ICE with `-Znext-solver` when accessing hir place

[trait-Cong]

I tried this code: (auto-reduce)

#![deny(rust_2021_incompatible_closure_captures)]
struct SendPointer();
struct CustomInt(*mut i32);
struct SyncPointer(<SendPointer as NewTrait1>::Assoc);
impl Send for CustomInt {}
fn test_multi_traits_issues() {
    let fptr1 = SyncPointer();
    thread::spawn(move ||  {
            *fptr1.0.0 = 20;
        })
        .join()
        .unwrap();
}

trait NewTrait1 {
    type Assoc;
}
impl NewTrait1 for SendPointer {
    type Assoc = CustomInt;
}
fn main(){}

The compiler hangs even with -Z next-solver=globally

Release channel	Result
Current Stable	error
Current Nightly (default solver)	error
Current Nightly (+ -Znext-solver=globally)	ICE

Meta

rustc --version --verbose:

rustc 1.95.0-nightly (39052daf9 2026-01-22)
binary: rustc
commit-hash: 39052daf937d46373ac29778e1b8853c52c0cc25
commit-date: 2026-01-22
host: x86_64-unknown-linux-gnu
release: 1.95.0-nightly
LLVM version: 21.1.8

Backtrace

thread 'rustc' panicked at /rustc-dev/39052daf937d46373ac29778e1b8853c52c0cc25/compiler/rustc_middle/src/ty/closure.rs:324:21:
Box<dyn Any>
stack backtrace:
   0:     0x7fdd2f1d863b - <std[34fb7373c7e72eb7]::backtrace::Backtrace>::create
   1:     0x7fdd2f1d8585 - <std[34fb7373c7e72eb7]::backtrace::Backtrace>::force_capture
   2:     0x7fdd2e1ec3e7 - std[34fb7373c7e72eb7]::panicking::update_hook::<alloc[bc4cb1e78b267867]::boxed::Box<rustc_driver_impl[4732efef1a955d17]::install_ice_hook::{closure#1}>>::{closure#0}
   3:     0x7fdd2f1eafc2 - std[34fb7373c7e72eb7]::panicking::panic_with_hook
   4:     0x7fdd2e220ff1 - std[34fb7373c7e72eb7]::panicking::begin_panic::<rustc_errors[8e75ca79703c1f3e]::ExplicitBug>::{closure#0}
   5:     0x7fdd2e219a66 - std[34fb7373c7e72eb7]::sys::backtrace::__rust_end_short_backtrace::<std[34fb7373c7e72eb7]::panicking::begin_panic<rustc_errors[8e75ca79703c1f3e]::ExplicitBug>::{closure#0}, !>
   6:     0x7fdd2e2177d9 - std[34fb7373c7e72eb7]::panicking::begin_panic::<rustc_errors[8e75ca79703c1f3e]::ExplicitBug>
   7:     0x7fdd2e22c1a1 - <rustc_errors[8e75ca79703c1f3e]::diagnostic::BugAbort as rustc_errors[8e75ca79703c1f3e]::diagnostic::EmissionGuarantee>::emit_producing_guarantee
   8:     0x7fdd2e7cd699 - rustc_middle[78d5c0086ff0cb14]::util::bug::opt_span_bug_fmt::<rustc_span[b65cb73ecde2ff03]::span_encoding::Span>::{closure#0}
   9:     0x7fdd2e7cd822 - rustc_middle[78d5c0086ff0cb14]::ty::context::tls::with_opt::<rustc_middle[78d5c0086ff0cb14]::util::bug::opt_span_bug_fmt<rustc_span[b65cb73ecde2ff03]::span_encoding::Span>::{closure#0}, !>::{closure#0}
  10:     0x7fdd2e7bea6b - rustc_middle[78d5c0086ff0cb14]::ty::context::tls::with_context_opt::<rustc_middle[78d5c0086ff0cb14]::ty::context::tls::with_opt<rustc_middle[78d5c0086ff0cb14]::util::bug::opt_span_bug_fmt<rustc_span[b65cb73ecde2ff03]::span_encoding::Span>::{closure#0}, !>::{closure#0}, !>
