rust-lang / rust-lang/rust

[ICE]: `assertion failed: !self.tcx.next_trait_solver_globally()`

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Since Feb 11, 2026.

C-bug F-type_alias_impl_trait I-ICE T-compiler WG-trait-system-refactor
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Rust
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Description

original:

//@compile-flags: -Znext-solver=globally
#![feature(type_alias_impl_trait)]
type Tait = impl Iterator<Item = impl Sized>;

#[define_opaque(Tait)]
fn a() {
    let _: Tait = IntoIterator::into_iter([0i32; 0i32]);
}

#[define_opaque(Tait)]
fn b() {
    let _: Tait = IntoIterator::into_iter([0i32; 42 /* <- */]);
}

fn main() {}

Version information

rustc 1.95.0-nightly (d00ba9225 2026-02-10)
binary: rustc
commit-hash: d00ba922591daa3d0a8b0f3cdf54c610097c24ea
commit-date: 2026-02-10
host: x86_64-unknown-linux-gnu
release: 1.95.0-nightly
LLVM version: 22.1.0

Possibly related line of code:
https://github.com/rust-lang/rust/blob/d00ba922591daa3d0a8b0f3cdf54c610097c24ea/compiler/rustc_hir_analysis/src/collect/type_of/opaque.rs#L128-L140

Command:
/home/matthias/.rustup/toolchains/master/bin/rustc -Znext-solver=globally

Program output 

error: concrete type differs from previous defining opaque type use
  --> a.rs:12:12
   |
12 |     let _: Tait = IntoIterator::into_iter([0i32; 42 /* <- */]);
   |            ^^^^ expected `std::array::IntoIter<i32, 0>`, got `std::array::IntoIter<i32, 42>`
   |
note: previous use here
  --> a.rs:7:12
   |
 7 |     let _: Tait = IntoIterator::into_iter([0i32; 0i32]);
   |            ^^^^


