ice: `async fn coroutine return type not an inference variable`

[matthiaskrgr]

auto-reduced (treereduce-rust):

mod first {
    trait Foo {
        async fn foo<'b>(self: &'b Foo<'a>) -> &() {
            self.0
        }
    }
}

original:

// run-rustfix
#![allow(dead_code)]
mod first {
    trait Foo {
    async fn foo<'b>(self: &'b Foo<'a>) -> &() { self.0 }
}
    fn foo<T: Foo>(a: T) {
        a.m(); //~ ERROR no method named `m` found
    }
}
mod second {
    use std::{
    rc::Rc,
    sync::Arc,
    pin::Pin,
};
    trait Bar { fn m(self: Arc<Self>); }
    fn bar(self: Box<Struct<'a>>, f: &u32) {
        b.m(); //~ ERROR no method named `m` found
    }
}

pub fn main() {
    let x: Box<_> = Box::new(X { a: 32 });
    let new_x = x.change();
    assert_eq!(new_x.a, 55);
}

Version information

rustc 1.77.0-nightly (bfd799f1a 2024-01-12)
binary: rustc
commit-hash: bfd799f1a5a86d16e6b8caa2857bcb4aac6e0174
commit-date: 2024-01-12
host: x86_64-unknown-linux-gnu
release: 1.77.0-nightly
LLVM version: 17.0.6

Command:
/home/matthias/.rustup/toolchains/master/bin/rustc

Program output

error[E0670]: `async fn` is not permitted in Rust 2015
 --> /tmp/icemaker_global_tempdir.PQIGPyZRffct/rustc_testrunner_tmpdir_reporting.a6Tk4AGEOF1i/mvce.rs:3:9
  |
3 |         async fn foo<'b>(self: &'b Foo<'a>) -> &() {
  |         ^^^^^ to use `async fn`, switch to Rust 2018 or later
  |
  = help: pass `--edition 2021` to `rustc`
  = note: for more on editions, read https://doc.rust-lang.org/edition-guide

error[E0261]: use of undeclared lifetime name `'a`
 --> /tmp/icemaker_global_tempdir.PQIGPyZRffct/rustc_testrunner_tmpdir_reporting.a6Tk4AGEOF1i/mvce.rs:3:40
  |
3 |         async fn foo<'b>(self: &'b Foo<'a>) -> &() {
  |                                        ^^ undeclared lifetime
  |
  = note: for more information on higher-ranked polymorphism, visit https://doc.rust-lang.org/nomicon/hrtb.html
help: consider making the bound lifetime-generic with a new `'a` lifetime
  |
3 |         async fn foo<'b>(self: &'b for<'a> Foo<'a>) -> &() {
  |                                    +++++++
help: consider introducing lifetime `'a` here
  |
3 |         async fn foo<'a, 'b>(self: &'b Foo<'a>) -> &() {
  |                      +++
help: consider introducing lifetime `'a` here
  |
2 |     trait Foo<'a> {
  |              ++++

error[E0106]: missing lifetime specifier
 --> /tmp/icemaker_global_tempdir.PQIGPyZRffct/rustc_testrunner_tmpdir_reporting.a6Tk4AGEOF1i/mvce.rs:3:48
  |
3 |         async fn foo<'b>(self: &'b Foo<'a>) -> &() {
  |                                -----------     ^ expected named lifetime parameter
  |
  = help: this function's return type contains a borrowed value with an elided lifetime, but the lifetime cannot be derived from the arguments
help: consider using the `'b` lifetime
  |
3 |         async fn foo<'b>(self: &'b Foo<'a>) -> &'b () {
  |                                                 ++

error[E0601]: `main` function not found in crate `mvce`
 --> /tmp/icemaker_global_tempdir.PQIGPyZRffct/rustc_testrunner_tmpdir_reporting.a6Tk4AGEOF1i/mvce.rs:7:2
  |
7 | }
  |  ^ consider adding a `main` function to `/tmp/icemaker_global_tempdir.PQIGPyZRffct/rustc_testrunner_tmpdir_reporting.a6Tk4AGEOF1i/mvce.rs`

