ICE `Unable to verify registry association` / `!worker_thread.is_null()`

[matthiaskrgr]

Code

with -Zthreads=2

use std:sync:OnceLock
struct WeakOnce< T >(OnceLock< Self >)
static ONCE : WeakOnce< Context >  
struct Context;

Meta

rustc --version --verbose:

rustc 1.94.0-nightly (503745e91 2026-01-16)
binary: rustc
commit-hash: 503745e9170b40841611aaaa634641edffd00b29
commit-date: 2026-01-16
host: x86_64-unknown-linux-gnu
release: 1.94.0-nightly
LLVM version: 21.1.8

Error output

thread 'rustc query cycle handler' (3937314) panicked at /rustc-dev/503745e9170b40841611aaaa634641edffd00b29/compiler/rustc_data_structures/src/sync/worker_local.rs:28:51:
Unable to verify registry association
stack backtrace:
   0:     0x7f1c54c417e3 - <<std[6d36f9ba992b6832]::sys::backtrace::BacktraceLock>::print::DisplayBacktrace as core[3d2156d5e39e5feb]::fmt::Display>::fmt
   1:     0x7f1c5520e248 - core[3d2156d5e39e5feb]::fmt::write
   2:     0x7f1c54c581d6 - <std[6d36f9ba992b6832]::sys::stdio::unix::Stderr as std[6d36f9ba992b6832]::io::Write>::write_fmt
   3:     0x7f1c54c17858 - std[6d36f9ba992b6832]::panicking::default_hook::{closure#0}
   4:     0x7f1c54c34f13 - std[6d36f9ba992b6832]::panicking::default_hook
   5:     0x7f1c53c096ba - std[6d36f9ba992b6832]::panicking::update_hook::<alloc[50e5b2f088044279]::boxed::Box<rustc_driver_impl[cc36a22c668daecf]::install_ice_hook::{closure#1}>>::{closure#0}
   6:     0x7f1c54c351f2 - std[6d36f9ba992b6832]::panicking::panic_with_hook
   7:     0x7f1c54c1794a - std[6d36f9ba992b6832]::panicking::panic_handler::{closure#0}
   8:     0x7f1c54c0be59 - std[6d36f9ba992b6832]::sys::backtrace::__rust_end_short_backtrace::<std[6d36f9ba992b6832]::panicking::panic_handler::{closure#0}, !>
   9:     0x7f1c54c193ed - __rustc[ba822077cedc0708]::rust_begin_unwind
  10:     0x7f1c5205666c - core[3d2156d5e39e5feb]::panicking::panic_fmt
  11:     0x7f1c52d7273a - rustc_data_structures[fc0e59b3c48140ab]::outline::<<rustc_data_structures[fc0e59b3c48140ab]::sync::worker_local::RegistryId>::verify::{closure#1}, usize>
  12:     0x7f1c55216e28 - rustc_query_impl[98b58b56d6576428]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[98b58b56d6576428]::query_impl::generics_of::dynamic_query::{closure#2}::{closure#0}, rustc_middle[9166020e8cee7914]::query::erase::Erased<[u8; 8usize]>>
  13:     0x7f1c55217405 - rustc_query_system[cdd3a9722b25439b]::query::plumbing::try_execute_query::<rustc_query_impl[98b58b56d6576428]::DynamicConfig<rustc_query_system[cdd3a9722b25439b]::query::caches::DefIdCache<rustc_middle[9166020e8cee7914]::query::erase::Erased<[u8; 8usize]>>, false, false, false>, rustc_query_impl[98b58b56d6576428]::plumbing::QueryCtxt, false>
  14:     0x7f1c5521712b - rustc_query_impl[98b58b56d6576428]::query_impl::generics_of::get_query_non_incr::__rust_end_short_backtrace
  15:     0x7f1c56643eb4 - <rustc_middle[9166020e8cee7914]::ty::print::pretty::FmtPrinter as rustc_middle[9166020e8cee7914]::ty::print::Printer>::print_def_path
  16:     0x7f1c56647e88 - <rustc_middle[9166020e8cee7914]::ty::print::pretty::FmtPrinter as rustc_middle[9166020e8cee7914]::ty::print::pretty::PrettyPrinter>::pretty_print_type
  17:     0x7f1c56647bac - <rustc_middle[9166020e8cee7914]::ty::Ty as core[3d2156d5e39e5feb]::fmt::Display>::fmt
  18:     0x7f1c5520e248 - core[3d2156d5e39e5feb]::fmt::write