  11:     0x7fdd2c52f084 - rustc_middle[78d5c0086ff0cb14]::util::bug::bug_fmt
  12:     0x7fdd3055fb91 - rustc_middle[78d5c0086ff0cb14]::ty::closure::place_to_string_for_capture
  13:     0x7fdd2e50ad42 - <rustc_hir_typeck[1a09b58f20181205]::fn_ctxt::FnCtxt>::perform_2229_migration_analysis
  14:     0x7fdd305ccf02 - <rustc_hir_typeck[1a09b58f20181205]::fn_ctxt::FnCtxt>::analyze_closure
  15:     0x7fdd2fab4f66 - <rustc_hir_typeck[1a09b58f20181205]::upvar::InferBorrowKindVisitor as rustc_hir[87f031771fbbadb6]::intravisit::Visitor>::visit_expr
  16:     0x7fdd2fab50e0 - <rustc_hir_typeck[1a09b58f20181205]::upvar::InferBorrowKindVisitor as rustc_hir[87f031771fbbadb6]::intravisit::Visitor>::visit_expr
  17:     0x7fdd2fab5113 - <rustc_hir_typeck[1a09b58f20181205]::upvar::InferBorrowKindVisitor as rustc_hir[87f031771fbbadb6]::intravisit::Visitor>::visit_expr
  18:     0x7fdd2fab5113 - <rustc_hir_typeck[1a09b58f20181205]::upvar::InferBorrowKindVisitor as rustc_hir[87f031771fbbadb6]::intravisit::Visitor>::visit_expr
  19:     0x7fdd2fab4db6 - <rustc_hir_typeck[1a09b58f20181205]::upvar::InferBorrowKindVisitor as rustc_hir[87f031771fbbadb6]::intravisit::Visitor>::visit_block
  20:     0x7fdd30581986 - rustc_hir_typeck[1a09b58f20181205]::typeck_with_inspect::{closure#0}
  21:     0x7fdd3057fcf0 - rustc_query_impl[a61ad378a11c2585]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[a61ad378a11c2585]::query_impl::typeck::dynamic_query::{closure#2}::{closure#0}, rustc_middle[78d5c0086ff0cb14]::query::erase::Erased<[u8; 8usize]>>
  22:     0x7fdd2faa7b2a - rustc_query_system[ef06f3046e437e5]::query::plumbing::try_execute_query::<rustc_query_impl[a61ad378a11c2585]::DynamicConfig<rustc_data_structures[173af339ef2774cb]::vec_cache::VecCache<rustc_span[b65cb73ecde2ff03]::def_id::LocalDefId, rustc_middle[78d5c0086ff0cb14]::query::erase::Erased<[u8; 8usize]>, rustc_query_system[ef06f3046e437e5]::dep_graph::graph::DepNodeIndex>, false, false, false>, rustc_query_impl[a61ad378a11c2585]::plumbing::QueryCtxt, false>
  23:     0x7fdd2faa7409 - rustc_query_impl[a61ad378a11c2585]::query_impl::typeck::get_query_non_incr::__rust_end_short_backtrace
  24:     0x7fdd3045c1ad - <rustc_middle[78d5c0086ff0cb14]::ty::context::TyCtxt>::par_hir_body_owners::<rustc_hir_analysis[fa2e1821763ac804]::check_crate::{closure#2}>::{closure#0}
  25:     0x7fdd3045bbe0 - rustc_hir_analysis[fa2e1821763ac804]::check_crate
  26:     0x7fdd2faa169b - rustc_interface[f6529d171d7be797]::passes::analysis
  27:     0x7fdd2faa12e7 - rustc_query_impl[a61ad378a11c2585]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[a61ad378a11c2585]::query_impl::analysis::dynamic_query::{closure#2}::{closure#0}, rustc_middle[78d5c0086ff0cb14]::query::erase::Erased<[u8; 0usize]>>
