internal compiler error: opaque type with non-universal region substs

[Luro02]

Code

pub fn ice(
    x: impl AsRef<str>,
) -> impl IntoIterator<Item = ()> {
    vec![].append(&mut ice(x.as_ref()));

    Vec::new()
}

fn main() {
}

playground

Meta

rustc --version --verbose:

rustc 1.63.0 (4b91a6ea7 2022-08-08)
binary: rustc
commit-hash: 4b91a6ea7258a947e59c6522cd5898e7c0a6a88f
commit-date: 2022-08-08
host: x86_64-pc-windows-msvc
release: 1.63.0
LLVM version: 14.0.5

This happens on latest nightly and stable.

Error output

   Compiling playground v0.0.1 (/playground)
warning: function cannot return without recursing
 --> src/main.rs:1:1
  |
1 | / pub fn ice(
2 | |     x: impl AsRef<str>,
3 | | ) -> impl IntoIterator<Item = ()> {
4 | |     vec![].append(&mut ice(x.as_ref()));
  | |                        --------------- recursive call site
5 | |
6 | |     Vec::new()
7 | | }
  | |_^ cannot return without recursing
  |
  = note: `#[warn(unconditional_recursion)]` on by default
  = help: a `loop` may express intention better if this is on purpose

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

error: internal compiler error: opaque type with non-universal region substs
 --> src/main.rs:4:5
  |
4 |     vec![].append(&mut ice(x.as_ref()));
  |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = note: delayed at compiler/rustc_borrowck/src/region_infer/opaque_types.rs:81:40

