErrCtxt as rustc_trait_selection[5f0f54a03cd0c301]::traits::error_reporting::TypeErrCtxtExt>::report_fulfillment_errors
  32:     0x7ff925664cbb - <rustc_hir_typeck[527c1058ba999897]::fn_ctxt::FnCtxt>::demand_coerce
  33:     0x7ff92560efd8 - <rustc_hir_typeck[527c1058ba999897]::inherited::Inherited as core[15ae0b8045847941]::ops::deref::Deref>::deref
  34:     0x7ff9246de669 - <rustc_query_impl[22fc8f5fe5921e7d]::on_disk_cache::CacheEncoder as rustc_type_ir[76501457ae8f3cde]::codec::TyEncoder>::encode_alloc_id
  35:     0x7ff9247447c5 - <&[(rustc_middle[1d4803ea9c08b419]::ty::Predicate, rustc_span[31f727a51b7d57bd]::span_encoding::Span)] as rustc_serialize[637af69557f69e4e]::serialize::Decodable<rustc_query_impl[22fc8f5fe5921e7d]::on_disk_cache::CacheDecoder>>::decode
  36:     0x7ff925ed08ad - <&[(rustc_middle[1d4803ea9c08b419]::ty::Clause, rustc_span[31f727a51b7d57bd]::span_encoding::Span)] as rustc_serialize[637af69557f69e4e]::serialize::Decodable<rustc_query_impl[22fc8f5fe5921e7d]::on_disk_cache::CacheDecoder>>::decode
  37:     0x7ff925da7093 - <rustc_query_impl[22fc8f5fe5921e7d]::Queries as rustc_middle[1d4803ea9c08b419]::ty::query::QueryEngine>::as_any
  38:     0x7ff9256b85d3 - <rustc_hir_typeck[527c1058ba999897]::fn_ctxt::FnCtxt>::resolve_fully_qualified_call
  39:     0x7ff92438b9d1 - <rustc_hir_typeck[527c1058ba999897]::inherited::Inherited>::build
  40:     0x7ff9246e043f - <rustc_query_impl[22fc8f5fe5921e7d]::on_disk_cache::CacheEncoder as rustc_type_ir[76501457ae8f3cde]::codec::TyEncoder>::encode_alloc_id
  41:     0x7ff92476376f - <&[(rustc_middle[1d4803ea9c08b419]::ty::Predicate, rustc_span[31f727a51b7d57bd]::span_encoding::Span)] as rustc_serialize[637af69557f69e4e]::serialize::Decodable<rustc_query_impl[22fc8f5fe5921e7d]::on_disk_cache::CacheDecoder>>::decode
  42:     0x7ff9247d24f1 - <&[(rustc_middle[1d4803ea9c08b419]::ty::Predicate, rustc_span[31f727a51b7d57bd]::span_encoding::Span)] as rustc_serialize[637af69557f69e4e]::serialize::Decodable<rustc_query_impl[22fc8f5fe5921e7d]::on_disk_cache::CacheDecoder>>::decode
  43:     0x7ff9246b3152 - <rustc_query_impl[22fc8f5fe5921e7d]::Queries as rustc_middle[1d4803ea9c08b419]::ty::query::QueryEngine>::try_mark_green
  44:     0x7ff9243ea1aa - <<dyn rustc_hir_analysis[9d3badbe7d08bcd8]::astconv::AstConv>::create_substs_for_ast_path::{closure#0}::SubstsForAstPathCtxt as rustc_hir_analysis[9d3badbe7d08bcd8]::astconv::CreateSubstsForGenericArgsCtxt>::inferred_kind
  45:     0x7ff9243e1ea9 - rustc_hir_analysis[9d3badbe7d08bcd8]::check_crate
  46:     0x7ff923cc2295 - rustc_interface[5b253cef4d5aad89]::passes::analysis
  47:     0x7ff9246dff1f - <rustc_query_impl[22fc8f5fe5921e7d]::on_disk_cache::CacheEncoder as rustc_type_ir[76501457ae8f3cde]::codec::TyEncoder>::encode_alloc_id
  48:     0x7ff92475ed19 - <&[(rustc_middle[1d4803ea9c08b419]::ty::Predicate, rustc_span[31f727a51b7d57bd]::span_encoding::Span)] as rustc_serialize[637af69557f69e4e]::serialize::Decodable<rustc_query_impl[22fc8f5fe5921e7d]::on_disk_cache::CacheDecoder>>::decode
  49:     0x7ff92484b611 - <&[(rustc_middle[1d4803ea9c08b419]::ty::Predicate, rustc_span[31f727a51b7d57bd]::span_encoding::Span)] as rustc_serialize[637af69557f69e4e]::serialize::Decodable<rustc_query_impl[22fc8f5fe5921e7d]::on_disk_cache::CacheDecoder>>::decode
  50:     0x7ff9246b094f - <rustc_query_impl[22fc8f5fe5921e7d]::Queries as rustc_middle[1d4803ea9c08b419]::ty::query::QueryEngine>::try_mark_green
  51:     0x7ff923c6d1a9 - <rustc_middle[1d4803ea9c08b419]::ty::SymbolName as core[15ae0b8045847941]::fmt::Debug>::fmt
  52:     0x7ff923c7e7fa - rustc_driver[fbeb20e0897b27eb]::args::arg_expand_all
  53:     0x7ff923c62ac1 - <unknown>
  54:     0x7ff923c6cacb - <rustc_middle[1d4803ea9c08b419]::ty::SymbolName as core[15ae0b8045847941]::fmt::Debug>::fmt
  55:     0x7ff923c6c319 - <rustc_middle[1d4803ea9c08b419]::ty::SymbolName as core[15ae0b8045847941]::fmt::Debug>::fmt
  56:     0x7ff923c6404d - <rustc_middle[1d4803ea9c08b419]::ty::SymbolName as core[15ae0b8045847941]::fmt::Debug>::fmt
  57:     0x7ff946f5021c - std::sys::windows::thread::Thread::new::hf7aab9c244c58572
  58:     0x7ff9b1647614 - BaseThreadInitThunk
  59:     0x7ff9b31c26a1 - RtlUserThreadStart

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 1.68.2 (9eb3afe9e 2023-03-27) running on x86_64-pc-windows-msvc

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

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

query stack during panic:
#0 [typeck] type-checking `b`
#1 [typeck_item_bodies] type-checking all item bodies
#2 [analysis] running analysis passes on this crate
end of query stack
error: could not compile `cool-ice`

[aliemjay]

This is #109361. It is fixed in the current beta/nightly.

Closing this in favor of #109361 which should track a possible backport to the stable version. Thanks for reporting!