ICE: `opaque type with non-universal region args`

[matthiaskrgr]

auto-reduced (treereduce-rust):

trait Trait<'a, 'b> {}
impl<'a, 'b, T> Trait<'a, 'b> for T {}

fn foo<'a: 'a, 'b: 'b>() -> impl Trait<'a, 'b> {
    let _: &'a () = foo::<'a, 'b>();

    loop {}
}

original:

trait Trait<'a, 'b> {}
impl<'a, 'b, T> Trait<'a, 'b> for T {}

fn foo<'a: 'a, 'b: 'b>() -> impl Trait<'a, 'b> {
    let _: &'a () = foo::<'a, 'b>();
    let _: &'b () = foo::<'a, 'b>();
    loop {}
}

Version information

rustc 1.78.0-nightly (52cea084b 2024-02-23)
binary: rustc
commit-hash: 52cea084bd5bbac12ecfa5c0499f5c777025c968
commit-date: 2024-02-23
host: x86_64-unknown-linux-gnu
release: 1.78.0-nightly
LLVM version: 18.1.0

Command:
/home/matthias/.rustup/toolchains/master/bin/rustc --crate-type=lib

Program output

warning: function cannot return without recursing
 --> /tmp/icemaker_global_tempdir.xEeeLtfZEdIS/rustc_testrunner_tmpdir_reporting.OoAOVBT9ivkN/mvce.rs:4:1
  |
4 | fn foo<'a: 'a, 'b: 'b>() -> impl Trait<'a, 'b> {
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ cannot return without recursing
5 |     let _: &'a () = foo::<'a, 'b>();
  |                     --------------- recursive call site
  |
  = help: a `loop` may express intention better if this is on purpose
  = note: `#[warn(unconditional_recursion)]` on by default

warning: trait `Trait` is never used
 --> /tmp/icemaker_global_tempdir.xEeeLtfZEdIS/rustc_testrunner_tmpdir_reporting.OoAOVBT9ivkN/mvce.rs:1:7
  |
1 | trait Trait<'a, 'b> {}
  |       ^^^^^
  |
  = note: `#[warn(dead_code)]` on by default

warning: function `foo` is never used
 --> /tmp/icemaker_global_tempdir.xEeeLtfZEdIS/rustc_testrunner_tmpdir_reporting.OoAOVBT9ivkN/mvce.rs:4:4
  |
4 | fn foo<'a: 'a, 'b: 'b>() -> impl Trait<'a, 'b> {
  |    ^^^

