ICE when using a constant as a pattern

[MoSal]

Bisected to 8c39296 (#137848).

Code

struct Foo<const V: u8>;

trait Bar<'b> {
    fn bar(n: u8);
}

// ICE *STILL* triggered if Foo doesn't have a const param
// ICE *NOT* if Bar doesn't have a lifetime param
// ICE *NOT* triggered obviously with correct `v if v == V`
impl<'b, const V: u8> Bar<'b> for Foo<V> {
    fn bar(n: u8) {
        match n {
            V => (),
            _ => (),
        }
    }
}

Meta

rustc --version --verbose:

rustc 1.87.0-nightly (f9e0239a7 2025-03-04)
binary: rustc
commit-hash: f9e0239a7bc813b4aceffc7f069f4797cde3175c
commit-date: 2025-03-04
host: x86_64-unknown-linux-gnu
release: 1.87.0-nightly
LLVM version: 20.1.0

Error output

error[E0158]: constant parameters cannot be referenced in patterns
  --> src/lib.rs:13:13
   |
10 | impl<'b, const V: u8> Bar<'b> for Foo<V> {
   |          ----------- constant defined here
...
13 |             V => (),
   |             ^ can't be used in patterns

Backtrace

thread 'rustc' panicked at compiler/rustc_mir_build/src/thir/util.rs:25:14:
Box<dyn Any>
stack backtrace:
   0:     0x7fc2987e4da5 - std::backtrace::Backtrace::create::hfef1a8f8aac33464
   1:     0x7fc296bc9ff5 - std::backtrace::Backtrace::force_capture::h8687f78d397650db
   2:     0x7fc295d30dee - std[2cce8494628f4585]::panicking::update_hook::<alloc[ea6342a0a5a8b9b1]::boxed::Box<rustc_driver_impl[e161daf9ab2d11d7]::install_ice_hook::{closure#1}>>::{closure#0}
   3:     0x7fc296be2903 - std::panicking::rust_panic_with_hook::h2c8894f8997fcf6a
   4:     0x7fc295d6d471 - std[2cce8494628f4585]::panicking::begin_panic::<rustc_errors[e90c28bb776fdfc0]::ExplicitBug>::{closure#0}
   5:     0x7fc295d61886 - std[2cce8494628f4585]::sys::backtrace::__rust_end_short_backtrace::<std[2cce8494628f4585]::panicking::begin_panic<rustc_errors[e90c28bb776fdfc0]::ExplicitBug>::{closure#0}, !>
   6:     0x7fc295d5e209 - std[2cce8494628f4585]::panicking::begin_panic::<rustc_errors[e90c28bb776fdfc0]::ExplicitBug>
   7:     0x7fc295d76e61 - <rustc_errors[e90c28bb776fdfc0]::diagnostic::BugAbort as rustc_errors[e90c28bb776fdfc0]::diagnostic::EmissionGuarantee>::emit_producing_guarantee
   8:     0x7fc296352236 - rustc_middle[2d5b20c791c56ad0]::util::bug::opt_span_bug_fmt::<rustc_span[6699764a695b2e79]::span_encoding::Span>::{closure#0}
   9:     0x7fc296339b5a - rustc_middle[2d5b20c791c56ad0]::ty::context::tls::with_opt::<rustc_middle[2d5b20c791c56ad0]::util::bug::opt_span_bug_fmt<rustc_span[6699764a695b2e79]::span_encoding::Span>::{closure#0}, !>::{closure#0}
  10:     0x7fc2963399cb - rustc_middle[2d5b20c791c56ad0]::ty::context::tls::with_context_opt::<rustc_middle[2d5b20c791c56ad0]::ty::context::tls::with_opt<rustc_middle[2d5b20c791c56ad0]::util::bug::opt_span_bug_fmt<rustc_span[6699764a695b2e79]::span_encoding::Span>::{closure#0}, !>::{closure#0}, !>
  11:     0x7fc2946fb380 - rustc_middle[2d5b20c791c56ad0]::util::bug::bug_fmt
