ICE with GAT + higher-ranked TAIT

[Dirbaio]

playground

#![feature(type_alias_impl_trait)]
#![feature(generic_associated_types)]

pub trait Trait {
    type Assoc<'a>;
}

pub type Foo = impl for<'a> Trait<Assoc<'a> = FooAssoc<'a>>;
pub type FooAssoc<'a> = impl Sized;

struct Struct;
impl Trait for Struct {
    type Assoc<'a> = &'a u32;
}

const FOO: Foo = Struct;

error: internal compiler error: compiler/rustc_trait_selection/src/opaque_types.rs:326:17: unexpected region kind in opaque type: RePlaceholder(Placeholder { universe: U1, name: BrNamed(DefId(0:8 ~ playground[9145]::Foo::{opaque#0}::'a), 'a) })

thread 'rustc' panicked at 'Box<dyn Any>', /rustc/42e1761c704f074b7b8c7ff8a7433acfd65d2ee9/compiler/rustc_errors/src/lib.rs:1335:9
stack backtrace:
   0:     0x7f5f8516ff8d - std::backtrace_rs::backtrace::libunwind::trace::h67b1c8cf8ce320d0
                               at /rustc/42e1761c704f074b7b8c7ff8a7433acfd65d2ee9/library/std/src/../../backtrace/src/backtrace/libunwind.rs:93:5
   1:     0x7f5f8516ff8d - std::backtrace_rs::backtrace::trace_unsynchronized::hd715d6ee36d01457
                               at /rustc/42e1761c704f074b7b8c7ff8a7433acfd65d2ee9/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x7f5f8516ff8d - std::sys_common::backtrace::_print_fmt::h86f2d6902c17b72b
                               at /rustc/42e1761c704f074b7b8c7ff8a7433acfd65d2ee9/library/std/src/sys_common/backtrace.rs:66:5
   3:     0x7f5f8516ff8d - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::h2f28719fc9d49991
                               at /rustc/42e1761c704f074b7b8c7ff8a7433acfd65d2ee9/library/std/src/sys_common/backtrace.rs:45:22
   4:     0x7f5f851cbc1c - core::fmt::write::h58d80b2387526c14
                               at /rustc/42e1761c704f074b7b8c7ff8a7433acfd65d2ee9/library/core/src/fmt/mod.rs:1196:17
   5:     0x7f5f85161661 - std::io::Write::write_fmt::h51e24b646b1d9dea
                               at /rustc/42e1761c704f074b7b8c7ff8a7433acfd65d2ee9/library/std/src/io/mod.rs:1654:15
   6:     0x7f5f85172ca5 - std::sys_common::backtrace::_print::h08306e60302c2601
                               at /rustc/42e1761c704f074b7b8c7ff8a7433acfd65d2ee9/library/std/src/sys_common/backtrace.rs:48:5
   7:     0x7f5f85172ca5 - std::sys_common::backtrace::print::h8bee5b1ce7ed0828
                               at /rustc/42e1761c704f074b7b8c7ff8a7433acfd65d2ee9/library/std/src/sys_common/backtrace.rs:35:9
   8:     0x7f5f85172ca5 - std::panicking::default_hook::{{closure}}::h0135f80d264aa3cb
                               at /rustc/42e1761c704f074b7b8c7ff8a7433acfd65d2ee9/library/std/src/panicking.rs:295:22
   9:     0x7f5f85172919 - std::panicking::default_hook::haf57ee52e612f636
                               at /rustc/42e1761c704f074b7b8c7ff8a7433acfd65d2ee9/library/std/src/panicking.rs:314:9
  10:     0x7f5f85938b21 - rustc_driver[52a5108fb431eaec]::DEFAULT_HOOK::{closure#0}::{closure#0}
  11:     0x7f5f85173476 - std::panicking::rust_panic_with_hook::h4cd397120086e208
                               at /rustc/42e1761c704f074b7b8c7ff8a7433acfd65d2ee9/library/std/src/panicking.rs:702:17
  12:     0x7f5f869c26a1 - std[6756e547c62c76a1]::panicking::begin_panic::<rustc_errors[a3b3cd9ac4cd0404]::ExplicitBug>::{closure#0}
