rust-lang / rust-lang/rust

ICE : `internal error: entered unreachable code`

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A-closures A-lints C-bug I-ICE L-rust_2021_incompatible_closure_captures S-bug-has-test S-has-mcve T-compiler T-types
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Rust
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Description

I tried this code:

#![deny(rust_2021_incompatible_closure_captures)]
struct Foo();
struct S;
impl Drop for S {
    fn drop() {}
}
struct T(S, S);
struct U(T, <Foo as NewTrait>::Assoc);
fn test_precise_analysis_long_path() {
    let u = U(T(S, S), );
     c = || {
        let _x = u.0.0;
         _x = u.0.1;
         _x = u.1.1;
    };
}
trait NewTrait {
    type Assoc;
}
impl NewTrait for Foo {
    type Assoc = T;
}
fn main(){}
Release channel Result
Current Stable ICE
Current Nightly ICE
Meta

rustc --version --verbose:

rustc 1.95.0-nightly (db3e99bba 2026-02-04)
binary: rustc
commit-hash: db3e99bbab28c6ca778b13222becdea54533d908
commit-date: 2026-02-04
host: x86_64-unknown-linux-gnu
release: 1.95.0-nightly
LLVM version: 22.1.0
Backtrace 

error[E0425]: cannot find value `c` in this scope
  --> bug.rs:11:6
   |
 3 | struct S;
   | --------- similarly named unit struct `S` defined here
...
11 |      c = || {
   |      ^
   |
help: a unit struct with a similar name exists
   |
11 -      c = || {
11 +      S = || {
   |
help: you might have meant to introduce a new binding
   |
11 |      let c = || {
   |      +++

error[E0186]: method `drop` has a `&mut self` declaration in the trait, but not in the impl
 --> bug.rs:5:5
  |
5 |     fn drop() {}
  |     ^^^^^^^^^ expected `&mut self` in impl
  |
  = note: `drop` from trait: `fn(&mut Self)`

error[E0061]: this struct takes 2 arguments but 1 argument was supplied
  --> bug.rs:10:13
   |
10 |     let u = U(T(S, S), );
   |             ^----------- argument #2 of type `T` is missing
   |
note: tuple struct defined here
  --> bug.rs:8:8
   |
 8 | struct U(T, <Foo as NewTrait>::Assoc);
   |        ^
help: provide the argument
   |
10 |     let u = U(T(S, S), /* T */);
   |                        +++++++


