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[ICE]: did not expect successful goal when collecting ambiguity errors #151648

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[ICE]: did not expect successful goal when collecting ambiguity errors#151648
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C-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.WG-trait-system-refactorThe Rustc Trait System Refactor Initiative (-Znext-solver)

Description

@matthiaskrgr
matthiaskrgr
opened on Jan 25, 2026

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:

rust/compiler/rustc_trait_selection/src/solve/fulfill/derive_errors.rs

Lines 115 to 127 in 9415853

// inference guidance that makes other goals go from ambig -> pass, for example.
//
// FIXME: We should probably just look into overflows here.
false,
),
Ok(GoalEvaluation { certainty: Certainty::Yes, .. }) => {
span_bug!(
root_obligation.cause.span,
"did not expect successful goal when collecting ambiguity errors for `{:?}`",
infcx.resolve_vars_if_possible(root_obligation.predicate),
)
}
Err(_) => {

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

Activity

  1. matthiaskrgr
    added
    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.
    C-bugCategory: This is a bug.
    on Jan 25, 2026
  2. rustbot
    added
    needs-triageThis issue may need triage. Remove when done. See docs forge.rust-lang.org/release/issue-triaging
    WG-trait-system-refactorThe Rustc Trait System Refactor Initiative (-Znext-solver)
    on Jan 25, 2026

  3. matthiaskrgr commented on Jan 25, 2026

    @matthiaskrgr
    matthiaskrgr
    on Jan 25, 2026
    MemberAuthor
    trait Trait<'a, 'b> {}
trait OtherTrait<'b> {}
impl<'a, T: OtherTrait /*<'a>*/> Trait<'a, 'b> for T {}
fn impl_hr<'b, T: for<'a> Trait<'a, 'b>>() {}
fn not_hr<'a, T: OtherTrait /*<'a>*/ + OtherTrait<'static>>() {
    impl_hr::<T>;
}
fn main() {}

  4. adwinwhite commented on Aug 13, 2026

    @adwinwhite
    adwinwhite
    on Aug 13, 2026
    Contributor

    This no longer causes ICE with the next solver.

  5. adwinwhite
    removed
    needs-triageThis issue may need triage. Remove when done. See docs forge.rust-lang.org/release/issue-triaging
    on Aug 13, 2026

  6. lcnr commented on Oct 8, 2026

    @lcnr
    lcnr
    on Oct 8, 2026
    Contributor

    this issue has been certainly fixed with #162782 merged which also adds relevant tests

  7. lcnr
    closed this as completedon Oct 8, 2026
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    C-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.WG-trait-system-refactorThe Rustc Trait System Refactor Initiative (-Znext-solver)

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