  28:     0x7fdd30a2c563 - rustc_query_system[ef06f3046e437e5]::query::plumbing::try_execute_query::<rustc_query_impl[a61ad378a11c2585]::DynamicConfig<rustc_query_system[ef06f3046e437e5]::query::caches::SingleCache<rustc_middle[78d5c0086ff0cb14]::query::erase::Erased<[u8; 0usize]>>, false, false, false>, rustc_query_impl[a61ad378a11c2585]::plumbing::QueryCtxt, false>
  29:     0x7fdd30a2c34e - rustc_query_impl[a61ad378a11c2585]::query_impl::analysis::get_query_non_incr::__rust_end_short_backtrace
  30:     0x7fdd30b755d1 - <rustc_interface[f6529d171d7be797]::passes::create_and_enter_global_ctxt<core[9e7909da24ebc1bc]::option::Option<rustc_interface[f6529d171d7be797]::queries::Linker>, rustc_driver_impl[4732efef1a955d17]::run_compiler::{closure#0}::{closure#2}>::{closure#2} as core[9e7909da24ebc1bc]::ops::function::FnOnce<(&rustc_session[551c966262bcd0c6]::session::Session, rustc_middle[78d5c0086ff0cb14]::ty::context::CurrentGcx, alloc[bc4cb1e78b267867]::sync::Arc<rustc_data_structures[173af339ef2774cb]::jobserver::Proxy>, &std[34fb7373c7e72eb7]::sync::once_lock::OnceLock<rustc_middle[78d5c0086ff0cb14]::ty::context::GlobalCtxt>, &rustc_data_structures[173af339ef2774cb]::sync::worker_local::WorkerLocal<rustc_middle[78d5c0086ff0cb14]::arena::Arena>, &rustc_data_structures[173af339ef2774cb]::sync::worker_local::WorkerLocal<rustc_hir[87f031771fbbadb6]::Arena>, rustc_driver_impl[4732efef1a955d17]::run_compiler::{closure#0}::{closure#2})>>::call_once::{shim:vtable#0}
  31:     0x7fdd309a3127 - rustc_interface[f6529d171d7be797]::interface::run_compiler::<(), rustc_driver_impl[4732efef1a955d17]::run_compiler::{closure#0}>::{closure#1}
  32:     0x7fdd309dd13e - std[34fb7373c7e72eb7]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[f6529d171d7be797]::util::run_in_thread_with_globals<rustc_interface[f6529d171d7be797]::util::run_in_thread_pool_with_globals<rustc_interface[f6529d171d7be797]::interface::run_compiler<(), rustc_driver_impl[4732efef1a955d17]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
  33:     0x7fdd309dd660 - <std[34fb7373c7e72eb7]::thread::lifecycle::spawn_unchecked<rustc_interface[f6529d171d7be797]::util::run_in_thread_with_globals<rustc_interface[f6529d171d7be797]::util::run_in_thread_pool_with_globals<rustc_interface[f6529d171d7be797]::interface::run_compiler<(), rustc_driver_impl[4732efef1a955d17]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core[9e7909da24ebc1bc]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  34:     0x7fdd309de528 - <std[34fb7373c7e72eb7]::sys::thread::unix::Thread>::new::thread_start
  35:     0x7fdd2a294ac3 - start_thread
                               at ./nptl/pthread_create.c:442:8
  36:     0x7fdd2a3268c0 - __GI___clone3
                               at ./misc/../sysdeps/unix/sysv/linux/x86_64/clone3.S:81:0
  37:                0x0 - <unknown>