warning: trait objects without an explicit `dyn` are deprecated
 --> /tmp/icemaker_global_tempdir.PQIGPyZRffct/rustc_testrunner_tmpdir_reporting.a6Tk4AGEOF1i/mvce.rs:3:36
  |
3 |         async fn foo<'b>(self: &'b Foo<'a>) -> &() {
  |                                    ^^^^^^^
  |
  = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
  = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
  = note: `#[warn(bare_trait_objects)]` on by default
help: use `dyn`
  |
3 |         async fn foo<'b>(self: &'b dyn Foo<'a>) -> &() {
  |                                    +++

error[E0107]: trait takes 0 lifetime arguments but 1 lifetime argument was supplied
 --> /tmp/icemaker_global_tempdir.PQIGPyZRffct/rustc_testrunner_tmpdir_reporting.a6Tk4AGEOF1i/mvce.rs:3:36
  |
3 |         async fn foo<'b>(self: &'b Foo<'a>) -> &() {
  |                                    ^^^---- help: remove these generics
  |                                    |
  |                                    expected 0 lifetime arguments
  |
note: trait defined here, with 0 lifetime parameters
 --> /tmp/icemaker_global_tempdir.PQIGPyZRffct/rustc_testrunner_tmpdir_reporting.a6Tk4AGEOF1i/mvce.rs:2:11
  |
2 |     trait Foo {
  |           ^^^

error: internal compiler error: compiler/rustc_hir_typeck/src/closure.rs:806:18: async fn coroutine return type not an inference variable: impl Future<Output = &'b ()>
 --> /tmp/icemaker_global_tempdir.PQIGPyZRffct/rustc_testrunner_tmpdir_reporting.a6Tk4AGEOF1i/mvce.rs:3:52
  |
3 |           async fn foo<'b>(self: &'b Foo<'a>) -> &() {
  |  ____________________________________________________^
4 | |             self.0
5 | |         }
  | |_________^

