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

[matthiaskrgr]

auto-reduced (treereduce-rust):

mod assert {
    use std::mem::{Assume, TransmuteFrom};

    pub fn Eq<Src, Dst>()
    where
        for<'a> &'a i32: TransmuteFrom<&'a &'a u8>,
    {
    }
}

original:

#![feature(transmutability)]
mod assert {
    use std::mem::{Assume, TransmuteFrom};

    pub fn Eq<Src, Dst>()
    where
        for<'a> &'a i32: TransmuteFrom<&'a &'a u8, { Assume::LIFETIMES }>,
    {}
}

fn main() {
    assert::is_transmutable::<&'static mut bool, &'static mut u8>() // An uninitialized byte is never a valid initialized byte.
}

Version information

rustc 1.88.0-nightly (f820b75fe 2025-04-08)
binary: rustc
commit-hash: f820b75feef00654924c9351a2faca8d34818339
commit-date: 2025-04-08
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 504 to 516 in f820b75

	tcx.mk_predicate(from.map_bound(|clause| PredicateKind::Clause(clause))).expect_clause()
	}
	}
	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)
	}
	}
	impl<'tcx> UpcastFrom<TyCtxt<'tcx>, TraitRef<'tcx>> for Clause<'tcx> {
	fn upcast_from(from: TraitRef<'tcx>, tcx: TyCtxt<'tcx>) -> Self {
	let p: Predicate<'tcx> = from.upcast(tcx);

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

Program output

warning: unused import: `Assume`
 --> /tmp/icemaker_global_tempdir.RFrjpFwaQw0Y/rustc_testrunner_tmpdir_reporting.lvU8HTDAX63w/mvce.rs:2:20
  |
2 |     use std::mem::{Assume, TransmuteFrom};
  |                    ^^^^^^
  |
  = note: `#[warn(unused_imports)]` on by default

error[E0601]: `main` function not found in crate `mvce`
 --> /tmp/icemaker_global_tempdir.RFrjpFwaQw0Y/rustc_testrunner_tmpdir_reporting.lvU8HTDAX63w/mvce.rs:9:2
  |
9 | }
  |  ^ consider adding a `main` function to `/tmp/icemaker_global_tempdir.RFrjpFwaQw0Y/rustc_testrunner_tmpdir_reporting.lvU8HTDAX63w/mvce.rs`

error[E0658]: use of unstable library feature `transmutability`
 --> /tmp/icemaker_global_tempdir.RFrjpFwaQw0Y/rustc_testrunner_tmpdir_reporting.lvU8HTDAX63w/mvce.rs:2:20
  |
2 |     use std::mem::{Assume, TransmuteFrom};
  |                    ^^^^^^
  |
  = note: see issue #99571 <https://github.com/rust-lang/rust/issues/99571> for more information
  = help: add `#![feature(transmutability)]` to the crate attributes to enable
  = note: this compiler was built on 2025-04-08; consider upgrading it if it is out of date

error[E0658]: use of unstable library feature `transmutability`
 --> /tmp/icemaker_global_tempdir.RFrjpFwaQw0Y/rustc_testrunner_tmpdir_reporting.lvU8HTDAX63w/mvce.rs:2:28
  |
2 |     use std::mem::{Assume, TransmuteFrom};
  |                            ^^^^^^^^^^^^^
  |
  = note: see issue #99571 <https://github.com/rust-lang/rust/issues/99571> for more information
  = help: add `#![feature(transmutability)]` to the crate attributes to enable
  = note: this compiler was built on 2025-04-08; consider upgrading it if it is out of date

error[E0658]: use of unstable library feature `transmutability`
 --> /tmp/icemaker_global_tempdir.RFrjpFwaQw0Y/rustc_testrunner_tmpdir_reporting.lvU8HTDAX63w/mvce.rs:6:26
  |
6 |         for<'a> &'a i32: TransmuteFrom<&'a &'a u8>,
  |                          ^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = note: see issue #99571 <https://github.com/rust-lang/rust/issues/99571> for more information
  = help: add `#![feature(transmutability)]` to the crate attributes to enable
  = note: this compiler was built on 2025-04-08; consider upgrading it if it is out of date