  13:     0x7f5f869bc886 - std[6756e547c62c76a1]::sys_common::backtrace::__rust_end_short_backtrace::<std[6756e547c62c76a1]::panicking::begin_panic<rustc_errors[a3b3cd9ac4cd0404]::ExplicitBug>::{closure#0}, !>
  14:     0x7f5f86951aa6 - std[6756e547c62c76a1]::panicking::begin_panic::<rustc_errors[a3b3cd9ac4cd0404]::ExplicitBug>
  15:     0x7f5f86907306 - std[6756e547c62c76a1]::panic::panic_any::<rustc_errors[a3b3cd9ac4cd0404]::ExplicitBug>
  16:     0x7f5f86903575 - <rustc_errors[a3b3cd9ac4cd0404]::HandlerInner>::bug::<&alloc[37b6f05715a7cc80]::string::String>
  17:     0x7f5f86902f80 - <rustc_errors[a3b3cd9ac4cd0404]::Handler>::bug::<&alloc[37b6f05715a7cc80]::string::String>
  18:     0x7f5f869cb05d - rustc_middle[98c7c48ec55f2d30]::ty::context::tls::with_opt::<rustc_middle[98c7c48ec55f2d30]::util::bug::opt_span_bug_fmt<rustc_span[6ccf8f5ca5317a27]::span_encoding::Span>::{closure#0}, ()>
  19:     0x7f5f869cb3d6 - rustc_middle[98c7c48ec55f2d30]::util::bug::opt_span_bug_fmt::<rustc_span[6ccf8f5ca5317a27]::span_encoding::Span>
  20:     0x7f5f869cb353 - rustc_middle[98c7c48ec55f2d30]::util::bug::bug_fmt
  21:     0x7f5f88183fd2 - <rustc_trait_selection[6e50549df9c71920]::opaque_types::ReverseMapper as rustc_middle[98c7c48ec55f2d30]::ty::fold::TypeFolder>::fold_region
  22:     0x7f5f88188465 - <rustc_middle[98c7c48ec55f2d30]::ty::Ty as rustc_middle[98c7c48ec55f2d30]::ty::fold::TypeFoldable>::super_fold_with::<rustc_trait_selection[6e50549df9c71920]::opaque_types::ReverseMapper>
  23:     0x7f5f881542fe - <rustc_infer[91e6494644033aa9]::infer::InferCtxt as rustc_trait_selection[6e50549df9c71920]::opaque_types::InferCtxtExt>::infer_opaque_definition_from_instantiation
  24:     0x7f5f872199f0 - <rustc_borrowck[7ebf6aea16ae1e27]::region_infer::RegionInferenceContext>::infer_opaque_types
  25:     0x7f5f871830f4 - rustc_borrowck[7ebf6aea16ae1e27]::nll::compute_regions
  26:     0x7f5f871eea2e - rustc_borrowck[7ebf6aea16ae1e27]::do_mir_borrowck
  27:     0x7f5f871e76b9 - rustc_borrowck[7ebf6aea16ae1e27]::mir_borrowck
  28:     0x7f5f871e4420 - <rustc_borrowck[7ebf6aea16ae1e27]::provide::{closure#0} as core[696ac347caa2bd44]::ops::function::FnOnce<(rustc_middle[98c7c48ec55f2d30]::ty::context::TyCtxt, rustc_span[6ccf8f5ca5317a27]::def_id::LocalDefId)>>::call_once
  29:     0x7f5f87414d50 - rustc_query_system[202e2af03b29f868]::query::plumbing::try_execute_query::<rustc_query_impl[571ef98d1fbb149a]::plumbing::QueryCtxt, rustc_query_system[202e2af03b29f868]::query::caches::DefaultCache<rustc_span[6ccf8f5ca5317a27]::def_id::LocalDefId, &rustc_middle[98c7c48ec55f2d30]::mir::query::BorrowCheckResult>>
  30:     0x7f5f873dfeea - <rustc_query_impl[571ef98d1fbb149a]::Queries as rustc_middle[98c7c48ec55f2d30]::ty::query::QueryEngine>::mir_borrowck
  31:     0x7f5f85d2ea50 - <rustc_typeck[bf5d8a66ba319940]::collect::type_of::find_opaque_ty_constraints::ConstraintLocator>::check
  32:     0x7f5f85d2e5b8 - <rustc_typeck[bf5d8a66ba319940]::collect::type_of::find_opaque_ty_constraints::ConstraintLocator as rustc_hir[c624ea387cefbc39]::intravisit::Visitor>::visit_item
  33:     0x7f5f85d2aed5 - <rustc_typeck[bf5d8a66ba319940]::collect::type_of::find_opaque_ty_constraints::ConstraintLocator as rustc_hir[c624ea387cefbc39]::intravisit::Visitor>::visit_nested_item
  34:     0x7f5f85c55c57 - rustc_hir[c624ea387cefbc39]::intravisit::walk_mod::<rustc_typeck[bf5d8a66ba319940]::collect::type_of::find_opaque_ty_constraints::ConstraintLocator>
