ICE with unused lifetime on recursive RPIT

[Jules-Bertholet]

Code

fn foo<'a>() -> impl Sized + 'a {
    let i: i32 = foo();
    i
}

Meta

rustc --version --verbose:

rustc 1.71.0-nightly (b628260df 2023-04-22)
binary: rustc
commit-hash: b628260df0587ae559253d8640ecb8738d3de613
commit-date: 2023-04-22
host: x86_64-unknown-linux-gnu
release: 1.71.0-nightly
LLVM version: 16.0.2

Error output

warning: function cannot return without recursing
 --> src/lib.rs:1:1
  |
1 | fn foo<'a>() -> impl Sized + 'a {
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ cannot return without recursing
2 |     let i: i32 = foo();
  |                  ----- recursive call site
  |
  = help: a `loop` may express intention better if this is on purpose
  = note: `#[warn(unconditional_recursion)]` on by default

warning: function `foo` is never used
 --> src/lib.rs:1:4
  |
1 | fn foo<'a>() -> impl Sized + 'a {
  |    ^^^
  |
  = note: `#[warn(dead_code)]` on by default

error: internal compiler error: no errors encountered even though `delay_span_bug` issued

error: internal compiler error: opaque type with non-universal region substs
 --> src/lib.rs:2:18
  |
2 |     let i: i32 = foo();
  |                  ^^^^^
  |