thread 'rustc' panicked at compiler/rustc_middle/src/ty/predicate.rs:510:9:
`<&'a u8 as std::marker::Freeze>` has escaping bound vars, so it cannot be wrapped in a dummy binder.
stack backtrace:
   0:     0x79293b0a4dc3 - <std::sys::backtrace::BacktraceLock::print::DisplayBacktrace as core::fmt::Display>::fmt::hdbd77ff8b2b4625d
   1:     0x79293b8060d1 - core::fmt::write::h59ddf58c32ba8370
   2:     0x79293c94ccd1 - std::io::Write::write_fmt::hd978f7148dbf4f94
   3:     0x79293b0a4c22 - std::sys::backtrace::BacktraceLock::print::haa162a292a95f004
   4:     0x79293b0a870a - std::panicking::default_hook::{{closure}}::h648e12101ccbca91
   5:     0x79293b0a828f - std::panicking::default_hook::h01d889849cf2590e
   6:     0x79293a0fe953 - std[c70faf4444c356cf]::panicking::update_hook::<alloc[26dac2529edcf36b]::boxed::Box<rustc_driver_impl[31967e99e58374d9]::install_ice_hook::{closure#1}>>::{closure#0}
   7:     0x79293b0a8f83 - std::panicking::rust_panic_with_hook::h611dda71d5135552
   8:     0x79293b0a8c7a - std::panicking::begin_panic_handler::{{closure}}::h387e63b926b726e3
   9:     0x79293b0a5289 - std::sys::backtrace::__rust_end_short_backtrace::h4b522480d1ebfbf4
  10:     0x79293b0a893d - __rustc[66ac2f581dc52575]::rust_begin_unwind
  11:     0x792937a96af0 - core::panicking::panic_fmt::h346c412299a9954e
  12:     0x79293d63cbef - <rustc_middle[ebbb3d5645075279]::ty::predicate::Predicate as rustc_type_ir[90e471eab3b07150]::upcast::UpcastFrom<rustc_middle[ebbb3d5645075279]::ty::context::TyCtxt, rustc_type_ir[90e471eab3b07150]::predicate::TraitRef<rustc_middle[ebbb3d5645075279]::ty::context::TyCtxt>>>::upcast_from.cold
  13:     0x79293adc3d9c - <rustc_infer[e1534b85a75186ba]::traits::Obligation<rustc_middle[ebbb3d5645075279]::ty::predicate::Predicate>>::with_depth::<rustc_type_ir[90e471eab3b07150]::predicate::TraitRef<rustc_middle[ebbb3d5645075279]::ty::context::TyCtxt>>
  14:     0x79293af738e3 - <rustc_trait_selection[bf33ff605ac02ad3]::traits::select::SelectionContext>::confirm_transmutability_candidate::flatten_answer_tree
  15:     0x79293b93ce3c - <rustc_trait_selection[bf33ff605ac02ad3]::traits::select::SelectionContext>::confirm_candidate
  16:     0x79293b9a0f53 - <rustc_trait_selection[bf33ff605ac02ad3]::traits::select::SelectionContext>::evaluate_candidate::{closure#0}::{closure#0}
  17:     0x79293b9a3d72 - <rustc_trait_selection[bf33ff605ac02ad3]::traits::select::SelectionContext>::evaluate_trait_predicate_recursively
  18:     0x79293b9727c5 - <rustc_trait_selection[bf33ff605ac02ad3]::traits::select::SelectionContext>::evaluate_root_obligation
  19:     0x79293b970f39 - rustc_traits[e4f8648fe5aebaf8]::evaluate_obligation::evaluate_obligation
  20:     0x79293b970a29 - rustc_query_impl[773a75df8eb5b81d]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[773a75df8eb5b81d]::query_impl::evaluate_obligation::dynamic_query::{closure#2}::{closure#0}, rustc_middle[ebbb3d5645075279]::query::erase::Erased<[u8; 2usize]>>
