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

[matthiaskrgr]

auto-reduced (treereduce-rust):

#![feature(non_lifetime_binders)]
trait v0 {}
fn kind()  -> (dyn v0<'static, > impl for<v4> v0<v4>) {}

original:

#![feature(non_lifetime_binders)]
trait v0 {}
fn kind()  -> (dyn v0<'static, > impl for<v4> v0<v4>) {}

fn main() {}

Version information

rustc 1.88.0-nightly (946aea0b3 2025-04-03)
binary: rustc
commit-hash: 946aea0b3d9f43e57953ce5094d8e4a2a244ce71
commit-date: 2025-04-03
host: x86_64-unknown-linux-gnu
release: 1.88.0-nightly
LLVM version: 20.1.2

Possibly related line of code:

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

Lines 462 to 474 in 946aea0

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

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

Program output

error: expected one of `)`, `+`, `,`, or `::`, found keyword `impl`
 --> /tmp/icemaker_global_tempdir.ShOGs7fNRhWu/rustc_testrunner_tmpdir_reporting.uYRB9lC4sTQY/mvce.rs:3:34
  |
3 | fn kind()  -> (dyn v0<'static, > impl for<v4> v0<v4>) {}
  |                                 -^^^^ expected one of `)`, `+`, `,`, or `::`
  |                                 |
  |                                 help: missing `,`

warning: the feature `non_lifetime_binders` is incomplete and may not be safe to use and/or cause compiler crashes
 --> /tmp/icemaker_global_tempdir.ShOGs7fNRhWu/rustc_testrunner_tmpdir_reporting.uYRB9lC4sTQY/mvce.rs:1:12
  |
1 | #![feature(non_lifetime_binders)]
  |            ^^^^^^^^^^^^^^^^^^^^
  |
  = note: see issue #108185 <https://github.com/rust-lang/rust/issues/108185> for more information
  = note: `#[warn(incomplete_features)]` on by default

warning: trait `v0` should have an upper camel case name
 --> /tmp/icemaker_global_tempdir.ShOGs7fNRhWu/rustc_testrunner_tmpdir_reporting.uYRB9lC4sTQY/mvce.rs:2:7
  |
2 | trait v0 {}
  |       ^^ help: convert the identifier to upper camel case (notice the capitalization): `V0`
  |
  = note: `#[warn(non_camel_case_types)]` on by default

warning: type parameter `v4` should have an upper camel case name
 --> /tmp/icemaker_global_tempdir.ShOGs7fNRhWu/rustc_testrunner_tmpdir_reporting.uYRB9lC4sTQY/mvce.rs:3:43
  |
3 | fn kind()  -> (dyn v0<'static, > impl for<v4> v0<v4>) {}
  |                                           ^^ help: convert the identifier to upper camel case (notice the capitalization): `V4`

error[E0601]: `main` function not found in crate `mvce`
 --> /tmp/icemaker_global_tempdir.ShOGs7fNRhWu/rustc_testrunner_tmpdir_reporting.uYRB9lC4sTQY/mvce.rs:3:57
  |
3 | fn kind()  -> (dyn v0<'static, > impl for<v4> v0<v4>) {}
  |                                                         ^ consider adding a `main` function to `/tmp/icemaker_global_tempdir.ShOGs7fNRhWu/rustc_testrunner_tmpdir_reporting.uYRB9lC4sTQY/mvce.rs`

error[E0107]: trait takes 0 lifetime arguments but 1 lifetime argument was supplied
 --> /tmp/icemaker_global_tempdir.ShOGs7fNRhWu/rustc_testrunner_tmpdir_reporting.uYRB9lC4sTQY/mvce.rs:3:20
  |
3 | fn kind()  -> (dyn v0<'static, > impl for<v4> v0<v4>) {}
  |                    ^^----------- help: remove the unnecessary generics
  |                    |
  |                    expected 0 lifetime arguments
  |
note: trait defined here, with 0 lifetime parameters
 --> /tmp/icemaker_global_tempdir.ShOGs7fNRhWu/rustc_testrunner_tmpdir_reporting.uYRB9lC4sTQY/mvce.rs:2:7
  |
2 | trait v0 {}
  |       ^^

