ice: `WARN rustc_infer::infer::generalize may incompletely handle alias type` / 'called `Result::unwrap_err()` on an `Ok` value: ?4t', ice + weird debug output

[matthiaskrgr]

auto-reduced (treereduce-rust):

trait ToUnit<'a> {
    type Unit;
}

struct LocalTy;
impl<'a> ToUnit<'a> for *const LocalTy {}

impl<'a, T: Copy + ?Sized> ToUnit<'a> for *const T {}

trait Overlap<T> {}

type Assoc<'a, T> = <*const T as ToUnit<'a>>::Unit;

impl<T> Overlap<T> for T {}

impl<T> Overlap<for<'a> fn(&'a (), Assoc<'a, T>)> for T where for<'a> *const T: Overlap<T> {}

original:

// revisions: old next
//[next] compile-flags: -Ztrait-solver=next

// A regression test for #105787

// Using the higher ranked projection hack to prevent us from replacing the projection
// with an inference variable.
trait ToUnit<'a> {
    type Unit;
}

struct LocalTy;
impl<'a> ToUnit<'a> for *const LocalTy {
    type Unit = ();
}

impl<'a, T: Copy + ?Sized> ToUnit<'a> for *const T {
    type Unit = ();
}

trait Overlap<T> {
    type Assoc;
}

type Assoc<'a, T> = <*const T as ToUnit<'a>>::Unit;

impl<T> Overlap<T> for T {
    type Assoc = usize;
}

impl<T> Overlap<for<'a> fn(&'a (), Assoc<'a, T>)> for T
//~^ ERROR conflicting implementations of trait
where
    for<'a> *const T: Overlap<T>,
{
    type Assoc = Box<usize>;
}

fn foo<T: Overlap<U>, U>(x: T::Assoc) -> T::Assoc {
    x
}

fn main() {
    foo::<for<'a> fn(&'a (), ()), for<'a> fn(&'a (), ())>(3usize);
}

Version information

rustc 1.76.0-nightly (f32d29837 2023-12-06)
binary: rustc
commit-hash: f32d29837d3642475e23716cd8af5711d00c01ae
commit-date: 2023-12-06
host: x86_64-unknown-linux-gnu
release: 1.76.0-nightly
LLVM version: 17.0.5

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

Program output

error[E0601]: `main` function not found in crate `mvce`
  --> /tmp/icemaker_global_tempdir.tY9BgKNIQG1j/rustc_testrunner_tmpdir_reporting.1KC2ZNRG81SS/mvce.rs:16:94
   |
16 | impl<T> Overlap<for<'a> fn(&'a (), Assoc<'a, T>)> for T where for<'a> *const T: Overlap<T> {}
   |                                                                                              ^ consider adding a `main` function to `/tmp/icemaker_global_tempdir.tY9BgKNIQG1j/rustc_testrunner_tmpdir_reporting.1KC2ZNRG81SS/mvce.rs`

