ICE: index out of bounds in snapshot_vec when chaining partition_map() calls

[xiyuzhai]

Code

use itertools::Itertools;

pub fn trigger_ice() {
    vec![1, 2, 3]
        .into_iter()
        .partition_map(|x| x)
        .partition_map(|x| x);
}

Meta

rustc --version --verbose:

rustc 1.91.0-nightly (f34ba774c 2025-08-03)
binary: rustc
commit-hash: f34ba774c78ea32b7c40598b8ad23e75cdac42a6
commit-date: 2025-08-03
host: x86_64-unknown-linux-gnu
release: 1.91.0-nightly
LLVM version: 20.1.8

Error output

error[E0308]: mismatched types
 --> src/lib.rs:6:28
  |
6 |         .partition_map(|x| x)
  |                            ^ expected `Either<_, _>`, found integer
  |
  = note: expected enum `Either<_, _>`
             found type `{integer}`
help: try wrapping the expression in a variant of `Either`
  |
6 |         .partition_map(|x| itertools::Either::Left(x))
  |                            ++++++++++++++++++++++++ +
6 |         .partition_map(|x| itertools::Either::Right(x))
  |                            +++++++++++++++++++++++++ +


thread 'rustc' panicked at /rust/deps/ena-0.14.3/src/snapshot_vec.rs:199:10:
index out of bounds: the len is 31 but the index is 37