thread 'rustc' panicked at /rustc/bfd799f1a5a86d16e6b8caa2857bcb4aac6e0174/compiler/rustc_errors/src/lib.rs:850:41:
Box<dyn Any>
stack backtrace:
   0:     0x7f1e657af7e6 - std::backtrace_rs::backtrace::libunwind::trace::h1bcd2ce8a0b49e2b
                               at /rustc/bfd799f1a5a86d16e6b8caa2857bcb4aac6e0174/library/std/src/../../backtrace/src/backtrace/libunwind.rs:104:5
   1:     0x7f1e657af7e6 - std::backtrace_rs::backtrace::trace_unsynchronized::hec545b0bca077b29
                               at /rustc/bfd799f1a5a86d16e6b8caa2857bcb4aac6e0174/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x7f1e657af7e6 - std::sys_common::backtrace::_print_fmt::hb1dc0973745fe00f
                               at /rustc/bfd799f1a5a86d16e6b8caa2857bcb4aac6e0174/library/std/src/sys_common/backtrace.rs:68:5
   3:     0x7f1e657af7e6 - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::hc0965f21650fbdf2
                               at /rustc/bfd799f1a5a86d16e6b8caa2857bcb4aac6e0174/library/std/src/sys_common/backtrace.rs:44:22
   4:     0x7f1e65801ec0 - core::fmt::rt::Argument::fmt::h0c3fb88d931991e7
                               at /rustc/bfd799f1a5a86d16e6b8caa2857bcb4aac6e0174/library/core/src/fmt/rt.rs:142:9
   5:     0x7f1e65801ec0 - core::fmt::write::h92f7f8a7341f441f
                               at /rustc/bfd799f1a5a86d16e6b8caa2857bcb4aac6e0174/library/core/src/fmt/mod.rs:1120:17
   6:     0x7f1e657a314f - std::io::Write::write_fmt::h107b5956b3204fe7
                               at /rustc/bfd799f1a5a86d16e6b8caa2857bcb4aac6e0174/library/std/src/io/mod.rs:1810:15
   7:     0x7f1e657af5c4 - std::sys_common::backtrace::_print::haa043cdd6fa0fe1b
                               at /rustc/bfd799f1a5a86d16e6b8caa2857bcb4aac6e0174/library/std/src/sys_common/backtrace.rs:47:5
   8:     0x7f1e657af5c4 - std::sys_common::backtrace::print::h47b083459941ac2d
                               at /rustc/bfd799f1a5a86d16e6b8caa2857bcb4aac6e0174/library/std/src/sys_common/backtrace.rs:34:9
   9:     0x7f1e657b2357 - std::panicking::default_hook::{{closure}}::h474e4c3474397153
  10:     0x7f1e657b20b9 - std::panicking::default_hook::h3bc7fb22936a8edd
                               at /rustc/bfd799f1a5a86d16e6b8caa2857bcb4aac6e0174/library/std/src/panicking.rs:292:9
  11:     0x7f1e62553b0c - std[f8082c656c94fd2d]::panicking::update_hook::<alloc[ef2fed1484295005]::boxed::Box<rustc_driver_impl[24914691d489c447]::install_ice_hook::{closure#0}>>::{closure#0}
  12:     0x7f1e657b2aa6 - <alloc::boxed::Box<F,A> as core::ops::function::Fn<Args>>::call::h98798404485c082c
                               at /rustc/bfd799f1a5a86d16e6b8caa2857bcb4aac6e0174/library/alloc/src/boxed.rs:2030:9
  13:     0x7f1e657b2aa6 - std::panicking::rust_panic_with_hook::hbfa459da89788d0f
                               at /rustc/bfd799f1a5a86d16e6b8caa2857bcb4aac6e0174/library/std/src/panicking.rs:785:13
  14:     0x7f1e62585a34 - std[f8082c656c94fd2d]::panicking::begin_panic::<rustc_errors[70acbb675511353e]::ExplicitBug>::{closure#0}
  15:     0x7f1e62582336 - std[f8082c656c94fd2d]::sys_common::backtrace::__rust_end_short_backtrace::<std[f8082c656c94fd2d]::panicking::begin_panic<rustc_errors[70acbb675511353e]::ExplicitBug>::{closure#0}, !>
  16:     0x7f1e62581fa6 - std[f8082c656c94fd2d]::panicking::begin_panic::<rustc_errors[70acbb675511353e]::ExplicitBug>
  17:     0x7f1e625909e1 - <rustc_errors[70acbb675511353e]::diagnostic_builder::BugAbort as rustc_errors[70acbb675511353e]::diagnostic_builder::EmissionGuarantee>::emit_producing_guarantee
  18:     0x7f1e626db65d - rustc_middle[4be5b913d7bf3685]::util::bug::opt_span_bug_fmt::<rustc_span[e31def1030f5178]::span_encoding::Span>::{closure#0}