WARN rustc_infer::infer::generalize may incompletely handle alias type: Alias(Projection, AliasTy { args: [*const ?1t, ReBound(DebruijnIndex(0), BoundRegion { var: 0, kind: BrNamed(DefId(0:23 ~ mvce[4d9c]::{impl#3}::'a#1), 'a) })], def_id: DefId(0:5 ~ mvce[4d9c]::ToUnit::Unit) })
WARN rustc_infer::infer::generalize may incompletely handle alias type: Alias(Projection, AliasTy { args: [*const ?1t, RePlaceholder(!3_BoundRegion { var: 0, kind: BrNamed(DefId(0:23 ~ mvce[4d9c]::{impl#3}::'a#1), 'a) })], def_id: DefId(0:5 ~ mvce[4d9c]::ToUnit::Unit) })
WARN rustc_infer::infer::generalize may incompletely handle alias type: Alias(Projection, AliasTy { args: [*const ?5t, RePlaceholder(!5_BoundRegion { var: 0, kind: BrNamed(DefId(0:23 ~ mvce[4d9c]::{impl#3}::'a#1), 'a) })], def_id: DefId(0:5 ~ mvce[4d9c]::ToUnit::Unit) })
thread 'rustc' panicked at compiler/rustc_infer/src/infer/generalize.rs:28:40:
called `Result::unwrap_err()` on an `Ok` value: ?4t
stack backtrace:
   0:     0x7fed605d745c - std::backtrace_rs::backtrace::libunwind::trace::h05b6a3fdb7984b42
                               at /rustc/f32d29837d3642475e23716cd8af5711d00c01ae/library/std/src/../../backtrace/src/backtrace/libunwind.rs:104:5
   1:     0x7fed605d745c - std::backtrace_rs::backtrace::trace_unsynchronized::h598b668ef45ec588
                               at /rustc/f32d29837d3642475e23716cd8af5711d00c01ae/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x7fed605d745c - std::sys_common::backtrace::_print_fmt::hbefb24ad1b1e1b2a
                               at /rustc/f32d29837d3642475e23716cd8af5711d00c01ae/library/std/src/sys_common/backtrace.rs:68:5
   3:     0x7fed605d745c - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::h4780316eb305e509
                               at /rustc/f32d29837d3642475e23716cd8af5711d00c01ae/library/std/src/sys_common/backtrace.rs:44:22
   4:     0x7fed6062a4a0 - core::fmt::rt::Argument::fmt::h5cb309a7c172eabe
                               at /rustc/f32d29837d3642475e23716cd8af5711d00c01ae/library/core/src/fmt/rt.rs:142:9
   5:     0x7fed6062a4a0 - core::fmt::write::h6308397b9e39079a
                               at /rustc/f32d29837d3642475e23716cd8af5711d00c01ae/library/core/src/fmt/mod.rs:1120:17
   6:     0x7fed605cb34f - std::io::Write::write_fmt::ha9de23c18c6ad43b
                               at /rustc/f32d29837d3642475e23716cd8af5711d00c01ae/library/std/src/io/mod.rs:1810:15
   7:     0x7fed605d7244 - std::sys_common::backtrace::_print::h12314f11f05d3175
                               at /rustc/f32d29837d3642475e23716cd8af5711d00c01ae/library/std/src/sys_common/backtrace.rs:47:5
   8:     0x7fed605d7244 - std::sys_common::backtrace::print::h2ee0c1070160e61c
                               at /rustc/f32d29837d3642475e23716cd8af5711d00c01ae/library/std/src/sys_common/backtrace.rs:34:9
   9:     0x7fed605d9ed7 - std::panicking::default_hook::{{closure}}::h8e9e3d82075b4ca5
  10:     0x7fed605d9c3f - std::panicking::default_hook::hc6307ef37ca7e274
                               at /rustc/f32d29837d3642475e23716cd8af5711d00c01ae/library/std/src/panicking.rs:292:9
  11:     0x7fed5d2f6f30 - std[f19864afa78103cd]::panicking::update_hook::<alloc[2aa8f2c60f7e6c66]::boxed::Box<rustc_driver_impl[5d68deab5a6eda66]::install_ice_hook::{closure#0}>>::{closure#0}
  12:     0x7fed605da618 - <alloc::boxed::Box<F,A> as core::ops::function::Fn<Args>>::call::h1331fce690faa3ac