thread 'rustc' (1644810) panicked at /rustc-dev/d00ba922591daa3d0a8b0f3cdf54c610097c24ea/compiler/rustc_hir_analysis/src/collect/type_of/opaque.rs:134:9:
assertion failed: !self.tcx.next_trait_solver_globally()
stack backtrace:
   0:     0x7f3f259951db - <<std[9af484578896a6a4]::sys::backtrace::BacktraceLock>::print::DisplayBacktrace as core[802d2132a31a6f72]::fmt::Display>::fmt
   1:     0x7f3f2600ed88 - core[802d2132a31a6f72]::fmt::write
   2:     0x7f3f259ac4c6 - <std[9af484578896a6a4]::sys::stdio::unix::Stderr as std[9af484578896a6a4]::io::Write>::write_fmt
   3:     0x7f3f2596b218 - std[9af484578896a6a4]::panicking::default_hook::{closure#0}
   4:     0x7f3f259885e3 - std[9af484578896a6a4]::panicking::default_hook
   5:     0x7f3f24967acf - std[9af484578896a6a4]::panicking::update_hook::<alloc[d9babc3d00cc4108]::boxed::Box<rustc_driver_impl[8e73ada93af8ee81]::install_ice_hook::{closure#1}>>::{closure#0}
   6:     0x7f3f259888c2 - std[9af484578896a6a4]::panicking::panic_with_hook
   7:     0x7f3f2596b30a - std[9af484578896a6a4]::panicking::panic_handler::{closure#0}
   8:     0x7f3f2595f849 - std[9af484578896a6a4]::sys::backtrace::__rust_end_short_backtrace::<std[9af484578896a6a4]::panicking::panic_handler::{closure#0}, !>
   9:     0x7f3f2596cd3d - __rustc[9bfdb1a8a4529abf]::rust_begin_unwind
  10:     0x7f3f229ba88c - core[802d2132a31a6f72]::panicking::panic_fmt
  11:     0x7f3f22015182 - core[802d2132a31a6f72]::panicking::panic
  12:     0x7f3f24aee556 - <rustc_hir_analysis[d8bfd681df41e63a]::collect::type_of::opaque::TaitConstraintLocator>::non_defining_use_in_defining_scope
  13:     0x7f3f24aee8bc - <rustc_hir_analysis[d8bfd681df41e63a]::collect::type_of::opaque::TaitConstraintLocator>::check
  14:     0x7f3f24b2e401 - rustc_hir_analysis[d8bfd681df41e63a]::collect::type_of::opaque::find_opaque_ty_constraints_for_tait
  15:     0x7f3f28013bd9 - rustc_hir_analysis[d8bfd681df41e63a]::collect::type_of::type_of_opaque.cold
  16:     0x7f3f2604d1ab - rustc_query_impl[96f5845f77133f74]::execution::try_execute_query::<rustc_query_system[c2f2fbd096e62cce]::query::caches::DefIdCache<rustc_middle[c89a18844a26074f]::query::erase::ErasedData<[u8; 8usize]>>, {rustc_query_impl[96f5845f77133f74]::QueryFlags { is_anon: false, is_depth_limit: false, is_feedable: false }}, false>
  17:     0x7f3f2727245a - rustc_query_impl[96f5845f77133f74]::query_impl::type_of_opaque::get_query_non_incr::__rust_end_short_backtrace
  18:     0x7f3f2669c788 - rustc_hir_analysis[d8bfd681df41e63a]::collect::type_of::type_of
  19:     0x7f3f26307e26 - rustc_query_impl[96f5845f77133f74]::query_impl::type_of::compute_fn::__rust_begin_short_backtrace
  20:     0x7f3f263c64f4 - rustc_query_impl[96f5845f77133f74]::execution::try_execute_query::<rustc_query_system[c2f2fbd096e62cce]::query::caches::DefIdCache<rustc_middle[c89a18844a26074f]::query::erase::ErasedData<[u8; 8usize]>>, {rustc_query_impl[96f5845f77133f74]::QueryFlags { is_anon: false, is_depth_limit: false, is_feedable: true }}, false>
  21:     0x7f3f263c609c - rustc_query_impl[96f5845f77133f74]::query_impl::type_of::get_query_non_incr::__rust_end_short_backtrace
  22:     0x7f3f2702739c - rustc_hir_analysis[d8bfd681df41e63a]::check::check::check_opaque
  23:     0x7f3f26850205 - rustc_hir_analysis[d8bfd681df41e63a]::check::check::check_item_type
  24:     0x7f3f268488ee - rustc_hir_analysis[d8bfd681df41e63a]::check::wfcheck::check_well_formed
  25:     0x7f3f268488cf - rustc_query_impl[96f5845f77133f74]::query_impl::check_well_formed::compute_fn::__rust_begin_short_backtrace
  26:     0x7f3f268480c6 - rustc_query_impl[96f5845f77133f74]::execution::try_execute_query::<rustc_data_structures[7d5eae3e30998a75]::vec_cache::VecCache<rustc_span[db7d19f050fdd233]::def_id::LocalDefId, rustc_middle[c89a18844a26074f]::query::erase::ErasedData<[u8; 1usize]>, rustc_query_system[c2f2fbd096e62cce]::dep_graph::graph::DepNodeIndex>, {rustc_query_impl[96f5845f77133f74]::QueryFlags { is_anon: false, is_depth_limit: false, is_feedable: false }}, false>
  27:     0x7f3f26847e42 - rustc_query_impl[96f5845f77133f74]::query_impl::check_well_formed::get_query_non_incr::__rust_end_short_backtrace
  28:     0x7f3f2684540a - rustc_hir_analysis[d8bfd681df41e63a]::check::wfcheck::check_type_wf