Backtrace

stack backtrace:
   0:     0x7a411b40a223 - <std::sys::backtrace::BacktraceLock::print::DisplayBacktrace as core::fmt::Display>::fmt::he94d81f4cc76bf03
   1:     0x7a411bc02d77 - core::fmt::write::h255510a3ffb8d55d
   2:     0x7a411b3ffe03 - std::io::Write::write_fmt::hf8ded1300f0b71a8
   3:     0x7a411b40a082 - std::sys::backtrace::BacktraceLock::print::h3bdc2b992c7e0515
   4:     0x7a411b40db27 - std::panicking::default_hook::{{closure}}::h876682ce5f8046c9
   5:     0x7a411b40d68b - std::panicking::default_hook::h708aafadea70e31d
   6:     0x7a411a47eac3 - std[a2e6032cce42d97f]::panicking::update_hook::<alloc[ff7d08515ebedc7]::boxed::Box<rustc_driver_impl[de6ab808e8043f3f]::install_ice_hook::{closure#1}>>::{closure#0}
   7:     0x7a411b40e36e - std::panicking::rust_panic_with_hook::hbc7edc3b462870f0
   8:     0x7a411b40e06a - std::panicking::begin_panic_handler::{{closure}}::hf9e5cd48d862b8ac
   9:     0x7a411b40a6f9 - std::sys::backtrace::__rust_end_short_backtrace::hd57bebce377ef2e9
  10:     0x7a411b40dd4d - __rustc[46d736129294a9b7]::rust_begin_unwind
  11:     0x7a4117ad2560 - core::panicking::panic_fmt::h21871f0b1dcaf625
  12:     0x7a4119b5357d - core::panicking::panic_bounds_check::h467c1ac80182d499
  13:     0x7a411d452153 - <ena[b295e11ac2687fa0]::unify::UnificationTable<ena[b295e11ac2687fa0]::unify::backing_vec::InPlace<rustc_infer[6623dba893894b6f]::infer::type_variable::TyVidEqKey, &mut alloc[ff7d08515ebedc7]::vec::Vec<ena[b295e11ac2687fa0]::unify::VarValue<rustc_infer[6623dba893894b6f]::infer::type_variable::TyVidEqKey>>, &mut rustc_infer[6623dba893894b6f]::infer::snapshot::undo_log::InferCtxtUndoLogs>>>::uninlined_get_root_key.cold
  14:     0x7a411c5720e9 - <rustc_infer[6623dba893894b6f]::infer::canonical::canonicalizer::Canonicalizer as rustc_type_ir[d433dbb56c274b65]::fold::TypeFolder<rustc_middle[e3248139c571040]::ty::context::TyCtxt>>::fold_ty
  15:     0x7a411c573ebb - <rustc_infer[6623dba893894b6f]::infer::canonical::canonicalizer::Canonicalizer as rustc_type_ir[d433dbb56c274b65]::fold::TypeFolder<rustc_middle[e3248139c571040]::ty::context::TyCtxt>>::fold_ty
  16:     0x7a411c570f2f - <rustc_infer[6623dba893894b6f]::infer::canonical::canonicalizer::Canonicalizer as rustc_type_ir[d433dbb56c274b65]::fold::TypeFolder<rustc_middle[e3248139c571040]::ty::context::TyCtxt>>::fold_predicate
  17:     0x7a411bce5870 - <rustc_infer[6623dba893894b6f]::infer::InferCtxt as rustc_trait_selection[2c4c2ad9bb59d34]::traits::query::evaluate_obligation::InferCtxtExt>::evaluate_obligation
  18:     0x7a411a6ed1e3 - <rustc_infer[6623dba893894b6f]::infer::InferCtxt as rustc_trait_selection[2c4c2ad9bb59d34]::infer::InferCtxtExt>::type_implements_trait::<&rustc_middle[e3248139c571040]::ty::list::RawList<(), rustc_middle[e3248139c571040]::ty::generic_args::GenericArg>>
  19:     0x7a411a7c1bfe - <rustc_hir_typeck[ad470676ecc79ec1]::fn_ctxt::FnCtxt>::report_no_match_method_error
  20:     0x7a411a803ccd - <rustc_hir_typeck[ad470676ecc79ec1]::fn_ctxt::FnCtxt>::report_method_error
  21:     0x7a411cac0f21 - <rustc_hir_typeck[ad470676ecc79ec1]::fn_ctxt::FnCtxt>::check_expr_with_expectation_and_args
  22:     0x7a411be8b646 - <rustc_hir_typeck[ad470676ecc79ec1]::fn_ctxt::FnCtxt>::check_expr_block
  23:     0x7a411cab23dd - <rustc_hir_typeck[ad470676ecc79ec1]::fn_ctxt::FnCtxt>::check_expr_with_expectation_and_args
  24:     0x7a411be95aa2 - rustc_hir_typeck[ad470676ecc79ec1]::check::check_fn
  25:     0x7a411ce10caf - rustc_hir_typeck[ad470676ecc79ec1]::typeck_with_inspect::{closure#0}
  26:     0x7a411cdfbfb0 - rustc_query_impl[3fd9c6a4ad24362]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[3fd9c6a4ad24362]::query_impl::typeck::dynamic_query::{closure#2}::{closure#0}, rustc_middle[e3248139c571040]::query::erase::Erased<[u8; 8usize]>>
  27:     0x7a411c18bf60 - rustc_query_system[7e37a266f75ec588]::query::plumbing::try_execute_query::<rustc_query_impl[3fd9c6a4ad24362]::DynamicConfig<rustc_data_structures[a57f2e4fad990afb]::vec_cache::VecCache<rustc_span[91be5049b842f401]::def_id::LocalDefId, rustc_middle[e3248139c571040]::query::erase::Erased<[u8; 8usize]>, rustc_query_system[7e37a266f75ec588]::dep_graph::graph::DepNodeIndex>, false, false, false>, rustc_query_impl[3fd9c6a4ad24362]::plumbing::QueryCtxt, true>
