ICE: `has escaping bound vars, so it cannot be wrapped in a dummy binder` with `unsafe_binders`

[cushionbadak]

Code

#![feature(unsafe_binders)]
#![allow(incomplete_features)]

#[derive(PartialEq, Eq)]
enum O<T> {
    Some(T),
    None,
}

const C: &[O<unsafe<'a, 'b> &'b Box<dyn Fn(Box<dyn Fn() -> &'a isize>)>>] = &[O::None];

fn main() {
    let x = O::None;
    match &[x][..] {
        C => (),
        _ => (),
    }
}

A mutant from glacier2's fixed/134764.rs

Meta

rustc --version --verbose:

rustc 1.89.0-nightly (2eef47813 2025-05-22)
binary: rustc
commit-hash: 2eef47813f25df637026ce3288880e5c587abd92
commit-date: 2025-05-22
host: x86_64-apple-darwin
release: 1.89.0-nightly
LLVM version: 20.1.5

Error output

command: rustc

thread 'rustc' panicked at compiler/rustc_middle/src/ty/predicate.rs:510:9:
`<std::boxed::Box<dyn std::ops::Fn(std::boxed::Box<dyn std::ops::Fn() -> &'a isize>)> as std::cmp::PartialEq>` has escaping bound vars, so it cannot be wrapped in a dummy binder.

Backtrace

stack backtrace:
   0: __rustc::rust_begin_unwind
   1: core::panicking::panic_fmt
   2: <rustc_middle::ty::predicate::Predicate as rustc_type_ir::upcast::UpcastFrom<rustc_middle::ty::context::TyCtxt, rustc_type_ir::predicate::TraitRef<rustc_middle::ty::context::TyCtxt>>>::upcast_from
   3: rustc_mir_build::thir::pattern::const_to_pat::type_has_partial_eq_impl
   4: <rustc_mir_build::thir::pattern::const_to_pat::extend_type_not_partial_eq::UsedParamsNeedInstantiationVisitor as rustc_type_ir::visit::TypeVisitor<rustc_middle::ty::context::TyCtxt>>::visit_ty
   5: <rustc_mir_build::thir::pattern::const_to_pat::extend_type_not_partial_eq::UsedParamsNeedInstantiationVisitor as rustc_type_ir::visit::TypeVisitor<rustc_middle::ty::context::TyCtxt>>::visit_ty
   6: <rustc_mir_build::thir::pattern::const_to_pat::extend_type_not_partial_eq::UsedParamsNeedInstantiationVisitor as rustc_type_ir::visit::TypeVisitor<rustc_middle::ty::context::TyCtxt>>::visit_ty
   7: <rustc_middle::ty::Ty as rustc_type_ir::visit::TypeSuperVisitable<rustc_middle::ty::context::TyCtxt>>::super_visit_with::<rustc_mir_build::thir::pattern::const_to_pat::extend_type_not_partial_eq::UsedParamsNeedInstantiationVisitor>
   8: <rustc_mir_build::thir::pattern::const_to_pat::extend_type_not_partial_eq::UsedParamsNeedInstantiationVisitor as rustc_type_ir::visit::TypeVisitor<rustc_middle::ty::context::TyCtxt>>::visit_ty
   9: <rustc_mir_build::thir::pattern::const_to_pat::extend_type_not_partial_eq::UsedParamsNeedInstantiationVisitor as rustc_type_ir::visit::TypeVisitor<rustc_middle::ty::context::TyCtxt>>::visit_ty
  10: <rustc_mir_build::thir::pattern::const_to_pat::extend_type_not_partial_eq::UsedParamsNeedInstantiationVisitor as rustc_type_ir::visit::TypeVisitor<rustc_middle::ty::context::TyCtxt>>::visit_ty
  11: <rustc_mir_build::thir::pattern::PatCtxt>::const_to_pat
  12: <rustc_mir_build::thir::pattern::PatCtxt>::lower_pat_expr
  13: <rustc_mir_build::thir::pattern::PatCtxt>::lower_pattern
  14: <rustc_mir_build::thir::cx::ThirBuildCx>::pattern_from_hir
  15: <rustc_mir_build::thir::cx::ThirBuildCx>::make_mirror_unadjusted::{closure#0}
  16: <rustc_mir_build::thir::cx::ThirBuildCx>::mirror_expr_inner
  17: <rustc_mir_build::thir::cx::ThirBuildCx>::mirror_block
  18: <rustc_mir_build::thir::cx::ThirBuildCx>::make_mirror_unadjusted::{closure#0}
  19: <rustc_mir_build::thir::cx::ThirBuildCx>::mirror_expr_inner
  20: rustc_mir_build::thir::cx::thir_body
      [... omitted 2 frames ...]
  21: rustc_mir_build::check_unsafety::check_unsafety
      [... omitted 1 frame ...]
  22: <rustc_middle::ty::context::TyCtxt>::par_hir_body_owners::<rustc_interface::passes::run_required_analyses::{closure#2}::{closure#0}>::{closure#0}
  23: rustc_interface::passes::run_required_analyses
  24: rustc_interface::passes::analysis
      [... omitted 1 frame ...]
  25: rustc_interface::passes::create_and_enter_global_ctxt::<core::option::Option<rustc_interface::queries::Linker>, rustc_driver_impl::run_compiler::{closure#0}::{closure#2}>
  26: rustc_interface::interface::run_compiler::<(), rustc_driver_impl::run_compiler::{closure#0}>::{closure#1}
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

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

note: please attach the file at `/Volumes/T7/workspace/scratch_250523/run_250522_250505_feat_unsafe_binder/scratch/rustc-ice-2025-05-23T05_41_54-40103.txt` to your bug report

query stack during panic:
#0 [thir_body] building THIR for `main`
#1 [check_unsafety] unsafety-checking `main`
#2 [analysis] running analysis passes on this crate
end of query stack

Bisects to

searched nightlies: from nightly-2024-05-01 to nightly-2025-05-22
regressed nightly: nightly-2024-12-25
searched commit range: bdc6b3d...409998c
regressed commit: f334342

bisected with cargo-bisect-rustc v0.6.9

Host triple: x86_64-unknown-linux-gnu
Reproduce with:

cargo bisect-rustc --end=2025-05-22 --regress ice --preserve --script rustc -- uncl1_r.rs

Notes

• ICE location: compiler/rustc_middle/src/ty/predicate.rs Line-510
  

  rust/compiler/rustc_middle/src/ty/predicate.rs

  Lines 508 to 512 in 2eef478

  	impl<'tcx> UpcastFrom<TyCtxt<'tcx>, TraitRef<'tcx>> for Predicate<'tcx> {
  	fn upcast_from(from: TraitRef<'tcx>, tcx: TyCtxt<'tcx>) -> Self {
  	ty::Binder::dummy(from).upcast(tcx)
  	}
  	}

• There are several other ICE issues with the same ICE location as this one, but require different feature and have different query stack.

@rustbot label +F-unsafe_binders