                               at /rustc/f32d29837d3642475e23716cd8af5711d00c01ae/library/alloc/src/boxed.rs:2021:9
  13:     0x7fed605da618 - std::panicking::rust_panic_with_hook::h966b13c595fb6a12
                               at /rustc/f32d29837d3642475e23716cd8af5711d00c01ae/library/std/src/panicking.rs:783:13
  14:     0x7fed605da36e - std::panicking::begin_panic_handler::{{closure}}::hfef9796ac34a1d90
                               at /rustc/f32d29837d3642475e23716cd8af5711d00c01ae/library/std/src/panicking.rs:657:13
  15:     0x7fed605d7926 - std::sys_common::backtrace::__rust_end_short_backtrace::h3b5384eeaf17c0a1
                               at /rustc/f32d29837d3642475e23716cd8af5711d00c01ae/library/std/src/sys_common/backtrace.rs:171:18
  16:     0x7fed605da0d2 - rust_begin_unwind
                               at /rustc/f32d29837d3642475e23716cd8af5711d00c01ae/library/std/src/panicking.rs:645:5
  17:     0x7fed60626b65 - core::panicking::panic_fmt::h4a9c5999dba52929
                               at /rustc/f32d29837d3642475e23716cd8af5711d00c01ae/library/core/src/panicking.rs:72:14
  18:     0x7fed60627273 - core::result::unwrap_failed::he5de6a6e1050fec5
                               at /rustc/f32d29837d3642475e23716cd8af5711d00c01ae/library/core/src/result.rs:1649:5
  19:     0x7fed5e65a276 - <rustc_infer[231235591c7201f1]::infer::combine::CombineFields>::instantiate
  20:     0x7fed5e63c28b - <rustc_infer[231235591c7201f1]::infer::sub::Sub as rustc_middle[abf3d24358494a96]::ty::relate::TypeRelation>::tys
  21:     0x7fed5ee6d1a4 - <core[c98a5e2a9f438e2a]::iter::adapters::enumerate::Enumerate<core[c98a5e2a9f438e2a]::iter::adapters::map::Map<core[c98a5e2a9f438e2a]::iter::adapters::chain::Chain<core[c98a5e2a9f438e2a]::iter::adapters::map::Map<core[c98a5e2a9f438e2a]::iter::adapters::zip::Zip<core[c98a5e2a9f438e2a]::slice::iter::Iter<rustc_middle[abf3d24358494a96]::ty::Ty>, core[c98a5e2a9f438e2a]::slice::iter::Iter<rustc_middle[abf3d24358494a96]::ty::Ty>>, <rustc_middle[abf3d24358494a96]::ty::sty::FnSig as rustc_middle[abf3d24358494a96]::ty::relate::Relate>::relate<rustc_infer[231235591c7201f1]::infer::sub::Sub>::{closure#0}>, core[c98a5e2a9f438e2a]::iter::sources::once::Once<((rustc_middle[abf3d24358494a96]::ty::Ty, rustc_middle[abf3d24358494a96]::ty::Ty), bool)>>, <rustc_middle[abf3d24358494a96]::ty::sty::FnSig as rustc_middle[abf3d24358494a96]::ty::relate::Relate>::relate<rustc_infer[231235591c7201f1]::infer::sub::Sub>::{closure#1}>> as core[c98a5e2a9f438e2a]::iter::traits::iterator::Iterator>::try_fold::<(), core[c98a5e2a9f438e2a]::iter::adapters::map::map_try_fold<(usize, core[c98a5e2a9f438e2a]::result::Result<rustc_middle[abf3d24358494a96]::ty::Ty, rustc_middle[abf3d24358494a96]::ty::error::TypeError>), core[c98a5e2a9f438e2a]::result::Result<rustc_middle[abf3d24358494a96]::ty::Ty, rustc_middle[abf3d24358494a96]::ty::error::TypeError>, (), core[c98a5e2a9f438e2a]::ops::control_flow::ControlFlow<core[c98a5e2a9f438e2a]::ops::control_flow::ControlFlow<rustc_middle[abf3d24358494a96]::ty::Ty>>, <rustc_middle[abf3d24358494a96]::ty::sty::FnSig as