Rare ICE in cstore_impl.rs with proc macro

This is a forwarding from the rust-analyzer repo upon request. Originally reported there as the ICE has only ever been reproduced when running RA's proc macro server.

I'm reporting a rare ICE that another developer is experiencing. The ICE appears to be related to using the snafu crate in a proc macro, and only happens rarely (once a day type of rare). This makes me suspect some type of incremental compilation issue with RA's proc macro server.

I am unable to provide a repo or reproducer at this time. I have been unable to piece together a reproducing example from the information I have. The original finder of this ICE has stated they can make the code public at a later time. (see community discord for more context)

The ICE appears only in rust-analyzer's logs and does not appear when using cargo.

Meta

rustc version: 1.89.0-nightly (8da623945 2025-06-13)

Error output

thread 'rustc' panicked at compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs:696:32:
Box<dyn Any>
stack backtrace:
   0:        0x110e05f30 - std::backtrace::Backtrace::create::h22ea715f59ec3ed0
   1:        0x10ef30af0 - std[df31d5d2efadd756]::panicking::update_hook::<alloc[9129d48d0341a7c4]::boxed::Box<rustc_driver_impl[1b35cf4ad33a8386]::install_ice_hook::{closure#1}>>::{closure#0}
   2:        0x110e23a28 - std::panicking::rust_panic_with_hook::h8625bb980bd8ff09
   3:        0x10efb4758 - std[df31d5d2efadd756]::panicking::begin_panic::<rustc_errors[cdab23ccf35dce2f]::ExplicitBug>::{closure#0}
   4:        0x10efa2938 - std[df31d5d2efadd756]::sys::backtrace::__rust_end_short_backtrace::<std[df31d5d2efadd756]::panicking::begin_panic<rustc_errors[cdab23ccf35dce2f]::ExplicitBug>::{closure#0}, !>
   5:        0x113ac6cc8 - std[df31d5d2efadd756]::panicking::begin_panic::<rustc_errors[cdab23ccf35dce2f]::ExplicitBug>
   6:        0x113ac70a0 - <rustc_errors[cdab23ccf35dce2f]::diagnostic::BugAbort as rustc_errors[cdab23ccf35dce2f]::diagnostic::EmissionGuarantee>::emit_producing_guarantee
   7:        0x113b40bc0 - rustc_middle[f8a6d707848327d8]::util::bug::opt_span_bug_fmt::<rustc_span[9a68fd476b92126f]::span_encoding::Span>::{closure#0}
   8:        0x10fbe60a4 - rustc_middle[f8a6d707848327d8]::ty::context::tls::with_opt::<rustc_middle[f8a6d707848327d8]::util::bug::opt_span_bug_fmt<rustc_span[9a68fd476b92126f]::span_encoding::Span>::{closure#0}, !>::{closure#0}
   9:        0x10fbe5b74 - rustc_middle[f8a6d707848327d8]::ty::context::tls::with_context_opt::<rustc_middle[f8a6d707848327d8]::ty::context::tls::with_opt<rustc_middle[f8a6d707848327d8]::util::bug::opt_span_bug_fmt<rustc_span[9a68fd476b92126f]::span_encoding::Span>::{closure#0}, !>::{closure#0}, !>
  10:        0x113b40ad8 - rustc_middle[f8a6d707848327d8]::util::bug::bug_fmt
  11:        0x10fa4cfcc - <rustc_metadata[3c511df3e6d27a03]::rmeta::decoder::cstore_impl::provide_cstore_hooks::{closure#0} as core[7caada9627f18b09]::ops::function::FnOnce<(rustc_middle[f8a6d707848327d8]::ty::context::TyCtxt, rustc_span[9a68fd476b92126f]::def_id::DefPathHash, rustc_span[9a68fd476b92126f]::def_id::StableCrateId)>>::call_once
  12:        0x10fbf6dcc - <rustc_middle[f8a6d707848327d8]::ty::context::TyCtxt>::def_path_hash_to_def_id
  13:        0x11056cc68 - rustc_query_impl[82f6920132d9c7e1]::plumbing::force_from_dep_node::<rustc_query_impl[82f6920132d9c7e1]::DynamicConfig<rustc_data_structures[80586ddf1de41c48]::vec_cache::VecCache<rustc_span[9a68fd476b92126f]::def_id::LocalDefId, rustc_middle[f8a6d707848327d8]::query::erase::Erased<[u8; 8usize]>, rustc_query_system[4741a984835d9de2]::dep_graph::graph::DepNodeIndex>, false, false, false>>
  14:        0x1104fa314 - <rustc_query_impl[82f6920132d9c7e1]::plumbing::query_callback<rustc_query_impl[82f6920132d9c7e1]::query_impl::local_def_id_to_hir_id::QueryType>::{closure#0} as core[7caada9627f18b09]::ops::function::FnOnce<(rustc_middle[f8a6d707848327d8]::ty::context::TyCtxt, rustc_query_system[4741a984835d9de2]::dep_graph::dep_node::DepNode, rustc_query_system[4741a984835d9de2]::dep_graph::serialized::SerializedDepNodeIndex)>>::call_once
  15:        0x1102fe4c8 - <rustc_query_system[4741a984835d9de2]::dep_graph::graph::DepGraphData<rustc_middle[f8a6d707848327d8]::dep_graph::DepsType>>::try_mark_previous_green::<rustc_query_impl[82f6920132d9c7e1]::plumbing::QueryCtxt>
