[ICE]: `!worker_thread.is_null()`

[matthiaskrgr]

Code

use std::num::NonZero;
fn main() {
    NonZero();
    format!("{}", 0);
}

Meta

rustc --version --verbose:

rustc 1.95.0-nightly (0a3cd3b6b 2026-01-18)
binary: rustc
commit-hash: 0a3cd3b6b6e1fa8fd3c75c1d13d2e22e64273f49
commit-date: 2026-01-18
host: x86_64-unknown-linux-gnu
release: 1.95.0-nightly
LLVM version: 21.1.8

Error output

rustc code.rs -Zthreads=2

<output>

Backtrace

thread 'rustc query cycle handler' (3275753) panicked at /rustc-dev/0a3cd3b6b6e1fa8fd3c75c1d13d2e22e64273f49/compiler/rustc_thread_pool/src/registry.rs:622:5:
assertion failed: !worker_thread.is_null()
stack backtrace:
   0:     0x7ff0d0e04693 - <<std[2f6e50ec0c8b9745]::sys::backtrace::BacktraceLock>::print::DisplayBacktrace as core[da33e28f739cfb7b]::fmt::Display>::fmt
   1:     0x7ff0d1409416 - core[da33e28f739cfb7b]::fmt::write
   2:     0x7ff0d0e1b086 - <std[2f6e50ec0c8b9745]::sys::stdio::unix::Stderr as std[2f6e50ec0c8b9745]::io::Write>::write_fmt
   3:     0x7ff0d0dda6c8 - std[2f6e50ec0c8b9745]::panicking::default_hook::{closure#0}
   4:     0x7ff0d0df7dc3 - std[2f6e50ec0c8b9745]::panicking::default_hook
   5:     0x7ff0cfddfcea - std[2f6e50ec0c8b9745]::panicking::update_hook::<alloc[4a7fd02e7796445d]::boxed::Box<rustc_driver_impl[76286615d137f620]::install_ice_hook::{closure#1}>>::{closure#0}
   6:     0x7ff0d0df80a2 - std[2f6e50ec0c8b9745]::panicking::panic_with_hook
   7:     0x7ff0d0dda7ba - std[2f6e50ec0c8b9745]::panicking::panic_handler::{closure#0}
   8:     0x7ff0d0dcec19 - std[2f6e50ec0c8b9745]::sys::backtrace::__rust_end_short_backtrace::<std[2f6e50ec0c8b9745]::panicking::panic_handler::{closure#0}, !>
   9:     0x7ff0d0ddc25d - __rustc[88c6a30cf430ade2]::rust_begin_unwind
  10:     0x7ff0cd8cf76c - core[da33e28f739cfb7b]::panicking::panic_fmt
  11:     0x7ff0cd5e2862 - core[da33e28f739cfb7b]::panicking::panic
  12:     0x7ff0d07be5a4 - <rustc_query_system[3fbf686053611ad7]::query::job::QueryLatch>::wait_on::<rustc_query_impl[44e5bb6bcee378f9]::plumbing::QueryCtxt>
  13:     0x7ff0d16fb3ee - rustc_query_system[3fbf686053611ad7]::query::plumbing::try_execute_query::<rustc_query_impl[44e5bb6bcee378f9]::DynamicConfig<rustc_data_structures[e27548a25accd315]::vec_cache::VecCache<rustc_span[bd6736dd76f04e02]::def_id::LocalDefId, rustc_middle[222e27930462787b]::query::erase::Erased<[u8; 8usize]>, rustc_query_system[3fbf686053611ad7]::dep_graph::graph::DepNodeIndex>, false, false, false>, rustc_query_impl[44e5bb6bcee378f9]::plumbing::QueryCtxt, false>
  14:     0x7ff0d16fae0b - rustc_query_impl[44e5bb6bcee378f9]::query_impl::local_def_id_to_hir_id::get_query_non_incr::__rust_end_short_backtrace
  15:     0x7ff0d1a024d4 - rustc_query_impl[44e5bb6bcee378f9]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[44e5bb6bcee378f9]::query_impl::def_span::dynamic_query::{closure#2}::{closure#0}, rustc_middle[222e27930462787b]::query::erase::Erased<[u8; 8usize]>>
  16:     0x7ff0d1416a05 - rustc_query_system[3fbf686053611ad7]::query::plumbing::try_execute_query::<rustc_query_impl[44e5bb6bcee378f9]::DynamicConfig<rustc_query_system[3fbf686053611ad7]::query::caches::DefIdCache<rustc_middle[222e27930462787b]::query::erase::Erased<[u8; 8usize]>>, false, false, false>, rustc_query_impl[44e5bb6bcee378f9]::plumbing::QueryCtxt, false>
  17:     0x7ff0d141666d - rustc_query_impl[44e5bb6bcee378f9]::query_impl::def_span::get_query_non_incr::__rust_end_short_backtrace
  18:     0x7ff0d045ed4a - <rustc_type_ir[5ecac172d71a4854]::binder::Binder<rustc_middle[222e27930462787b]::ty::context::TyCtxt, rustc_type_ir[5ecac172d71a4854]::predicate::TraitRef<rustc_middle[222e27930462787b]::ty::context::TyCtxt>> as rustc_middle[222e27930462787b]::query::keys::Key>::default_span
  19:     0x7ff0d07d083d - rustc_query_impl[44e5bb6bcee378f9]::plumbing::create_query_frame::<rustc_span[bd6736dd76f04e02]::def_id::LocalDefId>
  20:     0x7ff0d08ecddb - <rustc_query_impl[44e5bb6bcee378f9]::query_impl::local_def_id_to_hir_id::collect_active_jobs::{closure#0} as core[da33e28f739cfb7b]::ops::function::FnOnce<(rustc_middle[222e27930462787b]::ty::context::TyCtxt, rustc_span[bd6736dd76f04e02]::def_id::LocalDefId)>>::call_once
  21:     0x7ff0d07cb247 - <rustc_query_system[3fbf686053611ad7]::query::plumbing::QueryState<rustc_hir_id[4b10733f70ce9e73]::OwnerId>>::collect_active_jobs::<rustc_middle[222e27930462787b]::ty::context::TyCtxt>
  22:     0x7ff0d0859111 - rustc_query_impl[44e5bb6bcee378f9]::query_impl::local_def_id_to_hir_id::collect_active_jobs
  23:     0x7ff0d08856bf - <rustc_query_impl[44e5bb6bcee378f9]::plumbing::QueryCtxt as rustc_query_system[3fbf686053611ad7]::query::QueryContext>::collect_active_jobs
  24:     0x7ff0cfdd8d0c - std[2f6e50ec0c8b9745]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[e0d26bc9a9756595]::util::run_in_thread_pool_with_globals<rustc_interface[e0d26bc9a9756595]::interface::run_compiler<(), rustc_driver_impl[76286615d137f620]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#4}::{closure#1}, ()>
  25:     0x7ff0cfde4b07 - <std[2f6e50ec0c8b9745]::thread::lifecycle::spawn_unchecked<rustc_interface[e0d26bc9a9756595]::util::run_in_thread_pool_with_globals<rustc_interface[e0d26bc9a9756595]::interface::run_compiler<(), rustc_driver_impl[76286615d137f620]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#4}::{closure#1}, ()>::{closure#1} as core[da33e28f739cfb7b]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  26:     0x7ff0d251b244 - <std[2f6e50ec0c8b9745]::sys::thread::unix::Thread>::new::thread_start
  27:     0x7ff0cbe9698b - <unknown>
  28:     0x7ff0cbf1a9cc - <unknown>
  29:                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 `/home/matthias/vcs/github/CRED/rustc-ice-2026-01-19T06_20_54-3275732.txt` to your bug report

