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[ICE]: checks.rs: index out of bounds: the len is 0 but the index is 0 #153366

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#158044
Closed
[ICE]: checks.rs: index out of bounds: the len is 0 but the index is 0#153366
#158044
Labels
A-parallel-compilerArea: parallel compilerC-bugCategory: This is a bug.I-ICEIssue: The compiler panicked, giving an Internal Compilation Error (ICE) ❄️T-compilerRelevant to the compiler team, which will review and decide on the PR/issue.

Description

@matthiaskrgr
matthiaskrgr
opened on Mar 3, 2026

reduced

#![feature(unboxed_closures)]
fn iso<A>(a: Fn) -> Option<_>
where
    dyn Fn(A) -> (): Sized,
{
    Box::new(iso_un_option)
}
fn iso_un_option<B>() -> Box<_> {
    iso(())
}

fn main() {
    iso(())
}

original:

pub fn iso<A, B, B, F2>(a: Fn, b: F2) -> (Option<_>, Box<dyn Fn() -> A>)
    where
        F1: (Fn(A) -> B) + 'static,
        F2: (Fn(A) -> B) + 'static,
{
    (Box::new(iso_un_option), o_a::new(b))
}
pub fn iso_un_option<A, B>() -> (Box<_>, Box<dyn Fn(B) -> Option>) {
   let left = |o_a: Option<_>| o_a.unwrap();
    let _: &mut S = unsafe {
    let mut s = S;
    let x = &raw const s;
    let _: &S = unsafe { *x };
    //~^ ERROR mismatched types
    //~| HELP consider borrowing here

    let x = &raw mut s;
    let _: &mut S = unsafe { *x };
    //~^ ERROR mismatched types
    //~| HELP consider mutably borrowing here
};
    iso(left, right)
    //~^ ERROR overflow
}

fn main() {}

Version information

rustc 1.96.0-nightly (ec818fda3 2026-03-02)
binary: rustc
commit-hash: ec818fda361ca216eb186f5cf45131bd9c776bb4
commit-date: 2026-03-02
host: x86_64-unknown-linux-gnu
release: 1.96.0-nightly
LLVM version: 22.1.0

Possibly related line of code:

rust/compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs

Lines 1658 to 1668 in ec818fd

};
if let Some((params_with_generics, _)) = self.get_hir_param_info(def_id, is_method) {
debug_assert_eq!(params_with_generics.len(), matched_inputs.len());
for (idx, (generic_param, _)) in params_with_generics.iter_enumerated() {
if matched_inputs[idx].is_none() {
continue;
}
let Some((_, matched_arg_span)) = provided_arg_tys.get(idx.to_provided_idx())
else {

Command:
/home/matthias/.rustup/toolchains/master/bin/rustc -Zthreads=20
triggers around one in 3 times?

Program output 

warning: trait objects without an explicit `dyn` are deprecated
 --> code.rs:2:14
  |
2 | fn iso<A>(a: Fn) -> Option<_>
  |              ^^
  |
  = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
  = note: for more information, see <https://doc.rust-lang.org/edition-guide/rust-2021/warnings-promoted-to-error.html>
  = note: `#[warn(bare_trait_objects)]` (part of `#[warn(rust_2021_compatibility)]`) on by default
help: if this is a dyn-compatible trait, use `dyn`
  |
2 | fn iso<A>(a: dyn Fn) -> Option<_>
  |              +++

error[E0107]: missing generics for trait `Fn`
  --> code.rs:2:14
   |
 2 | fn iso<A>(a: Fn) -> Option<_>
   |              ^^ expected 1 generic argument
   |
note: trait defined here, with 1 generic parameter: `Args`
  --> /home/matthias/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/ops/function.rs:76:17
   |
76 | pub const trait Fn<Args: Tuple>: [const] FnMut<Args> {
   |                 ^^ ----
help: add missing generic argument
   |
 2 | fn iso<A>(a: Fn<Args>) -> Option<_>
   |                ++++++