rustc_middle[abf3d24358494a96]::ty::relate::Relate>::relate<rustc_infer[231235591c7201f1]::infer::sub::Sub>::{closure#2}, <core[c98a5e2a9f438e2a]::iter::adapters::GenericShunt<core[c98a5e2a9f438e2a]::iter::adapters::map::Map<core[c98a5e2a9f438e2a]::iter::adapters::enumerate::Enumerate<core[c98a5e2a9f438e2a]::iter::adapters::map::Map<core[c98a5e2a9f438e2a]::iter::adapters::chain::Chain<core[c98a5e2a9f438e2a]::iter::adapters::map::Map<core[c98a5e2a9f438e2a]::iter::adapters::zip::Zip<core[c98a5e2a9f438e2a]::slice::iter::Iter<rustc_middle[abf3d24358494a96]::ty::Ty>, core[c98a5e2a9f438e2a]::slice::iter::Iter<rustc_middle[abf3d24358494a96]::ty::Ty>>, <rustc_middle[abf3d24358494a96]::ty::sty::FnSig as rustc_middle[abf3d24358494a96]::ty::relate::Relate>::relate<rustc_infer[231235591c7201f1]::infer::sub::Sub>::{closure#0}>, core[c98a5e2a9f438e2a]::iter::sources::once::Once<((rustc_middle[abf3d24358494a96]::ty::Ty, rustc_middle[abf3d24358494a96]::ty::Ty), bool)>>, <rustc_middle[abf3d24358494a96]::ty::sty::FnSig as rustc_middle[abf3d24358494a96]::ty::relate::Relate>::relate<rustc_infer[231235591c7201f1]::infer::sub::Sub>::{closure#1}>>, <rustc_middle[abf3d24358494a96]::ty::sty::FnSig as rustc_middle[abf3d24358494a96]::ty::relate::Relate>::relate<rustc_infer[231235591c7201f1]::infer::sub::Sub>::{closure#2}>, core[c98a5e2a9f438e2a]::result::Result<core[c98a5e2a9f438e2a]::convert::Infallible, rustc_middle[abf3d24358494a96]::ty::error::TypeError>> as core[c98a5e2a9f438e2a]::iter::traits::iterator::Iterator>::try_fold<(), core[c98a5e2a9f438e2a]::iter::traits::iterator::Iterator::try_for_each::call<rustc_middle[abf3d24358494a96]::ty::Ty, core[c98a5e2a9f438e2a]::ops::control_flow::ControlFlow<rustc_middle[abf3d24358494a96]::ty::Ty>, core[c98a5e2a9f438e2a]::ops::control_flow::ControlFlow<rustc_middle[abf3d24358494a96]::ty::Ty>::Break>::{closure#0}, core[c98a5e2a9f438e2a]::ops::control_flow::ControlFlow<rustc_middle[abf3d24358494a96]::ty::Ty>>::{closure#0}>::{closure#0}, core[c98a5e2a9f438e2a]::ops::control_flow::ControlFlow<core[c98a5e2a9f438e2a]::ops::control_flow::ControlFlow<rustc_middle[abf3d24358494a96]::ty::Ty>>>
  22:     0x7fed5ee6cca7 - <rustc_infer[231235591c7201f1]::infer::combine::CombineFields>::higher_ranked_sub::<rustc_middle[abf3d24358494a96]::ty::sty::FnSig>
  23:     0x7fed5ee6c1f7 - <rustc_middle[abf3d24358494a96]::ty::sty::Binder<rustc_middle[abf3d24358494a96]::ty::sty::FnSig> as rustc_middle[abf3d24358494a96]::ty::relate::Relate>::relate::<rustc_infer[231235591c7201f1]::infer::equate::Equate>
  24:     0x7fed5e65c665 - <rustc_infer[231235591c7201f1]::infer::InferCtxt>::super_combine_tys::<rustc_infer[231235591c7201f1]::infer::equate::Equate>
  25:     0x7fed5e65a9a6 - <rustc_infer[231235591c7201f1]::infer::equate::Equate as rustc_middle[abf3d24358494a96]::ty::relate::TypeRelation>::tys
  26:     0x7fed5f04e229 - <rustc_trait_selection[18b1413cf292a40b]::traits::select::SelectionContext>::confirm_candidate
  27:     0x7fed5f03ee17 - <rustc_trait_selection[18b1413cf292a40b]::traits::select::SelectionContext>::evaluate_candidate
  28:     0x7fed5f013078 - <rustc_trait_selection[18b1413cf292a40b]::traits::select::SelectionContext>::evaluate_trait_predicate_recursively
  29:     0x7fed5f344d7f - <rustc_trait_selection[18b1413cf292a40b]::traits::select::SelectionContext>::evaluation_probe::<<rustc_trait_selection[18b1413cf292a40b]::traits::select::SelectionContext>::evaluate_root_obligation::{closure#0}>
  30:     0x7fed5f343308 - rustc_trait_selection[18b1413cf292a40b]::traits::coherence::overlap
  31:     0x7fed5ec2a8bd - <rustc_middle[abf3d24358494a96]::traits::specialization_graph::Children as rustc_trait_selection[18b1413cf292a40b]::traits::specialize::specialization_graph::ChildrenExt>::insert
