ICE: assertion failed: self.scc_universes[scc] == ty::UniverseIndex::ROOT

[matthiaskrgr]

Code

#![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
}

Meta

rustc --version --verbose:

<version>

required flags: --edition=2021 --crate-type lib

Nightly rustc 1.69.0-nightly (fdbc4329c 2023-02-22)

error: unconstrained opaque type
 --> 103348.rs:5:23
  |
5 | type FutNothing<'a> = impl 'a + Future<Output = ()>;
  |                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = note: `FutNothing` must be used in combination with a concrete type within the same module

master rustc rustc 1.69.0-nightly (07c993eba 2023-02-23):

Backtrace

thread 'rustc' panicked at 'assertion failed: self.scc_universes[scc] == ty::UniverseIndex::ROOT', compiler/rustc_borrowck/src/region_infer/mod.rs:792:9
stack backtrace:
   0:     0x7f38a316aaba - std::backtrace_rs::backtrace::libunwind::trace::h0cd32959c646dd58
                               at /rustc/07c993eba8b76eae497e98433ae075b00f01be10/library/std/src/../../backtrace/src/backtrace/libunwind.rs:93:5
   1:     0x7f38a316aaba - std::backtrace_rs::backtrace::trace_unsynchronized::h3b2629401c061fcd
                               at /rustc/07c993eba8b76eae497e98433ae075b00f01be10/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x7f38a316aaba - std::sys_common::backtrace::_print_fmt::h39e74da7196fd373
                               at /rustc/07c993eba8b76eae497e98433ae075b00f01be10/library/std/src/sys_common/backtrace.rs:65:5
   3:     0x7f38a316aaba - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::h8078aeef1fb809f3
                               at /rustc/07c993eba8b76eae497e98433ae075b00f01be10/library/std/src/sys_common/backtrace.rs:44:22
   4:     0x7f38a31caa3e - core::fmt::write::hfc052c4fbedc81c6
                               at /rustc/07c993eba8b76eae497e98433ae075b00f01be10/library/core/src/fmt/mod.rs:1232:17
   5:     0x7f38a315ae65 - std::io::Write::write_fmt::h1de78f6bbfa1f9b4
                               at /rustc/07c993eba8b76eae497e98433ae075b00f01be10/library/std/src/io/mod.rs:1684:15
   6:     0x7f38a316a885 - std::sys_common::backtrace::_print::hed82c65090f5ecac
                               at /rustc/07c993eba8b76eae497e98433ae075b00f01be10/library/std/src/sys_common/backtrace.rs:47:5
   7:     0x7f38a316a885 - std::sys_common::backtrace::print::ha75a593988590c58
                               at /rustc/07c993eba8b76eae497e98433ae075b00f01be10/library/std/src/sys_common/backtrace.rs:34:9
   8:     0x7f38a316d5ff - std::panicking::default_hook::{{closure}}::h889859cf66b4c9e0
                               at /rustc/07c993eba8b76eae497e98433ae075b00f01be10/library/std/src/panicking.rs:271:22
   9:     0x7f38a316d33b - std::panicking::default_hook::h880efa6ec073db9c
                               at /rustc/07c993eba8b76eae497e98433ae075b00f01be10/library/std/src/panicking.rs:290:9
  10:     0x7f38a646b555 - rustc_driver_impl[f83b883832371c75]::DEFAULT_HOOK::{closure#0}::{closure#0}
  11:     0x7f38a316de3d - <alloc::boxed::Box<F,A> as core::ops::function::Fn<Args>>::call::h1b7815fffd467b2d
                               at /rustc/07c993eba8b76eae497e98433ae075b00f01be10/library/alloc/src/boxed.rs:2002:9
  12:     0x7f38a316de3d - std::panicking::rust_panic_with_hook::h4e7f28681abccfd5
                               at /rustc/07c993eba8b76eae497e98433ae075b00f01be10/library/std/src/panicking.rs:696:13
  13:     0x7f38a316db72 - std::panicking::begin_panic_handler::{{closure}}::h90911033b946dbe6
                               at /rustc/07c993eba8b76eae497e98433ae075b00f01be10/library/std/src/panicking.rs:581:13
  14:     0x7f38a316af26 - std::sys_common::backtrace::__rust_end_short_backtrace::h798238d1ce7e9895