error[E0277]: the size for values of type `(dyn Fn(_) + 'static)` cannot be known at compilation time
 --> code.rs:9:5
  |
9 |     iso(())
  |     ^^^^^^^ doesn't have a size known at compile-time
  |
  = help: the trait `Sized` is not implemented for `(dyn Fn(_) + 'static)`
note: required by a bound in `iso`
 --> code.rs:4:22
  |
2 | fn iso<A>(a: Fn) -> Option<_>
  |    --- required by a bound in this function
3 | where
4 |     dyn Fn(A) -> (): Sized,
  |                      ^^^^^ required by this bound in `iso`


thread 'rustc' (762204) panicked at /rustc-dev/ec818fda361ca216eb186f5cf45131bd9c776bb4/compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs:1663:34:
index out of bounds: the len is 0 but the index is 0
stack backtrace:
   0:     0x7fb4471532bb - <<std[eb110dcb1455ebbb]::sys::backtrace::BacktraceLock>::print::DisplayBacktrace as core[89784ade3600f19b]::fmt::Display>::fmt
   1:     0x7fb4478202c8 - core[89784ade3600f19b]::fmt::write
   2:     0x7fb44716a2c6 - <std[eb110dcb1455ebbb]::sys::stdio::unix::Stderr as std[eb110dcb1455ebbb]::io::Write>::write_fmt
   3:     0x7fb447129398 - std[eb110dcb1455ebbb]::panicking::default_hook::{closure#0}
   4:     0x7fb447146723 - std[eb110dcb1455ebbb]::panicking::default_hook
   5:     0x7fb44613125c - std[eb110dcb1455ebbb]::panicking::update_hook::<alloc[29fb76bce34b892e]::boxed::Box<rustc_driver_impl[fb3bb71bcb51a2dc]::install_ice_hook::{closure#1}>>::{closure#0}
   6:     0x7fb447146a02 - std[eb110dcb1455ebbb]::panicking::panic_with_hook
   7:     0x7fb447129458 - std[eb110dcb1455ebbb]::panicking::panic_handler::{closure#0}
   8:     0x7fb447120189 - std[eb110dcb1455ebbb]::sys::backtrace::__rust_end_short_backtrace::<std[eb110dcb1455ebbb]::panicking::panic_handler::{closure#0}, !>
   9:     0x7fb44712aebd - __rustc[b5c62ea7d35cbfc4]::rust_begin_unwind
  10:     0x7fb443cce2fc - core[89784ade3600f19b]::panicking::panic_fmt
  11:     0x7fb444049b32 - core[89784ade3600f19b]::panicking::panic_bounds_check
  12:     0x7fb446422f5a - <rustc_hir_typeck[8a5d87c05ae1a325]::fn_ctxt::FnCtxt>::label_generic_mismatches
  13:     0x7fb44641e85a - <rustc_hir_typeck[8a5d87c05ae1a325]::fn_ctxt::FnCtxt>::report_arg_errors
  14:     0x7fb447bcf6ad - <rustc_hir_typeck[8a5d87c05ae1a325]::fn_ctxt::FnCtxt>::check_expr_call
  15:     0x7fb447bae350 - <rustc_hir_typeck[8a5d87c05ae1a325]::fn_ctxt::FnCtxt>::check_expr_with_expectation_and_args
  16:     0x7fb447ba8530 - <rustc_hir_typeck[8a5d87c05ae1a325]::fn_ctxt::FnCtxt>::check_expr_block
  17:     0x7fb447bae2d7 - <rustc_hir_typeck[8a5d87c05ae1a325]::fn_ctxt::FnCtxt>::check_expr_with_expectation_and_args
  18:     0x7fb447b7cfca - rustc_hir_typeck[8a5d87c05ae1a325]::check::check_fn
  19:     0x7fb44860eab2 - rustc_hir_typeck[8a5d87c05ae1a325]::typeck_with_inspect::{closure#0}
  20:     0x7fb44860d532 - rustc_query_impl[52bc1cae8cb1f0f9]::query_impl::typeck::invoke_provider_fn::__rust_begin_short_backtrace