  28:     0x7a411c18b300 - rustc_query_impl[3fd9c6a4ad24362]::query_impl::typeck::get_query_incr::__rust_end_short_backtrace
  29:     0x7a411c180c9b - rustc_hir_analysis[7c52b57a28bd59dd]::check_crate
  30:     0x7a411c185384 - rustc_interface[373d4675362b8f62]::passes::analysis
  31:     0x7a411c185047 - rustc_query_impl[3fd9c6a4ad24362]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[3fd9c6a4ad24362]::query_impl::analysis::dynamic_query::{closure#2}::{closure#0}, rustc_middle[e3248139c571040]::query::erase::Erased<[u8; 0usize]>>
  32:     0x7a411ce268c2 - rustc_query_system[7e37a266f75ec588]::query::plumbing::try_execute_query::<rustc_query_impl[3fd9c6a4ad24362]::DynamicConfig<rustc_query_system[7e37a266f75ec588]::query::caches::SingleCache<rustc_middle[e3248139c571040]::query::erase::Erased<[u8; 0usize]>>, false, false, false>, rustc_query_impl[3fd9c6a4ad24362]::plumbing::QueryCtxt, true>
  33:     0x7a411ce261ff - rustc_query_impl[3fd9c6a4ad24362]::query_impl::analysis::get_query_incr::__rust_end_short_backtrace
  34:     0x7a411cf6724b - rustc_interface[373d4675362b8f62]::passes::create_and_enter_global_ctxt::<core[606ee596359a9bc5]::option::Option<rustc_interface[373d4675362b8f62]::queries::Linker>, rustc_driver_impl[de6ab808e8043f3f]::run_compiler::{closure#0}::{closure#2}>::{closure#2}::{closure#0}
  35:     0x7a411cf56e71 - rustc_interface[373d4675362b8f62]::interface::run_compiler::<(), rustc_driver_impl[de6ab808e8043f3f]::run_compiler::{closure#0}>::{closure#1}
  36:     0x7a411cdb3241 - std[a2e6032cce42d97f]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[373d4675362b8f62]::util::run_in_thread_with_globals<rustc_interface[373d4675362b8f62]::util::run_in_thread_pool_with_globals<rustc_interface[373d4675362b8f62]::interface::run_compiler<(), rustc_driver_impl[de6ab808e8043f3f]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
  37:     0x7a411cdb2f22 - <<std[a2e6032cce42d97f]::thread::Builder>::spawn_unchecked_<rustc_interface[373d4675362b8f62]::util::run_in_thread_with_globals<rustc_interface[373d4675362b8f62]::util::run_in_thread_pool_with_globals<rustc_interface[373d4675362b8f62]::interface::run_compiler<(), rustc_driver_impl[de6ab808e8043f3f]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core[606ee596359a9bc5]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  38:     0x7a411cdb9085 - std::sys::pal::unix::thread::Thread::new::thread_start::hf6a510012528f331
  39:     0x7a411649caa4 - start_thread
                               at ./nptl/pthread_create.c:447:8
  40:     0x7a4116529c3c - clone3
                               at ./misc/../sysdeps/unix/sysv/linux/x86_64/clone3.S:78:0
  41:                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/xiyuzhai/rustc-ice-report0/rustc-ice-2025-08-04T03_50_57-336701.txt` to your bug report

note: compiler flags: --crate-type lib -C embed-bitcode=no -C debuginfo=2 -C incremental=[REDACTED]

note: some of the compiler flags provided by cargo are hidden

query stack during panic:
#0 [typeck] type-checking `trigger_ice`
#1 [analysis] running analysis passes on this crate
end of query stack

Additional Information

• The ICE occurs when attempting to chain .partition_map() calls from the itertools crate
• The panic happens in the unification table during type checking: index out of bounds: the len is 31 but the index is 37
• Minimal reproduction repository: https://github.com/xiyuzhai/rustc-ice-report0
• Dependencies: itertools = "0.13"
• Edition: 2024

[cyrgani]

smaller:

pub fn trigger_ice() {
    X.f().f();
}
trait I {}

struct X;
impl I for X {}

trait Tr {
    fn f<A>(self) -> (A,)
    where
        Self: Sized,
    {
        loop {}
    }
}

impl<T> Tr for T where T: I {}

[lqd]

Thanks for opening an issue!

This is a duplicate of #142488, closing it as such.

[xiyuzhai]

Sorry for creating a duplicate. It's hard to go through all the issues and tell.

Glad to know it's fixed!

[lqd]

It's fine, don't worry about it!