[ICE]: trait bounds on EII not yet supported

[Anonymous1-design]

Code

//@ compile-flags: -Znext-solver=globally

#![feature(extern_item_impls)]
#[eii] 
async fn hello_impl() {}

Meta

rustc --version --verbose:

rustc 1.96.0-nightly (23903d01c 2026-03-26)
binary: rustc
commit-hash: 23903d01c237d7c7d4fb62b82ca846bc45de4e0c
commit-date: 2026-03-26
host: x86_64-unknown-linux-gnu
release: 1.96.0-nightly
LLVM version: 22.1.2

Error output

error: functions in `extern` blocks cannot have `async` qualifier
 --> bug.rs:3:1
  |
2 | #[eii] 
  | ------ in this `extern` block
3 | async fn hello_impl() {}
  | ^^^^^ help: remove the `async` qualifier

error[E0601]: `main` function not found in crate `bug`
 --> bug.rs:3:25
  |
3 | async fn hello_impl() {}
  |                         ^ consider adding a `main` function to `bug.rs`

Backtrace

thread 'rustc' (1983380) panicked at /rustc-dev/23903d01c237d7c7d4fb62b82ca846bc45de4e0c/compiler/rustc_trait_selection/src/error_reporting/traits/suggestions.rs:3924:17:
trait bounds on EII not yet supported 
stack backtrace:
   0:     0x7f75400e79bb - <<std[b302fb27a3f91e2e]::sys::backtrace::BacktraceLock>::print::DisplayBacktrace as core[eeb74f28e99c9360]::fmt::Display>::fmt
   1:     0x7f7540793348 - core[eeb74f28e99c9360]::fmt::write
   2:     0x7f75400fe9c6 - <std[b302fb27a3f91e2e]::sys::stdio::unix::Stderr as std[b302fb27a3f91e2e]::io::Write>::write_fmt
   3:     0x7f75400bd9c8 - std[b302fb27a3f91e2e]::panicking::default_hook::{closure#0}
   4:     0x7f75400dadc3 - std[b302fb27a3f91e2e]::panicking::default_hook
   5:     0x7f753f0e029c - std[b302fb27a3f91e2e]::panicking::update_hook::<alloc[ae169e729e5df420]::boxed::Box<rustc_driver_impl[1043facd4a3b5a1e]::install_ice_hook::{closure#1}>>::{closure#0}
   6:     0x7f75400db0a2 - std[b302fb27a3f91e2e]::panicking::panic_with_hook
   7:     0x7f75400bdaba - std[b302fb27a3f91e2e]::panicking::panic_handler::{closure#0}
   8:     0x7f75400b47b9 - std[b302fb27a3f91e2e]::sys::backtrace::__rust_end_short_backtrace::<std[b302fb27a3f91e2e]::panicking::panic_handler::{closure#0}, !>
   9:     0x7f75400bf4ed - __rustc[8f8d3949772fcde8]::rust_begin_unwind
  10:     0x7f753d21116c - core[eeb74f28e99c9360]::panicking::panic_fmt
  11:     0x7f753fe0f724 - <rustc_trait_selection[4af0f86042d1add3]::error_reporting::TypeErrCtxt>::note_obligation_cause_code::<rustc_span[e6c053b2fe5f7640]::ErrorGuaranteed, rustc_middle[fca09ee1eeeaccd3]::ty::predicate::Predicate>
  12:     0x7f753fecb8d2 - <rustc_trait_selection[4af0f86042d1add3]::error_reporting::TypeErrCtxt>::note_obligation_cause
  13:     0x7f753e945a48 - <rustc_trait_selection[4af0f86042d1add3]::error_reporting::TypeErrCtxt>::report_fulfillment_errors
  14:     0x7f753f289b16 - rustc_hir_analysis[6a03357fbbae8c8c]::check::compare_eii::compare_eii_function_types
  15:     0x7f7541034bac - rustc_hir_analysis[6a03357fbbae8c8c]::check::wfcheck::check_item_fn
  16:     0x7f7540cbd487 - rustc_hir_analysis[6a03357fbbae8c8c]::check::check::check_item_type
  17:     0x7f7540cb9726 - rustc_hir_analysis[6a03357fbbae8c8c]::check::wfcheck::check_well_formed
  18:     0x7f7540cb9707 - rustc_query_impl[36767619dcd2566]::query_impl::check_well_formed::invoke_provider_fn::__rust_begin_short_backtrace
  19:     0x7f7540cb8d24 - rustc_query_impl[36767619dcd2566]::execution::try_execute_query::<rustc_data_structures[18b11a475be38cee]::vec_cache::VecCache<rustc_span[e6c053b2fe5f7640]::def_id::LocalDefId, rustc_middle[fca09ee1eeeaccd3]::query::erase::ErasedData<[u8; 1usize]>, rustc_middle[fca09ee1eeeaccd3]::dep_graph::graph::DepNodeIndex>, false>
