ICE (feature(type_alias_impl_trait)): self.scc_universes[scc] == ty::UniverseIndex::ROOT', compiler/rustc_borrowck/src/region_infer/mod.rs:721:9

[gendx]

Code

#![feature(type_alias_impl_trait)]

use std::future::Future;

struct Foo;

type FutBool<'a> = impl 'a + Future<Output = bool>;

impl Foo {
    async fn operation(&mut self) -> bool {
        unimplemented!()
    }

    async fn indirect(&mut self) {
        self.retry_loop(Foo::operation).await
    }

    async fn retry_loop<F>(&mut self, mut f: F)
    where
        for<'any> F: FnMut(&'any mut Foo) -> FutBool<'any>,
    {
        loop {
            if f(self).await {
                return;
            }
        }
    }
}

Meta

Using the Rust Playground.

note: rustc 1.66.0-nightly (dcb376115 2022-10-20) 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

Error output

   Compiling playground v0.0.1 (/playground)
thread 'rustc' panicked at 'assertion failed: self.scc_universes[scc] == ty::UniverseIndex::ROOT', compiler/rustc_borrowck/src/region_infer/mod.rs:721:9

stack backtrace: <omitted, see below>

error: internal compiler error: unexpected panic

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 1.66.0-nightly (dcb376115 2022-10-20) 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 `<impl at src/lib.rs:9:1: 9:9>::indirect::{closure#0}`
#1 [mir_borrowck] borrow-checking `<impl at src/lib.rs:9:1: 9:9>::indirect`
#2 [type_of] computing type of `FutBool::{opaque#0}`
#3 [check_mod_item_types] checking item types in top-level module
#4 [analysis] running analysis passes on this crate
end of query stack
error: could not compile `playground`