                               at /rustc/07c993eba8b76eae497e98433ae075b00f01be10/library/std/src/sys_common/backtrace.rs:137:18
  15:     0x7f38a316d8c2 - rust_begin_unwind
                               at /rustc/07c993eba8b76eae497e98433ae075b00f01be10/library/std/src/panicking.rs:579:5
  16:     0x7f38a31c73e3 - core::panicking::panic_fmt::h24144ffb3f3163ea
                               at /rustc/07c993eba8b76eae497e98433ae075b00f01be10/library/core/src/panicking.rs:64:14
  17:     0x7f38a31c747d - core::panicking::panic::h2a2cd64c1c1612ff
                               at /rustc/07c993eba8b76eae497e98433ae075b00f01be10/library/core/src/panicking.rs:114:5
  18:     0x7f38a53bc3f9 - <rustc_borrowck[e32dba551d3cd843]::region_infer::RegionInferenceContext>::solve
  19:     0x7f38a537ada6 - rustc_borrowck[e32dba551d3cd843]::nll::compute_regions
  20:     0x7f38a535d42c - rustc_borrowck[e32dba551d3cd843]::do_mir_borrowck
  21:     0x7f38a534ada3 - rustc_borrowck[e32dba551d3cd843]::mir_borrowck
  22:     0x7f38a4dc50ab - rustc_query_system[5752648da2a9c81a]::query::plumbing::try_execute_query::<rustc_query_impl[5767a176057dc243]::queries::mir_borrowck, rustc_query_impl[5767a176057dc243]::plumbing::QueryCtxt>
  23:     0x7f38a5e7451d - <rustc_query_impl[5767a176057dc243]::Queries as rustc_middle[48afdec4b3d5af25]::ty::query::QueryEngine>::mir_borrowck
  24:     0x7f38a544760f - <rustc_borrowck[e32dba551d3cd843]::type_check::TypeChecker>::prove_closure_bounds
  25:     0x7f38a5425cc8 - <rustc_borrowck[e32dba551d3cd843]::type_check::TypeChecker>::typeck_mir
  26:     0x7f38a538e558 - rustc_borrowck[e32dba551d3cd843]::type_check::type_check
  27:     0x7f38a537a9c5 - rustc_borrowck[e32dba551d3cd843]::nll::compute_regions
  28:     0x7f38a535d42c - rustc_borrowck[e32dba551d3cd843]::do_mir_borrowck
  29:     0x7f38a534ada3 - rustc_borrowck[e32dba551d3cd843]::mir_borrowck
  30:     0x7f38a4dc50ab - rustc_query_system[5752648da2a9c81a]::query::plumbing::try_execute_query::<rustc_query_impl[5767a176057dc243]::queries::mir_borrowck, rustc_query_impl[5767a176057dc243]::plumbing::QueryCtxt>
  31:     0x7f38a5e7451d - <rustc_query_impl[5767a176057dc243]::Queries as rustc_middle[48afdec4b3d5af25]::ty::query::QueryEngine>::mir_borrowck
  32:     0x7f38a65f7491 - <rustc_hir_analysis[3040e81d56faed42]::collect::type_of::find_opaque_ty_constraints_for_tait::ConstraintLocator>::check
  33:     0x7f38a65f4352 - <rustc_hir_analysis[3040e81d56faed42]::collect::type_of::find_opaque_ty_constraints_for_tait::ConstraintLocator as rustc_hir[ce80dd10cd19e57d]::intravisit::Visitor>::visit_nested_item
  34:     0x7f38a65ca9b8 - rustc_hir[ce80dd10cd19e57d]::intravisit::walk_mod::<rustc_hir_analysis[3040e81d56faed42]::collect::type_of::find_opaque_ty_constraints_for_tait::ConstraintLocator>
  35:     0x7f38a65f6bc1 - rustc_hir_analysis[3040e81d56faed42]::collect::type_of::find_opaque_ty_constraints_for_tait
  36:     0x7f38a5ae41f9 - rustc_hir_analysis[3040e81d56faed42]::collect::type_of::type_of
  37:     0x7f38a4ede91e - rustc_query_system[5752648da2a9c81a]::query::plumbing::get_query::<rustc_query_impl[5767a176057dc243]::queries::type_of, rustc_query_impl[5767a176057dc243]::plumbing::QueryCtxt, rustc_middle[48afdec4b3d5af25]::dep_graph::dep_node::DepKind>
  38:     0x7f38a4fc9f78 - rustc_hir_analysis[3040e81d56faed42]::check::check::check_mod_item_types
  39:     0x7f38a5a562bf - rustc_query_system[5752648da2a9c81a]::query::plumbing::try_execute_query::<rustc_query_impl[5767a176057dc243]::queries::check_mod_item_types, rustc_query_impl[5767a176057dc243]::plumbing::QueryCtxt>
  40:     0x7f38a5e73b0d - <rustc_query_impl[5767a176057dc243]::Queries as rustc_middle[48afdec4b3d5af25]::ty::query::QueryEngine>::check_mod_item_types