  20:     0x7f7540cb8abb - rustc_query_impl[36767619dcd2566]::query_impl::check_well_formed::execute_query_non_incr::__rust_end_short_backtrace
  21:     0x7f7540cb504b - rustc_hir_analysis[6a03357fbbae8c8c]::check::wfcheck::check_type_wf
  22:     0x7f7540cb4f55 - rustc_query_impl[36767619dcd2566]::query_impl::check_type_wf::invoke_provider_fn::__rust_begin_short_backtrace
  23:     0x7f754198fb10 - rustc_query_impl[36767619dcd2566]::execution::try_execute_query::<rustc_middle[fca09ee1eeeaccd3]::query::caches::SingleCache<rustc_middle[fca09ee1eeeaccd3]::query::erase::ErasedData<[u8; 1usize]>>, false>
  24:     0x7f754198f7e9 - rustc_query_impl[36767619dcd2566]::query_impl::check_type_wf::execute_query_non_incr::__rust_end_short_backtrace
  25:     0x7f7541179c73 - rustc_hir_analysis[6a03357fbbae8c8c]::check_crate
  26:     0x7f754087bb20 - rustc_interface[e1e6c05c12b55e19]::passes::analysis
  27:     0x7f7541992289 - rustc_query_impl[36767619dcd2566]::execution::try_execute_query::<rustc_middle[fca09ee1eeeaccd3]::query::caches::SingleCache<rustc_middle[fca09ee1eeeaccd3]::query::erase::ErasedData<[u8; 0usize]>>, false>
  28:     0x7f7541992069 - rustc_query_impl[36767619dcd2566]::query_impl::analysis::execute_query_non_incr::__rust_end_short_backtrace
  29:     0x7f75419503d4 - rustc_interface[e1e6c05c12b55e19]::interface::run_compiler::<(), rustc_driver_impl[1043facd4a3b5a1e]::run_compiler::{closure#0}>::{closure#1}
  30:     0x7f754193b5fe - std[b302fb27a3f91e2e]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[e1e6c05c12b55e19]::util::run_in_thread_with_globals<rustc_interface[e1e6c05c12b55e19]::util::run_in_thread_pool_with_globals<rustc_interface[e1e6c05c12b55e19]::interface::run_compiler<(), rustc_driver_impl[1043facd4a3b5a1e]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
  31:     0x7f754193bea0 - <std[b302fb27a3f91e2e]::thread::lifecycle::spawn_unchecked<rustc_interface[e1e6c05c12b55e19]::util::run_in_thread_with_globals<rustc_interface[e1e6c05c12b55e19]::util::run_in_thread_pool_with_globals<rustc_interface[e1e6c05c12b55e19]::interface::run_compiler<(), rustc_driver_impl[1043facd4a3b5a1e]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core[eeb74f28e99c9360]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  32:     0x7f754193cd2c - <std[b302fb27a3f91e2e]::sys::thread::unix::Thread>::new::thread_start
  33:     0x7f753b50a609 - start_thread
                               at /build/glibc-B3wQXB/glibc-2.31/nptl/pthread_create.c:477:8
  34:     0x7f753b42f353 - clone
                               at /build/glibc-B3wQXB/glibc-2.31/misc/../sysdeps/unix/sysv/linux/x86_64/clone.S:95:0
  35:                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: please attach the file at `Study/Traitor/trait-fuzzer/test/rustc-ice-2026-03-29T06_03_29-1983370.txt` to your bug report

note: rustc 1.96.0-nightly (23903d01c 2026-03-26) running on x86_64-unknown-linux-gnu

note: compiler flags: -Z next-solver=globally

query stack during panic:
#0 [check_well_formed] checking that `_::hello_impl` is well-formed
#1 [check_type_wf] checking that types are well-formed
... and 1 other queries... use `env RUST_BACKTRACE=1` to see the full query stack
error: aborting due to 2 previous errors

command: rustc -Znext-solver=globally

[Helios531]

@reddevilmidzy Can I work on this issue?

[reddevilmidzy]

@reddevilmidzy Can I work on this issue?

Sure, you can assign yourself use command @rustbot claim

[AsakuraMizu]

This issue is no longer reproducible. The last reproducible rustc version is nightly-2026-06-25. It seems that this has been fixed by #156742.