ICE: next solver: `future_not_send` on any async code

[matthiaskrgr]

Summary

// clippy-driver code.rs --edition=2021 -Znext-solver=globally
#![warn(clippy::future_not_send)]
async fn run() {}
fn main() {}

Version

rustc 1.99.0-nightly (b69e089eb 2026-07-12)
binary: rustc
commit-hash: b69e089eb3ec9976ddec602bf18c3d6a8ce72512
commit-date: 2026-07-12
host: x86_64-unknown-linux-gnu
release: 1.99.0-nightly
LLVM version: 22.1.8

Error output

Backtrace

warning: function `run` is never used
--> ./code.rs:2:10
|
2 | async fn run() {}
|          ^^^
|
= note: `#[warn(dead_code)]` (part of `#[warn(unused)]`) on by default

warning: 1 warning emitted

note: no errors encountered even though delayed bugs were created

note: those delayed bugs will now be shown as internal compiler errors

error: internal compiler error: OpaqueTypeStorage { opaque_types: {OpaqueTypeKey { def_id: DefId(0:4 ~ code[65d7]::run::{opaque#0}), args: [] }: ProvisionalHiddenType { span: ./code.rs:2:15: 2:15 (#6), ty: Coroutine(DefId(0:5 ~ code[65d7]::run::{closure#0}), [(), std::future::ResumeTy, (), (), ()]) }}, duplicate_entries: [] }
|
= note: delayed at /rustc-dev/b69e089eb3ec9976ddec602bf18c3d6a8ce72512/compiler/rustc_infer/src/infer/mod.rs:369:43
           0: <rustc_errors::DiagCtxtInner>::emit_diagnostic
           1: <rustc_errors::DiagCtxtHandle>::emit_diagnostic
           2: <rustc_span::ErrorGuaranteed as rustc_errors::diagnostic::EmissionGuarantee>::emit_producing_guarantee
           3: <rustc_errors::DiagCtxtHandle>::delayed_bug::<alloc::string::String>
           4: <rustc_infer::infer::InferCtxt as core::ops::drop::Drop>::drop
           5: core::ptr::drop_glue::<rustc_infer::infer::InferCtxt>
           6: <clippy_lints::future_not_send::FutureNotSend as rustc_lint::passes::LateLintPass>::check_fn
           7: <clippy_lints::CombinedLateLintPass as rustc_lint::passes::LateLintPass>::check_fn
           8: <rustc_lint::late::LateContextAndPass<rustc_lint::late::RuntimeCombinedLateLintPass> as rustc_hir::intravisit::Visitor>::visit_fn
           9: <rustc_lint::late::LateContextAndPass<rustc_lint::late::RuntimeCombinedLateLintPass> as rustc_hir::intravisit::Visitor>::visit_nested_item
          10: <rustc_lint::late::LateContextAndPass<rustc_lint::late::RuntimeCombinedLateLintPass>>::process_mod
          11: rustc_lint::late::check_crate::{closure#0}
          12: rustc_lint::late::check_crate
          13: rustc_interface::passes::analysis::{closure#0}::{closure#0}::{closure#2}
          14: rustc_data_structures::sync::parallel::par_fns
          15: rustc_interface::passes::analysis::{closure#0}::{closure#0}
          16: rustc_data_structures::sync::parallel::par_fns
          17: rustc_interface::passes::analysis
          18: rustc_query_impl::execution::try_execute_query::<rustc_middle::query::caches::SingleCache<rustc_middle::query::erase::ErasedData<[u8; 0]>>, false>
          19: rustc_query_impl::query_impl::analysis::execute_query_non_incr::__rust_end_short_backtrace
          20: rustc_interface::interface::run_compiler::<(), rustc_driver_impl::run_compiler::{closure#0}>::{closure#1}
          21: std::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface::util::run_in_thread_with_globals<rustc_interface::util::run_in_thread_pool_with_globals<rustc_interface::interface::run_compiler<(), rustc_driver_impl::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
          22: <std::thread::lifecycle::spawn_unchecked<rustc_interface::util::run_in_thread_with_globals<rustc_interface::util::run_in_thread_pool_with_globals<rustc_interface::interface::run_compiler<(), rustc_driver_impl::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
          23: <std::sys::thread::unix::Thread>::new::thread_start
          24: <unknown>
          25: <unknown>


note: we would appreciate a bug report: https://github.com/rust-lang/rust-clippy/issues/new?template=ice.yml

note: please make sure that you have updated to the latest nightly

note: please attach the file at `/home/matthias/vcs/github/CRED/rustc-ice-2026-07-12T09_25_10-4005091.txt` to your bug report

note: rustc 1.99.0-nightly (b69e089eb 2026-07-12) running on x86_64-unknown-linux-gnu

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

query stack during panic:
end of query stack
note: Clippy version: clippy 0.1.99 (b69e089eb3 2026-07-12)

[Gri-ffin]

@rustbot claim

[adwinwhite]

@Gri-ffin Hi, are you still working on this?

As we get close to enable the next solver on nightly, I'd like to get clippy working with the next solver. Let me know if you need any help on the rustc side.

[Gri-ffin]

Hi, yes I'm still working on this, I've been trying to understand how the next solver works, I'm gonna push the fix very soon. And thanks a lot for your offer I appreciate it.