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 - ::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 - as core::ops::function::Fn>::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 - ::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:: 23: 0x7f38a5e7451d - ::mir_borrowck 24: 0x7f38a544760f - ::prove_closure_bounds 25: 0x7f38a5425cc8 - ::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:: 31: 0x7f38a5e7451d - ::mir_borrowck 32: 0x7f38a65f7491 - ::check 33: 0x7f38a65f4352 - ::visit_nested_item 34: 0x7f38a65ca9b8 - rustc_hir[ce80dd10cd19e57d]::intravisit::walk_mod:: 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:: 38: 0x7f38a4fc9f78 - rustc_hir_analysis[3040e81d56faed42]::check::check::check_mod_item_types 39: 0x7f38a5a562bf - rustc_query_system[5752648da2a9c81a]::query::plumbing::try_execute_query:: 40: 0x7f38a5e73b0d - ::check_mod_item_types 41: 0x7f38a49dbaf7 - ::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:: 45: 0x7f38a5e6d75a - ::analysis 46: 0x7f38a5ada266 - ::enter::> 47: 0x7f38a56e194c - ::enter::, rustc_errors[6785960a74f5dba1]::ErrorGuaranteed>> 48: 0x7f38a56dfa24 - rustc_span[da5d5abcbe0cb70f]::with_source_map::, rustc_interface[fa0b2b03ae23a7ba]::interface::run_compiler, rustc_driver_impl[f83b883832371c75]::run_compiler::{closure#1}>::{closure#0}::{closure#0}> 49: 0x7f38a56def8c - std[195e6cd746373230]::sys_common::backtrace::__rust_begin_short_backtrace::, 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 - <::spawn_unchecked_, 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 - as core::ops::function::FnOnce>::call_once::h533fa800d0f50b92 at /rustc/07c993eba8b76eae497e98433ae075b00f01be10/library/alloc/src/boxed.rs:1988:9 52: 0x7f38a3177cc3 - as core::ops::function::FnOnce>::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 - 55: 0x7f38a2f89d90 - 56: 0x0 - 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 , https://github.com/rust-lang/rust/pull/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 https://github.com/rust-lang/rust/issues/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 https://github.com/rust-lang/rust/issues/108399#issuecomment-1476300391

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.