  12:     0x7fc298d70e37 - rustc_mir_build[e0917d4cd90e2920]::thir::util::user_args_applied_to_ty_of_hir_id.cold
  13:     0x7fc297d1d777 - <rustc_mir_build[e0917d4cd90e2920]::thir::pattern::PatCtxt>::lower_variant_or_leaf
  14:     0x7fc297d1dfb2 - <rustc_mir_build[e0917d4cd90e2920]::thir::pattern::PatCtxt>::lower_pat_expr
  15:     0x7fc297d1a272 - <rustc_mir_build[e0917d4cd90e2920]::thir::pattern::PatCtxt>::lower_pattern
  16:     0x7fc297d18e8a - <rustc_mir_build[e0917d4cd90e2920]::thir::cx::ThirBuildCx>::pattern_from_hir
  17:     0x7fc297d12a06 - <rustc_mir_build[e0917d4cd90e2920]::thir::cx::ThirBuildCx>::mirror_expr
  18:     0x7fc297d12801 - <rustc_mir_build[e0917d4cd90e2920]::thir::cx::ThirBuildCx>::mirror_expr
  19:     0x7fc297d2714b - rustc_mir_build[e0917d4cd90e2920]::thir::cx::thir_body
  20:     0x7fc297d26c28 - rustc_query_impl[b4e30529d2c77c57]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[b4e30529d2c77c57]::query_impl::thir_body::dynamic_query::{closure#2}::{closure#0}, rustc_middle[2d5b20c791c56ad0]::query::erase::Erased<[u8; 16usize]>>
  21:     0x7fc297f1d406 - rustc_query_system[cb43291f2de4de55]::query::plumbing::try_execute_query::<rustc_query_impl[b4e30529d2c77c57]::DynamicConfig<rustc_data_structures[38628b744a74ab57]::vec_cache::VecCache<rustc_span[6699764a695b2e79]::def_id::LocalDefId, rustc_middle[2d5b20c791c56ad0]::query::erase::Erased<[u8; 16usize]>, rustc_query_system[cb43291f2de4de55]::dep_graph::graph::DepNodeIndex>, false, false, false>, rustc_query_impl[b4e30529d2c77c57]::plumbing::QueryCtxt, true>
  22:     0x7fc2985d96a2 - rustc_query_impl[b4e30529d2c77c57]::plumbing::force_from_dep_node::<rustc_query_impl[b4e30529d2c77c57]::DynamicConfig<rustc_data_structures[38628b744a74ab57]::vec_cache::VecCache<rustc_span[6699764a695b2e79]::def_id::LocalDefId, rustc_middle[2d5b20c791c56ad0]::query::erase::Erased<[u8; 16usize]>, rustc_query_system[cb43291f2de4de55]::dep_graph::graph::DepNodeIndex>, false, false, false>>
  23:     0x7fc2985d956d - <rustc_query_impl[b4e30529d2c77c57]::plumbing::query_callback<rustc_query_impl[b4e30529d2c77c57]::query_impl::thir_body::QueryType>::{closure#0} as core[e3f8cccd6bff4ec3]::ops::function::FnOnce<(rustc_middle[2d5b20c791c56ad0]::ty::context::TyCtxt, rustc_query_system[cb43291f2de4de55]::dep_graph::dep_node::DepNode)>>::call_once
  24:     0x7fc2974259ba - <rustc_query_system[cb43291f2de4de55]::dep_graph::graph::DepGraphData<rustc_middle[2d5b20c791c56ad0]::dep_graph::DepsType>>::try_mark_previous_green::<rustc_query_impl[b4e30529d2c77c57]::plumbing::QueryCtxt>
  25:     0x7fc29789c7fd - rustc_query_system[cb43291f2de4de55]::query::plumbing::ensure_must_run::<rustc_query_impl[b4e30529d2c77c57]::DynamicConfig<rustc_data_structures[38628b744a74ab57]::vec_cache::VecCache<rustc_span[6699764a695b2e79]::def_id::LocalDefId, rustc_middle[2d5b20c791c56ad0]::query::erase::Erased<[u8; 8usize]>, rustc_query_system[cb43291f2de4de55]::dep_graph::graph::DepNodeIndex>, false, false, false>, rustc_query_impl[b4e30529d2c77c57]::plumbing::QueryCtxt>