Backtrace

stack backtrace:
   0:     0x7f447d92c6e0 - std::backtrace_rs::backtrace::libunwind::trace::h8a97a876471793dd
                               at /rustc/dcb376115066d111dbf5f13d5ac2a2dbe8c12add/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   1:     0x7f447d92c6e0 - std::backtrace_rs::backtrace::trace_unsynchronized::h9cfb1ead53ce6391
                               at /rustc/dcb376115066d111dbf5f13d5ac2a2dbe8c12add/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x7f447d92c6e0 - std::sys_common::backtrace::_print_fmt::h7e2b375eb8fa2a0f
                               at /rustc/dcb376115066d111dbf5f13d5ac2a2dbe8c12add/library/std/src/sys_common/backtrace.rs:65:5
   3:     0x7f447d92c6e0 - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::h328fac798ac4d78b
                               at /rustc/dcb376115066d111dbf5f13d5ac2a2dbe8c12add/library/std/src/sys_common/backtrace.rs:44:22
   4:     0x7f447d9885fe - core::fmt::write::h9918c5d46fb26a95
                               at /rustc/dcb376115066d111dbf5f13d5ac2a2dbe8c12add/library/core/src/fmt/mod.rs:1209:17
   5:     0x7f447d91c855 - std::io::Write::write_fmt::h8bdef35768df65fb
                               at /rustc/dcb376115066d111dbf5f13d5ac2a2dbe8c12add/library/std/src/io/mod.rs:1682:15
   6:     0x7f447d92c4a5 - std::sys_common::backtrace::_print::h61bb89f8f9c96b43
                               at /rustc/dcb376115066d111dbf5f13d5ac2a2dbe8c12add/library/std/src/sys_common/backtrace.rs:47:5
   7:     0x7f447d92c4a5 - std::sys_common::backtrace::print::h53e2d871c27ec697
                               at /rustc/dcb376115066d111dbf5f13d5ac2a2dbe8c12add/library/std/src/sys_common/backtrace.rs:34:9
   8:     0x7f447d92f2af - std::panicking::default_hook::{{closure}}::hf026ee6cf2eeddf9
                               at /rustc/dcb376115066d111dbf5f13d5ac2a2dbe8c12add/library/std/src/panicking.rs:267:22
   9:     0x7f447d92efea - std::panicking::default_hook::hd5cb312341f39aef
                               at /rustc/dcb376115066d111dbf5f13d5ac2a2dbe8c12add/library/std/src/panicking.rs:286:9
  10:     0x7f4480252064 - <rustc_driver[dee52b203546d4b9]::DEFAULT_HOOK::{closure#0}::{closure#0} as core[1f8c2a04cb6cf969]::ops::function::FnOnce<(&core[1f8c2a04cb6cf969]::panic::panic_info::PanicInfo,)>>::call_once::{shim:vtable#0}
  11:     0x7f447d92fad9 - <alloc::boxed::Box<F,A> as core::ops::function::Fn<Args>>::call::h31051551973288af
                               at /rustc/dcb376115066d111dbf5f13d5ac2a2dbe8c12add/library/alloc/src/boxed.rs:2001:9
  12:     0x7f447d92fad9 - std::panicking::rust_panic_with_hook::h947adac41cfe0ba4
                               at /rustc/dcb376115066d111dbf5f13d5ac2a2dbe8c12add/library/std/src/panicking.rs:692:13
  13:     0x7f447d92f811 - std::panicking::begin_panic_handler::{{closure}}::h041150cce8779853
                               at /rustc/dcb376115066d111dbf5f13d5ac2a2dbe8c12add/library/std/src/panicking.rs:577:13
  14:     0x7f447d92cb8c - std::sys_common::backtrace::__rust_end_short_backtrace::he8e354ca27e9339b
                               at /rustc/dcb376115066d111dbf5f13d5ac2a2dbe8c12add/library/std/src/sys_common/backtrace.rs:137:18
  15:     0x7f447d92f572 - rust_begin_unwind
                               at /rustc/dcb376115066d111dbf5f13d5ac2a2dbe8c12add/library/std/src/panicking.rs:575:5
  16:     0x7f447d984fe3 - core::panicking::panic_fmt::h0a6a176ea99bdf45
                               at /rustc/dcb376115066d111dbf5f13d5ac2a2dbe8c12add/library/core/src/panicking.rs:65:14
  17:     0x7f447d9850bd - core::panicking::panic::hf246f345ecb873f3
                               at /rustc/dcb376115066d111dbf5f13d5ac2a2dbe8c12add/library/core/src/panicking.rs:115:5
  18:     0x7f447f1662e4 - <rustc_borrowck[42f65ce1f29278a6]::region_infer::RegionInferenceContext>::solve
  19:     0x7f447f10636d - rustc_borrowck[42f65ce1f29278a6]::nll::compute_regions
  20:     0x7f447f0d9998 - rustc_borrowck[42f65ce1f29278a6]::do_mir_borrowck
  21:     0x7f447f0d82c0 - rustc_borrowck[42f65ce1f29278a6]::mir_borrowck
  22:     0x7f447f0d7c51 - <rustc_borrowck[42f65ce1f29278a6]::provide::{closure#0} as core[1f8c2a04cb6cf969]::ops::function::FnOnce<(rustc_middle[989ec2019b2ab48d]::ty::context::TyCtxt, rustc_span[e83a3af72256ca7e]::def_id::LocalDefId)>>::call_once