  41:     0x7f38a49dbaf7 - <rustc_session[c35ef6b175fc9185]::session::Session>::time::<(), rustc_hir_analysis[3040e81d56faed42]::check_crate::{closure#6}>
  42:     0x7f38a49d95a8 - rustc_hir_analysis[3040e81d56faed42]::check_crate
  43:     0x7f38a49ceef2 - rustc_interface[fa0b2b03ae23a7ba]::passes::analysis
  44:     0x7f38a5c8a672 - rustc_query_system[5752648da2a9c81a]::query::plumbing::try_execute_query::<rustc_query_impl[5767a176057dc243]::queries::analysis, rustc_query_impl[5767a176057dc243]::plumbing::QueryCtxt>
  45:     0x7f38a5e6d75a - <rustc_query_impl[5767a176057dc243]::Queries as rustc_middle[48afdec4b3d5af25]::ty::query::QueryEngine>::analysis
  46:     0x7f38a5ada266 - <rustc_middle[48afdec4b3d5af25]::ty::context::GlobalCtxt>::enter::<rustc_driver_impl[f83b883832371c75]::run_compiler::{closure#1}::{closure#2}::{closure#4}, core[5b2b83b4efe70cd5]::result::Result<(), rustc_errors[6785960a74f5dba1]::ErrorGuaranteed>>
  47:     0x7f38a56e194c - <rustc_interface[fa0b2b03ae23a7ba]::interface::Compiler>::enter::<rustc_driver_impl[f83b883832371c75]::run_compiler::{closure#1}::{closure#2}, core[5b2b83b4efe70cd5]::result::Result<core[5b2b83b4efe70cd5]::option::Option<rustc_interface[fa0b2b03ae23a7ba]::queries::Linker>, rustc_errors[6785960a74f5dba1]::ErrorGuaranteed>>
  48:     0x7f38a56dfa24 - rustc_span[da5d5abcbe0cb70f]::with_source_map::<core[5b2b83b4efe70cd5]::result::Result<(), rustc_errors[6785960a74f5dba1]::ErrorGuaranteed>, rustc_interface[fa0b2b03ae23a7ba]::interface::run_compiler<core[5b2b83b4efe70cd5]::result::Result<(), rustc_errors[6785960a74f5dba1]::ErrorGuaranteed>, rustc_driver_impl[f83b883832371c75]::run_compiler::{closure#1}>::{closure#0}::{closure#0}>
  49:     0x7f38a56def8c - std[195e6cd746373230]::sys_common::backtrace::__rust_begin_short_backtrace::<rustc_interface[fa0b2b03ae23a7ba]::util::run_in_thread_pool_with_globals<rustc_interface[fa0b2b03ae23a7ba]::interface::run_compiler<core[5b2b83b4efe70cd5]::result::Result<(), rustc_errors[6785960a74f5dba1]::ErrorGuaranteed>, rustc_driver_impl[f83b883832371c75]::run_compiler::{closure#1}>::{closure#0}, core[5b2b83b4efe70cd5]::result::Result<(), rustc_errors[6785960a74f5dba1]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[5b2b83b4efe70cd5]::result::Result<(), rustc_errors[6785960a74f5dba1]::ErrorGuaranteed>>
  50:     0x7f38a56de9ba - <<std[195e6cd746373230]::thread::Builder>::spawn_unchecked_<rustc_interface[fa0b2b03ae23a7ba]::util::run_in_thread_pool_with_globals<rustc_interface[fa0b2b03ae23a7ba]::interface::run_compiler<core[5b2b83b4efe70cd5]::result::Result<(), rustc_errors[6785960a74f5dba1]::ErrorGuaranteed>, rustc_driver_impl[f83b883832371c75]::run_compiler::{closure#1}>::{closure#0}, core[5b2b83b4efe70cd5]::result::Result<(), rustc_errors[6785960a74f5dba1]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[5b2b83b4efe70cd5]::result::Result<(), rustc_errors[6785960a74f5dba1]::ErrorGuaranteed>>::{closure#1} as core[5b2b83b4efe70cd5]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  51:     0x7f38a3177cc3 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h533fa800d0f50b92
                               at /rustc/07c993eba8b76eae497e98433ae075b00f01be10/library/alloc/src/boxed.rs:1988:9
  52:     0x7f38a3177cc3 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h4ed7863a7d2ef51a
                               at /rustc/07c993eba8b76eae497e98433ae075b00f01be10/library/alloc/src/boxed.rs:1988:9
  53:     0x7f38a3177cc3 - std::sys::unix::thread::Thread::new::thread_start::h975090723601c6b9
                               at /rustc/07c993eba8b76eae497e98433ae075b00f01be10/library/std/src/sys/unix/thread.rs:108:17
  54:     0x7f38a2f07bb5 - <unknown>
  55:     0x7f38a2f89d90 - <unknown>
  56:                0x0 - <unknown>

