[ICE] Unresolved HRTB lifetime in APIT

[jackh726]

This ICEs on nightly, but only errors in stable or beta: fn test_argument_position(x: impl for<'a> Tr<'a, Assoc = impl Copy + 'a>) {}

playground

Code

trait Tr<'a> {
	type Assoc;
}
fn test_argument_position(x: impl for<'a> Tr<'a, Assoc = impl Copy + 'a>)  {}
fn main() {}

Backtrace

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

error: internal compiler error: Could not resolve lifetime(HirId { owner: DefId(0:6 ~ playground[24bf]::test_argument_position), local_id: 9 }: 'a) in scope Binder {
                                    lifetimes: {},
                                    next_early_index: 2,
                                    track_lifetime_uses: true,
                                    opaque_type_parent: false,
                                    scope_type: Normal,
                                    hir_id: HirId {
                                        owner: DefId(0:6 ~ playground[24bf]::test_argument_position),
                                        local_id: 11,
                                    },
                                    s: TraitRefBoundary {
                                        s: Binder {
                                            lifetimes: {},
                                            next_early_index: 2,
                                            track_lifetime_uses: false,
                                            opaque_type_parent: true,
                                            scope_type: Normal,
                                            hir_id: HirId {
                                                owner: DefId(0:6 ~ playground[24bf]::test_argument_position),
                                                local_id: 0,
                                            },
                                            s: Root,
                                            allow_late_bound: true,
                                        },
                                    },
                                    allow_late_bound: true,
                                }
 --> src/main.rs:5:70
  |
5 | fn test_argument_position(x: impl for<'a> Tr<'a, Assoc = impl Copy + 'a>)  {}
  |                                                                      ^^
  |
  = note: delayed at compiler/rustc_resolve/src/late/lifetimes.rs:2316:27

error: internal compiler error: unelided lifetime in signature
 --> src/main.rs:5:70
  |
5 | fn test_argument_position(x: impl for<'a> Tr<'a, Assoc = impl Copy + 'a>)  {}
  |                                                                      ^^
  |
  = note: delayed at compiler/rustc_typeck/src/astconv/mod.rs:250:30