thread 'rustc' panicked at 'Box<dyn Any>', compiler/rustc_errors/src/lib.rs:1425:13
stack backtrace:
   0:     0x7f9e5d24e18d - std::backtrace_rs::backtrace::libunwind::trace::h8217d0a8f3fd2f41
                               at /rustc/4b91a6ea7258a947e59c6522cd5898e7c0a6a88f/library/std/src/../../backtrace/src/backtrace/libunwind.rs:93:5
   1:     0x7f9e5d24e18d - std::backtrace_rs::backtrace::trace_unsynchronized::h308103876b3af410
                               at /rustc/4b91a6ea7258a947e59c6522cd5898e7c0a6a88f/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x7f9e5d24e18d - std::sys_common::backtrace::_print_fmt::hc208018c6153605e
                               at /rustc/4b91a6ea7258a947e59c6522cd5898e7c0a6a88f/library/std/src/sys_common/backtrace.rs:66:5
   3:     0x7f9e5d24e18d - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::hf89a7ed694dfb585
                               at /rustc/4b91a6ea7258a947e59c6522cd5898e7c0a6a88f/library/std/src/sys_common/backtrace.rs:45:22
   4:     0x7f9e5d2a9f7c - core::fmt::write::h21038c1382fe4264
                               at /rustc/4b91a6ea7258a947e59c6522cd5898e7c0a6a88f/library/core/src/fmt/mod.rs:1197:17
   5:     0x7f9e5d23f8a1 - std::io::Write::write_fmt::h7dbb1c9a3c254aef
                               at /rustc/4b91a6ea7258a947e59c6522cd5898e7c0a6a88f/library/std/src/io/mod.rs:1672:15
   6:     0x7f9e5d250e55 - std::sys_common::backtrace::_print::h4e8889719c9ddeb8
                               at /rustc/4b91a6ea7258a947e59c6522cd5898e7c0a6a88f/library/std/src/sys_common/backtrace.rs:48:5
   7:     0x7f9e5d250e55 - std::sys_common::backtrace::print::h1506fe2cb3022667
                               at /rustc/4b91a6ea7258a947e59c6522cd5898e7c0a6a88f/library/std/src/sys_common/backtrace.rs:35:9
   8:     0x7f9e5d250e55 - std::panicking::default_hook::{{closure}}::hd9d7ce2a8a782440
                               at /rustc/4b91a6ea7258a947e59c6522cd5898e7c0a6a88f/library/std/src/panicking.rs:295:22
   9:     0x7f9e5d250b76 - std::panicking::default_hook::h5b16ec25444b1b5d
                               at /rustc/4b91a6ea7258a947e59c6522cd5898e7c0a6a88f/library/std/src/panicking.rs:314:9
  10:     0x7f9e5da2bb54 - rustc_driver[e01eec72899701d3]::DEFAULT_HOOK::{closure#0}::{closure#0}
  11:     0x7f9e5d25152a - std::panicking::rust_panic_with_hook::hb0138cb6e6fea3e4
                               at /rustc/4b91a6ea7258a947e59c6522cd5898e7c0a6a88f/library/std/src/panicking.rs:702:17
  12:     0x7f9e5ebe7a91 - std[f9ee9c7d4fd68eda]::panicking::begin_panic::<rustc_errors[b2e8492a1747ee42]::ExplicitBug>::{closure#0}
  13:     0x7f9e5ebe5036 - std[f9ee9c7d4fd68eda]::sys_common::backtrace::__rust_end_short_backtrace::<std[f9ee9c7d4fd68eda]::panicking::begin_panic<rustc_errors[b2e8492a1747ee42]::ExplicitBug>::{closure#0}, !>
  14:     0x7f9e5ebf4806 - std[f9ee9c7d4fd68eda]::panicking::begin_panic::<rustc_errors[b2e8492a1747ee42]::ExplicitBug>
  15:     0x7f9e5ebf1ad6 - std[f9ee9c7d4fd68eda]::panic::panic_any::<rustc_errors[b2e8492a1747ee42]::ExplicitBug>
  16:     0x7f9e604abcec - <rustc_errors[b2e8492a1747ee42]::HandlerInner as core[3edb0f9afb6adb32]::ops::drop::Drop>::drop
  17:     0x7f9e5fbd6348 - core[3edb0f9afb6adb32]::ptr::drop_in_place::<rustc_session[72c90254a58d88d1]::parse::ParseSess>
  18:     0x7f9e5fbd92e3 - <alloc[59e4fb8ddcfb913c]::rc::Rc<rustc_session[72c90254a58d88d1]::session::Session> as core[3edb0f9afb6adb32]::ops::drop::Drop>::drop
  19:     0x7f9e5fbd86bd - core[3edb0f9afb6adb32]::ptr::drop_in_place::<rustc_interface[be6c6c80f2cd8cf2]::interface::Compiler>
  20:     0x7f9e5fbd5c54 - rustc_span[fb9cf5df1e5e5539]::with_source_map::<core[3edb0f9afb6adb32]::result::Result<(), rustc_errors[b2e8492a1747ee42]::ErrorGuaranteed>, rustc_interface[be6c6c80f2cd8cf2]::interface::create_compiler_and_run<core[3edb0f9afb6adb32]::result::Result<(), rustc_errors[b2e8492a1747ee42]::ErrorGuaranteed>, rustc_driver[e01eec72899701d3]::run_compiler::{closure#1}>::{closure#1}>
  21:     0x7f9e5fbdd302 - <scoped_tls[134a193f706323ee]::ScopedKey<rustc_span[fb9cf5df1e5e5539]::SessionGlobals>>::set::<rustc_interface[be6c6c80f2cd8cf2]::interface::run_compiler<core[3edb0f9afb6adb32]::result::Result<(), rustc_errors[b2e8492a1747ee42]::ErrorGuaranteed>, rustc_driver[e01eec72899701d3]::run_compiler::{closure#1}>::{closure#0}, core[3edb0f9afb6adb32]::result::Result<(), rustc_errors[b2e8492a1747ee42]::ErrorGuaranteed>>
  22:     0x7f9e5fc0099f - std[f9ee9c7d4fd68eda]::sys_common::backtrace::__rust_begin_short_backtrace::<rustc_interface[be6c6c80f2cd8cf2]::util::run_in_thread_pool_with_globals<rustc_interface[be6c6c80f2cd8cf2]::interface::run_compiler<core[3edb0f9afb6adb32]::result::Result<(), rustc_errors[b2e8492a1747ee42]::ErrorGuaranteed>, rustc_driver[e01eec72899701d3]::run_compiler::{closure#1}>::{closure#0}, core[3edb0f9afb6adb32]::result::Result<(), rustc_errors[b2e8492a1747ee42]::ErrorGuaranteed>>::{closure#0}, core[3edb0f9afb6adb32]::result::Result<(), rustc_errors[b2e8492a1747ee42]::ErrorGuaranteed>>
  23:     0x7f9e5fbf2529 - <<std[f9ee9c7d4fd68eda]::thread::Builder>::spawn_unchecked_<rustc_interface[be6c6c80f2cd8cf2]::util::run_in_thread_pool_with_globals<rustc_interface[be6c6c80f2cd8cf2]::interface::run_compiler<core[3edb0f9afb6adb32]::result::Result<(), rustc_errors[b2e8492a1747ee42]::ErrorGuaranteed>, rustc_driver[e01eec72899701d3]::run_compiler::{closure#1}>::{closure#0}, core[3edb0f9afb6adb32]::result::Result<(), rustc_errors[b2e8492a1747ee42]::ErrorGuaranteed>>::{closure#0}, core[3edb0f9afb6adb32]::result::Result<(), rustc_errors[b2e8492a1747ee42]::ErrorGuaranteed>>::{closure#1} as core[3edb0f9afb6adb32]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  24:     0x7f9e5d25b463 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h1680342795a2dc08
                               at /rustc/4b91a6ea7258a947e59c6522cd5898e7c0a6a88f/library/alloc/src/boxed.rs:1951:9
  25:     0x7f9e5d25b463 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h45204a69827b0e83
                               at /rustc/4b91a6ea7258a947e59c6522cd5898e7c0a6a88f/library/alloc/src/boxed.rs:1951:9
  26:     0x7f9e5d25b463 - std::sys::unix::thread::Thread::new::thread_start::h5d4e11bbda4161c8
                               at /rustc/4b91a6ea7258a947e59c6522cd5898e7c0a6a88f/library/std/src/sys/unix/thread.rs:108:17
  27:     0x7f9e5d181609 - start_thread
  28:     0x7f9e5d0a4133 - clone
  29:                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 1.63.0 (4b91a6ea7 2022-08-08) 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
warning: `playground` (bin "playground") generated 1 warning
error: could not compile `playground`; 1 warning emitted

