[ICE]: `adding a def'n for node-id NodeId(35) and def kind LifetimeParam but a previous def'n exists`

[matthiaskrgr]

snippet:

trait Trait<'a, T, const F: fn(&CStr) -> usize> {
    fn foo<'x: 'x, A, B>(&self) {}
}

reuse Trait::foo;

Version information

rustc 1.96.0-nightly (f82485388 2026-03-06)
binary: rustc
commit-hash: f82485388963286763f8c8a9261ac227627f6a18
commit-date: 2026-03-06
host: x86_64-unknown-linux-gnu
release: 1.96.0-nightly
LLVM version: 22.1.0

Possibly related line of code:

rust/compiler/rustc_ast_lowering/src/lib.rs

Lines 586 to 598 in f824853

	def_kind: DefKind,
	def_path_data: DefPathData,
	span: Span,
	) -> LocalDefId {
	let parent = self.current_hir_id_owner.def_id;
	assert_ne!(node_id, ast::DUMMY_NODE_ID);
	assert!(
	self.opt_local_def_id(node_id).is_none(),
	"adding a def'n for node-id {:?} and def kind {:?} but a previous def'n exists: {:?}",
	node_id,
	def_kind,
	self.tcx.hir_def_key(self.local_def_id(node_id)),
	);

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

Program output

error[E0425]: cannot find type `CStr` in this scope
 --> /tmp/icemaker_global_tempdir.6SGfY0f9qCPf/rustc_testrunner_tmpdir_reporting.EEKipKas9tub/mvce.rs:1:33
  |
1 | trait Trait<'a, T, const F: fn(&CStr) -> usize> {
  |                                 ^^^^ not found in this scope
  |
help: consider importing this struct
  |
1 + use std::ffi::CStr;
  |

error[E0658]: functions delegation is not yet fully implemented
 --> /tmp/icemaker_global_tempdir.6SGfY0f9qCPf/rustc_testrunner_tmpdir_reporting.EEKipKas9tub/mvce.rs:5:1
  |
5 | reuse Trait::foo;
  | ^^^^^^^^^^^^^^^^^
  |
  = note: see issue #118212 <https://github.com/rust-lang/rust/issues/118212> for more information
  = help: add `#![feature(fn_delegation)]` to the crate attributes to enable
  = note: this compiler was built on 2026-03-06; consider upgrading it if it is out of date