warning: 3 warnings emitted

note: no errors encountered even though delayed bugs were created

note: those delayed bugs will now be shown as internal compiler errors

error: internal compiler error: opaque type with non-universal region args
 --> /tmp/icemaker_global_tempdir.xEeeLtfZEdIS/rustc_testrunner_tmpdir_reporting.OoAOVBT9ivkN/mvce.rs:5:12
  |
5 |     let _: &'a () = foo::<'a, 'b>();
  |            ^^^^^^
  |
note: delayed at compiler/rustc_borrowck/src/region_infer/opaque_types.rs:97:25
         0: <rustc_errors::DiagCtxtInner>::emit_diagnostic
         1: <rustc_errors::DiagCtxt>::emit_diagnostic
         2: <rustc_span::ErrorGuaranteed as rustc_errors::diagnostic::EmissionGuarantee>::emit_producing_guarantee
         3: <rustc_borrowck::region_infer::RegionInferenceContext>::infer_opaque_types::{closure#0}::{closure#1}.cold.0
         4: <&rustc_middle::ty::list::List<rustc_middle::ty::generic_args::GenericArg> as rustc_type_ir::fold::TypeFoldable<rustc_middle::ty::context::TyCtxt>>::try_fold_with::<rustc_middle::ty::fold::RegionFolder>
         5: rustc_borrowck::nll::compute_regions
         6: rustc_borrowck::do_mir_borrowck
         7: rustc_borrowck::mir_borrowck
         8: rustc_query_impl::plumbing::__rust_begin_short_backtrace::<rustc_query_impl::query_impl::mir_borrowck::dynamic_query::{closure#2}::{closure#0}, rustc_middle::query::erase::Erased<[u8; 8]>>
         9: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::DynamicConfig<rustc_query_system::query::caches::VecCache<rustc_span::def_id::LocalDefId, rustc_middle::query::erase::Erased<[u8; 8]>>, false, false, false>, rustc_query_impl::plumbing::QueryCtxt, false>
        10: rustc_query_impl::query_impl::mir_borrowck::get_query_non_incr::__rust_end_short_backtrace
        11: rustc_middle::query::plumbing::query_get_at::<rustc_query_system::query::caches::VecCache<rustc_span::def_id::LocalDefId, rustc_middle::query::erase::Erased<[u8; 8]>>>
        12: rustc_hir_analysis::collect::type_of::type_of_opaque
        13: rustc_query_impl::plumbing::__rust_begin_short_backtrace::<rustc_query_impl::query_impl::type_of_opaque::dynamic_query::{closure#2}::{closure#0}, rustc_middle::query::erase::Erased<[u8; 8]>>
        14: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::DynamicConfig<rustc_query_system::query::caches::DefIdCache<rustc_middle::query::erase::Erased<[u8; 8]>>, false, false, false>, rustc_query_impl::plumbing::QueryCtxt, false>
        15: rustc_query_impl::query_impl::type_of_opaque::get_query_non_incr::__rust_end_short_backtrace
        16: rustc_middle::query::plumbing::query_get_at::<rustc_query_system::query::caches::DefIdCache<rustc_middle::query::erase::Erased<[u8; 8]>>>
        17: rustc_hir_analysis::collect::type_of::type_of
        18: rustc_query_impl::plumbing::__rust_begin_short_backtrace::<rustc_query_impl::query_impl::type_of::dynamic_query::{closure#2}::{closure#0}, rustc_middle::query::erase::Erased<[u8; 8]>>
        19: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::DynamicConfig<rustc_query_system::query::caches::DefIdCache<rustc_middle::query::erase::Erased<[u8; 8]>>, false, false, false>, rustc_query_impl::plumbing::QueryCtxt, false>
        20: rustc_query_impl::query_impl::type_of::get_query_non_incr::__rust_end_short_backtrace
        21: rustc_middle::query::plumbing::query_get_at::<rustc_query_system::query::caches::DefIdCache<rustc_middle::query::erase::Erased<[u8; 8]>>>
        22: rustc_hir_analysis::check::check::check_item_type
        23: rustc_hir_analysis::check::wfcheck::check_well_formed
        24: rustc_query_impl::plumbing::__rust_begin_short_backtrace::<rustc_query_impl::query_impl::check_well_formed::dynamic_query::{closure#2}::{closure#0}, rustc_middle::query::erase::Erased<[u8; 1]>>
        25: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::DynamicConfig<rustc_query_system::query::caches::VecCache<rustc_hir::hir_id::OwnerId, rustc_middle::query::erase::Erased<[u8; 1]>>, false, false, false>, rustc_query_impl::plumbing::QueryCtxt, false>
        26: rustc_query_impl::query_impl::check_well_formed::get_query_non_incr::__rust_end_short_backtrace