  19:     0x7f1e626dbb0a - rustc_middle[4be5b913d7bf3685]::ty::context::tls::with_opt::<rustc_middle[4be5b913d7bf3685]::util::bug::opt_span_bug_fmt<rustc_span[e31def1030f5178]::span_encoding::Span>::{closure#0}, !>::{closure#0}
  20:     0x7f1e626ccd58 - rustc_middle[4be5b913d7bf3685]::ty::context::tls::with_context_opt::<rustc_middle[4be5b913d7bf3685]::ty::context::tls::with_opt<rustc_middle[4be5b913d7bf3685]::util::bug::opt_span_bug_fmt<rustc_span[e31def1030f5178]::span_encoding::Span>::{closure#0}, !>::{closure#0}, !>
  21:     0x7f1e618cc9b4 - rustc_middle[4be5b913d7bf3685]::util::bug::span_bug_fmt::<rustc_span[e31def1030f5178]::span_encoding::Span>
  22:     0x7f1e646ddafa - <rustc_hir_typeck[4037b9c3a0b702b2]::fn_ctxt::FnCtxt>::supplied_sig_of_closure
  23:     0x7f1e63edaa56 - <rustc_hir_typeck[4037b9c3a0b702b2]::fn_ctxt::FnCtxt>::check_expr_closure
  24:     0x7f1e642e0299 - <rustc_hir_typeck[4037b9c3a0b702b2]::fn_ctxt::FnCtxt>::check_expr_with_expectation_and_args
  25:     0x7f1e63e67b08 - rustc_hir_typeck[4037b9c3a0b702b2]::check::check_fn
  26:     0x7f1e63ad21b6 - rustc_hir_typeck[4037b9c3a0b702b2]::typeck
  27:     0x7f1e63ad1535 - rustc_query_impl[5a6eb46947cbd595]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[5a6eb46947cbd595]::query_impl::typeck::dynamic_query::{closure#2}::{closure#0}, rustc_middle[4be5b913d7bf3685]::query::erase::Erased<[u8; 8usize]>>
  28:     0x7f1e63ceaab9 - rustc_query_system[8201af163ac5a48f]::query::plumbing::try_execute_query::<rustc_query_impl[5a6eb46947cbd595]::DynamicConfig<rustc_query_system[8201af163ac5a48f]::query::caches::VecCache<rustc_span[e31def1030f5178]::def_id::LocalDefId, rustc_middle[4be5b913d7bf3685]::query::erase::Erased<[u8; 8usize]>>, false, false, false>, rustc_query_impl[5a6eb46947cbd595]::plumbing::QueryCtxt, false>
  29:     0x7f1e63cea750 - rustc_query_impl[5a6eb46947cbd595]::query_impl::typeck::get_query_non_incr::__rust_end_short_backtrace
  30:     0x7f1e6481030b - rustc_hir_analysis[a63d9bfdcc7a8c2c]::collect::type_of::type_of_opaque
  31:     0x7f1e6481011b - rustc_query_impl[5a6eb46947cbd595]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[5a6eb46947cbd595]::query_impl::type_of_opaque::dynamic_query::{closure#2}::{closure#0}, rustc_middle[4be5b913d7bf3685]::query::erase::Erased<[u8; 8usize]>>
  32:     0x7f1e6385f4d4 - rustc_query_system[8201af163ac5a48f]::query::plumbing::try_execute_query::<rustc_query_impl[5a6eb46947cbd595]::DynamicConfig<rustc_query_system[8201af163ac5a48f]::query::caches::DefaultCache<rustc_span[e31def1030f5178]::def_id::DefId, rustc_middle[4be5b913d7bf3685]::query::erase::Erased<[u8; 8usize]>>, false, false, false>, rustc_query_impl[5a6eb46947cbd595]::plumbing::QueryCtxt, false>
  33:     0x7f1e648487a2 - rustc_query_impl[5a6eb46947cbd595]::query_impl::type_of_opaque::get_query_non_incr::__rust_end_short_backtrace
  34:     0x7f1e6385e06e - rustc_middle[4be5b913d7bf3685]::query::plumbing::query_get_at::<rustc_query_system[8201af163ac5a48f]::query::caches::DefaultCache<rustc_span[e31def1030f5178]::def_id::DefId, rustc_middle[4be5b913d7bf3685]::query::erase::Erased<[u8; 8usize]>>>
  35:     0x7f1e61ac6f48 - rustc_hir_analysis[a63d9bfdcc7a8c2c]::collect::type_of::type_of
  36:     0x7f1e63860666 - rustc_query_impl[5a6eb46947cbd595]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[5a6eb46947cbd595]::query_impl::type_of::dynamic_query::{closure#2}::{closure#0}, rustc_middle[4be5b913d7bf3685]::query::erase::Erased<[u8; 8usize]>>
