[ICE]: `foreign item sig`

[cushionbadak]

Code

#![feature(extern_item_impls)]

struct Foo;

#[eii]
pub fn Foo(x: u64) {}

fn main() {}

A mutant of tests/ui/eii/default/local_crate_explicit.rs

Meta

rustc --version --verbose:

rustc 1.95.0-nightly (7f99507f5 2026-02-19)
binary: rustc
commit-hash: 7f99507f57e6c4aa0dce3daf6a13cca8cd4dd312
commit-date: 2026-02-19
host: x86_64-apple-darwin
release: 1.95.0-nightly
LLVM version: 22.1.0

Error output

Command: rustc

error[E0428]: the name `Foo` is defined multiple times
 --> iter8_73cda55fdec9bb35.rs:6:1
  |
3 | struct Foo;
  | ----------- previous definition of the value `Foo` here
...
6 | pub fn Foo(x: u64) {}
  | ^^^^^^^^^^^^^^^^^^ `Foo` redefined here
  |
  = note: `Foo` must be defined only once in the value namespace of this module


thread 'rustc' (15613403) panicked at /rustc-dev/7f99507f57e6c4aa0dce3daf6a13cca8cd4dd312/compiler/rustc_hir_analysis/src/check/compare_eii.rs:276:68:
foreign item sig

Backtrace

thread 'rustc' (15613403) panicked at /rustc-dev/7f99507f57e6c4aa0dce3daf6a13cca8cd4dd312/compiler/rustc_hir_analysis/src/check/compare_eii.rs:276:68:
foreign item sig
stack backtrace:
   0: __rustc::rust_begin_unwind
   1: core::panicking::panic_fmt
   2: core::option::expect_failed
   3: rustc_hir_analysis::check::compare_eii::compare_eii_function_types
   4: rustc_hir_analysis::check::wfcheck::check_item_fn
   5: rustc_hir_analysis::check::check::check_item_type
   6: rustc_hir_analysis::check::wfcheck::check_well_formed
      [... omitted 1 frame ...]
   7: rustc_hir_analysis::check::wfcheck::check_type_wf
      [... omitted 1 frame ...]
   8: rustc_hir_analysis::check_crate
   9: rustc_interface::passes::analysis
  10: rustc_query_impl::execution::try_execute_query::<rustc_middle::query::caches::SingleCache<rustc_middle::query::erase::ErasedData<[u8; 0]>>, {rustc_query_impl::QueryFlags { is_anon: false, is_depth_limit: false, is_feedable: false }}, false>
  11: rustc_interface::passes::create_and_enter_global_ctxt::<core::option::Option<rustc_interface::queries::Linker>, rustc_driver_impl::run_compiler::{closure#0}::{closure#2}>
  12: 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.

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: please attach the file at `/Volumes/T7/workspace/out-260219/scratch/rustc-ice-2026-02-20T08_45_54-97550.txt` to your bug report

note: rustc 1.95.0-nightly (7f99507f5 2026-02-19) running on x86_64-apple-darwin

query stack during panic:
#0 [check_well_formed] checking that `_::Foo` is well-formed
#1 [check_type_wf] checking that types are well-formed
#2 [analysis] running analysis passes on crate `iter8_73cda55fdec9bb35`
end of query stack
error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0428`.

Notes

• ICE location: compiler/rustc_hir_analysis/src/check/compare_eii.rs Line-276
  

  rust/compiler/rustc_hir_analysis/src/check/compare_eii.rs

  Lines 262 to 276 in ef70767

  	fn report_number_of_arguments_mismatch<'tcx>(
  	tcx: TyCtxt<'tcx>,
  	external_impl: LocalDefId,
  	declaration: DefId,
  	eii_name: Symbol,
  	eii_attr_span: Span,
  	declaration_number_args: usize,
  	external_impl_number_args: usize,
  	) -> ErrorGuaranteed {
  	let external_impl_name = tcx.item_name(external_impl.to_def_id());
  	let declaration_span = declaration
  	.as_local()
  	.and_then(|def_id| {
  	let declaration_sig = get_declaration_sig(tcx, def_id).expect("foreign item sig");

@rustbot label +F-extern_item_impls

[reddevilmidzy]

fixed: #153571

The code is very similar to the test added in the PR, but since the ICE message is different, I will add the E-needs-test label, instead of closing,.

I think it would be good to add it to this test.

[reddevilmidzy]

Test added in #154799