[ICE]: `unexpected rigid alias in layout_of after normalization`

[matthiaskrgr]

auto-reduced (treereduce-rust):

pub trait MyFnOnce {
    type Output;

    fn call_my_fn_once(self) -> Self::Output;
}

pub struct WrapFnOnce<F>(F);

impl<F: FnOnce() -> D, D: MyFnOnce> MyFnOnce for WrapFnOnce<F> {
    type Output = D::Output;

    fn call_my_fn_once(self) -> Self::Output {
        D::call_my_fn_once(self.0())
    }
}

impl<F: FnOnce() -> D, D: MyFnOnce> MyFnOnce for F {
    type Output = D::Output;

    fn call_my_fn_once(self) -> Self::Output {
        D::call_my_fn_once(self())
    }
}

pub fn my_fn_1() -> impl MyFnOnce {
    my_fn_2
}

pub fn my_fn_2() -> impl MyFnOnce {
    WrapFnOnce(my_fn_1)
}

fn main() {
    let v = my_fn_1();

    let _ = v.call_my_fn_once();
}

original:

// ICE failed to resolve instance for <fn() -> impl MyFnOnce  ...
// issue: rust-lang/rust#105488
//@ build-fail
//~^^^ ERROR overflow evaluating the requirement `fn() -> impl MyFnOnce

pub trait MyFnOnce {
    type Output;

    fn call_my_fn_once(self) -> Self::Output;
}

pub struct WrapFnOnce<F>(F);

impl<F: FnOnce() -> D, D: MyFnOnce> MyFnOnce for WrapFnOnce<F> {
    type Output = D::Output;

    fn call_my_fn_once(self) -> Self::Output {
        D::call_my_fn_once(self.0())
    }
}

impl<F: FnOnce() -> D, D: MyFnOnce> MyFnOnce for F {
    type Output = D::Output;

    fn call_my_fn_once(self) -> Self::Output {
        D::call_my_fn_once(self())
    }
}

pub fn my_fn_1() -> impl MyFnOnce {
    my_fn_2
}

pub fn my_fn_2() -> impl MyFnOnce {
    WrapFnOnce(my_fn_1)
}

fn main() {
    let v = my_fn_1();

    let _ = v.call_my_fn_once();
}

Version information

rustc 1.100.0-nightly (b0ca9c712 2026-08-22)
binary: rustc
commit-hash: b0ca9c712455d865c3bf0bf5325a3e79677a2d97
commit-date: 2026-08-22
host: x86_64-unknown-linux-gnu
release: 1.100.0-nightly
LLVM version: 23.1.0