  35:     0x7f5f85d2e300 - rustc_typeck[bf5d8a66ba319940]::collect::type_of::find_opaque_ty_constraints
  36:     0x7f5f86f32bb2 - rustc_typeck[bf5d8a66ba319940]::collect::type_of::type_of
  37:     0x7f5f8745b517 - rustc_query_system[202e2af03b29f868]::query::plumbing::get_query::<rustc_query_impl[571ef98d1fbb149a]::queries::type_of, rustc_query_impl[571ef98d1fbb149a]::plumbing::QueryCtxt>
  38:     0x7f5f86f3bc95 - rustc_typeck[bf5d8a66ba319940]::check::check::check_item_type
  39:     0x7f5f86f411fb - rustc_typeck[bf5d8a66ba319940]::check::check::check_mod_item_types
  40:     0x7f5f87416d70 - rustc_query_system[202e2af03b29f868]::query::plumbing::try_execute_query::<rustc_query_impl[571ef98d1fbb149a]::plumbing::QueryCtxt, rustc_query_system[202e2af03b29f868]::query::caches::DefaultCache<rustc_span[6ccf8f5ca5317a27]::def_id::LocalDefId, ()>>
  41:     0x7f5f87f6aae3 - rustc_query_system[202e2af03b29f868]::query::plumbing::get_query::<rustc_query_impl[571ef98d1fbb149a]::queries::check_mod_item_types, rustc_query_impl[571ef98d1fbb149a]::plumbing::QueryCtxt>
  42:     0x7f5f87c8685d - <rustc_middle[98c7c48ec55f2d30]::hir::map::Map>::for_each_module::<rustc_typeck[bf5d8a66ba319940]::check_crate::{closure#6}::{closure#0}>
  43:     0x7f5f87c64668 - <rustc_session[abce4e7f97e3a707]::session::Session>::time::<(), rustc_typeck[bf5d8a66ba319940]::check_crate::{closure#6}>
  44:     0x7f5f87c4ce68 - rustc_typeck[bf5d8a66ba319940]::check_crate
  45:     0x7f5f879e6e87 - rustc_interface[f634dffaf1f1ed4]::passes::analysis
  46:     0x7f5f87f38574 - rustc_query_system[202e2af03b29f868]::query::plumbing::try_execute_query::<rustc_query_impl[571ef98d1fbb149a]::plumbing::QueryCtxt, rustc_query_system[202e2af03b29f868]::query::caches::DefaultCache<(), core[696ac347caa2bd44]::result::Result<(), rustc_errors[a3b3cd9ac4cd0404]::ErrorGuaranteed>>>
  47:     0x7f5f87f79c7e - rustc_query_system[202e2af03b29f868]::query::plumbing::get_query::<rustc_query_impl[571ef98d1fbb149a]::queries::analysis, rustc_query_impl[571ef98d1fbb149a]::plumbing::QueryCtxt>
  48:     0x7f5f879c78e7 - <rustc_interface[f634dffaf1f1ed4]::passes::QueryContext>::enter::<rustc_driver[52a5108fb431eaec]::run_compiler::{closure#1}::{closure#2}::{closure#3}, core[696ac347caa2bd44]::result::Result<(), rustc_errors[a3b3cd9ac4cd0404]::ErrorGuaranteed>>
  49:     0x7f5f879b2938 - <rustc_interface[f634dffaf1f1ed4]::interface::Compiler>::enter::<rustc_driver[52a5108fb431eaec]::run_compiler::{closure#1}::{closure#2}, core[696ac347caa2bd44]::result::Result<core[696ac347caa2bd44]::option::Option<rustc_interface[f634dffaf1f1ed4]::queries::Linker>, rustc_errors[a3b3cd9ac4cd0404]::ErrorGuaranteed>>
  50:     0x7f5f879db02f - rustc_span[6ccf8f5ca5317a27]::with_source_map::<core[696ac347caa2bd44]::result::Result<(), rustc_errors[a3b3cd9ac4cd0404]::ErrorGuaranteed>, rustc_interface[f634dffaf1f1ed4]::interface::create_compiler_and_run<core[696ac347caa2bd44]::result::Result<(), rustc_errors[a3b3cd9ac4cd0404]::ErrorGuaranteed>, rustc_driver[52a5108fb431eaec]::run_compiler::{closure#1}>::{closure#1}>
  51:     0x7f5f879b35a4 - rustc_interface[f634dffaf1f1ed4]::interface::create_compiler_and_run::<core[696ac347caa2bd44]::result::Result<(), rustc_errors[a3b3cd9ac4cd0404]::ErrorGuaranteed>, rustc_driver[52a5108fb431eaec]::run_compiler::{closure#1}>
