[ICE]: error performing operation: fully_perform: triggered by a sealed supertrait + associated-type-bound subtraits

I found this ICE when upgrading to +nightly-2026-09-04 (+nightly-2026-06-05 worked fine). I have a crate with a sealed ImplicitBounds = Bounds<&'a Self> + for<'a> supertrait + associated-type-bound subtraits, something in which is triggering the error. I used an LLM to reduce the set of traits to the MRE below:

Code

mod sealed {
    pub trait Sealed: Sized {}
    pub struct Bounds<T>(T);
    impl<T> Sealed for Bounds<T> {}
}
use sealed::{Bounds, Sealed};

trait Op {
    type V;
}

trait Jac: Op {
    fn jacobian(&self, x: &Self::V);
}

trait EqnsRef<'a, ImplicitBounds: Sealed = Bounds<&'a Self>>: Op {
    type Rhs: Op<V = Self::V>;
}

trait Eqns: for<'a> EqnsRef<'a> {
    fn rhs(&self) -> <Self as EqnsRef<'_>>::Rhs;
}

trait EqnsImplicit: Eqns<Rhs: Jac<V = Self::V>> {}
impl<T> EqnsImplicit for T where T: Eqns<Rhs: Jac<V = T::V>> {}

struct MyEqns;
struct MyRhs<'a>(&'a MyEqns);

impl Op for MyRhs<'_> {
    type V = f64;
}
impl Jac for MyRhs<'_> {
    fn jacobian(&self, _x: &f64) {}
}
impl Op for MyEqns {
    type V = f64;
}
impl<'a> EqnsRef<'a> for MyEqns {
    type Rhs = MyRhs<'a>;
}
impl Eqns for MyEqns {
    fn rhs(&self) -> <Self as EqnsRef<'_>>::Rhs {
        MyRhs(self)
    }
}

fn inner() -> impl EqnsImplicit<V = f64> {
    MyEqns
}

pub fn outer() {
    inner().rhs().jacobian(&0.0);
}

Meta

rustc +nightly --version --verbose:

rustc 1.100.0-nightly (0ed41eb41 2026-09-04)
binary: rustc
commit-hash: 0ed41eb4142dda2df61eb1145a312c1a9d62eb56
commit-date: 2026-09-04
host: x86_64-unknown-linux-gnu
release: 1.100.0-nightly
LLVM version: 23.1.1

Error output

❯ RUST_BACKTRACE=1 cargo +nightly build
   Compiling ice-mre v0.0.0 (/home/mrobins/git/tmp/ice-mre)
warning: field `0` is never read
  --> src/lib.rs:28:18
   |
28 | struct MyRhs<'a>(&'a MyEqns);
   |        -----     ^^^^^^^^^^
   |        |
   |        field in this struct
   |
   = help: consider removing this field
   = note: `#[warn(dead_code)]` (part of `#[warn(unused)]`) on by default

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: error performing operation: fully_perform
  --> src/lib.rs:53:5
   |
53 |     inner().rhs().jacobian(&0.0);
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
note: delayed at /rustc-dev/0ed41eb4142dda2df61eb1145a312c1a9d62eb56/compiler/rustc_trait_selection/src/traits/query/type_op/custom.rs:126:26
         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>::span_delayed_bug::<rustc_span::span_encoding::Span, alloc::string::String>
         4: <rustc_borrowck::type_check::TypeChecker as rustc_middle::mir::visit::Visitor>::visit_body
         5: rustc_borrowck::borrowck_collect_region_constraints
         6: <rustc_borrowck::root_cx::BorrowCheckRootCtxt>::do_mir_borrowck
         7: rustc_borrowck::mir_borrowck
         8: rustc_query_impl::query_vtables::mir_borrowck::invoke_provider_fn::__rust_begin_short_backtrace
         9: 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>, true>
        10: rustc_query_impl::query_vtables::mir_borrowck::execute_query_incr::__rust_end_short_backtrace
        11: <rustc_middle::ty::context::TyCtxt>::par_hir_body_owners::<rustc_interface::passes::run_required_analyses::{closure#2}::{closure#0}>::{closure#0}
        12: rustc_interface::passes::analysis
        13: rustc_query_impl::execution::try_execute_query::<rustc_middle::query::caches::SingleCache<rustc_middle::query::erase::ErasedData<[u8; 0]>>, true>
        14: rustc_query_impl::query_vtables::analysis::execute_query_incr::__rust_end_short_backtrace
        15: rustc_interface::interface::run_compiler::<(), rustc_driver_impl::run_compiler::{closure#0}>::{closure#2}
        16: 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}, ()>
        17: <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}
        18: <std::sys::thread::unix::Thread>::new::thread_start
        19: start_thread
                   at ./nptl/pthread_create.c:454:8
        20: clone
                   at ./misc/../sysdeps/unix/sysv/linux/x86_64/clone.S:100:0

  --> src/lib.rs:53:5
   |
53 |     inner().rhs().jacobian(&0.0);
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^

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: please attach the file at `/home/mrobins/git/tmp/ice-mre/rustc-ice-2026-09-05T09_39_28-1345463.txt` to your bug report

note: rustc 1.100.0-nightly (0ed41eb41 2026-09-04) running on x86_64-unknown-linux-gnu

note: compiler flags: --crate-type lib -Z embed-metadata=no -C embed-bitcode=no -C debuginfo=2 -C incremental=[REDACTED]

note: some of the compiler flags provided by cargo are hidden

query stack during panic:
end of query stack
warning: `ice-mre` (lib) generated 1 warning
error: could not compile `ice-mre` (lib); 1 warning emitted

Reproduce the ICE with the MRE in src/lib.rs by running cargo +nightly build. Start with the delayed-bug location in compiler/rustc_trait_selection/src/traits/query/type_op/custom.rs and the borrow-checking frames in the report. Done means the reduced case no longer produces an internal compiler error and a regression test covers it.