thread 'rustc' (2028239) panicked at /rustc-dev/db3e99bbab28c6ca778b13222becdea54533d908/compiler/rustc_hir_typeck/src/upvar.rs:1685:18:
internal error: entered unreachable code
stack backtrace:
   0:     0x7fd12377438b - <<std[5b6453b30570829a]::sys::backtrace::BacktraceLock>::print::DisplayBacktrace as core[94716341d7c778ad]::fmt::Display>::fmt
   1:     0x7fd123d3fd08 - core[94716341d7c778ad]::fmt::write
   2:     0x7fd12378b676 - <std[5b6453b30570829a]::sys::stdio::unix::Stderr as std[5b6453b30570829a]::io::Write>::write_fmt
   3:     0x7fd12374a388 - std[5b6453b30570829a]::panicking::default_hook::{closure#0}
   4:     0x7fd123767763 - std[5b6453b30570829a]::panicking::default_hook
   5:     0x7fd1227570ad - std[5b6453b30570829a]::panicking::update_hook::<alloc[4b4e8be454901a39]::boxed::Box<rustc_driver_impl[70175e87f37eb535]::install_ice_hook::{closure#1}>>::{closure#0}
   6:     0x7fd123767a42 - std[5b6453b30570829a]::panicking::panic_with_hook
   7:     0x7fd12374a47a - std[5b6453b30570829a]::panicking::panic_handler::{closure#0}
   8:     0x7fd12373e9b9 - std[5b6453b30570829a]::sys::backtrace::__rust_end_short_backtrace::<std[5b6453b30570829a]::panicking::panic_handler::{closure#0}, !>
   9:     0x7fd12374bead - __rustc[c8a7c5c4b6a2cdce]::rust_begin_unwind
  10:     0x7fd1209b010c - core[94716341d7c778ad]::panicking::panic_fmt
  11:     0x7fd11ff08a82 - core[94716341d7c778ad]::panicking::panic
  12:     0x7fd122a5a3e9 - <rustc_hir_typeck[5789e0bb21a211b9]::fn_ctxt::FnCtxt>::has_significant_drop_outside_of_captures
  13:     0x7fd122a5a2ab - <rustc_hir_typeck[5789e0bb21a211b9]::fn_ctxt::FnCtxt>::has_significant_drop_outside_of_captures
  14:     0x7fd122a5698e - <rustc_hir_typeck[5789e0bb21a211b9]::fn_ctxt::FnCtxt>::perform_2229_migration_analysis
  15:     0x7fd12492aaa4 - <rustc_hir_typeck[5789e0bb21a211b9]::fn_ctxt::FnCtxt>::analyze_closure
  16:     0x7fd12402b012 - <rustc_hir_typeck[5789e0bb21a211b9]::upvar::InferBorrowKindVisitor as rustc_hir[a9e131cadb307f85]::intravisit::Visitor>::visit_expr
  17:     0x7fd12402b327 - <rustc_hir_typeck[5789e0bb21a211b9]::upvar::InferBorrowKindVisitor as rustc_hir[a9e131cadb307f85]::intravisit::Visitor>::visit_expr
  18:     0x7fd12402ae62 - <rustc_hir_typeck[5789e0bb21a211b9]::upvar::InferBorrowKindVisitor as rustc_hir[a9e131cadb307f85]::intravisit::Visitor>::visit_block
  19:     0x7fd124ae14d7 - rustc_hir_typeck[5789e0bb21a211b9]::typeck_with_inspect::{closure#0}
  20:     0x7fd124adf8b0 - rustc_query_impl[5ce950bad06ac490]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[5ce950bad06ac490]::query_impl::typeck::make_query_vtable::{closure#1}::{closure#0}, rustc_middle[945890ed1064710a]::query::erase::ErasedData<[u8; 8usize]>>
  21:     0x7fd1242a2d36 - rustc_query_system[cb5650c2b33f578c]::query::plumbing::try_execute_query::<rustc_query_impl[5ce950bad06ac490]::SemiDynamicQueryDispatcher<rustc_data_structures[1e615b1a93145c8c]::vec_cache::VecCache<rustc_span[64ec0f452ae8c55c]::def_id::LocalDefId, rustc_middle[945890ed1064710a]::query::erase::ErasedData<[u8; 8usize]>, rustc_query_system[cb5650c2b33f578c]::dep_graph::graph::DepNodeIndex>, {rustc_query_impl[5ce950bad06ac490]::QueryFlags { is_anon: false, is_depth_limit: false, is_feedable: false }}>, false>
  22:     0x7fd1242a2909 - rustc_query_impl[5ce950bad06ac490]::query_impl::typeck::get_query_non_incr::__rust_end_short_backtrace
  23:     0x7fd1242a94cc - <rustc_middle[945890ed1064710a]::ty::context::TyCtxt>::par_hir_body_owners::<rustc_hir_analysis[e217d8de9cc0e6b4]::check_crate::{closure#2}>::{closure#0}
  24:     0x7fd1242a8ee6 - rustc_hir_analysis[e217d8de9cc0e6b4]::check_crate
  25:     0x7fd12429ca1b - rustc_interface[391380b3dd77dca3]::passes::analysis
  26:     0x7fd12429c66b - rustc_query_impl[5ce950bad06ac490]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[5ce950bad06ac490]::query_impl::analysis::make_query_vtable::{closure#1}::{closure#0}, rustc_middle[945890ed1064710a]::query::erase::ErasedData<[u8; 0usize]>>