thread 'rustc' panicked at 'Box<dyn Any>', compiler/rustc_errors/src/lib.rs:1369:13
stack backtrace:
   0:     0x7f076b75be7d - std::backtrace_rs::backtrace::libunwind::trace::h85cc47332f2b05a9
                               at /rustc/ecd44958e0a21110d09862ee080d95a4ca6c52f8/library/std/src/../../backtrace/src/backtrace/libunwind.rs:93:5
   1:     0x7f076b75be7d - std::backtrace_rs::backtrace::trace_unsynchronized::h822c2fc2b1a1a752
                               at /rustc/ecd44958e0a21110d09862ee080d95a4ca6c52f8/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x7f076b75be7d - std::sys_common::backtrace::_print_fmt::h678c9b8abf6c5083
                               at /rustc/ecd44958e0a21110d09862ee080d95a4ca6c52f8/library/std/src/sys_common/backtrace.rs:66:5
   3:     0x7f076b75be7d - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::h2fb21895faf729c2
                               at /rustc/ecd44958e0a21110d09862ee080d95a4ca6c52f8/library/std/src/sys_common/backtrace.rs:45:22
   4:     0x7f076b7b7afc - core::fmt::write::h6dc4a63f2d3360d8
                               at /rustc/ecd44958e0a21110d09862ee080d95a4ca6c52f8/library/core/src/fmt/mod.rs:1196:17
   5:     0x7f076b74d561 - std::io::Write::write_fmt::h8fe2d520dd3fbf2e
                               at /rustc/ecd44958e0a21110d09862ee080d95a4ca6c52f8/library/std/src/io/mod.rs:1654:15
   6:     0x7f076b75eb95 - std::sys_common::backtrace::_print::h6c3478d5fa62e7d8
                               at /rustc/ecd44958e0a21110d09862ee080d95a4ca6c52f8/library/std/src/sys_common/backtrace.rs:48:5
   7:     0x7f076b75eb95 - std::sys_common::backtrace::print::hd6d4473e0c0113a9
                               at /rustc/ecd44958e0a21110d09862ee080d95a4ca6c52f8/library/std/src/sys_common/backtrace.rs:35:9
   8:     0x7f076b75eb95 - std::panicking::default_hook::{{closure}}::h4dec78d051eecf7c
                               at /rustc/ecd44958e0a21110d09862ee080d95a4ca6c52f8/library/std/src/panicking.rs:295:22
   9:     0x7f076b75e809 - std::panicking::default_hook::hc13b58dcc91e88ba
                               at /rustc/ecd44958e0a21110d09862ee080d95a4ca6c52f8/library/std/src/panicking.rs:314:9
  10:     0x7f076bf20b21 - rustc_driver[d4386f1a79afc323]::DEFAULT_HOOK::{closure#0}::{closure#0}
  11:     0x7f076b75f366 - std::panicking::rust_panic_with_hook::h3dd403ae323eac6a
                               at /rustc/ecd44958e0a21110d09862ee080d95a4ca6c52f8/library/std/src/panicking.rs:702:17
  12:     0x7f076d08c921 - std[d9fedb1e1dbc9663]::panicking::begin_panic::<rustc_errors[b91ec0213766c8bc]::ExplicitBug>::{closure#0}
  13:     0x7f076d08b716 - std[d9fedb1e1dbc9663]::sys_common::backtrace::__rust_end_short_backtrace::<std[d9fedb1e1dbc9663]::panicking::begin_panic<rustc_errors[b91ec0213766c8bc]::ExplicitBug>::{closure#0}, !>
  14:     0x7f076d09d786 - std[d9fedb1e1dbc9663]::panicking::begin_panic::<rustc_errors[b91ec0213766c8bc]::ExplicitBug>
  15:     0x7f076d0a1816 - std[d9fedb1e1dbc9663]::panic::panic_any::<rustc_errors[b91ec0213766c8bc]::ExplicitBug>
  16:     0x7f076e85adcb - <rustc_errors[b91ec0213766c8bc]::HandlerInner as core[9ba3ef39911e8828]::ops::drop::Drop>::drop
  17:     0x7f076dfb2bb8 - core[9ba3ef39911e8828]::ptr::drop_in_place::<rustc_session[93b3d23ec172418c]::parse::ParseSess>
  18:     0x7f076dfb4ec3 - <alloc[4e51958440f9dea6]::rc::Rc<rustc_session[93b3d23ec172418c]::session::Session> as core[9ba3ef39911e8828]::ops::drop::Drop>::drop
  19:     0x7f076dfb197d - core[9ba3ef39911e8828]::ptr::drop_in_place::<rustc_interface[50aa842067ddf2a9]::interface::Compiler>
  20:     0x7f076dfb1124 - rustc_span[5ada1bf86533b524]::with_source_map::<core[9ba3ef39911e8828]::result::Result<(), rustc_errors[b91ec0213766c8bc]::ErrorGuaranteed>, rustc_interface[50aa842067ddf2a9]::interface::create_compiler_and_run<core[9ba3ef39911e8828]::result::Result<(), rustc_errors[b91ec0213766c8bc]::ErrorGuaranteed>, rustc_driver[d4386f1a79afc323]::run_compiler::{closure#1}>::{closure#1}>