  21:     0x79293c056a76 - rustc_query_system[23f296fe80b9d1a]::query::plumbing::try_execute_query::<rustc_query_impl[773a75df8eb5b81d]::DynamicConfig<rustc_query_system[23f296fe80b9d1a]::query::caches::DefaultCache<rustc_type_ir[90e471eab3b07150]::canonical::CanonicalQueryInput<rustc_middle[ebbb3d5645075279]::ty::context::TyCtxt, rustc_middle[ebbb3d5645075279]::ty::ParamEnvAnd<rustc_middle[ebbb3d5645075279]::ty::predicate::Predicate>>, rustc_middle[ebbb3d5645075279]::query::erase::Erased<[u8; 2usize]>>, false, false, false>, rustc_query_impl[773a75df8eb5b81d]::plumbing::QueryCtxt, true>
  22:     0x79293c055726 - rustc_query_impl[773a75df8eb5b81d]::query_impl::evaluate_obligation::get_query_incr::__rust_end_short_backtrace
  23:     0x79293caa6e6c - <rustc_trait_selection[bf33ff605ac02ad3]::traits::fulfill::FulfillProcessor>::process_trait_obligation
  24:     0x79293c1fa242 - <rustc_trait_selection[bf33ff605ac02ad3]::traits::fulfill::FulfillProcessor as rustc_data_structures[371315f59bf8c1a7]::obligation_forest::ObligationProcessor>::process_obligation
  25:     0x79293b807c88 - <rustc_data_structures[371315f59bf8c1a7]::obligation_forest::ObligationForest<rustc_trait_selection[bf33ff605ac02ad3]::traits::fulfill::PendingPredicateObligation>>::process_obligations::<rustc_trait_selection[bf33ff605ac02ad3]::traits::fulfill::FulfillProcessor>
  26:     0x79293bf86916 - rustc_trait_selection[bf33ff605ac02ad3]::traits::impossible_predicates
  27:     0x79293bf858ef - <rustc_mir_transform[3ded69e58d16e7b9]::impossible_predicates::ImpossiblePredicates as rustc_mir_transform[3ded69e58d16e7b9]::pass_manager::MirPass>::run_pass
  28:     0x79293b80c0e8 - rustc_mir_transform[3ded69e58d16e7b9]::run_analysis_to_runtime_passes
  29:     0x79293ba1471e - rustc_mir_transform[3ded69e58d16e7b9]::mir_drops_elaborated_and_const_checked
  30:     0x79293ba14119 - rustc_query_impl[773a75df8eb5b81d]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[773a75df8eb5b81d]::query_impl::mir_drops_elaborated_and_const_checked::dynamic_query::{closure#2}::{closure#0}, rustc_middle[ebbb3d5645075279]::query::erase::Erased<[u8; 8usize]>>
  31:     0x79293ba0c19b - rustc_query_system[23f296fe80b9d1a]::query::plumbing::try_execute_query::<rustc_query_impl[773a75df8eb5b81d]::DynamicConfig<rustc_data_structures[371315f59bf8c1a7]::vec_cache::VecCache<rustc_span[7e698d9580936219]::def_id::LocalDefId, rustc_middle[ebbb3d5645075279]::query::erase::Erased<[u8; 8usize]>, rustc_query_system[23f296fe80b9d1a]::dep_graph::graph::DepNodeIndex>, false, false, false>, rustc_query_impl[773a75df8eb5b81d]::plumbing::QueryCtxt, true>
  32:     0x79293bb37c92 - rustc_query_impl[773a75df8eb5b81d]::query_impl::mir_drops_elaborated_and_const_checked::get_query_incr::__rust_end_short_backtrace
  33:     0x79293c3017ab - rustc_interface[6d50c1beb4a63bd8]::passes::run_required_analyses
  34:     0x79293c83985e - rustc_interface[6d50c1beb4a63bd8]::passes::analysis