Backtrace

   Compiling playground v0.0.1 (/playground)
warning: function cannot return without recursing
 --> src/main.rs:1:1
  |
1 | / pub fn ice(
2 | |     x: impl AsRef<str>,
3 | | ) -> impl IntoIterator<Item = ()> {
4 | |     vec![].append(&mut ice(x.as_ref()));
  | |                        --------------- recursive call site
5 | |
6 | |     Vec::new()
7 | | }
  | |_^ cannot return without recursing
  |
  = note: `#[warn(unconditional_recursion)]` on by default
  = help: a `loop` may express intention better if this is on purpose

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

error: internal compiler error: opaque type with non-universal region substs
 --> src/main.rs:4:5
  |
4 |     vec![].append(&mut ice(x.as_ref()));
  |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = note: delayed at compiler/rustc_borrowck/src/region_infer/opaque_types.rs:81:40

thread 'rustc' panicked at 'Box<dyn Any>', compiler/rustc_errors/src/lib.rs:1425:13
stack backtrace:
   0: std::panicking::begin_panic::<rustc_errors::ExplicitBug>
   1: std::panic::panic_any::<rustc_errors::ExplicitBug>
   2: <rustc_errors::HandlerInner as core::ops::drop::Drop>::drop
   3: core::ptr::drop_in_place::<rustc_session::parse::ParseSess>
   4: <alloc::rc::Rc<rustc_session::session::Session> as core::ops::drop::Drop>::drop
   5: core::ptr::drop_in_place::<rustc_interface::interface::Compiler>
   6: rustc_span::with_source_map::<core::result::Result<(), rustc_errors::ErrorGuaranteed>, rustc_interface::interface::create_compiler_and_run<core::result::Result<(), rustc_errors::ErrorGuaranteed>, rustc_driver::run_compiler::{closure#1}>::{closure#1}>
   7: <scoped_tls::ScopedKey<rustc_span::SessionGlobals>>::set::<rustc_interface::interface::run_compiler<core::result::Result<(), rustc_errors::ErrorGuaranteed>, rustc_driver::run_compiler::{closure#1}>::{closure#0}, core::result::Result<(), rustc_errors::ErrorGuaranteed>>
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

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 1.63.0 (4b91a6ea7 2022-08-08) 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
warning: `playground` (bin "playground") generated 1 warning
error: could not compile `playground`; 1 warning emitted

[lqd]

This regressed in nightly-2022-03-31, and out of these:

• Rollup of 4 pull requests #95448 - Dylan-DPC:rollup-wpj5yto, r=Dylan-DPC
• update miri #95455 - RalfJung:miri, r=RalfJung
• Lazy type-alias-impl-trait take two #94081 - oli-obk:lazy_tait_take_two, r=nikomatsakis
• Rollup of 5 pull requests #95466 - Dylan-DPC:rollup-g7ddr8y, r=Dylan-DPC
• Strict Provenance MVP #95241 - Gankra:cleaned-provenance, r=workingjubilee
• allow arbitrary inherent impls for builtin types in core #94963 - lcnr:inherent-impls-std, r=oli-obk,m-ou-se
• Sync rustfmt subtree #95458 - calebcartwright:sync-rustfmt-subtree, r=calebcartwright
• Yet more parse_tt improvements #95425 - nnethercote:yet-more-parse_tt-improvements, r=petrochenkov

@oli-obk's #94081 lazy taits looks a likely cause for the ICE ?

[lqd]

This ICEs on stable since 1.61 so the correct label is regression-from-stable-to-stable, right ?

I'll mark it untriaged, so people can correct me.

[oli-obk]

This went from an error

error[E0308]: mismatched types
 --> <source>:4:19
  |
3 | ) -> impl IntoIterator<Item = ()> {
  |      ---------------------------- the found opaque type
4 |     vec![].append(&mut ice(x.as_ref()));
  |                   ^^^^^^^^^^^^^^^^^^^^ expected struct `Vec`, found opaque type
  |
  = note: expected mutable reference `&mut Vec<_>`
             found mutable reference `&mut impl IntoIterator<Item = ()>`

to an ICE in 1.61 yes