ICE: overflow evaluating the requirement / impl was matchable against binder but now it is not

[matthiaskrgr]

Code

trait a {
    type b;
}
impl<c> a for c
where
    c: d,
{
    type b = <(c,) as a>::b;
}
trait d {}
struct e;
impl d for <e as a>::b {}

pub fn main() {}

Meta

rustc --version --verbose:

rustc 1.89.0-nightly (16d2276fa 2025-05-16)
binary: rustc
commit-hash: 16d2276fa6fccb0cc239a542d4c3f0eb46f660ec
commit-date: 2025-05-16
host: x86_64-unknown-linux-gnu
release: 1.89.0-nightly
LLVM version: 20.1.4

Error output

warning: trait `a` should have an upper camel case name
 --> code.rs:1:7
  |
1 | trait a {
  |       ^ help: convert the identifier to upper camel case: `A`
  |
  = note: `#[warn(non_camel_case_types)]` on by default

warning: associated type `b` should have an upper camel case name
 --> code.rs:2:10
  |
2 |     type b;
  |          ^ help: convert the identifier to upper camel case: `B`

warning: type parameter `c` should have an upper camel case name
 --> code.rs:4:6
  |
4 | impl<c> a for c
  |      ^ help: convert the identifier to upper camel case (notice the capitalization): `C`

warning: trait `d` should have an upper camel case name
  --> code.rs:10:7
   |
10 | trait d {}
   |       ^ help: convert the identifier to upper camel case: `D`

warning: type `e` should have an upper camel case name
  --> code.rs:11:8
   |
11 | struct e;
   |        ^ help: convert the identifier to upper camel case: `E`

error[E0275]: overflow evaluating the requirement `(((((((...,),),),),),),): Sized`
 --> code.rs:8:14
  |
8 |     type b = <(c,) as a>::b;
  |              ^^^^^^^^^^^^^^
  |
  = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`code`)
note: required for `(((((((((((((((((((((((((((((((((((((((((((((((((((...,),),),),),),),),),),),),),),),),),),),),),),),),),),),),),),),),),),),),),),),),),),),),),),),),),),)` to implement `a`
 --> code.rs:4:9
  |
4 | impl<c> a for c
  |      -  ^     ^
  |      |
  |      unsatisfied trait bound introduced here
  = note: the full name for the type has been written to 'code.long-type-5344617421428250298.txt'
  = note: consider using `--verbose` to print the full type name to the console

Backtrace

error: internal compiler error: compiler/rustc_trait_selection/src/traits/select/mod.rs:2463:17: impl DefId(0:11 ~ code[7efa]::{impl#1}) was matchable against Binder { value: TraitPredicate(<((e,),) as d>, polarity:Positive), bound_vars: [] } but now is not