  16:        0x1102fe28c - <rustc_query_system[4741a984835d9de2]::dep_graph::graph::DepGraphData<rustc_middle[f8a6d707848327d8]::dep_graph::DepsType>>::try_mark_green::<rustc_query_impl[82f6920132d9c7e1]::plumbing::QueryCtxt>
  17:        0x110348280 - rustc_query_system[4741a984835d9de2]::query::plumbing::try_execute_query::<rustc_query_impl[82f6920132d9c7e1]::DynamicConfig<rustc_query_system[4741a984835d9de2]::query::caches::DefIdCache<rustc_middle[f8a6d707848327d8]::query::erase::Erased<[u8; 8usize]>>, false, false, false>, rustc_query_impl[82f6920132d9c7e1]::plumbing::QueryCtxt, true>
  18:        0x1105affa0 - rustc_query_impl[82f6920132d9c7e1]::query_impl::def_span::get_query_incr::__rust_end_short_backtrace
  19:        0x1101fe468 - rustc_passes[8601956eadf0dd58]::entry::entry_fn
  20:        0x110574a38 - rustc_query_impl[82f6920132d9c7e1]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[82f6920132d9c7e1]::query_impl::entry_fn::dynamic_query::{closure#2}::{closure#0}, rustc_middle[f8a6d707848327d8]::query::erase::Erased<[u8; 12usize]>>
  21:        0x110357448 - rustc_query_system[4741a984835d9de2]::query::plumbing::try_execute_query::<rustc_query_impl[82f6920132d9c7e1]::DynamicConfig<rustc_query_system[4741a984835d9de2]::query::caches::SingleCache<rustc_middle[f8a6d707848327d8]::query::erase::Erased<[u8; 12usize]>>, false, false, false>, rustc_query_impl[82f6920132d9c7e1]::plumbing::QueryCtxt, true>
  22:        0x1105d0170 - rustc_query_impl[82f6920132d9c7e1]::query_impl::entry_fn::get_query_incr::__rust_end_short_backtrace
  23:        0x10f83dbc4 - rustc_interface[41d3ece343fba094]::passes::run_required_analyses
  24:        0x10f8400c4 - rustc_interface[41d3ece343fba094]::passes::analysis
  25:        0x11057497c - rustc_query_impl[82f6920132d9c7e1]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[82f6920132d9c7e1]::query_impl::analysis::dynamic_query::{closure#2}::{closure#0}, rustc_middle[f8a6d707848327d8]::query::erase::Erased<[u8; 0usize]>>
  26:        0x11034bebc - rustc_query_system[4741a984835d9de2]::query::plumbing::try_execute_query::<rustc_query_impl[82f6920132d9c7e1]::DynamicConfig<rustc_query_system[4741a984835d9de2]::query::caches::SingleCache<rustc_middle[f8a6d707848327d8]::query::erase::Erased<[u8; 0usize]>>, false, false, false>, rustc_query_impl[82f6920132d9c7e1]::plumbing::QueryCtxt, true>
  27:        0x11058094c - rustc_query_impl[82f6920132d9c7e1]::query_impl::analysis::get_query_incr::__rust_end_short_backtrace
  28:        0x10eee1e4c - rustc_interface[41d3ece343fba094]::passes::create_and_enter_global_ctxt::<core[7caada9627f18b09]::option::Option<rustc_interface[41d3ece343fba094]::queries::Linker>, rustc_driver_impl[1b35cf4ad33a8386]::run_compiler::{closure#0}::{closure#2}>
  29:        0x10ef2d8c0 - rustc_interface[41d3ece343fba094]::interface::run_compiler::<(), rustc_driver_impl[1b35cf4ad33a8386]::run_compiler::{closure#0}>::{closure#1}
  30:        0x10ef2005c - std[df31d5d2efadd756]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[41d3ece343fba094]::util::run_in_thread_with_globals<rustc_interface[41d3ece343fba094]::util::run_in_thread_pool_with_globals<rustc_interface[41d3ece343fba094]::interface::run_compiler<(), rustc_driver_impl[1b35cf4ad33a8386]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
  31:        0x10ef340d8 - <<std[df31d5d2efadd756]::thread::Builder>::spawn_unchecked_<rustc_interface[41d3ece343fba094]::util::run_in_thread_with_globals<rustc_interface[41d3ece343fba094]::util::run_in_thread_pool_with_globals<rustc_interface[41d3ece343fba094]::interface::run_compiler<(), rustc_driver_impl[1b35cf4ad33a8386]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core[7caada9627f18b09]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  32:        0x110e26de8 - std::sys::pal::unix::thread::Thread::new::thread_start::hcd1d9414b76a54c1
  33:        0x188b4c2e4 - __pthread_deallocate


rustc version: 1.89.0-nightly (8da623945 2025-06-13)
platform: aarch64-apple-darwin

query stack during panic:
#0 [def_span] looking up span for `main`
#1 [entry_fn] looking up the entry function of a crate
#2 [analysis] running analysis passes on this crate
end of query stack

Start at compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs:696 and follow the def_path_hash_to_def_id query stack through entry_fn and analysis. Compare reproduction in rust-analyzer's proc macro server with cargo when public code or a reproducer becomes available; done means isolating the incremental-compilation cause and preventing this ICE.