  21:     0x7f076df89824 - rustc_interface[50aa842067ddf2a9]::interface::create_compiler_and_run::<core[9ba3ef39911e8828]::result::Result<(), rustc_errors[b91ec0213766c8bc]::ErrorGuaranteed>, rustc_driver[d4386f1a79afc323]::run_compiler::{closure#1}>
  22:     0x7f076df870d2 - <scoped_tls[48edcdfa9356486f]::ScopedKey<rustc_span[5ada1bf86533b524]::SessionGlobals>>::set::<rustc_interface[50aa842067ddf2a9]::interface::run_compiler<core[9ba3ef39911e8828]::result::Result<(), rustc_errors[b91ec0213766c8bc]::ErrorGuaranteed>, rustc_driver[d4386f1a79afc323]::run_compiler::{closure#1}>::{closure#0}, core[9ba3ef39911e8828]::result::Result<(), rustc_errors[b91ec0213766c8bc]::ErrorGuaranteed>>
  23:     0x7f076df9e1ef - std[d9fedb1e1dbc9663]::sys_common::backtrace::__rust_begin_short_backtrace::<rustc_interface[50aa842067ddf2a9]::util::run_in_thread_pool_with_globals<rustc_interface[50aa842067ddf2a9]::interface::run_compiler<core[9ba3ef39911e8828]::result::Result<(), rustc_errors[b91ec0213766c8bc]::ErrorGuaranteed>, rustc_driver[d4386f1a79afc323]::run_compiler::{closure#1}>::{closure#0}, core[9ba3ef39911e8828]::result::Result<(), rustc_errors[b91ec0213766c8bc]::ErrorGuaranteed>>::{closure#0}, core[9ba3ef39911e8828]::result::Result<(), rustc_errors[b91ec0213766c8bc]::ErrorGuaranteed>>
  24:     0x7f076df9e329 - <<std[d9fedb1e1dbc9663]::thread::Builder>::spawn_unchecked_<rustc_interface[50aa842067ddf2a9]::util::run_in_thread_pool_with_globals<rustc_interface[50aa842067ddf2a9]::interface::run_compiler<core[9ba3ef39911e8828]::result::Result<(), rustc_errors[b91ec0213766c8bc]::ErrorGuaranteed>, rustc_driver[d4386f1a79afc323]::run_compiler::{closure#1}>::{closure#0}, core[9ba3ef39911e8828]::result::Result<(), rustc_errors[b91ec0213766c8bc]::ErrorGuaranteed>>::{closure#0}, core[9ba3ef39911e8828]::result::Result<(), rustc_errors[b91ec0213766c8bc]::ErrorGuaranteed>>::{closure#1} as core[9ba3ef39911e8828]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  25:     0x7f076b769273 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h8e61158325523155
                               at /rustc/ecd44958e0a21110d09862ee080d95a4ca6c52f8/library/alloc/src/boxed.rs:1872:9
  26:     0x7f076b769273 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::ha439966d612c01d5
                               at /rustc/ecd44958e0a21110d09862ee080d95a4ca6c52f8/library/alloc/src/boxed.rs:1872:9
  27:     0x7f076b769273 - std::sys::unix::thread::Thread::new::thread_start::hf215f8619fb489d4
                               at /rustc/ecd44958e0a21110d09862ee080d95a4ca6c52f8/library/std/src/sys/unix/thread.rs:108:17
  28:     0x7f076b699609 - start_thread
  29:     0x7f076b5b2163 - clone
  30:                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 (ecd44958e 2022-05-10) running on x86_64-unknown-linux-gnu

note: compiler flags: --crate-type bin -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:
end of query stack

[matthiaskrgr]

This regressed in #95779

searched toolchains 878c7833f6c1ff10e2fd89074e5bd4ef5ff15936 through ec77f252434a532fdb5699ae4f21a3072d211edd


********************************************************************************
Regression in 1ec2c136b35bd4660cba778346f8df7daf2ab173
********************************************************************************

[jackh726]

cc @cjgillot

[cjgillot]

The bug comes from a difference between the old and the new analysis. The old analysis was incorrect in that case: there should not be an error, impl Copy + 'a resolves to the for<'a> lifetime.
I'm not really sure what the correct fix should be.

[jackh726]

Related discussion: https://rust-lang.zulipchat.com/#narrow/stream/245100-t-compiler.2Fwg-prioritization.2Falerts/topic/.2396194.20nested.20RPIT.20and.20HRTB.3A.20unclear.20semantics.20and.20future.20i.E2.80.A6/near/282011425

Correct fix (at least for now) is probably to change this back to an error - along with the case above. After that, correct fix is probably to treat this as a for<'a> (which is done in associated type bounds).

[apiraino]

Assigning priority as discussed in the Zulip thread of the Prioritization Working Group.

@rustbot label -I-prioritize +P-medium