  37:     0x7f1e6385f4d4 - rustc_query_system[8201af163ac5a48f]::query::plumbing::try_execute_query::<rustc_query_impl[5a6eb46947cbd595]::DynamicConfig<rustc_query_system[8201af163ac5a48f]::query::caches::DefaultCache<rustc_span[e31def1030f5178]::def_id::DefId, rustc_middle[4be5b913d7bf3685]::query::erase::Erased<[u8; 8usize]>>, false, false, false>, rustc_query_impl[5a6eb46947cbd595]::plumbing::QueryCtxt, false>
  38:     0x7f1e6385f09d - rustc_query_impl[5a6eb46947cbd595]::query_impl::type_of::get_query_non_incr::__rust_end_short_backtrace
  39:     0x7f1e6385e06e - rustc_middle[4be5b913d7bf3685]::query::plumbing::query_get_at::<rustc_query_system[8201af163ac5a48f]::query::caches::DefaultCache<rustc_span[e31def1030f5178]::def_id::DefId, rustc_middle[4be5b913d7bf3685]::query::erase::Erased<[u8; 8usize]>>>
  40:     0x7f1e643ac0a9 - rustc_hir_analysis[a63d9bfdcc7a8c2c]::check::check::check_item_type
  41:     0x7f1e63f79cd9 - rustc_hir_analysis[a63d9bfdcc7a8c2c]::check::wfcheck::check_well_formed
  42:     0x7f1e63f78b73 - rustc_query_impl[5a6eb46947cbd595]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[5a6eb46947cbd595]::query_impl::check_well_formed::dynamic_query::{closure#2}::{closure#0}, rustc_middle[4be5b913d7bf3685]::query::erase::Erased<[u8; 1usize]>>
  43:     0x7f1e63f78271 - rustc_query_system[8201af163ac5a48f]::query::plumbing::try_execute_query::<rustc_query_impl[5a6eb46947cbd595]::DynamicConfig<rustc_query_system[8201af163ac5a48f]::query::caches::VecCache<rustc_hir[fbff31adfa839dea]::hir_id::OwnerId, rustc_middle[4be5b913d7bf3685]::query::erase::Erased<[u8; 1usize]>>, false, false, false>, rustc_query_impl[5a6eb46947cbd595]::plumbing::QueryCtxt, false>
  44:     0x7f1e63f77fdb - rustc_query_impl[5a6eb46947cbd595]::query_impl::check_well_formed::get_query_non_incr::__rust_end_short_backtrace
  45:     0x7f1e63f75977 - rustc_hir_analysis[a63d9bfdcc7a8c2c]::check::wfcheck::check_mod_type_wf
  46:     0x7f1e63f758bb - rustc_query_impl[5a6eb46947cbd595]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[5a6eb46947cbd595]::query_impl::check_mod_type_wf::dynamic_query::{closure#2}::{closure#0}, rustc_middle[4be5b913d7bf3685]::query::erase::Erased<[u8; 1usize]>>
  47:     0x7f1e63f74a7b - rustc_query_system[8201af163ac5a48f]::query::plumbing::try_execute_query::<rustc_query_impl[5a6eb46947cbd595]::DynamicConfig<rustc_query_system[8201af163ac5a48f]::query::caches::DefaultCache<rustc_span[e31def1030f5178]::def_id::LocalModDefId, rustc_middle[4be5b913d7bf3685]::query::erase::Erased<[u8; 1usize]>>, false, false, false>, rustc_query_impl[5a6eb46947cbd595]::plumbing::QueryCtxt, false>
  48:     0x7f1e63f74813 - rustc_query_impl[5a6eb46947cbd595]::query_impl::check_mod_type_wf::get_query_non_incr::__rust_end_short_backtrace
  49:     0x7f1e63ce7f5a - <rustc_middle[4be5b913d7bf3685]::hir::map::Map>::try_par_for_each_module::<rustc_hir_analysis[a63d9bfdcc7a8c2c]::check_crate::{closure#4}::{closure#0}>::{closure#0}
  50:     0x7f1e63ce8790 - rustc_hir_analysis[a63d9bfdcc7a8c2c]::check_crate
  51:     0x7f1e64419499 - rustc_interface[e8d89524f3b9ea3d]::passes::analysis
  52:     0x7f1e644190df - rustc_query_impl[5a6eb46947cbd595]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[5a6eb46947cbd595]::query_impl::analysis::dynamic_query::{closure#2}::{closure#0}, rustc_middle[4be5b913d7bf3685]::query::erase::Erased<[u8; 1usize]>>
  53:     0x7f1e647d52e4 - rustc_query_system[8201af163ac5a48f]::query::plumbing::try_execute_query::<rustc_query_impl[5a6eb46947cbd595]::DynamicConfig<rustc_query_system[8201af163ac5a48f]::query::caches::SingleCache<rustc_middle[4be5b913d7bf3685]::query::erase::Erased<[u8; 1usize]>>, false, false, false>, rustc_query_impl[5a6eb46947cbd595]::plumbing::QueryCtxt, false>
  54:     0x7f1e647d50d5 - rustc_query_impl[5a6eb46947cbd595]::query_impl::analysis::get_query_non_incr::__rust_end_short_backtrace
