[ICE]: ` did not expect successful goal when collecting ambiguity errors`
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Nobody has claimed this yet.
C-bug
I-ICE
T-compiler
WG-trait-system-refactor
- Dominant language
- Rust
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Description
auto-reduced (treereduce-rust):
//@compile-flags: -Znext-solver=globally
trait Trait<'a, 'b> {}
trait OtherTrait<'b> {}
impl<'a, 'a, T: OtherTrait<'b>> Trait<'a, 'b> for T {}
fn impl_hr<'b, T: for<'a> Trait<'a, 'b>>() {}
fn not_hr<'a, T: for<'b> OtherTrait<'a, 'b> + OtherTrait<'static>>() {
impl_hr::<T>();
}
original:
//@ revisions: current next
//@ ignore-compare-mode-next-solver (explicit revisions)
//@[next] compile-flags: -Znext-solver
//@ check-pass
// cc #119820
trait Trait<'a, 'b> {}
trait OtherTrait<'b> {}
impl<'a, 'a, T: OtherTrait<'b>> Trait<'a, 'b> for T {}
fn impl_hr<'b, T: for<'a> Trait<'a, 'b>>() {}
fn not_hr<'a, T: for<'b> OtherTrait<'a, 'b> + OtherTrait<'static>>() {
impl_hr::<T>();
}
fn main() {}
Version information
rustc 1.95.0-nightly (941585327 2026-01-25)
binary: rustc
commit-hash: 9415853279dda1394c1f7d4114e1fe1e3ced76ec
commit-date: 2026-01-25
host: x86_64-unknown-linux-gnu
release: 1.95.0-nightly
LLVM version: 21.1.8
Possibly related line of code:
https://github.com/rust-lang/rust/blob/9415853279dda1394c1f7d4114e1fe1e3ced76ec/compiler/rustc_trait_selection/src/solve/fulfill/derive_errors.rs#L115-L127
Command:
/home/matthias/.rustup/toolchains/master/bin/rustc -Znext-solver=globally
Program output
error[E0403]: the name `'a` is already used for a generic parameter in this item's generic parameters
--> /tmp/icemaker_global_tempdir.T11Rhen9ppY6/rustc_testrunner_tmpdir_reporting.FkrqTiLp60vK/mvce.rs:4:10
|
4 | impl<'a, 'a, T: OtherTrait<'b>> Trait<'a, 'b> for T {}
| -- ^^ already used
| |
| first use of `'a`
error[E0261]: use of undeclared lifetime name `'b`
--> /tmp/icemaker_global_tempdir.T11Rhen9ppY6/rustc_testrunner_tmpdir_reporting.FkrqTiLp60vK/mvce.rs:4:43
|
4 | impl<'a, 'a, T: OtherTrait<'b>> Trait<'a, 'b> for T {}
| ^^ undeclared lifetime
|
help: consider introducing lifetime `'b` here
|
4 | impl<'b, 'a, 'a, T: OtherTrait<'b>> Trait<'a, 'b> for T {}
| +++
error[E0261]: use of undeclared lifetime name `'b`
--> /tmp/icemaker_global_tempdir.T11Rhen9ppY6/rustc_testrunner_tmpdir_reporting.FkrqTiLp60vK/mvce.rs:4:28
|
4 | impl<'a, 'a, T: OtherTrait<'b>> Trait<'a, 'b> for T {}
| ^^ undeclared lifetime
|
= note: for more information on higher-ranked polymorphism, visit https://doc.rust-lang.org/nomicon/hrtb.html
help: consider making the bound lifetime-generic with a new `'b` lifetime
|
4 | impl<'a, 'a, T: for<'b> OtherTrait<'b>> Trait<'a, 'b> for T {}
| +++++++
help: consider introducing lifetime `'b` here
|
4 | impl<'b, 'a, 'a, T: OtherTrait<'b>> Trait<'a, 'b> for T {}
| +++
error[E0601]: `main` function not found in crate `mvce`
--> /tmp/icemaker_global_tempdir.T11Rhen9ppY6/rustc_testrunner_tmpdir_reporting.FkrqTiLp60vK/mvce.rs:10:2
|
10 | }
| ^ consider adding a `main` function to `/tmp/icemaker_global_tempdir.T11Rhen9ppY6/rustc_testrunner_tmpdir_reporting.FkrqTiLp60vK/mvce.rs`