  52:     0x7f5f879b0e42 - <scoped_tls[5bcfd69aea41704b]::ScopedKey<rustc_span[6ccf8f5ca5317a27]::SessionGlobals>>::set::<rustc_interface[f634dffaf1f1ed4]::interface::run_compiler<core[696ac347caa2bd44]::result::Result<(), rustc_errors[a3b3cd9ac4cd0404]::ErrorGuaranteed>, rustc_driver[52a5108fb431eaec]::run_compiler::{closure#1}>::{closure#0}, core[696ac347caa2bd44]::result::Result<(), rustc_errors[a3b3cd9ac4cd0404]::ErrorGuaranteed>>
  53:     0x7f5f879c7f6f - std[6756e547c62c76a1]::sys_common::backtrace::__rust_begin_short_backtrace::<rustc_interface[f634dffaf1f1ed4]::util::run_in_thread_pool_with_globals<rustc_interface[f634dffaf1f1ed4]::interface::run_compiler<core[696ac347caa2bd44]::result::Result<(), rustc_errors[a3b3cd9ac4cd0404]::ErrorGuaranteed>, rustc_driver[52a5108fb431eaec]::run_compiler::{closure#1}>::{closure#0}, core[696ac347caa2bd44]::result::Result<(), rustc_errors[a3b3cd9ac4cd0404]::ErrorGuaranteed>>::{closure#0}, core[696ac347caa2bd44]::result::Result<(), rustc_errors[a3b3cd9ac4cd0404]::ErrorGuaranteed>>
  54:     0x7f5f879c80a9 - <<std[6756e547c62c76a1]::thread::Builder>::spawn_unchecked_<rustc_interface[f634dffaf1f1ed4]::util::run_in_thread_pool_with_globals<rustc_interface[f634dffaf1f1ed4]::interface::run_compiler<core[696ac347caa2bd44]::result::Result<(), rustc_errors[a3b3cd9ac4cd0404]::ErrorGuaranteed>, rustc_driver[52a5108fb431eaec]::run_compiler::{closure#1}>::{closure#0}, core[696ac347caa2bd44]::result::Result<(), rustc_errors[a3b3cd9ac4cd0404]::ErrorGuaranteed>>::{closure#0}, core[696ac347caa2bd44]::result::Result<(), rustc_errors[a3b3cd9ac4cd0404]::ErrorGuaranteed>>::{closure#1} as core[696ac347caa2bd44]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  55:     0x7f5f8517d393 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h14e46baa6d22d347
                               at /rustc/42e1761c704f074b7b8c7ff8a7433acfd65d2ee9/library/alloc/src/boxed.rs:1872:9
  56:     0x7f5f8517d393 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h6ebfb42aa2b9da7a
                               at /rustc/42e1761c704f074b7b8c7ff8a7433acfd65d2ee9/library/alloc/src/boxed.rs:1872:9
  57:     0x7f5f8517d393 - std::sys::unix::thread::Thread::new::thread_start::hff1811d6a35504cb
                               at /rustc/42e1761c704f074b7b8c7ff8a7433acfd65d2ee9/library/std/src/sys/unix/thread.rs:108:17
  58:     0x7f5f850ad609 - start_thread
  59:     0x7f5f84fc6133 - clone
  60:                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 1.63.0-nightly (42e1761c7 2022-05-15) running on x86_64-unknown-linux-gnu

note: compiler flags: --crate-type lib -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_borrowck] borrow-checking `FOO`
#1 [type_of] computing type of `Foo::{opaque#0}`
#2 [check_mod_item_types] checking item types in top-level module
#3 [analysis] running analysis passes on this crate
end of query stack

rustc 1.63.0-nightly (42e1761 2022-05-15)

[aliemjay]

Related to #96146

@rustbot label F-type_alias_impl_trait C-bug T-compiler

@rustbot claim

[oli-obk]

The current error is

thread 'rustc' panicked at 'assertion failed: self.scc_universes[scc] == ty::UniverseIndex::ROOT', compiler/rustc_borrowck/src/region_infer/mod.rs:710:9

So this is probably the same cause as #99945 (higher ranked TAITs are just broken)