error: 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 1.69.0-nightly (07c993eba 2023-02-23) running on x86_64-unknown-linux-gnu

note: compiler flags: --crate-type lib

query stack during panic:
#0 [mir_borrowck] borrow-checking `indirect::{closure#0}`
#1 [mir_borrowck] borrow-checking `indirect`
#2 [type_of] computing type of `FutNothing::{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

[matthiaskrgr]

Crashes since #108357 , #108315 looks a bit suspicious to me

[compiler-errors]

I doubt it's #108315 -- it's probably #108342.

[aliemjay]

The ICE here is due to #96146, which is expected. I'm actually more concerned that it used to compile! (edit: it was an error "unconstrained opaque type", which is less concerning)

@rustbot label F-type_alias_impl_trait

[aliemjay]

I can confirm that the previously emitted error of "unconstrained opaque type" is indeed bogus and is due to #108498. Here is a variant of #108498 that emits the same error:

#![feature(type_alias_impl_trait)]

use std::future::Future;

type Opaque = impl Future;

async fn get_rpit() {}

fn query(_: impl FnOnce() -> Opaque) {}

fn test() {
    query(get_rpit);
}

The ICE here is what I expect due to #96146. So I think this should be closed in favor of these issues.

[EqualMa]

I ran into this issue even without type_alias_impl_trait. Here is the code and playground link.

trait OutputStr<'a> {
    type Output;
}

impl<'a> OutputStr<'a> for () {
    type Output = &'a str;
}

fn test() -> impl for<'a> OutputStr<'a, Output = impl ToString> {}

[matthiaskrgr]

Another example, very similar to #108399 (comment)

trait Tr<'a> {
    type Assoc;
}

impl<'a> Tr<'a> for () {
    type Assoc = &'a ()
}

fn g() -> impl for<'a> Tr<'a, Assoc = impl + 'a> {}

[JohnTitor]

Triage: Fixed on the latest nightly, @rustbot labels: +E-needs-test

[ilyvion]

I think this issue might be covering two different problems, because as JohnTitor says, the code from the OP and aliemjay no longer causes an ICE on nightly, but the later examples by EqualMa and matthiaskrgr still do.