error[E0107]: trait takes 0 generic arguments but 1 generic argument was supplied
 --> /tmp/icemaker_global_tempdir.ShOGs7fNRhWu/rustc_testrunner_tmpdir_reporting.uYRB9lC4sTQY/mvce.rs:3:47
  |
3 | fn kind()  -> (dyn v0<'static, > impl for<v4> v0<v4>) {}
  |                                               ^^---- help: remove the unnecessary generics
  |                                               |
  |                                               expected 0 generic arguments
  |
note: trait defined here, with 0 generic parameters
 --> /tmp/icemaker_global_tempdir.ShOGs7fNRhWu/rustc_testrunner_tmpdir_reporting.uYRB9lC4sTQY/mvce.rs:2:7
  |
2 | trait v0 {}
  |       ^^


thread 'rustc' panicked at compiler/rustc_middle/src/ty/predicate.rs:468:9:
`WellFormed(^"v4")` has escaping bound vars, so it cannot be wrapped in a dummy binder.
stack backtrace:
   0:     0x731e3246bf43 - <std::sys::backtrace::BacktraceLock::print::DisplayBacktrace as core::fmt::Display>::fmt::hde263b85c5db2e5f
   1:     0x731e32c06111 - core::fmt::write::h9b8038f00f576ae0
   2:     0x731e34099291 - std::io::Write::write_fmt::hf04ec7828273ae13
   3:     0x731e3246bda2 - std::sys::backtrace::BacktraceLock::print::h944578450d8a8c30
   4:     0x731e3246f88a - std::panicking::default_hook::{{closure}}::h4e55257e05dc0eaf
   5:     0x731e3246f40f - std::panicking::default_hook::h79a253b530fabb9d
   6:     0x731e314e7930 - std[f6562b0534d53c43]::panicking::update_hook::<alloc[e2be6985779dab61]::boxed::Box<rustc_driver_impl[1b5918a4900d57a3]::install_ice_hook::{closure#1}>>::{closure#0}
   7:     0x731e32470103 - std::panicking::rust_panic_with_hook::h4b5a473804813370
   8:     0x731e3246fdfa - std::panicking::begin_panic_handler::{{closure}}::h4734d8630efce563
   9:     0x731e3246c419 - std::sys::backtrace::__rust_end_short_backtrace::hf5306bd179a9758e
  10:     0x731e3246fabd - __rustc[7a6e3b08990bd1b9]::rust_begin_unwind
  11:     0x731e2eea1530 - core::panicking::panic_fmt::h23b650f0efa75d6d
  12:     0x731e347ac81d - <rustc_middle[26df542b903f2b2a]::ty::predicate::Predicate as rustc_type_ir[d2925d285d1bace9]::upcast::UpcastFrom<rustc_middle[26df542b903f2b2a]::ty::context::TyCtxt, rustc_type_ir[d2925d285d1bace9]::predicate_kind::PredicateKind<rustc_middle[26df542b903f2b2a]::ty::context::TyCtxt>>>::upcast_from.cold
  13:     0x731e315cde97 - <rustc_infer[5ec55a8f82fe16e]::traits::Obligation<rustc_middle[26df542b903f2b2a]::ty::predicate::Predicate>>::with_depth::<rustc_type_ir[d2925d285d1bace9]::predicate_kind::PredicateKind<rustc_middle[26df542b903f2b2a]::ty::context::TyCtxt>>
  14:     0x731e316e04f9 - <rustc_hir_analysis[e7d0ddac047c6029]::hir_wf_check::diagnostic_hir_wf_check::HirWfCheck as rustc_hir[7d99c1a77ed599c4]::intravisit::Visitor>::visit_ty
  15:     0x731e315e3d55 - rustc_hir[7d99c1a77ed599c4]::intravisit::walk_generic_args::<rustc_hir_analysis[e7d0ddac047c6029]::hir_wf_check::diagnostic_hir_wf_check::HirWfCheck>
  16:     0x731e315e38a5 - rustc_hir[7d99c1a77ed599c4]::intravisit::walk_param_bound::<rustc_hir_analysis[e7d0ddac047c6029]::hir_wf_check::diagnostic_hir_wf_check::HirWfCheck>
  17:     0x731e316e080e - <rustc_hir_analysis[e7d0ddac047c6029]::hir_wf_check::diagnostic_hir_wf_check::HirWfCheck as rustc_hir[7d99c1a77ed599c4]::intravisit::Visitor>::visit_ty
  18:     0x731e316e0958 - <rustc_hir_analysis[e7d0ddac047c6029]::hir_wf_check::diagnostic_hir_wf_check::HirWfCheck as rustc_hir[7d99c1a77ed599c4]::intravisit::Visitor>::visit_ty
  19:     0x731e316dfd77 - rustc_hir_analysis[e7d0ddac047c6029]::hir_wf_check::diagnostic_hir_wf_check