error[E0107]: trait takes 1 lifetime argument but 2 lifetime arguments were supplied
--> /tmp/icemaker_global_tempdir.T11Rhen9ppY6/rustc_testrunner_tmpdir_reporting.FkrqTiLp60vK/mvce.rs:8:26
|
8 | fn not_hr<'a, T: for<'b> OtherTrait<'a, 'b> + OtherTrait<'static>>() {
| ^^^^^^^^^^ ---- help: remove the lifetime argument
| |
| expected 1 lifetime argument
|
note: trait defined here, with 1 lifetime parameter: `'b`
--> /tmp/icemaker_global_tempdir.T11Rhen9ppY6/rustc_testrunner_tmpdir_reporting.FkrqTiLp60vK/mvce.rs:3:7
|
3 | trait OtherTrait<'b> {}
| ^^^^^^^^^^ --
error: internal compiler error: /rustc-dev/9415853279dda1394c1f7d4114e1fe1e3ced76ec/compiler/rustc_trait_selection/src/solve/fulfill/derive_errors.rs:121:17: did not expect successful goal when collecting ambiguity errors for `Binder { value: TraitPredicate(<T as Trait<'a, '_>>, polarity:Positive), bound_vars: [Region(BrNamed(DefId(0:15 ~ mvce[e936]::impl_hr::'a)))] }`
--> /tmp/icemaker_global_tempdir.T11Rhen9ppY6/rustc_testrunner_tmpdir_reporting.FkrqTiLp60vK/mvce.rs:9:5
|
9 | impl_hr::<T>();
| ^^^^^^^^^^^^^^
thread 'rustc' (1267291) panicked at /rustc-dev/9415853279dda1394c1f7d4114e1fe1e3ced76ec/compiler/rustc_trait_selection/src/solve/fulfill/derive_errors.rs:121:17:
Box<dyn Any>
stack backtrace:
0: 0x7fa633234853 - <<std[d1378798ed0df37d]::sys::backtrace::BacktraceLock>::print::DisplayBacktrace as core[61c54f01bfa55c5f]::fmt::Display>::fmt
1: 0x7fa63380e688 - core[61c54f01bfa55c5f]::fmt::write
2: 0x7fa63324afe6 - <std[d1378798ed0df37d]::sys::stdio::unix::Stderr as std[d1378798ed0df37d]::io::Write>::write_fmt
3: 0x7fa63320a858 - std[d1378798ed0df37d]::panicking::default_hook::{closure#0}
4: 0x7fa633227fb3 - std[d1378798ed0df37d]::panicking::default_hook
5: 0x7fa63221535d - std[d1378798ed0df37d]::panicking::update_hook::<alloc[3f0665886d0cb995]::boxed::Box<rustc_driver_impl[e7cd29ff173f18b7]::install_ice_hook::{closure#1}>>::{closure#0}
6: 0x7fa633228292 - std[d1378798ed0df37d]::panicking::panic_with_hook
7: 0x7fa632249861 - std[d1378798ed0df37d]::panicking::begin_panic::<rustc_errors[4412d669ad9ac0d9]::ExplicitBug>::{closure#0}
8: 0x7fa632242576 - std[d1378798ed0df37d]::sys::backtrace::__rust_end_short_backtrace::<std[d1378798ed0df37d]::panicking::begin_panic<rustc_errors[4412d669ad9ac0d9]::ExplicitBug>::{closure#0}, !>
9: 0x7fa6322422ea - std[d1378798ed0df37d]::panicking::begin_panic::<rustc_errors[4412d669ad9ac0d9]::ExplicitBug>
10: 0x7fa6322549d1 - <rustc_errors[4412d669ad9ac0d9]::diagnostic::BugAbort as rustc_errors[4412d669ad9ac0d9]::diagnostic::EmissionGuarantee>::emit_producing_guarantee
11: 0x7fa6327d97cc - <rustc_errors[4412d669ad9ac0d9]::DiagCtxtHandle>::span_bug::<rustc_span[221d93c9354447ee]::span_encoding::Span, alloc[3f0665886d0cb995]::string::String>
12: 0x7fa632802076 - rustc_middle[87068083d1557a2c]::util::bug::opt_span_bug_fmt::<rustc_span[221d93c9354447ee]::span_encoding::Span>::{closure#0}
13: 0x7fa632802222 - rustc_middle[87068083d1557a2c]::ty::context::tls::with_opt::<rustc_middle[87068083d1557a2c]::util::bug::opt_span_bug_fmt<rustc_span[221d93c9354447ee]::span_encoding::Span>::{closure#0}, !>::{closure#0}