rustc version: 1.95.0-nightly (39052daf9 2026-01-22)
platform: x86_64-unknown-linux-gnu

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

[SpriteOvO]

Unable to reproduce.

rustc +nightly --version --verbose
rustc 1.95.0-nightly (d222ddc4d 2026-01-23)
binary: rustc
commit-hash: d222ddc4d90743dfc1e53b610be8fc9d95893d2c
commit-date: 2026-01-23
host: x86_64-unknown-linux-gnu
release: 1.95.0-nightly
LLVM version: 21.1.8

[trait-Cong]

This is reproducible for me on the same nightly:

rustc 1.95.0-nightly (d222ddc4d 2026-01-23)

but only with the new solver -Z next-solver=globally

error[E0433]: failed to resolve: use of unresolved module or unlinked crate `thread`
 --> bug.rs:8:5
  |
8 |     thread::spawn(move ||  {
  |     ^^^^^^ use of unresolved module or unlinked crate `thread`
  |
  = help: you might be missing a crate named `thread`
help: consider importing this module
  |
2 + use std::thread;
  |

error[E0200]: the trait `Send` requires an `unsafe impl` declaration
 --> bug.rs:5:1
  |
5 | impl Send for CustomInt {}
  | ^^^^^^^^^^^^^^^^^^^^^^^
  |
  = note: the trait `Send` enforces invariants that the compiler can't check. Review the trait documentation and make sure this implementation upholds those invariants before adding the `unsafe` keyword
help: add `unsafe` to this trait implementation
  |
5 | unsafe impl Send for CustomInt {}
  | ++++++

error[E0061]: this struct takes 1 argument but 0 arguments were supplied
 --> bug.rs:7:17
  |
7 |     let fptr1 = SyncPointer();
  |                 ^^^^^^^^^^^-- argument #1 of type `CustomInt` is missing
  |
note: tuple struct defined here
 --> bug.rs:4:8
  |
4 | struct SyncPointer(<SendPointer as NewTrait1>::Assoc);
  |        ^^^^^^^^^^^
help: provide the argument
  |
7 |     let fptr1 = SyncPointer(/* CustomInt */);
  |                             +++++++++++++++

error: internal compiler error: /rustc-dev/d222ddc4d90743dfc1e53b610be8fc9d95893d2c/compiler/rustc_middle/src/ty/closure.rs:324:21: Field projection applied to a type other than Adt or Tuple: Alias(Projection, AliasTy { args: [SendPointer], def_id: DefId(0:15 ~ bug[8d3d]::NewTrait1::Assoc), .. }).