thread 'rustc' (3547296) panicked at /rustc-dev/f82485388963286763f8c8a9261ac227627f6a18/compiler/rustc_ast_lowering/src/lib.rs:592:9:
adding a def'n for node-id NodeId(35) and def kind LifetimeParam but a previous def'n exists: DefKey { parent: Some(DefIndex(3)), disambiguated_data: DisambiguatedDefPathData { data: DesugaredAnonymousLifetime, disambiguator: 0 } }
stack backtrace:
   0:     0x7fb408f5df6b - <<std[1ac9ec7f151dc343]::sys::backtrace::BacktraceLock>::print::DisplayBacktrace as core[2185e438fa60127]::fmt::Display>::fmt
   1:     0x7fb409622a08 - core[2185e438fa60127]::fmt::write
   2:     0x7fb408f74f76 - <std[1ac9ec7f151dc343]::sys::stdio::unix::Stderr as std[1ac9ec7f151dc343]::io::Write>::write_fmt
   3:     0x7fb408f34058 - std[1ac9ec7f151dc343]::panicking::default_hook::{closure#0}
   4:     0x7fb408f513e3 - std[1ac9ec7f151dc343]::panicking::default_hook
   5:     0x7fb407f37e4c - std[1ac9ec7f151dc343]::panicking::update_hook::<alloc[1b3f84b8c09c25b1]::boxed::Box<rustc_driver_impl[6e789f234d303bfb]::install_ice_hook::{closure#1}>>::{closure#0}
   6:     0x7fb408f516c2 - std[1ac9ec7f151dc343]::panicking::panic_with_hook
   7:     0x7fb408f34118 - std[1ac9ec7f151dc343]::panicking::panic_handler::{closure#0}
   8:     0x7fb408f28669 - std[1ac9ec7f151dc343]::sys::backtrace::__rust_end_short_backtrace::<std[1ac9ec7f151dc343]::panicking::panic_handler::{closure#0}, !>
   9:     0x7fb408f35b7d - __rustc[3c4f6ba47a7fa14c]::rust_begin_unwind
  10:     0x7fb405b4543c - core[2185e438fa60127]::panicking::panic_fmt
  11:     0x7fb409e54aad - <rustc_ast_lowering[b95fdc7cdede6051]::LoweringContext>::lifetime_res_to_generic_param
  12:     0x7fb409e2a134 - <rustc_ast_lowering[b95fdc7cdede6051]::LoweringContext>::lower_lifetime_binder::{closure#0}
  13:     0x7fb40987c22f - <rustc_ast_lowering[b95fdc7cdede6051]::LoweringContext>::lower_ty
  14:     0x7fb409e21fd8 - <rustc_ast_lowering[b95fdc7cdede6051]::LoweringContext>::lower_generic_param
  15:     0x7fb407a5dfbe - <<rustc_ast_lowering[b95fdc7cdede6051]::delegation::generics::HirOrAstGenerics>::into_hir_generics::{closure#0} as core[2185e438fa60127]::ops::function::FnOnce<(&mut rustc_ast[f8ca33bbd9947925]::ast::Generics,)>>::call_once
  16:     0x7fb407a450bd - <rustc_ast_lowering[b95fdc7cdede6051]::delegation::generics::HirOrAstGenerics>::into_hir_generics
  17:     0x7fb407a400c1 - <rustc_ast_lowering[b95fdc7cdede6051]::LoweringContext>::lower_delegation
  18:     0x7fb409e35dd5 - <rustc_ast_lowering[b95fdc7cdede6051]::LoweringContext>::lower_item_kind
  19:     0x7fb409e43976 - <rustc_ast_lowering[b95fdc7cdede6051]::item::ItemLowerer>::lower_node
  20:     0x7fb409e42327 - rustc_ast_lowering[b95fdc7cdede6051]::lower_to_hir
  21:     0x7fb40a884a28 - rustc_query_impl[234cac1489f93c02]::query_impl::hir_crate::invoke_provider_fn::__rust_begin_short_backtrace
  22:     0x7fb40a883944 - rustc_query_impl[234cac1489f93c02]::execution::try_execute_query::<rustc_middle[6c1cd5853b8c3360]::query::caches::SingleCache<rustc_middle[6c1cd5853b8c3360]::query::erase::ErasedData<[u8; 8usize]>>, false>
  23:     0x7fb40a8833cf - rustc_query_impl[234cac1489f93c02]::query_impl::hir_crate::execute_query_non_incr::__rust_end_short_backtrace
  24:     0x7fb4096c0c83 - rustc_query_impl[234cac1489f93c02]::query_impl::opt_hir_owner_nodes::invoke_provider_fn::__rust_begin_short_backtrace
  25:     0x7fb4096bfe4a - rustc_query_impl[234cac1489f93c02]::execution::try_execute_query::<rustc_data_structures[b1d728af8bd319df]::vec_cache::VecCache<rustc_span[bde3ed91d4975fd3]::def_id::LocalDefId, rustc_middle[6c1cd5853b8c3360]::query::erase::ErasedData<[u8; 8usize]>, rustc_middle[6c1cd5853b8c3360]::dep_graph::graph::DepNodeIndex>, false>
  26:     0x7fb4096bfac5 - rustc_query_impl[234cac1489f93c02]::query_impl::opt_hir_owner_nodes::execute_query_non_incr::__rust_end_short_backtrace
  27:     0x7fb409f6fda6 - <rustc_middle[6c1cd5853b8c3360]::ty::context::TyCtxt>::hir_owner_node
  28:     0x7fb40a88a1d1 - rustc_middle[6c1cd5853b8c3360]::hir::map::hir_crate_items
  29:     0x7fb40a88589d - rustc_query_impl[234cac1489f93c02]::query_impl::hir_crate_items::invoke_provider_fn::__rust_begin_short_backtrace
  30:     0x7fb40a883944 - rustc_query_impl[234cac1489f93c02]::execution::try_execute_query::<rustc_middle[6c1cd5853b8c3360]::query::caches::SingleCache<rustc_middle[6c1cd5853b8c3360]::query::erase::ErasedData<[u8; 8usize]>>, false>
  31:     0x7fb40a88430b - rustc_query_impl[234cac1489f93c02]::query_impl::hir_crate_items::execute_query_non_incr::__rust_end_short_backtrace
  32:     0x7fb4096bc6e2 - rustc_interface[c926bcc183cff181]::passes::analysis
  33:     0x7fb40a882760 - rustc_query_impl[234cac1489f93c02]::execution::try_execute_query::<rustc_middle[6c1cd5853b8c3360]::query::caches::SingleCache<rustc_middle[6c1cd5853b8c3360]::query::erase::ErasedData<[u8; 0usize]>>, false>
  34:     0x7fb40a882447 - rustc_query_impl[234cac1489f93c02]::query_impl::analysis::execute_query_non_incr::__rust_end_short_backtrace
  35:     0x7fb40a83da6d - rustc_interface[c926bcc183cff181]::interface::run_compiler::<(), rustc_driver_impl[6e789f234d303bfb]::run_compiler::{closure#0}>::{closure#1}
  36:     0x7fb40a86613e - std[1ac9ec7f151dc343]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[c926bcc183cff181]::util::run_in_thread_with_globals<rustc_interface[c926bcc183cff181]::util::run_in_thread_pool_with_globals<rustc_interface[c926bcc183cff181]::interface::run_compiler<(), rustc_driver_impl[6e789f234d303bfb]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
  37:     0x7fb40a8669e0 - <std[1ac9ec7f151dc343]::thread::lifecycle::spawn_unchecked<rustc_interface[c926bcc183cff181]::util::run_in_thread_with_globals<rustc_interface[c926bcc183cff181]::util::run_in_thread_pool_with_globals<rustc_interface[c926bcc183cff181]::interface::run_compiler<(), rustc_driver_impl[6e789f234d303bfb]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core[2185e438fa60127]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  38:     0x7fb40a86786c - <std[1ac9ec7f151dc343]::sys::thread::unix::Thread>::new::thread_start
  39:     0x7fb4042a598b - <unknown>
  40:     0x7fb404329a0c - <unknown>
  41:                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 1.96.0-nightly (f82485388 2026-03-06) running on x86_64-unknown-linux-gnu

query stack during panic:
#0 [hir_crate] getting the crate HIR
#1 [opt_hir_owner_nodes] getting HIR owner items in ``
#2 [hir_crate_items] getting HIR crate items
#3 [analysis] running analysis passes on crate `mvce`
end of query stack
error: aborting due to 2 previous errors

Some errors have detailed explanations: E0425, E0658.
For more information about an error, try `rustc --explain E0425`.

[matthiaskrgr]

#![feature(fn_delegation)]
use std::ffi::CStr;

trait Trait<const F: fn(&CStr)> {
    fn foo();
}
reuse Trait::foo;