  19:     0x7f1c5520e0ab - alloc[50e5b2f088044279]::fmt::format::format_inner
  20:     0x7f1c5424fdad - rustc_middle[9166020e8cee7914]::query::descs::layout_of
  21:     0x7f1c5461e749 - rustc_query_impl[98b58b56d6576428]::plumbing::create_query_frame::<rustc_middle[9166020e8cee7914]::ty::PseudoCanonicalInput<rustc_middle[9166020e8cee7914]::ty::Ty>>
  22:     0x7f1c5473e230 - <rustc_query_impl[98b58b56d6576428]::query_impl::layout_of::collect_active_jobs::{closure#0} as core[3d2156d5e39e5feb]::ops::function::FnOnce<(rustc_middle[9166020e8cee7914]::ty::context::TyCtxt, rustc_middle[9166020e8cee7914]::ty::PseudoCanonicalInput<rustc_middle[9166020e8cee7914]::ty::Ty>)>>::call_once
  23:     0x7f1c54600f92 - <rustc_query_system[cdd3a9722b25439b]::query::plumbing::QueryState<rustc_middle[9166020e8cee7914]::ty::PseudoCanonicalInput<rustc_middle[9166020e8cee7914]::ty::Ty>>>::collect_active_jobs::<rustc_middle[9166020e8cee7914]::ty::context::TyCtxt>
  24:     0x7f1c546a9061 - rustc_query_impl[98b58b56d6576428]::query_impl::layout_of::collect_active_jobs
  25:     0x7f1c546bcbdf - <rustc_query_impl[98b58b56d6576428]::plumbing::QueryCtxt as rustc_query_system[cdd3a9722b25439b]::query::QueryContext>::collect_active_jobs
  26:     0x7f1c53c0200c - std[6d36f9ba992b6832]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[2164ba223c61a5e9]::util::run_in_thread_pool_with_globals<rustc_interface[2164ba223c61a5e9]::interface::run_compiler<(), rustc_driver_impl[cc36a22c668daecf]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#4}::{closure#1}, ()>
  27:     0x7f1c53c0d607 - <std[6d36f9ba992b6832]::thread::lifecycle::spawn_unchecked<rustc_interface[2164ba223c61a5e9]::util::run_in_thread_pool_with_globals<rustc_interface[2164ba223c61a5e9]::interface::run_compiler<(), rustc_driver_impl[cc36a22c668daecf]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#4}::{closure#1}, ()>::{closure#1} as core[3d2156d5e39e5feb]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  28:     0x7f1c56276338 - <std[6d36f9ba992b6832]::sys::thread::unix::Thread>::new::thread_start
  29:     0x7f1c4fc9698b - <unknown>
  30:     0x7f1c4fd1a9cc - <unknown>
  31:                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 `/tmp/im/rustc-ice-2026-01-16T20_45_59-3937308.txt` to your bug report

note: rustc 1.94.0-nightly (503745e91 2026-01-16) running on x86_64-unknown-linux-gnu

note: compiler flags: -Z threads=2

query stack during panic:
panicked at /rustc-dev/503745e9170b40841611aaaa634641edffd00b29/compiler/rustc_thread_pool/src/registry.rs:622:5:
assertion failed: !worker_thread.is_null()
thread panicked while processing panic. aborting.
[1]    3937308 IOT instruction  ~/.rustup/toolchains/master/bin/rustc code.rs -Zthreads=2

Backtrace

<backtrace>

[matthiaskrgr]

cleaned up a bit

use std::sync::OnceLock;
struct WeakOnce<T>(OnceLock<Self>);
static ONCE: WeakOnce<Context> = todo!();
struct Context;
fn main() {}

[matthiaskrgr]

I suspect this is related to #151203 cc @nnethercote

[matthiaskrgr]

smaller

struct A<T>(std::sync::OnceLock<Self>);
static B: A<()> = todo!();
fn main() {}

[nnethercote]

Query spaghetti code and parallel-front end spaghetti code giving spaghetti squared :( A potential fix is in #151350.

[zetanumbers]

To be fair that spaghetti was that way before #151203 on purpose.