  35:     0x79293c839833 - rustc_query_impl[773a75df8eb5b81d]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[773a75df8eb5b81d]::query_impl::analysis::dynamic_query::{closure#2}::{closure#0}, rustc_middle[ebbb3d5645075279]::query::erase::Erased<[u8; 0usize]>>
  36:     0x79293c8360fd - rustc_query_system[23f296fe80b9d1a]::query::plumbing::try_execute_query::<rustc_query_impl[773a75df8eb5b81d]::DynamicConfig<rustc_query_system[23f296fe80b9d1a]::query::caches::SingleCache<rustc_middle[ebbb3d5645075279]::query::erase::Erased<[u8; 0usize]>>, false, false, false>, rustc_query_impl[773a75df8eb5b81d]::plumbing::QueryCtxt, true>
  37:     0x79293c835a21 - rustc_query_impl[773a75df8eb5b81d]::query_impl::analysis::get_query_incr::__rust_end_short_backtrace
  38:     0x79293cb2190b - rustc_interface[6d50c1beb4a63bd8]::passes::create_and_enter_global_ctxt::<core[69ddc073adf9e1df]::option::Option<rustc_interface[6d50c1beb4a63bd8]::queries::Linker>, rustc_driver_impl[31967e99e58374d9]::run_compiler::{closure#0}::{closure#2}>::{closure#2}::{closure#0}
  39:     0x79293c95da39 - rustc_interface[6d50c1beb4a63bd8]::interface::run_compiler::<(), rustc_driver_impl[31967e99e58374d9]::run_compiler::{closure#0}>::{closure#1}
  40:     0x79293c7b5c85 - std[c70faf4444c356cf]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[6d50c1beb4a63bd8]::util::run_in_thread_with_globals<rustc_interface[6d50c1beb4a63bd8]::util::run_in_thread_pool_with_globals<rustc_interface[6d50c1beb4a63bd8]::interface::run_compiler<(), rustc_driver_impl[31967e99e58374d9]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
  41:     0x79293c7b656b - <<std[c70faf4444c356cf]::thread::Builder>::spawn_unchecked_<rustc_interface[6d50c1beb4a63bd8]::util::run_in_thread_with_globals<rustc_interface[6d50c1beb4a63bd8]::util::run_in_thread_pool_with_globals<rustc_interface[6d50c1beb4a63bd8]::interface::run_compiler<(), rustc_driver_impl[31967e99e58374d9]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core[69ddc073adf9e1df]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  42:     0x79293c7b7977 - std::sys::pal::unix::thread::Thread::new::thread_start::h04ddb6eb66f748e1
  43:     0x79293665d70a - <unknown>
  44:     0x7929366e1aac - <unknown>
  45:                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 (f820b75fe 2025-04-08) running on x86_64-unknown-linux-gnu

note: compiler flags: -Z incremental-verify-ich=yes -C incremental=[REDACTED] -C debuginfo=2 -C link-dead-code=true -Z validate-mir

query stack during panic:
#0 [evaluate_obligation] evaluating trait selection obligation `for<'a> &'a i32: core::mem::transmutability::TransmuteFrom<&'a &'a u8, core::mem::transmutability::Assume { alignment: false, lifetimes: false, safety: false, validity: false }>`
#1 [mir_drops_elaborated_and_const_checked] elaborating drops for `assert::Eq`
#2 [analysis] running analysis passes on this crate
end of query stack
error: aborting due to 4 previous errors; 1 warning emitted

Some errors have detailed explanations: E0601, E0658.
For more information about an error, try `rustc --explain E0601`.

@rustbot label +F-transmutability +-Zvalidate-mir