  20:     0x731e31f6000f - rustc_query_impl[a177b0cf2514e65]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[a177b0cf2514e65]::query_impl::diagnostic_hir_wf_check::dynamic_query::{closure#2}::{closure#0}, rustc_middle[26df542b903f2b2a]::query::erase::Erased<[u8; 8usize]>>
  21:     0x731e31f385d3 - <rustc_query_impl[a177b0cf2514e65]::query_impl::diagnostic_hir_wf_check::dynamic_query::{closure#2} as core[dcee7a2746af8d03]::ops::function::FnOnce<(rustc_middle[26df542b903f2b2a]::ty::context::TyCtxt, (rustc_middle[26df542b903f2b2a]::ty::predicate::Predicate, rustc_middle[26df542b903f2b2a]::traits::WellFormedLoc))>>::call_once
  22:     0x731e31ea47f2 - rustc_query_system[d06e27ff9a2bb429]::query::plumbing::try_execute_query::<rustc_query_impl[a177b0cf2514e65]::DynamicConfig<rustc_query_system[d06e27ff9a2bb429]::query::caches::DefaultCache<(rustc_middle[26df542b903f2b2a]::ty::predicate::Predicate, rustc_middle[26df542b903f2b2a]::traits::WellFormedLoc), rustc_middle[26df542b903f2b2a]::query::erase::Erased<[u8; 8usize]>>, false, false, false>, rustc_query_impl[a177b0cf2514e65]::plumbing::QueryCtxt, false>
  23:     0x731e31f9a0c0 - rustc_query_impl[a177b0cf2514e65]::query_impl::diagnostic_hir_wf_check::get_query_non_incr::__rust_end_short_backtrace
  24:     0x731e322846b5 - <rustc_trait_selection[b2017cfa88f3bdb1]::error_reporting::TypeErrCtxt>::report_selection_error
  25:     0x731e322e61df - <rustc_trait_selection[b2017cfa88f3bdb1]::error_reporting::TypeErrCtxt>::report_fulfillment_errors
  26:     0x731e33253000 - rustc_hir_analysis[e7d0ddac047c6029]::check::wfcheck::check_item_fn
  27:     0x731e3333c0e2 - rustc_hir_analysis[e7d0ddac047c6029]::check::wfcheck::check_well_formed
  28:     0x731e3333a251 - rustc_query_impl[a177b0cf2514e65]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[a177b0cf2514e65]::query_impl::check_well_formed::dynamic_query::{closure#2}::{closure#0}, rustc_middle[26df542b903f2b2a]::query::erase::Erased<[u8; 1usize]>>
  29:     0x731e33339afa - rustc_query_system[d06e27ff9a2bb429]::query::plumbing::try_execute_query::<rustc_query_impl[a177b0cf2514e65]::DynamicConfig<rustc_data_structures[a49c47847d07a40c]::vec_cache::VecCache<rustc_span[f4fedfef03388269]::def_id::LocalDefId, rustc_middle[26df542b903f2b2a]::query::erase::Erased<[u8; 1usize]>, rustc_query_system[d06e27ff9a2bb429]::dep_graph::graph::DepNodeIndex>, false, false, false>, rustc_query_impl[a177b0cf2514e65]::plumbing::QueryCtxt, false>
  30:     0x731e333395d7 - rustc_query_impl[a177b0cf2514e65]::query_impl::check_well_formed::get_query_non_incr::__rust_end_short_backtrace
  31:     0x731e33336a6d - rustc_hir_analysis[e7d0ddac047c6029]::check::wfcheck::check_mod_type_wf
  32:     0x731e33336895 - rustc_query_impl[a177b0cf2514e65]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[a177b0cf2514e65]::query_impl::check_mod_type_wf::dynamic_query::{closure#2}::{closure#0}, rustc_middle[26df542b903f2b2a]::query::erase::Erased<[u8; 1usize]>>
  33:     0x731e33c09759 - rustc_query_system[d06e27ff9a2bb429]::query::plumbing::try_execute_query::<rustc_query_impl[a177b0cf2514e65]::DynamicConfig<rustc_query_system[d06e27ff9a2bb429]::query::caches::DefaultCache<rustc_span[f4fedfef03388269]::def_id::LocalModDefId, rustc_middle[26df542b903f2b2a]::query::erase::Erased<[u8; 1usize]>>, false, false, false>, rustc_query_impl[a177b0cf2514e65]::plumbing::QueryCtxt, false>
  34:     0x731e33c094ca - rustc_query_impl[a177b0cf2514e65]::query_impl::check_mod_type_wf::get_query_non_incr::__rust_end_short_backtrace