note: rustc 1.95.0-nightly (0a3cd3b6b 2026-01-18) running on x86_64-unknown-linux-gnu

note: compiler flags: -Z threads=2

query stack during panic:
#0 [def_span] looking up span for `Default`
end of query stack
internal compiler error: query cycle handler thread panicked, aborting process
[1]    3275732 IOT instruction  rustc code.rs -Zthreads=2

[matthiaskrgr]

without threads:

error[E0391]: cycle detected when getting HIR ID of `Default`
  |
  = note: ...which requires getting the crate HIR...
  = note: ...which requires perform lints prior to AST lowering...
  = note: ...which requires looking up span for `Default`...
  = note: ...which again requires getting HIR ID of `Default`, completing the cycle
  = note: cycle used when getting the resolver for lowering
  = note: see https://rustc-dev-guide.rust-lang.org/overview.html#queries and https://rustc-dev-guide.rust-lang.org/query.html for more information

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0391`

[nnethercote]

I can't reproduce this. With a just-checked out rev (d940e56) I get this output with -Zthreads=2:

error[E0423]: cannot initialize a tuple struct which contains private fields
   --> z2.rs:3:5
    |
  3 |     NonZero();
    |     ^^^^^^^
    |
note: constructor is not visible here due to private fields
   --> library/core/src/num/nonzero.rs:127:42
    |
127 | pub struct NonZero<T: ZeroablePrimitive>(T::NonZeroInner);
    |                                          ^^^^^^^^^^^^^^^ private field
help: you might have meant to use an associated function to build this type
    |
  3 -     NonZero();
  3 +     NonZero::new_unchecked(_);
    |
  3 -     NonZero();
  3 +     NonZero::from_be(_);
    |
  3 -     NonZero();
  3 +     NonZero::from_le(_);
    |
  3 -     NonZero();
  3 +     NonZero::from_be(_);
    |
    = and 21 other candidates

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0423`.

[matthiaskrgr]

humm, maybe I messed up the reduction.
I'll see if I can find another repro tonight

[matthiaskrgr]

ah I just missed the first line when copying 🙄

trait Default {}
use std::num::NonZero;
fn main() {
    NonZero();
    todo!(); // any macro can go here maybe?? 
}

[nnethercote]

I'm just going to revert #151203 :/