14: 0x7fa6327f384b - rustc_middle[87068083d1557a2c]::ty::context::tls::with_context_opt::<rustc_middle[87068083d1557a2c]::ty::context::tls::with_opt<rustc_middle[87068083d1557a2c]::util::bug::opt_span_bug_fmt<rustc_span[221d93c9354447ee]::span_encoding::Span>::{closure#0}, !>::{closure#0}, !>
15: 0x7fa630116a58 - rustc_middle[87068083d1557a2c]::util::bug::span_bug_fmt::<rustc_span[221d93c9354447ee]::span_encoding::Span>
16: 0x7fa634959c25 - <rustc_trait_selection[9c3e7a31c96833d9]::traits::FulfillmentError as rustc_infer[5fb91953f074b4d]::traits::engine::FromSolverError<rustc_trait_selection[9c3e7a31c96833d9]::solve::fulfill::NextSolverError>>::from_solver_error
17: 0x7fa6343972f3 - <rustc_trait_selection[9c3e7a31c96833d9]::solve::fulfill::FulfillmentCtxt<rustc_trait_selection[9c3e7a31c96833d9]::traits::FulfillmentError> as rustc_infer[5fb91953f074b4d]::traits::engine::TraitEngine<rustc_trait_selection[9c3e7a31c96833d9]::traits::FulfillmentError>>::collect_remaining_errors
18: 0x7fa6345d19e7 - rustc_hir_typeck[f50ab56e4a53d4fa]::typeck_with_inspect::{closure#0}
19: 0x7fa6345cbcba - rustc_query_impl[6985c40abc7256ba]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[6985c40abc7256ba]::query_impl::typeck::dynamic_query::{closure#2}::{closure#0}, rustc_middle[87068083d1557a2c]::query::erase::Erased<[u8; 8usize]>>
20: 0x7fa63397bbaa - rustc_query_system[dcb5fa8d85d36a30]::query::plumbing::try_execute_query::<rustc_query_impl[6985c40abc7256ba]::DynamicConfig<rustc_data_structures[b55cda6142c8c008]::vec_cache::VecCache<rustc_span[221d93c9354447ee]::def_id::LocalDefId, rustc_middle[87068083d1557a2c]::query::erase::Erased<[u8; 8usize]>, rustc_query_system[dcb5fa8d85d36a30]::dep_graph::graph::DepNodeIndex>, false, false, false>, rustc_query_impl[6985c40abc7256ba]::plumbing::QueryCtxt, false>
21: 0x7fa63397b489 - rustc_query_impl[6985c40abc7256ba]::query_impl::typeck::get_query_non_incr::__rust_end_short_backtrace
22: 0x7fa633e009ed - <rustc_middle[87068083d1557a2c]::ty::context::TyCtxt>::par_hir_body_owners::<rustc_hir_analysis[338edc8e857fcf79]::check_crate::{closure#2}>::{closure#0}
23: 0x7fa633e003e2 - rustc_hir_analysis[338edc8e857fcf79]::check_crate
24: 0x7fa63397565b - rustc_interface[52cbc3f18da608ee]::passes::analysis
25: 0x7fa6339752a5 - rustc_query_impl[6985c40abc7256ba]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[6985c40abc7256ba]::query_impl::analysis::dynamic_query::{closure#2}::{closure#0}, rustc_middle[87068083d1557a2c]::query::erase::Erased<[u8; 0usize]>>
26: 0x7fa63496dd51 - rustc_query_system[dcb5fa8d85d36a30]::query::plumbing::try_execute_query::<rustc_query_impl[6985c40abc7256ba]::DynamicConfig<rustc_query_system[dcb5fa8d85d36a30]::query::caches::SingleCache<rustc_middle[87068083d1557a2c]::query::erase::Erased<[u8; 0usize]>>, false, false, false>, rustc_query_impl[6985c40abc7256ba]::plumbing::QueryCtxt, false>
27: 0x7fa63496db3c - rustc_query_impl[6985c40abc7256ba]::query_impl::analysis::get_query_non_incr::__rust_end_short_backtrace