  21:     0x7fb44797858a - rustc_query_impl[52bc1cae8cb1f0f9]::execution::try_execute_query::<rustc_data_structures[d0096a8ffe6a0514]::vec_cache::VecCache<rustc_span[566afffa9b4ced27]::def_id::LocalDefId, rustc_middle[35e622c0033dd948]::query::erase::ErasedData<[u8; 8usize]>, rustc_middle[35e622c0033dd948]::dep_graph::graph::DepNodeIndex>, false>
  22:     0x7fb447977f03 - rustc_query_impl[52bc1cae8cb1f0f9]::query_impl::typeck::execute_query_non_incr::__rust_end_short_backtrace
  23:     0x7fb447f2dfc9 - rustc_hir_analysis[eb8396faa04d2a8f]::collect::lower_fn_sig_recovering_infer_ret_ty
  24:     0x7fb447abc157 - rustc_hir_analysis[eb8396faa04d2a8f]::collect::fn_sig
  25:     0x7fb447abb826 - rustc_query_impl[52bc1cae8cb1f0f9]::query_impl::fn_sig::invoke_provider_fn::__rust_begin_short_backtrace
  26:     0x7fb447abff4e - rustc_query_impl[52bc1cae8cb1f0f9]::execution::try_execute_query::<rustc_middle[35e622c0033dd948]::query::caches::DefIdCache<rustc_middle[35e622c0033dd948]::query::erase::ErasedData<[u8; 24usize]>>, false>
  27:     0x7fb447abf425 - rustc_query_impl[52bc1cae8cb1f0f9]::query_impl::fn_sig::execute_query_non_incr::__rust_end_short_backtrace
  28:     0x7fb44810bb18 - rustc_hir_analysis[eb8396faa04d2a8f]::check::check::check_item_type
  29:     0x7fb448106ba6 - rustc_hir_analysis[eb8396faa04d2a8f]::check::wfcheck::check_well_formed
  30:     0x7fb448106b87 - rustc_query_impl[52bc1cae8cb1f0f9]::query_impl::check_well_formed::invoke_provider_fn::__rust_begin_short_backtrace
  31:     0x7fb448106119 - rustc_query_impl[52bc1cae8cb1f0f9]::execution::try_execute_query::<rustc_data_structures[d0096a8ffe6a0514]::vec_cache::VecCache<rustc_span[566afffa9b4ced27]::def_id::LocalDefId, rustc_middle[35e622c0033dd948]::query::erase::ErasedData<[u8; 1usize]>, rustc_middle[35e622c0033dd948]::dep_graph::graph::DepNodeIndex>, false>
  32:     0x7fb448105e7b - rustc_query_impl[52bc1cae8cb1f0f9]::query_impl::check_well_formed::execute_query_non_incr::__rust_end_short_backtrace
  33:     0x7fb44629619a - <rustc_middle[35e622c0033dd948]::hir::ModuleItems>::par_opaques::<rustc_hir_analysis[eb8396faa04d2a8f]::check::wfcheck::check_type_wf::{closure#5}>::{closure#0}
  34:     0x7fb44632835b - <rustc_thread_pool[6e6cbbf42ebd39ad]::job::HeapJob<<rustc_thread_pool[6e6cbbf42ebd39ad]::scope::Scope>::spawn<rustc_data_structures[d0096a8ffe6a0514]::sync::parallel::par_slice<&rustc_hir[386fa4b273d4e920]::hir::ImplItemId, rustc_data_structures[d0096a8ffe6a0514]::sync::parallel::try_par_for_each_in<&[rustc_hir[386fa4b273d4e920]::hir::ImplItemId], rustc_span[566afffa9b4ced27]::ErrorGuaranteed, <rustc_middle[35e622c0033dd948]::hir::ModuleItems>::par_impl_items<rustc_hir_analysis[eb8396faa04d2a8f]::check::wfcheck::check_type_wf::{closure#1}>::{closure#0}>::{closure#0}::{closure#0}>::{closure#0}::{closure#0}>::{closure#0}> as rustc_thread_pool[6e6cbbf42ebd39ad]::job::Job>::execute
  35:     0x7fb446e484bf - <rustc_thread_pool[6e6cbbf42ebd39ad]::registry::WorkerThread>::wait_or_steal_until_cold