  32:     0x7fed5ec29ea9 - <rustc_middle[abf3d24358494a96]::traits::specialization_graph::Graph as rustc_trait_selection[18b1413cf292a40b]::traits::specialize::specialization_graph::GraphExt>::insert
  33:     0x7fed5f1024ca - rustc_trait_selection[18b1413cf292a40b]::traits::specialize::specialization_graph_provider
  34:     0x7fed5f101ef2 - rustc_query_impl[516b0f6d3c576e47]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[516b0f6d3c576e47]::query_impl::specialization_graph_of::dynamic_query::{closure#2}::{closure#0}, rustc_middle[abf3d24358494a96]::query::erase::Erased<[u8; 8usize]>>
  35:     0x7fed5e6513d4 - rustc_query_system[63b2eb5e5eb99e14]::query::plumbing::try_execute_query::<rustc_query_impl[516b0f6d3c576e47]::DynamicConfig<rustc_query_system[63b2eb5e5eb99e14]::query::caches::DefaultCache<rustc_span[24843a324ed31ab0]::def_id::DefId, rustc_middle[abf3d24358494a96]::query::erase::Erased<[u8; 8usize]>>, false, false, false>, rustc_query_impl[516b0f6d3c576e47]::plumbing::QueryCtxt, false>
  36:     0x7fed5ea468a2 - rustc_query_impl[516b0f6d3c576e47]::query_impl::specialization_graph_of::get_query_non_incr::__rust_end_short_backtrace
  37:     0x7fed5ea46c9d - rustc_hir_analysis[650abdd69e2e0337]::coherence::coherent_trait
  38:     0x7fed5ea46b89 - rustc_query_impl[516b0f6d3c576e47]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[516b0f6d3c576e47]::query_impl::coherent_trait::dynamic_query::{closure#2}::{closure#0}, rustc_middle[abf3d24358494a96]::query::erase::Erased<[u8; 0usize]>>
  39:     0x7fed5f0114bd - rustc_query_system[63b2eb5e5eb99e14]::query::plumbing::try_execute_query::<rustc_query_impl[516b0f6d3c576e47]::DynamicConfig<rustc_query_system[63b2eb5e5eb99e14]::query::caches::DefaultCache<rustc_span[24843a324ed31ab0]::def_id::DefId, rustc_middle[abf3d24358494a96]::query::erase::Erased<[u8; 0usize]>>, false, false, false>, rustc_query_impl[516b0f6d3c576e47]::plumbing::QueryCtxt, false>
  40:     0x7fed5f01124d - rustc_query_impl[516b0f6d3c576e47]::query_impl::coherent_trait::get_query_non_incr::__rust_end_short_backtrace
  41:     0x7fed5f0364ea - rustc_hir_analysis[650abdd69e2e0337]::check_crate
  42:     0x7fed5eec32e2 - rustc_interface[403c7d9aab312e25]::passes::analysis
  43:     0x7fed5eec2f1d - rustc_query_impl[516b0f6d3c576e47]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[516b0f6d3c576e47]::query_impl::analysis::dynamic_query::{closure#2}::{closure#0}, rustc_middle[abf3d24358494a96]::query::erase::Erased<[u8; 1usize]>>
  44:     0x7fed5f560a00 - rustc_query_system[63b2eb5e5eb99e14]::query::plumbing::try_execute_query::<rustc_query_impl[516b0f6d3c576e47]::DynamicConfig<rustc_query_system[63b2eb5e5eb99e14]::query::caches::SingleCache<rustc_middle[abf3d24358494a96]::query::erase::Erased<[u8; 1usize]>>, false, false, false>, rustc_query_impl[516b0f6d3c576e47]::plumbing::QueryCtxt, false>
  45:     0x7fed5f560807 - rustc_query_impl[516b0f6d3c576e47]::query_impl::analysis::get_query_non_incr::__rust_end_short_backtrace
  46:     0x7fed5f56f0e2 - rustc_interface[403c7d9aab312e25]::interface::run_compiler::<core[c98a5e2a9f438e2a]::result::Result<(), rustc_span[24843a324ed31ab0]::ErrorGuaranteed>, rustc_driver_impl[5d68deab5a6eda66]::run_compiler::{closure#0}>::{closure#0}