28: 0x7fa634b2a514 - <rustc_interface[52cbc3f18da608ee]::passes::create_and_enter_global_ctxt<core[61c54f01bfa55c5f]::option::Option<rustc_interface[52cbc3f18da608ee]::queries::Linker>, rustc_driver_impl[e7cd29ff173f18b7]::run_compiler::{closure#0}::{closure#2}>::{closure#2} as core[61c54f01bfa55c5f]::ops::function::FnOnce<(&rustc_session[5f2250ac9f179614]::session::Session, rustc_middle[87068083d1557a2c]::ty::context::CurrentGcx, alloc[3f0665886d0cb995]::sync::Arc<rustc_data_structures[b55cda6142c8c008]::jobserver::Proxy>, &std[d1378798ed0df37d]::sync::once_lock::OnceLock<rustc_middle[87068083d1557a2c]::ty::context::GlobalCtxt>, &rustc_data_structures[b55cda6142c8c008]::sync::worker_local::WorkerLocal<rustc_middle[87068083d1557a2c]::arena::Arena>, &rustc_data_structures[b55cda6142c8c008]::sync::worker_local::WorkerLocal<rustc_hir[fb98bda4945cef24]::Arena>, rustc_driver_impl[e7cd29ff173f18b7]::run_compiler::{closure#0}::{closure#2})>>::call_once::{shim:vtable#0}
29: 0x7fa634980e4f - rustc_interface[52cbc3f18da608ee]::interface::run_compiler::<(), rustc_driver_impl[e7cd29ff173f18b7]::run_compiler::{closure#0}>::{closure#1}
30: 0x7fa6349bc9be - std[d1378798ed0df37d]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[52cbc3f18da608ee]::util::run_in_thread_with_globals<rustc_interface[52cbc3f18da608ee]::util::run_in_thread_pool_with_globals<rustc_interface[52cbc3f18da608ee]::interface::run_compiler<(), rustc_driver_impl[e7cd29ff173f18b7]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
31: 0x7fa6349bcee0 - <std[d1378798ed0df37d]::thread::lifecycle::spawn_unchecked<rustc_interface[52cbc3f18da608ee]::util::run_in_thread_with_globals<rustc_interface[52cbc3f18da608ee]::util::run_in_thread_pool_with_globals<rustc_interface[52cbc3f18da608ee]::interface::run_compiler<(), rustc_driver_impl[e7cd29ff173f18b7]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core[61c54f01bfa55c5f]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
32: 0x7fa6349bdd6c - <std[d1378798ed0df37d]::sys::thread::unix::Thread>::new::thread_start
33: 0x7fa62e29698b - <unknown>
34: 0x7fa62e31a9cc - <unknown>
35: 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: rustc 1.95.0-nightly (941585327 2026-01-25) running on x86_64-unknown-linux-gnu
note: compiler flags: -Z next-solver=globally -Z dump-mir-dir=dir
query stack during panic:
#0 [typeck] type-checking `not_hr`
#1 [analysis] running analysis passes on crate `mvce`
end of query stack
error: aborting due to 6 previous errors
Some errors have detailed explanations: E0107, E0261, E0403, E0601.
For more information about an error, try `rustc --explain E0107`.
@rustbot label +WG-trait-system-refactor
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Reproduce the reduced Rust program with -Znext-solver=globally and confirm the internal compiler error. Then inspect compiler/rustc_trait_selection/src/solve/fulfill/derive_errors.rs, especially lines 115-127, and trace the ambiguity-error collection entry point. Done means the example no longer triggers an ICE and reports the appropriate result.
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
- Quiet
- Clarity
- Mostly clear
- Newbie friendliness
- 48/100