  36:     0x7fb446e46f02 - <rustc_thread_pool[6e6cbbf42ebd39ad]::registry::ThreadBuilder>::run
  37:     0x7fb446129d1c - std[eb110dcb1455ebbb]::sys::backtrace::__rust_begin_short_backtrace::<<rustc_thread_pool[6e6cbbf42ebd39ad]::ThreadPoolBuilder>::build_scoped<rustc_interface[e910a3c7e0b41bdb]::util::run_in_thread_pool_with_globals<rustc_interface[e910a3c7e0b41bdb]::interface::run_compiler<(), rustc_driver_impl[fb3bb71bcb51a2dc]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#5}::{closure#0}::{closure#0}, rustc_interface[e910a3c7e0b41bdb]::util::run_in_thread_pool_with_globals<rustc_interface[e910a3c7e0b41bdb]::interface::run_compiler<(), rustc_driver_impl[fb3bb71bcb51a2dc]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#5}::{closure#0}::{closure#1}, ()>::{closure#0}::{closure#0}::{closure#0}, ()>
  38:     0x7fb446133e23 - <std[eb110dcb1455ebbb]::thread::lifecycle::spawn_unchecked<<rustc_thread_pool[6e6cbbf42ebd39ad]::ThreadPoolBuilder>::build_scoped<rustc_interface[e910a3c7e0b41bdb]::util::run_in_thread_pool_with_globals<rustc_interface[e910a3c7e0b41bdb]::interface::run_compiler<(), rustc_driver_impl[fb3bb71bcb51a2dc]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#5}::{closure#0}::{closure#0}, rustc_interface[e910a3c7e0b41bdb]::util::run_in_thread_pool_with_globals<rustc_interface[e910a3c7e0b41bdb]::interface::run_compiler<(), rustc_driver_impl[fb3bb71bcb51a2dc]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#5}::{closure#0}::{closure#1}, ()>::{closure#0}::{closure#0}::{closure#0}, ()>::{closure#1} as core[89784ade3600f19b]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  39:     0x7fb448a0e9ac - <std[eb110dcb1455ebbb]::sys::thread::unix::Thread>::new::thread_start
  40:     0x7fb4424a598b - <unknown>
  41:     0x7fb442529a0c - <unknown>
  42:                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/matthias/vcs/github/CRED/rustc-ice-2026-03-03T21_14_41-762183.txt` to your bug report

note: rustc 1.96.0-nightly (ec818fda3 2026-03-02) running on x86_64-unknown-linux-gnu

note: compiler flags: -Z threads=20

query stack during panic:
#0 [typeck] type-checking `iso_un_option`
#1 [fn_sig] computing function signature of `iso_un_option`
#2 [check_well_formed] checking that `iso_un_option` is well-formed
#3 [check_type_wf] checking that types are well-formed
#4 [analysis] running analysis passes on crate `code`
end of query stack
error: aborting due to 2 previous errors; 1 warning emitted

Some errors have detailed explanations: E0107, E0277.
For more information about an error, try `rustc --explain E0107`.

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    A-parallel-compilerArea: parallel compilerC-bugCategory: This is a bug.I-ICEIssue: The compiler panicked, giving an Internal Compilation Error (ICE) ❄️T-compilerRelevant to the compiler team, which will review and decide on the PR/issue.

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