  29:     0x7f3f268452ab - rustc_query_impl[96f5845f77133f74]::query_impl::check_type_wf::compute_fn::__rust_begin_short_backtrace
  30:     0x7f3f272438eb - rustc_query_impl[96f5845f77133f74]::execution::try_execute_query::<rustc_query_system[c2f2fbd096e62cce]::query::caches::SingleCache<rustc_middle[c89a18844a26074f]::query::erase::ErasedData<[u8; 1usize]>>, {rustc_query_impl[96f5845f77133f74]::QueryFlags { is_anon: false, is_depth_limit: false, is_feedable: false }}, false>
  31:     0x7f3f272436c2 - rustc_query_impl[96f5845f77133f74]::query_impl::check_type_wf::get_query_non_incr::__rust_end_short_backtrace
  32:     0x7f3f26c0c5b3 - rustc_hir_analysis[d8bfd681df41e63a]::check_crate
  33:     0x7f3f26c10a59 - rustc_interface[277f9a2595fb6ae7]::passes::analysis
  34:     0x7f3f2724081a - rustc_query_impl[96f5845f77133f74]::execution::try_execute_query::<rustc_query_system[c2f2fbd096e62cce]::query::caches::SingleCache<rustc_middle[c89a18844a26074f]::query::erase::ErasedData<[u8; 0usize]>>, {rustc_query_impl[96f5845f77133f74]::QueryFlags { is_anon: false, is_depth_limit: false, is_feedable: false }}, false>
  35:     0x7f3f272405d0 - rustc_query_impl[96f5845f77133f74]::query_impl::analysis::get_query_non_incr::__rust_end_short_backtrace
  36:     0x7f3f273eb327 - <rustc_interface[277f9a2595fb6ae7]::passes::create_and_enter_global_ctxt<core[802d2132a31a6f72]::option::Option<rustc_interface[277f9a2595fb6ae7]::queries::Linker>, rustc_driver_impl[8e73ada93af8ee81]::run_compiler::{closure#0}::{closure#2}>::{closure#2} as core[802d2132a31a6f72]::ops::function::FnOnce<(&rustc_session[4eca5f9ae8c0e42d]::session::Session, rustc_middle[c89a18844a26074f]::ty::context::CurrentGcx, alloc[d9babc3d00cc4108]::sync::Arc<rustc_data_structures[7d5eae3e30998a75]::jobserver::Proxy>, &std[9af484578896a6a4]::sync::once_lock::OnceLock<rustc_middle[c89a18844a26074f]::ty::context::GlobalCtxt>, &rustc_data_structures[7d5eae3e30998a75]::sync::worker_local::WorkerLocal<rustc_middle[c89a18844a26074f]::arena::Arena>, &rustc_data_structures[7d5eae3e30998a75]::sync::worker_local::WorkerLocal<rustc_hir[687ec13789e9964d]::Arena>, rustc_driver_impl[8e73ada93af8ee81]::run_compiler::{closure#0}::{closure#2})>>::call_once::{shim:vtable#0}
  37:     0x7f3f27252c39 - rustc_interface[277f9a2595fb6ae7]::interface::run_compiler::<(), rustc_driver_impl[8e73ada93af8ee81]::run_compiler::{closure#0}>::{closure#1}
  38:     0x7f3f27223bfe - std[9af484578896a6a4]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[277f9a2595fb6ae7]::util::run_in_thread_with_globals<rustc_interface[277f9a2595fb6ae7]::util::run_in_thread_pool_with_globals<rustc_interface[277f9a2595fb6ae7]::interface::run_compiler<(), rustc_driver_impl[8e73ada93af8ee81]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
  39:     0x7f3f27224120 - <std[9af484578896a6a4]::thread::lifecycle::spawn_unchecked<rustc_interface[277f9a2595fb6ae7]::util::run_in_thread_with_globals<rustc_interface[277f9a2595fb6ae7]::util::run_in_thread_pool_with_globals<rustc_interface[277f9a2595fb6ae7]::interface::run_compiler<(), rustc_driver_impl[8e73ada93af8ee81]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core[802d2132a31a6f72]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  40:     0x7f3f27224fac - <std[9af484578896a6a4]::sys::thread::unix::Thread>::new::thread_start
  41:     0x7f3f20a9698b - <unknown>
  42:     0x7f3f20b1a9cc - <unknown>
  43:                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 `/tmp/im/rustc-ice-2026-02-10T16_58_17-1644808.txt` to your bug report

note: rustc 1.95.0-nightly (d00ba9225 2026-02-10) running on x86_64-unknown-linux-gnu

note: compiler flags: -Z next-solver=globally

query stack during panic:
#0 [type_of_opaque] computing type of opaque `Tait::{opaque#0}::{opaque#0}`
#1 [type_of] computing type of `Tait::{opaque#0}::{opaque#0}`
#2 [check_well_formed] checking that `Tait::{opaque#0}::{opaque#0}` is well-formed
#3 [check_type_wf] checking that types are well-formed
#4 [analysis] running analysis passes on crate `a`
end of query stack
error: aborting due to 1 previous error

@rustbot label +F-type_alias_impl_trait +WG-trait-system-refactor

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