  23:     0x7f447f6cb765 - rustc_query_system[661881e0d67edf5]::query::plumbing::try_execute_query::<rustc_query_impl[ea081be71f8b839d]::plumbing::QueryCtxt, rustc_query_system[661881e0d67edf5]::query::caches::DefaultCache<rustc_span[e83a3af72256ca7e]::def_id::LocalDefId, &rustc_middle[989ec2019b2ab48d]::mir::query::BorrowCheckResult>>
  24:     0x7f44801206ee - <rustc_query_impl[ea081be71f8b839d]::Queries as rustc_middle[989ec2019b2ab48d]::ty::query::QueryEngine>::mir_borrowck
  25:     0x7f447f1c64e8 - <rustc_borrowck[42f65ce1f29278a6]::type_check::TypeChecker>::prove_closure_bounds
  26:     0x7f447f1a3677 - <rustc_borrowck[42f65ce1f29278a6]::type_check::TypeChecker>::typeck_mir
  27:     0x7f447f114ab1 - rustc_borrowck[42f65ce1f29278a6]::type_check::type_check
  28:     0x7f447f106018 - rustc_borrowck[42f65ce1f29278a6]::nll::compute_regions
  29:     0x7f447f0d9998 - rustc_borrowck[42f65ce1f29278a6]::do_mir_borrowck
  30:     0x7f447f0d82c0 - rustc_borrowck[42f65ce1f29278a6]::mir_borrowck
  31:     0x7f447f0d7c51 - <rustc_borrowck[42f65ce1f29278a6]::provide::{closure#0} as core[1f8c2a04cb6cf969]::ops::function::FnOnce<(rustc_middle[989ec2019b2ab48d]::ty::context::TyCtxt, rustc_span[e83a3af72256ca7e]::def_id::LocalDefId)>>::call_once
  32:     0x7f447f6cb765 - rustc_query_system[661881e0d67edf5]::query::plumbing::try_execute_query::<rustc_query_impl[ea081be71f8b839d]::plumbing::QueryCtxt, rustc_query_system[661881e0d67edf5]::query::caches::DefaultCache<rustc_span[e83a3af72256ca7e]::def_id::LocalDefId, &rustc_middle[989ec2019b2ab48d]::mir::query::BorrowCheckResult>>
  33:     0x7f44801206ee - <rustc_query_impl[ea081be71f8b839d]::Queries as rustc_middle[989ec2019b2ab48d]::ty::query::QueryEngine>::mir_borrowck
  34:     0x7f44804b4d7d - <rustc_hir_analysis[1b95098e02ece987]::collect::type_of::find_opaque_ty_constraints_for_tait::ConstraintLocator>::check
  35:     0x7f44804adc91 - <rustc_hir_analysis[1b95098e02ece987]::collect::type_of::find_opaque_ty_constraints_for_tait::ConstraintLocator as rustc_hir[be644558139ea832]::intravisit::Visitor>::visit_nested_impl_item
  36:     0x7f44804f5135 - rustc_hir[be644558139ea832]::intravisit::walk_item::<rustc_hir_analysis[1b95098e02ece987]::collect::type_of::find_opaque_ty_constraints_for_tait::ConstraintLocator>
  37:     0x7f44804adbac - <rustc_hir_analysis[1b95098e02ece987]::collect::type_of::find_opaque_ty_constraints_for_tait::ConstraintLocator as rustc_hir[be644558139ea832]::intravisit::Visitor>::visit_nested_item
  38:     0x7f44804f1407 - rustc_hir[be644558139ea832]::intravisit::walk_mod::<rustc_hir_analysis[1b95098e02ece987]::collect::type_of::find_opaque_ty_constraints_for_tait::ConstraintLocator>
  39:     0x7f44804b4441 - rustc_hir_analysis[1b95098e02ece987]::collect::type_of::find_opaque_ty_constraints_for_tait
  40:     0x7f447fedc7e3 - rustc_hir_analysis[1b95098e02ece987]::collect::type_of::type_of
  41:     0x7f447f6f2fcc - rustc_query_system[661881e0d67edf5]::query::plumbing::get_query::<rustc_query_impl[ea081be71f8b839d]::queries::type_of, rustc_query_impl[ea081be71f8b839d]::plumbing::QueryCtxt>
  42:     0x7f447f82b62c - rustc_hir_analysis[1b95098e02ece987]::check::check::check_mod_item_types
  43:     0x7f447f8c1075 - rustc_query_system[661881e0d67edf5]::query::plumbing::try_execute_query::<rustc_query_impl[ea081be71f8b839d]::plumbing::QueryCtxt, rustc_query_system[661881e0d67edf5]::query::caches::DefaultCache<rustc_span[e83a3af72256ca7e]::def_id::LocalDefId, ()>>
  44:     0x7f447fc77d69 - rustc_query_system[661881e0d67edf5]::query::plumbing::get_query::<rustc_query_impl[ea081be71f8b839d]::queries::check_mod_item_types, rustc_query_impl[ea081be71f8b839d]::plumbing::QueryCtxt>
  45:     0x7f447ff3f4fc - <rustc_middle[989ec2019b2ab48d]::hir::map::Map>::for_each_module::<rustc_hir_analysis[1b95098e02ece987]::check_crate::{closure#6}::{closure#0}>
  46:     0x7f447fc3edf5 - rustc_hir_analysis[1b95098e02ece987]::check_crate
  47:     0x7f447fc3e927 - rustc_interface[f12b024add2f54c5]::passes::analysis
  48:     0x7f447ffe6204 - rustc_query_system[661881e0d67edf5]::query::plumbing::try_execute_query::<rustc_query_impl[ea081be71f8b839d]::plumbing::QueryCtxt, rustc_query_system[661881e0d67edf5]::query::caches::DefaultCache<(), core[1f8c2a04cb6cf969]::result::Result<(), rustc_errors[d53503ea0d0ac288]::ErrorGuaranteed>>>
  49:     0x7f447ffe5f37 - rustc_query_system[661881e0d67edf5]::query::plumbing::get_query::<rustc_query_impl[ea081be71f8b839d]::queries::analysis, rustc_query_impl[ea081be71f8b839d]::plumbing::QueryCtxt>