thread 'rustc' (3582913) panicked at /rustc-dev/d222ddc4d90743dfc1e53b610be8fc9d95893d2c/compiler/rustc_middle/src/ty/closure.rs:324:21:
Box<dyn Any>
stack backtrace:
   0:     0x7fabcac28123 - <<std[f475c8dea6bc1f1c]::sys::backtrace::BacktraceLock>::print::DisplayBacktrace as core[61603b96a07b8ff9]::fmt::Display>::fmt
   1:     0x7fabcb20e688 - core[61603b96a07b8ff9]::fmt::write
   2:     0x7fabcac3e8b6 - <std[f475c8dea6bc1f1c]::sys::stdio::unix::Stderr as std[f475c8dea6bc1f1c]::io::Write>::write_fmt
   3:     0x7fabcabfe128 - std[f475c8dea6bc1f1c]::panicking::default_hook::{closure#0}
   4:     0x7fabcac1b883 - std[f475c8dea6bc1f1c]::panicking::default_hook
   5:     0x7fabc9c0a60d - std[f475c8dea6bc1f1c]::panicking::update_hook::<alloc[cd9c1527bed1fc96]::boxed::Box<rustc_driver_impl[5f67874deb35e28a]::install_ice_hook::{closure#1}>>::{closure#0}
   6:     0x7fabcac1bb62 - std[f475c8dea6bc1f1c]::panicking::panic_with_hook
   7:     0x7fabc9c3ea61 - std[f475c8dea6bc1f1c]::panicking::begin_panic::<rustc_errors[2cc469b56d7ff1c9]::ExplicitBug>::{closure#0}
   8:     0x7fabc9c37776 - std[f475c8dea6bc1f1c]::sys::backtrace::__rust_end_short_backtrace::<std[f475c8dea6bc1f1c]::panicking::begin_panic<rustc_errors[2cc469b56d7ff1c9]::ExplicitBug>::{closure#0}, !>
   9:     0x7fabc9c374ea - std[f475c8dea6bc1f1c]::panicking::begin_panic::<rustc_errors[2cc469b56d7ff1c9]::ExplicitBug>
  10:     0x7fabc9c49bd1 - <rustc_errors[2cc469b56d7ff1c9]::diagnostic::BugAbort as rustc_errors[2cc469b56d7ff1c9]::diagnostic::EmissionGuarantee>::emit_producing_guarantee
  11:     0x7fabca1f74d9 - rustc_middle[323d677696c3953f]::util::bug::opt_span_bug_fmt::<rustc_span[ddbbc3270fa539b]::span_encoding::Span>::{closure#0}
  12:     0x7fabca1f7662 - rustc_middle[323d677696c3953f]::ty::context::tls::with_opt::<rustc_middle[323d677696c3953f]::util::bug::opt_span_bug_fmt<rustc_span[ddbbc3270fa539b]::span_encoding::Span>::{closure#0}, !>::{closure#0}
  13:     0x7fabca1e875b - rustc_middle[323d677696c3953f]::ty::context::tls::with_context_opt::<rustc_middle[323d677696c3953f]::ty::context::tls::with_opt<rustc_middle[323d677696c3953f]::util::bug::opt_span_bug_fmt<rustc_span[ddbbc3270fa539b]::span_encoding::Span>::{closure#0}, !>::{closure#0}, !>
  14:     0x7fabc7876d74 - rustc_middle[323d677696c3953f]::util::bug::bug_fmt
  15:     0x7fabcbf83511 - rustc_middle[323d677696c3953f]::ty::closure::place_to_string_for_capture
  16:     0x7fabc9f3438e - <rustc_hir_typeck[abd9435c796a8ed5]::fn_ctxt::FnCtxt>::perform_2229_migration_analysis
  17:     0x7fabcc00312f - <rustc_hir_typeck[abd9435c796a8ed5]::fn_ctxt::FnCtxt>::analyze_closure
  18:     0x7fabcb4e9a26 - <rustc_hir_typeck[abd9435c796a8ed5]::upvar::InferBorrowKindVisitor as rustc_hir[efbd91fb3c2f0b84]::intravisit::Visitor>::visit_expr
  19:     0x7fabcb4e9ba0 - <rustc_hir_typeck[abd9435c796a8ed5]::upvar::InferBorrowKindVisitor as rustc_hir[efbd91fb3c2f0b84]::intravisit::Visitor>::visit_expr
  20:     0x7fabcb4e9bd3 - <rustc_hir_typeck[abd9435c796a8ed5]::upvar::InferBorrowKindVisitor as rustc_hir[efbd91fb3c2f0b84]::intravisit::Visitor>::visit_expr
  21:     0x7fabcb4e9bd3 - <rustc_hir_typeck[abd9435c796a8ed5]::upvar::InferBorrowKindVisitor as rustc_hir[efbd91fb3c2f0b84]::intravisit::Visitor>::visit_expr
  22:     0x7fabcb4e9876 - <rustc_hir_typeck[abd9435c796a8ed5]::upvar::InferBorrowKindVisitor as rustc_hir[efbd91fb3c2f0b84]::intravisit::Visitor>::visit_block
  23:     0x7fabcbf972c1 - rustc_hir_typeck[abd9435c796a8ed5]::typeck_with_inspect::{closure#0}
  24:     0x7fabcbf955f8 - rustc_query_impl[bf9f47c0be6c5cea]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[bf9f47c0be6c5cea]::query_impl::typeck::dynamic_query::{closure#2}::{closure#0}, rustc_middle[323d677696c3953f]::query::erase::Erased<[u8; 8usize]>>
