ICE: `add_outlives_bounds: unexpected regions`

Nobody has claimed this yet.

I tried this code:

#![feature(adt_const_params)]
#![feature(unsized_const_params)]
trait Config {
    const DATA: &[&[u8]];
}
struct Provider;
impl Config for Provider {
    const DATA: &[&[u8]] = &[&[]];
}
struct Box<const DATA: &'static [&'static [u8]]> {}
impl Drop for Box<{ Provider::DATA }> {
    fn drop(& mut self) {}
}
fn main() {
    let _ = Box::<{ Provider::DATA }>;
}

Related to #152891

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rustc --version --verbose:

rustc 1.95.0-nightly (6a979b3e3 2026-02-26)
binary: rustc
commit-hash: 6a979b3e32522049d0acb4a47f7ae44b7c8abfd5
commit-date: 2026-02-26
host: x86_64-unknown-linux-gnu
release: 1.95.0-nightly
LLVM version: 22.1.0

Backtrace

error[E0423]: expected value, found struct `Box`
  --> bug.rs:15:13
   |
10 | struct Box<const DATA: &'static [&'static [u8]]> {}
   | --------------------------------------------------- `Box` defined here
...
15 |     let _ = Box::<{ Provider::DATA }>;
   |             ^^^^^^^^^^^^^^^^^^^^^^^^^ help: use struct literal syntax instead: `Box {}`

warning: the feature `unsized_const_params` is incomplete and may not be safe to use and/or cause compiler crashes
 --> bug.rs:2:12
  |
2 | #![feature(unsized_const_params)]
  |            ^^^^^^^^^^^^^^^^^^^^
  |
  = note: see issue #95174 <https://github.com/rust-lang/rust/issues/95174> for more information
  = note: `#[warn(incomplete_features)]` on by default

error[E0366]: `Drop` impls cannot be specialized
  --> bug.rs:11:1
   |
11 | impl Drop for Box<{ Provider::DATA }> {
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: `{ Provider::DATA }` is not a generic parameter
note: use the same sequence of generic lifetime, type and const parameters as the struct definition
  --> bug.rs:10:1
   |
10 | struct Box<const DATA: &'static [&'static [u8]]> {}
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: internal compiler error: /rustc-dev/6a979b3e32522049d0acb4a47f7ae44b7c8abfd5/compiler/rustc_infer/src/infer/outlives/env.rs:85:26: add_outlives_bounds: unexpected regions: (ReLateParam(DefId(0:13 ~ bug[42c3]::{impl#1}::drop), LateNamed(DefId(2:61573 ~ core[fe7c]::ops::drop::Drop::drop::'_))), '{erased})


thread 'rustc' (929314) panicked at /rustc-dev/6a979b3e32522049d0acb4a47f7ae44b7c8abfd5/compiler/rustc_infer/src/infer/outlives/env.rs:85:26:
Box<dyn Any>
stack backtrace:
   0: std::panicking::begin_panic::<rustc_errors::ExplicitBug>
   1: <rustc_errors::diagnostic::BugAbort as rustc_errors::diagnostic::EmissionGuarantee>::emit_producing_guarantee
   2: rustc_middle::util::bug::opt_span_bug_fmt::<rustc_span::span_encoding::Span>::{closure#0}
   3: rustc_middle::ty::context::tls::with_opt::<rustc_middle::util::bug::opt_span_bug_fmt<rustc_span::span_encoding::Span>::{closure#0}, !>::{closure#0}
   4: rustc_middle::ty::context::tls::with_context_opt::<rustc_middle::ty::context::tls::with_opt<rustc_middle::util::bug::opt_span_bug_fmt<rustc_span::span_encoding::Span>::{closure#0}, !>::{closure#0}, !>
   5: rustc_middle::util::bug::bug_fmt
   6: <rustc_infer::infer::outlives::env::OutlivesEnvironment as rustc_trait_selection::regions::OutlivesEnvironmentBuildExt>::new_with_implied_bounds_compat::<indexmap::set::IndexSet<rustc_middle::ty::Ty, rustc_hash::FxBuildHasher>>
   7: rustc_hir_analysis::check::compare_impl_item::compare_impl_item
      [... omitted 1 frame ...]
   8: rustc_hir_analysis::check::check::check_item_type
   9: rustc_hir_analysis::check::wfcheck::check_well_formed
      [... omitted 1 frame ...]
  10: rustc_hir_analysis::check::wfcheck::check_type_wf
      [... omitted 1 frame ...]
  11: rustc_hir_analysis::check_crate
  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]>>, false>
  14: 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.

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 `test/rustc-ice-2026-03-01T04_47_53-929216.txt` to your bug report

note: rustc 1.95.0-nightly (6a979b3e3 2026-02-26) running on x86_64-unknown-linux-gnu

query stack during panic:
#0 [compare_impl_item] checking assoc item `<impl at test.rs:11:1: 11:38>::drop` is compatible with trait definition
#1 [check_well_formed] checking that `<impl at test.rs:11:1: 11:38>` is well-formed
#2 [check_type_wf] checking that types are well-formed
#3 [analysis] running analysis passes on crate `test`
end of query stack
error: aborting due to 3 previous errors; 1 warning emitted

Some errors have detailed explanations: E0366, E0423.
For more information about an error, try `rustc --explain E0366`.

Start by reproducing the provided snippet with the reported nightly compiler, then inspect compiler/rustc_infer/src/infer/outlives/env.rs at add_outlives_bounds and the compare_impl_item query shown in the stack. Trace how the Drop implementation reaches the unexpected-regions assertion. Done means the reproducer no longer triggers an internal compiler error and produces an appropriate diagnostic.

Written by the indexing model from the issue text.

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ICE: `add_outlives_bounds: unexpected regions`

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