  35:     0x731e32ebae57 - rustc_hir_analysis[e7d0ddac047c6029]::check_crate
  36:     0x731e32f7425d - rustc_interface[e6a7fad6374939eb]::passes::run_required_analyses
  37:     0x731e33c0329e - rustc_interface[e6a7fad6374939eb]::passes::analysis
  38:     0x731e33c03273 - rustc_query_impl[a177b0cf2514e65]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[a177b0cf2514e65]::query_impl::analysis::dynamic_query::{closure#2}::{closure#0}, rustc_middle[26df542b903f2b2a]::query::erase::Erased<[u8; 0usize]>>
  39:     0x731e33bca483 - rustc_query_system[d06e27ff9a2bb429]::query::plumbing::try_execute_query::<rustc_query_impl[a177b0cf2514e65]::DynamicConfig<rustc_query_system[d06e27ff9a2bb429]::query::caches::SingleCache<rustc_middle[26df542b903f2b2a]::query::erase::Erased<[u8; 0usize]>>, false, false, false>, rustc_query_impl[a177b0cf2514e65]::plumbing::QueryCtxt, false>
  40:     0x731e33bca17e - rustc_query_impl[a177b0cf2514e65]::query_impl::analysis::get_query_non_incr::__rust_end_short_backtrace
  41:     0x731e33d7448d - rustc_interface[e6a7fad6374939eb]::passes::create_and_enter_global_ctxt::<core[dcee7a2746af8d03]::option::Option<rustc_interface[e6a7fad6374939eb]::queries::Linker>, rustc_driver_impl[1b5918a4900d57a3]::run_compiler::{closure#0}::{closure#2}>::{closure#2}::{closure#0}
  42:     0x731e33da722a - rustc_interface[e6a7fad6374939eb]::interface::run_compiler::<(), rustc_driver_impl[1b5918a4900d57a3]::run_compiler::{closure#0}>::{closure#1}
  43:     0x731e33ba4b88 - std[f6562b0534d53c43]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[e6a7fad6374939eb]::util::run_in_thread_with_globals<rustc_interface[e6a7fad6374939eb]::util::run_in_thread_pool_with_globals<rustc_interface[e6a7fad6374939eb]::interface::run_compiler<(), rustc_driver_impl[1b5918a4900d57a3]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
  44:     0x731e33ba5474 - <<std[f6562b0534d53c43]::thread::Builder>::spawn_unchecked_<rustc_interface[e6a7fad6374939eb]::util::run_in_thread_with_globals<rustc_interface[e6a7fad6374939eb]::util::run_in_thread_pool_with_globals<rustc_interface[e6a7fad6374939eb]::interface::run_compiler<(), rustc_driver_impl[1b5918a4900d57a3]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core[dcee7a2746af8d03]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  45:     0x731e33ba6877 - std::sys::pal::unix::thread::Thread::new::thread_start::hc68e48949b6c9c5b
  46:     0x731e2daa370a - <unknown>
  47:     0x731e2db27aac - <unknown>
  48:                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: please make sure that you have updated to the latest nightly

note: rustc 1.88.0-nightly (946aea0b3 2025-04-03) running on x86_64-unknown-linux-gnu

query stack during panic:
#0 [diagnostic_hir_wf_check] performing HIR wf-checking for predicate `Binder { value: TraitPredicate(<dyn v0 as core::marker::Sized>, polarity:Positive), bound_vars: [] }` at item `Param { function: DefId(0:4 ~ mvce[4bf8]::kind), param_idx: 0 }`
#1 [check_well_formed] checking that `kind` is well-formed
#2 [check_mod_type_wf] checking that types are well-formed in top-level module
#3 [analysis] running analysis passes on this crate
end of query stack
error: aborting due to 4 previous errors; 3 warnings emitted

Some errors have detailed explanations: E0107, E0601.
For more information about an error, try `rustc --explain E0107`.

@rustbot label +F-non_lifetime_binders

[matthiaskrgr]

yeet

#![feature(non_lifetime_binders)]
trait A {}
fn b() -> (dyn A impl for<C> A<C>) {}