  50:     0x7f447efac214 - <rustc_interface[f12b024add2f54c5]::passes::QueryContext>::enter::<rustc_driver[dee52b203546d4b9]::run_compiler::{closure#1}::{closure#2}::{closure#3}, core[1f8c2a04cb6cf969]::result::Result<(), rustc_errors[d53503ea0d0ac288]::ErrorGuaranteed>>
  51:     0x7f447efa8746 - <rustc_interface[f12b024add2f54c5]::interface::Compiler>::enter::<rustc_driver[dee52b203546d4b9]::run_compiler::{closure#1}::{closure#2}, core[1f8c2a04cb6cf969]::result::Result<core[1f8c2a04cb6cf969]::option::Option<rustc_interface[f12b024add2f54c5]::queries::Linker>, rustc_errors[d53503ea0d0ac288]::ErrorGuaranteed>>
  52:     0x7f447ef9ffcc - rustc_span[e83a3af72256ca7e]::with_source_map::<core[1f8c2a04cb6cf969]::result::Result<(), rustc_errors[d53503ea0d0ac288]::ErrorGuaranteed>, rustc_interface[f12b024add2f54c5]::interface::run_compiler<core[1f8c2a04cb6cf969]::result::Result<(), rustc_errors[d53503ea0d0ac288]::ErrorGuaranteed>, rustc_driver[dee52b203546d4b9]::run_compiler::{closure#1}>::{closure#0}::{closure#1}>
  53:     0x7f447ef9f992 - <scoped_tls[97f16809030deaad]::ScopedKey<rustc_span[e83a3af72256ca7e]::SessionGlobals>>::set::<rustc_interface[f12b024add2f54c5]::interface::run_compiler<core[1f8c2a04cb6cf969]::result::Result<(), rustc_errors[d53503ea0d0ac288]::ErrorGuaranteed>, rustc_driver[dee52b203546d4b9]::run_compiler::{closure#1}>::{closure#0}, core[1f8c2a04cb6cf969]::result::Result<(), rustc_errors[d53503ea0d0ac288]::ErrorGuaranteed>>
  54:     0x7f447ef9e0bf - std[a715974fba7b1ef7]::sys_common::backtrace::__rust_begin_short_backtrace::<rustc_interface[f12b024add2f54c5]::util::run_in_thread_pool_with_globals<rustc_interface[f12b024add2f54c5]::interface::run_compiler<core[1f8c2a04cb6cf969]::result::Result<(), rustc_errors[d53503ea0d0ac288]::ErrorGuaranteed>, rustc_driver[dee52b203546d4b9]::run_compiler::{closure#1}>::{closure#0}, core[1f8c2a04cb6cf969]::result::Result<(), rustc_errors[d53503ea0d0ac288]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[1f8c2a04cb6cf969]::result::Result<(), rustc_errors[d53503ea0d0ac288]::ErrorGuaranteed>>
  55:     0x7f447ef9df2f - <<std[a715974fba7b1ef7]::thread::Builder>::spawn_unchecked_<rustc_interface[f12b024add2f54c5]::util::run_in_thread_pool_with_globals<rustc_interface[f12b024add2f54c5]::interface::run_compiler<core[1f8c2a04cb6cf969]::result::Result<(), rustc_errors[d53503ea0d0ac288]::ErrorGuaranteed>, rustc_driver[dee52b203546d4b9]::run_compiler::{closure#1}>::{closure#0}, core[1f8c2a04cb6cf969]::result::Result<(), rustc_errors[d53503ea0d0ac288]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[1f8c2a04cb6cf969]::result::Result<(), rustc_errors[d53503ea0d0ac288]::ErrorGuaranteed>>::{closure#1} as core[1f8c2a04cb6cf969]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  56:     0x7f447d9395f3 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::he83788182cfe83e3
                               at /rustc/dcb376115066d111dbf5f13d5ac2a2dbe8c12add/library/alloc/src/boxed.rs:1987:9
  57:     0x7f447d9395f3 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::hae7c5d9eef577dff
                               at /rustc/dcb376115066d111dbf5f13d5ac2a2dbe8c12add/library/alloc/src/boxed.rs:1987:9
  58:     0x7f447d9395f3 - std::sys::unix::thread::Thread::new::thread_start::h3a23096bb91d75fc
                               at /rustc/dcb376115066d111dbf5f13d5ac2a2dbe8c12add/library/std/src/sys/unix/thread.rs:108:17
  59:     0x7f447d80b609 - start_thread
  60:     0x7f447d72e133 - clone
  61:                0x0 - <unknown>

[gendx]

This code was previously published as part of this blog post in December 2020: https://gendignoux.com/blog/2020/12/17/rust-async-type-system-limits.html.
I uploaded it on the Rust Playground back then (see the blog post links) and don't remember an ICE at the time.

Minimized example:

#![feature(type_alias_impl_trait)]

use std::future::Future;

type FutNothing<'a> = impl 'a + Future<Output = ()>;

async fn operation(x: &mut ()) -> () {
    ()
}

async fn indirect() {
    call(operation).await
}

async fn call<F>(mut f: F)
where
    for<'any> F: FnMut(&'any mut ()) -> FutNothing<'any>,
{
    f(&mut ()).await
}

[Rageking8]

@rustbot label +F-type_alias_impl_trait

[matthiaskrgr]

See also https://github.com/rust-lang/rust/issues?q=is%3Aissue+is%3Aopen+%22self.scc_universes%5Bscc%5D+%3D%3D+ty%3A%3AUniverseIndex%3A%3AROOT%22 / #97099 (probably duplicate)

[aliemjay]

I confirm this is a duplicate of #97099, which should be fixed by #100503. This can be closed as such!