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

Program output

note: no errors encountered even though delayed bugs were created

note: those delayed bugs will now be shown as internal compiler errors

error: internal compiler error: unexpected rigid alias in layout_of after normalization: Alias(Yes, Alias { kind: Projection { def_id: DefId(0:4 ~ mvce[ec7e]::MyFnOnce::Output) }, args: [Alias(Yes, Alias { kind: Opaque { def_id: DefId(0:21 ~ mvce[ec7e]::my_fn_1::{opaque#0}) }, args: [], .. })], .. })
  |
  = note: delayed at /rustc-dev/b0ca9c712455d865c3bf0bf5325a3e79677a2d97/compiler/rustc_ty_utils/src/layout.rs:835:61
             0: <rustc_errors::DiagCtxtInner>::emit_diagnostic
             1: <rustc_errors::DiagCtxtHandle>::emit_diagnostic
             2: <rustc_span::ErrorGuaranteed as rustc_errors::diagnostic::EmissionGuarantee>::emit_producing_guarantee
             3: <rustc_errors::DiagCtxtHandle>::delayed_bug::<alloc::string::String>
             4: rustc_ty_utils::layout::layout_of_uncached
             5: rustc_ty_utils::layout::layout_of
             6: rustc_query_impl::query_vtables::layout_of::invoke_provider_fn::__rust_begin_short_backtrace
             7: rustc_query_impl::execution::try_execute_query::<rustc_middle::query::caches::DefaultCache<rustc_middle::ty::PseudoCanonicalInput<rustc_middle::ty::Ty>, rustc_middle::query::erase::ErasedData<[u8; 16]>>, false>
             8: rustc_query_impl::query_vtables::layout_of::execute_query_non_incr::__rust_end_short_backtrace
             9: <rustc_mir_transform::known_panics_lint::KnownPanicsLint as rustc_mir_transform::pass_manager::MirLint>::run_lint
            10: rustc_mir_transform::run_analysis_to_runtime_passes
            11: rustc_mir_transform::mir_drops_elaborated_and_const_checked
            12: rustc_query_impl::execution::try_execute_query::<rustc_data_structures::vec_cache::VecCache<rustc_span::def_id::LocalDefId, rustc_middle::query::erase::ErasedData<[u8; 8]>, rustc_middle::dep_graph::graph::DepNodeIndex>, false>
            13: rustc_query_impl::query_vtables::mir_drops_elaborated_and_const_checked::execute_query_non_incr::__rust_end_short_backtrace
            14: <rustc_middle::ty::context::TyCtxt>::par_hir_body_owners::<rustc_interface::passes::run_required_analyses::{closure#2}::{closure#0}>::{closure#0}
            15: rustc_interface::passes::analysis
            16: rustc_query_impl::execution::try_execute_query::<rustc_middle::query::caches::SingleCache<rustc_middle::query::erase::ErasedData<[u8; 0]>>, false>
            17: rustc_query_impl::query_vtables::analysis::execute_query_non_incr::__rust_end_short_backtrace
            18: rustc_interface::interface::run_compiler::<(), rustc_driver_impl::run_compiler::{closure#0}>::{closure#2}
            19: std::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface::util::run_in_thread_with_globals<rustc_interface::util::run_in_thread_pool_with_globals<rustc_interface::interface::run_compiler<(), rustc_driver_impl::run_compiler::{closure#0}>::{closure#2}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
            20: <std::thread::lifecycle::spawn_unchecked<rustc_interface::util::run_in_thread_with_globals<rustc_interface::util::run_in_thread_pool_with_globals<rustc_interface::interface::run_compiler<(), rustc_driver_impl::run_compiler::{closure#0}>::{closure#2}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
            21: <std::sys::thread::unix::Thread>::new::thread_start
            22: <unknown>
            23: <unknown>
          

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: please make sure that you have updated to the latest nightly

note: rustc 1.100.0-nightly (b0ca9c712 2026-08-22) running on x86_64-unknown-linux-gnu

query stack during panic:
end of query stack

[matthiaskrgr]

This used to error before, now it just ICEs without any diagnostics

error[E0275]: overflow evaluating the requirement `fn() -> impl MyFnOnce {my_fn_2}: MyFnOnce`
   |
   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`a`)
note: required for `WrapFnOnce<fn() -> impl MyFnOnce {my_fn_1}>` to implement `MyFnOnce`
  --> a.rs:14:37
   |
14 | impl<F: FnOnce() -> D, D: MyFnOnce> MyFnOnce for WrapFnOnce<F> {
   |                           --------  ^^^^^^^^     ^^^^^^^^^^^^^
   |                           |
   |                           unsatisfied trait bound introduced here
   = note: 126 redundant requirements hidden
   = note: required for `WrapFnOnce<fn() -> impl MyFnOnce {my_fn_1}>` to implement `MyFnOnce`

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0275`.

[matthiaskrgr]

smaller

trait MyFnOnce {
    type Output;
    fn call_my_fn_once(self) -> Self::Output;
}
impl<F: FnOnce() -> D, D: MyFnOnce> MyFnOnce for F {
    type Output = D::Output;
    fn call_my_fn_once(self) -> Self::Output {
        D::call_my_fn_once(self())
    }
}
fn my_fn_1() -> impl MyFnOnce {
    my_fn_2
}
fn my_fn_2() -> impl MyFnOnce {
    my_fn_1
}
fn main() {
    my_fn_1.call_my_fn_once();
}

[lcnr]

cc @jdonszelmann @adwinwhite not only clippy lints are affected 😁

[matthiaskrgr]

the fun part is that this is just tests/ui/impl-trait/failed-to-resolve-instance-ice-105488.rs which makes me wonder if anyone ran the test suit at least once with the new solver enabled before pushing this into nightly 🤔

[jdonszelmann]

Ah...

[berkus]

Is that a dupe of #161495? Or they are just related

[matthiaskrgr]

I dont think so. #161495 is triggered by a specific clippy lint (which rustc does not know anything about).
The fix https://github.com/rust-lang/rust-clippy/pull/17601/changes also is contained to the clippy repo so it should not change how rustc behaves

[adwinwhite]

the fun part is that this is just tests/ui/impl-trait/failed-to-resolve-instance-ice-105488.rs which makes me wonder if anyone ran the test suit at least once with the new solver enabled before pushing this into nightly 🤔

It's on the ui test regression list