  47:     0x7fed5f5624c9 - std[f19864afa78103cd]::sys_common::backtrace::__rust_begin_short_backtrace::<rustc_interface[403c7d9aab312e25]::util::run_in_thread_with_globals<rustc_interface[403c7d9aab312e25]::util::run_in_thread_pool_with_globals<rustc_interface[403c7d9aab312e25]::interface::run_compiler<core[c98a5e2a9f438e2a]::result::Result<(), rustc_span[24843a324ed31ab0]::ErrorGuaranteed>, rustc_driver_impl[5d68deab5a6eda66]::run_compiler::{closure#0}>::{closure#0}, core[c98a5e2a9f438e2a]::result::Result<(), rustc_span[24843a324ed31ab0]::ErrorGuaranteed>>::{closure#0}, core[c98a5e2a9f438e2a]::result::Result<(), rustc_span[24843a324ed31ab0]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[c98a5e2a9f438e2a]::result::Result<(), rustc_span[24843a324ed31ab0]::ErrorGuaranteed>>
  48:     0x7fed5f5622f3 - <<std[f19864afa78103cd]::thread::Builder>::spawn_unchecked_<rustc_interface[403c7d9aab312e25]::util::run_in_thread_with_globals<rustc_interface[403c7d9aab312e25]::util::run_in_thread_pool_with_globals<rustc_interface[403c7d9aab312e25]::interface::run_compiler<core[c98a5e2a9f438e2a]::result::Result<(), rustc_span[24843a324ed31ab0]::ErrorGuaranteed>, rustc_driver_impl[5d68deab5a6eda66]::run_compiler::{closure#0}>::{closure#0}, core[c98a5e2a9f438e2a]::result::Result<(), rustc_span[24843a324ed31ab0]::ErrorGuaranteed>>::{closure#0}, core[c98a5e2a9f438e2a]::result::Result<(), rustc_span[24843a324ed31ab0]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[c98a5e2a9f438e2a]::result::Result<(), rustc_span[24843a324ed31ab0]::ErrorGuaranteed>>::{closure#1} as core[c98a5e2a9f438e2a]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  49:     0x7fed605e44a5 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::ha603a9d78630b4d9
                               at /rustc/f32d29837d3642475e23716cd8af5711d00c01ae/library/alloc/src/boxed.rs:2007:9
  50:     0x7fed605e44a5 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::hdd9615f963a03fca
                               at /rustc/f32d29837d3642475e23716cd8af5711d00c01ae/library/alloc/src/boxed.rs:2007:9
  51:     0x7fed605e44a5 - std::sys::unix::thread::Thread::new::thread_start::h15fde3375b9b660d
                               at /rustc/f32d29837d3642475e23716cd8af5711d00c01ae/library/std/src/sys/unix/thread.rs:108:17
  52:     0x7fed5a4aa9eb - <unknown>
  53:     0x7fed5a52e7cc - <unknown>
  54:                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 1.76.0-nightly (f32d29837 2023-12-06) running on x86_64-unknown-linux-gnu

query stack during panic:
#0 [specialization_graph_of] building specialization graph of trait `Overlap`
#1 [coherent_trait] coherence checking all impls of trait `Overlap`
#2 [analysis] running analysis passes on this crate
end of query stack
error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0601`.

[matthiaskrgr]

[spastorino]

I think this is fixed by #118710. Maybe worth adding the test case produced by @matthiaskrgr

[matthiaskrgr]

fwiw the ICE is fixed but I can still see the warnings comming from here
https://github.com/rust-lang/rust/blob/master/compiler/rustc_infer/src/infer/generalize.rs#L353
cc @lcnr

[lcnr]

yeah, the warning is expected and also present in the original ui test 🤔 I personally think that the added debug assert in #118710 is sufficient to prevent any regressions here, given that it triggers when compiling std without the fix. closing 👍 nice to see that there's some repro without rustdoc though ^^

[spastorino]

Should we add this test?

[lcnr]

🤷 I think that adding broken code as tests for unrelated stuff is a bit :/ so I would personally let it be