  27:     0x7fd124ebb5e6 - rustc_query_system[cb5650c2b33f578c]::query::plumbing::try_execute_query::<rustc_query_impl[5ce950bad06ac490]::SemiDynamicQueryDispatcher<rustc_query_system[cb5650c2b33f578c]::query::caches::SingleCache<rustc_middle[945890ed1064710a]::query::erase::ErasedData<[u8; 0usize]>>, {rustc_query_impl[5ce950bad06ac490]::QueryFlags { is_anon: false, is_depth_limit: false, is_feedable: false }}>, false>
  28:     0x7fd124ebb348 - rustc_query_impl[5ce950bad06ac490]::query_impl::analysis::get_query_non_incr::__rust_end_short_backtrace
  29:     0x7fd12502bda7 - <rustc_interface[391380b3dd77dca3]::passes::create_and_enter_global_ctxt<core[94716341d7c778ad]::option::Option<rustc_interface[391380b3dd77dca3]::queries::Linker>, rustc_driver_impl[70175e87f37eb535]::run_compiler::{closure#0}::{closure#2}>::{closure#2} as core[94716341d7c778ad]::ops::function::FnOnce<(&rustc_session[79dda06290ce4e69]::session::Session, rustc_middle[945890ed1064710a]::ty::context::CurrentGcx, alloc[4b4e8be454901a39]::sync::Arc<rustc_data_structures[1e615b1a93145c8c]::jobserver::Proxy>, &std[5b6453b30570829a]::sync::once_lock::OnceLock<rustc_middle[945890ed1064710a]::ty::context::GlobalCtxt>, &rustc_data_structures[1e615b1a93145c8c]::sync::worker_local::WorkerLocal<rustc_middle[945890ed1064710a]::arena::Arena>, &rustc_data_structures[1e615b1a93145c8c]::sync::worker_local::WorkerLocal<rustc_hir[a9e131cadb307f85]::Arena>, rustc_driver_impl[70175e87f37eb535]::run_compiler::{closure#0}::{closure#2})>>::call_once::{shim:vtable#0}
  30:     0x7fd124edd0be - rustc_interface[391380b3dd77dca3]::interface::run_compiler::<(), rustc_driver_impl[70175e87f37eb535]::run_compiler::{closure#0}>::{closure#1}
  31:     0x7fd124f1f6fe - std[5b6453b30570829a]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[391380b3dd77dca3]::util::run_in_thread_with_globals<rustc_interface[391380b3dd77dca3]::util::run_in_thread_pool_with_globals<rustc_interface[391380b3dd77dca3]::interface::run_compiler<(), rustc_driver_impl[70175e87f37eb535]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
  32:     0x7fd124f1fc20 - <std[5b6453b30570829a]::thread::lifecycle::spawn_unchecked<rustc_interface[391380b3dd77dca3]::util::run_in_thread_with_globals<rustc_interface[391380b3dd77dca3]::util::run_in_thread_pool_with_globals<rustc_interface[391380b3dd77dca3]::interface::run_compiler<(), rustc_driver_impl[70175e87f37eb535]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core[94716341d7c778ad]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  33:     0x7fd124f20aac - <std[5b6453b30570829a]::sys::thread::unix::Thread>::new::thread_start
  34:     0x7fd11ead8609 - start_thread
                               at /build/glibc-B3wQXB/glibc-2.31/nptl/pthread_create.c:477:8
  35:     0x7fd11e9fd353 - clone
                               at /build/glibc-B3wQXB/glibc-2.31/misc/../sysdeps/unix/sysv/linux/x86_64/clone.S:95:0
  36:                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: rustc 1.95.0-nightly (db3e99bba 2026-02-04) running on x86_64-unknown-linux-gnu

query stack during panic:
#0 [typeck] type-checking `test_precise_analysis_long_path`
#1 [analysis] running analysis passes on crate `bug`
end of query stack
error: aborting due to 3 previous errors

Some errors have detailed explanations: E0061, E0186, E0425.
For more information about an error, try `rustc --explain E0061`.

@rustbot label +I-ICE +T-compiler +C-bug

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Reproduce the ICE with the code in the issue, then start at rustc_hir_typeck/src/upvar.rs:1685 and inspect has_significant_drop_outside_of_captures during type-checking test_precise_analysis_long_path. Done means the compiler handles this malformed-input case without panicking; use the provided backtrace and query stack to narrow the regression.

Written by the indexing model from the issue text.

Assessment

Tech stack
rust
Domain
compilers
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
38/100

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