  25:     0x7fabcb38776a - rustc_query_system[c53c5369b4d54c12]::query::plumbing::try_execute_query::<rustc_query_impl[bf9f47c0be6c5cea]::DynamicConfig<rustc_data_structures[169de96c3a3bf2b5]::vec_cache::VecCache<rustc_span[ddbbc3270fa539b]::def_id::LocalDefId, rustc_middle[323d677696c3953f]::query::erase::Erased<[u8; 8usize]>, rustc_query_system[c53c5369b4d54c12]::dep_graph::graph::DepNodeIndex>, false, false, false>, rustc_query_impl[bf9f47c0be6c5cea]::plumbing::QueryCtxt, false>
  26:     0x7fabcb387049 - rustc_query_impl[bf9f47c0be6c5cea]::query_impl::typeck::get_query_non_incr::__rust_end_short_backtrace
  27:     0x7fabcbe5bb2d - <rustc_middle[323d677696c3953f]::ty::context::TyCtxt>::par_hir_body_owners::<rustc_hir_analysis[ae5f01f7b13d6b97]::check_crate::{closure#2}>::{closure#0}
  28:     0x7fabcbe5b522 - rustc_hir_analysis[ae5f01f7b13d6b97]::check_crate
  29:     0x7fabcb38121b - rustc_interface[64e9028641784d78]::passes::analysis
  30:     0x7fabcb380e65 - rustc_query_impl[bf9f47c0be6c5cea]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[bf9f47c0be6c5cea]::query_impl::analysis::dynamic_query::{closure#2}::{closure#0}, rustc_middle[323d677696c3953f]::query::erase::Erased<[u8; 0usize]>>
  31:     0x7fabcc36f751 - rustc_query_system[c53c5369b4d54c12]::query::plumbing::try_execute_query::<rustc_query_impl[bf9f47c0be6c5cea]::DynamicConfig<rustc_query_system[c53c5369b4d54c12]::query::caches::SingleCache<rustc_middle[323d677696c3953f]::query::erase::Erased<[u8; 0usize]>>, false, false, false>, rustc_query_impl[bf9f47c0be6c5cea]::plumbing::QueryCtxt, false>
  32:     0x7fabcc36f53c - rustc_query_impl[bf9f47c0be6c5cea]::query_impl::analysis::get_query_non_incr::__rust_end_short_backtrace
  33:     0x7fabcc5554d4 - <rustc_interface[64e9028641784d78]::passes::create_and_enter_global_ctxt<core[61603b96a07b8ff9]::option::Option<rustc_interface[64e9028641784d78]::queries::Linker>, rustc_driver_impl[5f67874deb35e28a]::run_compiler::{closure#0}::{closure#2}>::{closure#2} as core[61603b96a07b8ff9]::ops::function::FnOnce<(&rustc_session[80cc42b19f2be7ae]::session::Session, rustc_middle[323d677696c3953f]::ty::context::CurrentGcx, alloc[cd9c1527bed1fc96]::sync::Arc<rustc_data_structures[169de96c3a3bf2b5]::jobserver::Proxy>, &std[f475c8dea6bc1f1c]::sync::once_lock::OnceLock<rustc_middle[323d677696c3953f]::ty::context::GlobalCtxt>, &rustc_data_structures[169de96c3a3bf2b5]::sync::worker_local::WorkerLocal<rustc_middle[323d677696c3953f]::arena::Arena>, &rustc_data_structures[169de96c3a3bf2b5]::sync::worker_local::WorkerLocal<rustc_hir[efbd91fb3c2f0b84]::Arena>, rustc_driver_impl[5f67874deb35e28a]::run_compiler::{closure#0}::{closure#2})>>::call_once::{shim:vtable#0}
  34:     0x7fabcc38350f - rustc_interface[64e9028641784d78]::interface::run_compiler::<(), rustc_driver_impl[5f67874deb35e28a]::run_compiler::{closure#0}>::{closure#1}
  35:     0x7fabcc3e16be - std[f475c8dea6bc1f1c]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[64e9028641784d78]::util::run_in_thread_with_globals<rustc_interface[64e9028641784d78]::util::run_in_thread_pool_with_globals<rustc_interface[64e9028641784d78]::interface::run_compiler<(), rustc_driver_impl[5f67874deb35e28a]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
  36:     0x7fabcc3e1be0 - <std[f475c8dea6bc1f1c]::thread::lifecycle::spawn_unchecked<rustc_interface[64e9028641784d78]::util::run_in_thread_with_globals<rustc_interface[64e9028641784d78]::util::run_in_thread_pool_with_globals<rustc_interface[64e9028641784d78]::interface::run_compiler<(), rustc_driver_impl[5f67874deb35e28a]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core[61603b96a07b8ff9]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  37:     0x7fabcc3e2a6c - <std[f475c8dea6bc1f1c]::sys::thread::unix::Thread>::new::thread_start
  38:     0x7fabc5c94ac3 - start_thread
                               at ./nptl/pthread_create.c:442:8
  39:     0x7fabc5d268c0 - __GI___clone3
                               at ./misc/../sysdeps/unix/sysv/linux/x86_64/clone3.S:81:0
  40:                0x0 - <unknown>