Backtrace

  = note: delayed at    0: <rustc_errors::HandlerInner>::emit_diagnostic
             1: <rustc_errors::Handler>::delay_span_bug::<rustc_span::span_encoding::Span, &str>
             2: <rustc_borrowck::region_infer::RegionInferenceContext>::infer_opaque_types::{closure#0}::{closure#2}
             3: <&rustc_middle::ty::list::List<rustc_middle::ty::subst::GenericArg> as rustc_type_ir::fold::TypeFoldable<rustc_middle::ty::context::TyCtxt>>::try_fold_with::<rustc_middle::ty::fold::RegionFolder>
             4: <rustc_borrowck::region_infer::RegionInferenceContext>::infer_opaque_types
             5: rustc_borrowck::nll::compute_regions
             6: rustc_borrowck::do_mir_borrowck
             7: rustc_borrowck::mir_borrowck
             8: <std::thread::local::LocalKey<core::cell::Cell<*const ()>>>::with::<rustc_middle::ty::context::tls::enter_context<rustc_query_system::query::plumbing::execute_job_incr<rustc_query_impl::queries::mir_borrowck, rustc_query_impl::plumbing::QueryCtxt>::{closure#2}, (rustc_middle::query::erase::Erased<[u8; 8]>, rustc_query_system::dep_graph::graph::DepNodeIndex)>::{closure#0}, (rustc_middle::query::erase::Erased<[u8; 8]>, rustc_query_system::dep_graph::graph::DepNodeIndex)>
             9: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::queries::mir_borrowck, rustc_query_impl::plumbing::QueryCtxt>
            10: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::mir_borrowck
            11: rustc_hir_analysis::collect::type_of::type_of
            12: <std::thread::local::LocalKey<core::cell::Cell<*const ()>>>::with::<rustc_middle::ty::context::tls::enter_context<rustc_query_system::query::plumbing::execute_job_incr<rustc_query_impl::queries::type_of, rustc_query_impl::plumbing::QueryCtxt>::{closure#2}, (rustc_middle::query::erase::Erased<[u8; 8]>, rustc_query_system::dep_graph::graph::DepNodeIndex)>::{closure#0}, (rustc_middle::query::erase::Erased<[u8; 8]>, rustc_query_system::dep_graph::graph::DepNodeIndex)>
            13: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::queries::type_of, rustc_query_impl::plumbing::QueryCtxt>
            14: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::type_of
            15: rustc_hir_analysis::check::check::check_mod_item_types
            16: <std::thread::local::LocalKey<core::cell::Cell<*const ()>>>::with::<rustc_middle::ty::context::tls::enter_context<rustc_query_system::query::plumbing::execute_job_incr<rustc_query_impl::queries::check_mod_item_types, rustc_query_impl::plumbing::QueryCtxt>::{closure#2}, (rustc_middle::query::erase::Erased<[u8; 0]>, rustc_query_system::dep_graph::graph::DepNodeIndex)>::{closure#0}, (rustc_middle::query::erase::Erased<[u8; 0]>, rustc_query_system::dep_graph::graph::DepNodeIndex)>
            17: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::queries::check_mod_item_types, rustc_query_impl::plumbing::QueryCtxt>
            18: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::check_mod_item_types
            19: <rustc_middle::hir::map::Map>::for_each_module::<rustc_hir_analysis::check_crate::{closure#6}::{closure#0}>
            20: rustc_hir_analysis::check_crate
            21: rustc_interface::passes::analysis
            22: <std::thread::local::LocalKey<core::cell::Cell<*const ()>>>::with::<rustc_middle::ty::context::tls::enter_context<rustc_query_system::query::plumbing::execute_job_incr<rustc_query_impl::queries::analysis, rustc_query_impl::plumbing::QueryCtxt>::{closure#2}, (rustc_middle::query::erase::Erased<[u8; 1]>, rustc_query_system::dep_graph::graph::DepNodeIndex)>::{closure#0}, (rustc_middle::query::erase::Erased<[u8; 1]>, rustc_query_system::dep_graph::graph::DepNodeIndex)>
            23: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::queries::analysis, rustc_query_impl::plumbing::QueryCtxt>
            24: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::analysis
            25: <rustc_middle::ty::context::GlobalCtxt>::enter::<rustc_driver_impl::run_compiler::{closure#1}::{closure#2}::{closure#4}, core::result::Result<(), rustc_span::ErrorGuaranteed>>
            26: <rustc_interface::interface::Compiler>::enter::<rustc_driver_impl::run_compiler::{closure#1}::{closure#2}, core::result::Result<core::option::Option<rustc_interface::queries::Linker>, rustc_span::ErrorGuaranteed>>
            27: rustc_span::set_source_map::<core::result::Result<(), rustc_span::ErrorGuaranteed>, rustc_interface::interface::run_compiler<core::result::Result<(), rustc_span::ErrorGuaranteed>, rustc_driver_impl::run_compiler::{closure#1}>::{closure#0}::{closure#0}>
            28: <scoped_tls::ScopedKey<rustc_span::SessionGlobals>>::set::<rustc_interface::interface::run_compiler<core::result::Result<(), rustc_span::ErrorGuaranteed>, rustc_driver_impl::run_compiler::{closure#1}>::{closure#0}, core::result::Result<(), rustc_span::ErrorGuaranteed>>
            29: std::sys_common::backtrace::__rust_begin_short_backtrace::<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#1}>::{closure#0}, core::result::Result<(), rustc_span::ErrorGuaranteed>>::{closure#0}::{closure#0}, core::result::Result<(), rustc_span::ErrorGuaranteed>>
            30: <<std::thread::Builder>::spawn_unchecked_<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#1}>::{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}
            31: <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once
                       at /rustc/b628260df0587ae559253d8640ecb8738d3de613/library/alloc/src/boxed.rs:1962:9
            32: <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once
                       at /rustc/b628260df0587ae559253d8640ecb8738d3de613/library/alloc/src/boxed.rs:1962:9
            33: std::sys::unix::thread::Thread::new::thread_start
                       at /rustc/b628260df0587ae559253d8640ecb8738d3de613/library/std/src/sys/unix/thread.rs:108:17
            34: start_thread
            35: clone3
          

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 1.71.0-nightly (b628260df 2023-04-22) running on x86_64-unknown-linux-gnu

note: compiler flags: --crate-type lib -C embed-bitcode=no -C debuginfo=2 -C linker=clang -C incremental=[REDACTED] -C link-arg=-fuse-ld=/usr/bin/mold

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

query stack during panic:
end of query stack

Found on Zulip: https://rust-lang.zulipchat.com/#narrow/stream/122651-general/topic/RPIT.20on.20recursive.20function/near/352032124

[Jules-Bertholet]

Regressed (from error) in #94081