  55:     0x7f1e64542808 - rustc_interface[e8d89524f3b9ea3d]::interface::run_compiler::<core[1ed11a116379b956]::result::Result<(), rustc_span[e31def1030f5178]::ErrorGuaranteed>, rustc_driver_impl[24914691d489c447]::run_compiler::{closure#0}>::{closure#0}
  56:     0x7f1e647ef8c6 - std[f8082c656c94fd2d]::sys_common::backtrace::__rust_begin_short_backtrace::<rustc_interface[e8d89524f3b9ea3d]::util::run_in_thread_with_globals<rustc_interface[e8d89524f3b9ea3d]::util::run_in_thread_pool_with_globals<rustc_interface[e8d89524f3b9ea3d]::interface::run_compiler<core[1ed11a116379b956]::result::Result<(), rustc_span[e31def1030f5178]::ErrorGuaranteed>, rustc_driver_impl[24914691d489c447]::run_compiler::{closure#0}>::{closure#0}, core[1ed11a116379b956]::result::Result<(), rustc_span[e31def1030f5178]::ErrorGuaranteed>>::{closure#0}, core[1ed11a116379b956]::result::Result<(), rustc_span[e31def1030f5178]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[1ed11a116379b956]::result::Result<(), rustc_span[e31def1030f5178]::ErrorGuaranteed>>
  57:     0x7f1e647ef6f3 - <<std[f8082c656c94fd2d]::thread::Builder>::spawn_unchecked_<rustc_interface[e8d89524f3b9ea3d]::util::run_in_thread_with_globals<rustc_interface[e8d89524f3b9ea3d]::util::run_in_thread_pool_with_globals<rustc_interface[e8d89524f3b9ea3d]::interface::run_compiler<core[1ed11a116379b956]::result::Result<(), rustc_span[e31def1030f5178]::ErrorGuaranteed>, rustc_driver_impl[24914691d489c447]::run_compiler::{closure#0}>::{closure#0}, core[1ed11a116379b956]::result::Result<(), rustc_span[e31def1030f5178]::ErrorGuaranteed>>::{closure#0}, core[1ed11a116379b956]::result::Result<(), rustc_span[e31def1030f5178]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[1ed11a116379b956]::result::Result<(), rustc_span[e31def1030f5178]::ErrorGuaranteed>>::{closure#1} as core[1ed11a116379b956]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  58:     0x7f1e657bc9d5 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h3db22e8983525486
                               at /rustc/bfd799f1a5a86d16e6b8caa2857bcb4aac6e0174/library/alloc/src/boxed.rs:2016:9
  59:     0x7f1e657bc9d5 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h663b592a11904d0d
                               at /rustc/bfd799f1a5a86d16e6b8caa2857bcb4aac6e0174/library/alloc/src/boxed.rs:2016:9
  60:     0x7f1e657bc9d5 - std::sys::unix::thread::Thread::new::thread_start::h3ab1fb11620916ea
                               at /rustc/bfd799f1a5a86d16e6b8caa2857bcb4aac6e0174/library/std/src/sys/unix/thread.rs:108:17
  61:     0x7f1e5f6749eb - <unknown>
  62:     0x7f1e5f6f87cc - <unknown>
  63:                0x0 - <unknown>

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 1.77.0-nightly (bfd799f1a 2024-01-12) running on x86_64-unknown-linux-gnu

query stack during panic:
#0 [typeck] type-checking `first::Foo::foo`
#1 [type_of_opaque] computing type of opaque `first::Foo::foo::{opaque#0}`
#2 [type_of] computing type of `first::Foo::foo::{opaque#0}`
#3 [check_well_formed] checking that `first::Foo::foo::{opaque#0}` is well-formed
#4 [check_mod_type_wf] checking that types are well-formed in module `first`
#5 [analysis] running analysis passes on this crate
end of query stack
error: aborting due to 6 previous errors; 1 warning emitted

Some errors have detailed explanations: E0106, E0107, E0261, E0601, E0670.
For more information about an error, try `rustc --explain E0106`.

[fmease]

Also ices in Rust 2021 in case anybody was wondering. Further reduced:

trait Foo {
    async fn foo<'a>(self: &'a Foo) -> &'a () {
        self.0
    }
}

[fmease]

I don't have time to do a bisection but I presume that it regressed in #119148. (see below)

[matthiaskrgr]

It's #117449 of course 🙃