ICE with `miri nextest run`

[joshlf]

I'm experimenting with getting AI to write reproducer instructions, so apologies for the overly-verbose bug report. I've read it over and it's accurate, if a bit formal.

This report relates to this build failure on this PR in zerocopy.

---

Miri Panic During Test Discovery with zerocopy

When running Miri on the zerocopy test suite with the nightly-2025-11-17 toolchain, Miri panics during test discovery.

Steps to Reproduce

1. Clone the zerocopy repository:

   git clone https://github.com/google/zerocopy.git
   cd zerocopy

2. Check out the failing branch:

   git remote add fork https://github.com/google-pr-creation-bot/zerocopy.git
   git fetch fork
   git checkout roll-pinned-nightly-toolchain-to-nightly-2025-11-17-for-main

3. Install the nightly-2025-11-17 toolchain with the miri component:

   rustup toolchain install nightly-2025-11-17 --component miri

4. Run Miri:

   RUSTFLAGS="--cfg __ZEROCOPY_INTERNAL_USE_ONLY_NIGHTLY_FEATURES_IN_TESTS --cfg zerocopy_derive_union_into_bytes --cfg __ZEROCOPY_TOOLCHAIN=\"nightly\" " MIRIFLAGS="-Zmiri-strict-provenance -Zmiri-backtrace=full" cargo +nightly-2025-11-17 miri nextest run --test-threads 2 --package zerocopy --target x86_64-unknown-linux-gnu

Expected Behavior

Miri should run the tests.

Actual Behavior

Miri panics with the following error:

thread 'rustc' panicked at compiler/rustc_errors/src/lib.rs:1788:9:
assertion failed: self.stashed_diagnostics.is_empty()
stack backtrace:
   0:     0x7fbd26b0183b - std::backtrace::Backtrace::create::h448a9db553d26bef
   1:     0x7fbd26b01785 - std::backtrace::Backtrace::force_capture::he474997f3a313e31
   2:     0x7fbd25b4031e - std[d45af2a1259e8800]::panicking::update_hook::<alloc[58b5be5fbc54de9e]::boxed::Box<rustc_driver_impl[d2f42e81b9c37b75]::install_ice_hook::{closure#1}>>::{closure#0}
   3:     0x7fbd26b026f2 - std::panicking::panic_with_hook::h2172996bacdba2d7
   4:     0x7fbd26b024ba - std::panicking::panic_handler::{{closure}}::hc36cea0dc92c48aa
   5:     0x7fbd26afc3f9 - std::sys::backtrace::__rust_end_short_backtrace::hd4b38282c54e463b
   6:     0x7fbd26add6dd - __rustc[f20bc1530c389e91]::rust_begin_unwind
   7:     0x7fbd23a9c23c - core::panicking::panic_fmt::hda6de8e6488d2e11
   8:     0x7fbd233b08c2 - core::panicking::panic::h961d00b971108021
   9:     0x7fbd282cf616 - <rustc_errors[c3fdbdd0639f3724]::DiagCtxtInner>::flush_delayed
  10:     0x7fbd282cf3ed - <rustc_errors[c3fdbdd0639f3724]::DiagCtxtHandle>::flush_delayed
  11:     0x560f0f4ee0d7 - <miri[4e9c49b669df4bd8]::MiriCompilerCalls as rustc_driver_impl[d2f42e81b9c37b75]::Callbacks>::after_analysis
  12:     0x7fbd2853ebb3 - <rustc_interface[67c0c783642d6c76]::passes::create_and_enter_global_ctxt<core[7c9280adad8818af]::option::Option<rustc_interface[67c0c783642d6c76]::queries::Linker>, rustc_driver_impl[d2f42e81b9c37b75]::run_compiler::{closure#0}::{closure#2}>::{closure#2} as core[7c9280adad8818af]::ops::function::FnOnce<(&rustc_session[54c87533a8d99824]::session::Session, rustc_middle[65c3dfc665d99b31]::ty::context::CurrentGcx, alloc[58b5be5fbc54de9e]::sync::Arc<rustc_data_structures[7b18bb195bd0e66b]::jobserver::Proxy>, &std[d45af2a1259e8800]::sync::once_lock::OnceLock<rustc_middle[65c3dfc665d99b31]::ty::context::GlobalCtxt>, &rustc_data_structures[7b18bb195bd0e66b]::sync::worker_local::WorkerLocal<rustc_middle[65c3dfc665d99b31]::arena::Arena>, &rustc_data_structures[7b18bb195bd0e66b]::sync::worker_local::WorkerLocal<rustc_hir[afdf7e16091c21f7]::Arena>, rustc_driver_impl[d2f42e81b9c37b75]::run_compiler::{closure#0}::{closure#2})>>::call_once::{shim:vtable#0}
  13:     0x7fbd283d6105 - rustc_interface[67c0c783642d6c76]::interface::run_compiler::<(), rustc_driver_impl[d2f42e81b9c37b75]::run_compiler::{closure#0}>::{closure#1}
  14:     0x7fbd2832afba - std[d45af2a1259e8800]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[67c0c783642d6c76]::util::run_in_thread_with_globals<rustc_interface[67c0c783642d6c76]::util::run_in_thread_pool_with_globals<rustc_interface[67c0c783642d6c76]::interface::run_compiler<(), rustc_driver_impl[d2f42e81b9c37b75]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
  15:     0x7fbd2832aca8 - <<std[d45af2a1259e8800]::thread::Builder>::spawn_unchecked_<rustc_interface[67c0c783642d6c76]::util::run_in_thread_with_globals<rustc_interface[67c0c783642d6c76]::util::run_in_thread_pool_with_globals<rustc_interface[67c0c783642d6c76]::interface::run_compiler<(), rustc_driver_impl[d2f42e81b9c37b75]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core[7c9280adad8818af]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  16:     0x7fbd283309af - std::sys::thread::unix::Thread::new::thread_start::h544843a2b008d4a8
  17:     0x7fbd21e8aaa4 - start_thread
                               at ./nptl/pthread_create.c:447:8
  18:     0x7fbd21f17c6c - clone3
                               at ./misc/../sysdeps/unix/sysv/linux/x86_64/clone3.S:78:0
  19:                0x0 - <unknown>


rustc version: 1.93.0-nightly (518b42830 2025-11-16)
platform: x86_64-unknown-linux-gnu

query stack during panic:
end of query stack

[saethlin]

I think this is a duplicate of #4709.

[RalfJung]

Indeed. This should be already fixed in nightly-2025-11-18.

[joshlf]

Yep, that fix seems to work.