        27: rustc_hir_analysis::check::wfcheck::check_mod_type_wf
        28: rustc_query_impl::plumbing::__rust_begin_short_backtrace::<rustc_query_impl::query_impl::check_mod_type_wf::dynamic_query::{closure#2}::{closure#0}, rustc_middle::query::erase::Erased<[u8; 1]>>
        29: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::DynamicConfig<rustc_query_system::query::caches::DefaultCache<rustc_span::def_id::LocalModDefId, rustc_middle::query::erase::Erased<[u8; 1]>>, false, false, false>, rustc_query_impl::plumbing::QueryCtxt, false>
        30: rustc_query_impl::query_impl::check_mod_type_wf::get_query_non_incr::__rust_end_short_backtrace
        31: rustc_middle::query::plumbing::query_ensure_error_guaranteed::<rustc_query_system::query::caches::DefaultCache<rustc_span::def_id::LocalModDefId, rustc_middle::query::erase::Erased<[u8; 1]>>, ()>
        32: rustc_hir_analysis::check_crate
        33: rustc_interface::passes::analysis
        34: rustc_query_impl::plumbing::__rust_begin_short_backtrace::<rustc_query_impl::query_impl::analysis::dynamic_query::{closure#2}::{closure#0}, rustc_middle::query::erase::Erased<[u8; 1]>>
        35: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::DynamicConfig<rustc_query_system::query::caches::SingleCache<rustc_middle::query::erase::Erased<[u8; 1]>>, false, false, false>, rustc_query_impl::plumbing::QueryCtxt, false>
        36: rustc_query_impl::query_impl::analysis::get_query_non_incr::__rust_end_short_backtrace
        37: rustc_interface::interface::run_compiler::<core::result::Result<(), rustc_span::ErrorGuaranteed>, rustc_driver_impl::run_compiler::{closure#0}>::{closure#0}
        38: std::sys_common::backtrace::__rust_begin_short_backtrace::<rustc_interface::util::run_in_thread_with_globals<rustc_interface::util::run_in_thread_pool_with_globals<rustc_interface::interface::run_compiler<core::result::Result<(), rustc_span::ErrorGuaranteed>, rustc_driver_impl::run_compiler::{closure#0}>::{closure#0}, core::result::Result<(), rustc_span::ErrorGuaranteed>>::{closure#0}, core::result::Result<(), rustc_span::ErrorGuaranteed>>::{closure#0}::{closure#0}, core::result::Result<(), rustc_span::ErrorGuaranteed>>
        39: <<std::thread::Builder>::spawn_unchecked_<rustc_interface::util::run_in_thread_with_globals<rustc_interface::util::run_in_thread_pool_with_globals<rustc_interface::interface::run_compiler<core::result::Result<(), rustc_span::ErrorGuaranteed>, rustc_driver_impl::run_compiler::{closure#0}>::{closure#0}, core::result::Result<(), rustc_span::ErrorGuaranteed>>::{closure#0}, core::result::Result<(), rustc_span::ErrorGuaranteed>>::{closure#0}::{closure#0}, core::result::Result<(), rustc_span::ErrorGuaranteed>>::{closure#1} as core::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
        40: <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once
                   at /rustc/52cea084bd5bbac12ecfa5c0499f5c777025c968/library/alloc/src/boxed.rs:2016:9
        41: <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once
                   at /rustc/52cea084bd5bbac12ecfa5c0499f5c777025c968/library/alloc/src/boxed.rs:2016:9
        42: std::sys::pal::unix::thread::Thread::new::thread_start
                   at /rustc/52cea084bd5bbac12ecfa5c0499f5c777025c968/library/std/src/sys/pal/unix/thread.rs:108:17
        43: <unknown>
        44: <unknown>
 --> /tmp/icemaker_global_tempdir.xEeeLtfZEdIS/rustc_testrunner_tmpdir_reporting.OoAOVBT9ivkN/mvce.rs:5:12
  |
5 |     let _: &'a () = foo::<'a, 'b>();
  |            ^^^^^^

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 1.78.0-nightly (52cea084b 2024-02-23) running on x86_64-unknown-linux-gnu

note: compiler flags: --crate-type lib -Z dump-mir-dir=dir

query stack during panic:
end of query stack

[matthiaskrgr]

It looks like this ICEs since #121491 can't run bisection yet as we don't have the per-pr artifacts yet.

[matthiaskrgr]

The original example crashes since #121479 cc @lcnr

[lcnr]

doesn't this already crash since pretty much forever? https://rust.godbolt.org/z/noc3hrv95

[matthiaskrgr]

This first example yes
the second example: no

[matthiaskrgr]

This was fixed by #116891