  26:     0x7fc297899a13 - rustc_query_impl[b4e30529d2c77c57]::query_impl::check_unsafety::get_query_incr::__rust_end_short_backtrace
  27:     0x7fc297ad5ac8 - rustc_interface[5fc383e867bdd00e]::passes::run_required_analyses
  28:     0x7fc298332dba - rustc_interface[5fc383e867bdd00e]::passes::analysis
  29:     0x7fc298332d99 - rustc_query_impl[b4e30529d2c77c57]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[b4e30529d2c77c57]::query_impl::analysis::dynamic_query::{closure#2}::{closure#0}, rustc_middle[2d5b20c791c56ad0]::query::erase::Erased<[u8; 0usize]>>
  30:     0x7fc298697faa - rustc_query_system[cb43291f2de4de55]::query::plumbing::try_execute_query::<rustc_query_impl[b4e30529d2c77c57]::DynamicConfig<rustc_query_system[cb43291f2de4de55]::query::caches::SingleCache<rustc_middle[2d5b20c791c56ad0]::query::erase::Erased<[u8; 0usize]>>, false, false, false>, rustc_query_impl[b4e30529d2c77c57]::plumbing::QueryCtxt, true>
  31:     0x7fc2986979a2 - rustc_query_impl[b4e30529d2c77c57]::query_impl::analysis::get_query_incr::__rust_end_short_backtrace
  32:     0x7fc29849fc7d - rustc_interface[5fc383e867bdd00e]::passes::create_and_enter_global_ctxt::<core[e3f8cccd6bff4ec3]::option::Option<rustc_interface[5fc383e867bdd00e]::queries::Linker>, rustc_driver_impl[e161daf9ab2d11d7]::run_compiler::{closure#0}::{closure#2}>::{closure#2}::{closure#0}
  33:     0x7fc2984e66e0 - rustc_interface[5fc383e867bdd00e]::interface::run_compiler::<(), rustc_driver_impl[e161daf9ab2d11d7]::run_compiler::{closure#0}>::{closure#1}
  34:     0x7fc298337588 - std[2cce8494628f4585]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[5fc383e867bdd00e]::util::run_in_thread_with_globals<rustc_interface[5fc383e867bdd00e]::util::run_in_thread_pool_with_globals<rustc_interface[5fc383e867bdd00e]::interface::run_compiler<(), rustc_driver_impl[e161daf9ab2d11d7]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
  35:     0x7fc298337e74 - <<std[2cce8494628f4585]::thread::Builder>::spawn_unchecked_<rustc_interface[5fc383e867bdd00e]::util::run_in_thread_with_globals<rustc_interface[5fc383e867bdd00e]::util::run_in_thread_pool_with_globals<rustc_interface[5fc383e867bdd00e]::interface::run_compiler<(), rustc_driver_impl[e161daf9ab2d11d7]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core[e3f8cccd6bff4ec3]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  36:     0x7fc298339277 - std::sys::pal::unix::thread::Thread::new::thread_start::h6a5943b86725331d
  37:     0x7fc2924a370a - <unknown>
  38:     0x7fc292527aac - <unknown>
  39:                0x0 - <unknown>


rustc version: 1.87.0-nightly (f9e0239a7 2025-03-04)
platform: x86_64-unknown-linux-gnu

query stack during panic:
#0 [thir_body] building THIR for `<impl at src/lib.rs:10:1: 10:41>::bar`
#1 [analysis] running analysis passes on this crate
end of query stack

[cyrgani]

a bit smaller:

struct Foo;

impl<'b> Foo {
    fn bar<const V: u8>() {
        let V;
    }
}

[Eclips4]

Bisects to #137617