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/laix/Study/Traitor/trait-fuzzer/test/rustc-ice-2026-01-24T08_46_47-3582798.txt` to your bug report

note: rustc 1.95.0-nightly (d222ddc4d 2026-01-23) running on x86_64-unknown-linux-gnu

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

query stack during panic:
#0 [typeck] type-checking `test_multi_traits_issues`
#1 [analysis] running analysis passes on crate `bug`
end of query stack
error: aborting due to 4 previous errors

Some errors have detailed explanations: E0061, E0200, E0433.
For more information about an error, try `rustc --explain E0061`.

[SpriteOvO]

Weird. 🤔

/tmp/temp> RUSTFLAGS="-Znext-solver=globally" cargo +nightly build
   Compiling temp v0.1.0 (/tmp/temp)
error[E0433]: failed to resolve: use of unresolved module or unlinked crate `thread`
 --> src/main.rs:8:5
  |
8 |     thread::spawn(move ||  {
  |     ^^^^^^ use of unresolved module or unlinked crate `thread`
  |
  = help: if you wanted to use a crate named `thread`, use `cargo add thread` to add it to your `Cargo.toml`
help: consider importing this module
  |
2 + use std::thread;
  |

error[E0200]: the trait `Send` requires an `unsafe impl` declaration
 --> src/main.rs:5:1
  |
5 | impl Send for CustomInt {}
  | ^^^^^^^^^^^^^^^^^^^^^^^
  |
  = note: the trait `Send` enforces invariants that the compiler can't check. Review the trait documentation and make sure this implementation upholds those invariants before adding the `unsafe` keyword
help: add `unsafe` to this trait implementation
  |
5 | unsafe impl Send for CustomInt {}
  | ++++++

error[E0061]: this struct takes 1 argument but 0 arguments were supplied
 --> src/main.rs:7:17
  |
7 |     let fptr1 = SyncPointer();
  |                 ^^^^^^^^^^^-- argument #1 of type `CustomInt` is missing
  |
note: tuple struct defined here
 --> src/main.rs:4:8
  |
4 | struct SyncPointer(<SendPointer as NewTrait1>::Assoc);
  |        ^^^^^^^^^^^
help: provide the argument
  |
7 |     let fptr1 = SyncPointer(/* CustomInt */);
  |                             +++++++++++++++

Some errors have detailed explanations: E0061, E0200, E0433.
For more information about an error, try `rustc --explain E0061`.
error: could not compile `temp` (bin "temp") due to 3 previous errors

/tmp/temp> rustc +nightly --version --verbose
rustc 1.95.0-nightly (d222ddc4d 2026-01-23)
binary: rustc
commit-hash: d222ddc4d90743dfc1e53b610be8fc9d95893d2c
commit-date: 2026-01-23
host: x86_64-unknown-linux-gnu
release: 1.95.0-nightly
LLVM version: 21.1.8

[trait-Cong]

Maybe try invoking rustc directly?

rustc +nightly -Z next-solver=globally bug.rs

[SpriteOvO]

rustc +nightly src/main.rs -Z next-solver=globally reproduces.

rustc +nightly src/main.rs -Z next-solver=globally --edition=2024 does not reproduce. Cargo appended --edition=2024 to override the default edition 2015.

Also ICE on edition=2018, works fine on edition=2021. If lint rust_2021_incompatible_closure_captures is removed, no ICE on all editions.