[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 ```Rust mod sealed { pub trait Sealed: Sized {} pub struct Bounds(T); impl Sealed for Bounds {} } 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; } trait Eqns: for<'a> EqnsRef<'a> { fn rhs(&self) -> >::Rhs; } trait EqnsImplicit: Eqns> {} impl EqnsImplicit for T where T: Eqns> {} 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) -> >::Rhs { MyRhs(self) } } fn inner() -> impl EqnsImplicit { 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: ::emit_diagnostic 1: ::emit_diagnostic 2: ::emit_producing_guarantee 3: ::span_delayed_bug:: 4: ::visit_body 5: rustc_borrowck::borrowck_collect_region_constraints 6: ::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_middle::dep_graph::graph::DepNodeIndex>, true> 10: rustc_query_impl::query_vtables::mir_borrowck::execute_query_incr::__rust_end_short_backtrace 11: ::par_hir_body_owners::::{closure#0} 12: rustc_interface::passes::analysis 13: rustc_query_impl::execution::try_execute_query::>, 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::::{closure#2}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()> 17: ::{closure#2}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core::ops::function::FnOnce<()>>::call_once::{shim:vtable#0} 18: ::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 ```