thread 'rustc' panicked at compiler/rustc_trait_selection/src/traits/select/mod.rs:2463:17:
Box<dyn Any>
stack backtrace:
   0:     0x7f6eca165b33 - <std::sys::backtrace::BacktraceLock::print::DisplayBacktrace as core::fmt::Display>::fmt::h8ce760ad42a959df
   1:     0x7f6eca805977 - core::fmt::write::h17deacb9d093717d
   2:     0x7f6ecb85bdd1 - std::io::Write::write_fmt::h8edc637e3ed34e58
   3:     0x7f6eca165992 - std::sys::backtrace::BacktraceLock::print::hf4e931b5b8f47af6
   4:     0x7f6eca16958a - std::panicking::default_hook::{{closure}}::h1aa602af6f79c655
   5:     0x7f6eca16910f - std::panicking::default_hook::hb6d5039bf2b4cecd
   6:     0x7f6ec9194e13 - std[23b1014898398f3a]::panicking::update_hook::<alloc[189bd33173793ff9]::boxed::Box<rustc_driver_impl[c8796dbdb0a790d0]::install_ice_hook::{closure#1}>>::{closure#0}
   7:     0x7f6eca169e03 - std::panicking::rust_panic_with_hook::h1a38b2651d61b684
   8:     0x7f6ec91d1281 - std[23b1014898398f3a]::panicking::begin_panic::<rustc_errors[84d6361680d21c4f]::ExplicitBug>::{closure#0}
   9:     0x7f6ec91c5156 - std[23b1014898398f3a]::sys::backtrace::__rust_end_short_backtrace::<std[23b1014898398f3a]::panicking::begin_panic<rustc_errors[84d6361680d21c4f]::ExplicitBug>::{closure#0}, !>
  10:     0x7f6ec91c513b - std[23b1014898398f3a]::panicking::begin_panic::<rustc_errors[84d6361680d21c4f]::ExplicitBug>
  11:     0x7f6ec91db9f1 - <rustc_errors[84d6361680d21c4f]::diagnostic::BugAbort as rustc_errors[84d6361680d21c4f]::diagnostic::EmissionGuarantee>::emit_producing_guarantee
  12:     0x7f6ec984a14a - rustc_middle[3cba1f9493d37f78]::util::bug::opt_span_bug_fmt::<rustc_span[10508ddd74bd9d4e]::span_encoding::Span>::{closure#0}
  13:     0x7f6ec982394a - rustc_middle[3cba1f9493d37f78]::ty::context::tls::with_opt::<rustc_middle[3cba1f9493d37f78]::util::bug::opt_span_bug_fmt<rustc_span[10508ddd74bd9d4e]::span_encoding::Span>::{closure#0}, !>::{closure#0}
  14:     0x7f6ec98237bb - rustc_middle[3cba1f9493d37f78]::ty::context::tls::with_context_opt::<rustc_middle[3cba1f9493d37f78]::ty::context::tls::with_opt<rustc_middle[3cba1f9493d37f78]::util::bug::opt_span_bug_fmt<rustc_span[10508ddd74bd9d4e]::span_encoding::Span>::{closure#0}, !>::{closure#0}, !>
  15:     0x7f6ec6a87ff0 - rustc_middle[3cba1f9493d37f78]::util::bug::bug_fmt
  16:     0x7f6eca99b058 - <rustc_trait_selection[c3f3da74ab5cc5d9]::traits::select::SelectionContext>::confirm_candidate
  17:     0x7f6ecb2cc36f - <rustc_trait_selection[c3f3da74ab5cc5d9]::traits::fulfill::FulfillProcessor as rustc_data_structures[766a8a49e9a623b6]::obligation_forest::ObligationProcessor>::process_obligation
  18:     0x7f6eca807fd5 - <rustc_data_structures[766a8a49e9a623b6]::obligation_forest::ObligationForest<rustc_trait_selection[c3f3da74ab5cc5d9]::traits::fulfill::PendingPredicateObligation>>::process_obligations::<rustc_trait_selection[c3f3da74ab5cc5d9]::traits::fulfill::FulfillProcessor>
  19:     0x7f6ecafd43ab - <rustc_trait_selection[c3f3da74ab5cc5d9]::traits::fulfill::FulfillmentContext<rustc_trait_selection[c3f3da74ab5cc5d9]::traits::FulfillmentError> as rustc_infer[7388de4d28332a4e]::traits::engine::TraitEngine<rustc_trait_selection[c3f3da74ab5cc5d9]::traits::FulfillmentError>>::select_all_or_error
  20:     0x7f6ecb05fea8 - rustc_hir_analysis[2ff1991ffb30aa1a]::check::wfcheck::check_well_formed
  21:     0x7f6ecb05e90b - rustc_query_impl[efffa611636c8e5b]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[efffa611636c8e5b]::query_impl::check_well_formed::dynamic_query::{closure#2}::{closure#0}, rustc_middle[3cba1f9493d37f78]::query::erase::Erased<[u8; 1usize]>>
  22:     0x7f6ecb05e1b1 - rustc_query_system[194713339954f907]::query::plumbing::try_execute_query::<rustc_query_impl[efffa611636c8e5b]::DynamicConfig<rustc_data_structures[766a8a49e9a623b6]::vec_cache::VecCache<rustc_span[10508ddd74bd9d4e]::def_id::LocalDefId, rustc_middle[3cba1f9493d37f78]::query::erase::Erased<[u8; 1usize]>, rustc_query_system[194713339954f907]::dep_graph::graph::DepNodeIndex>, false, false, false>, rustc_query_impl[efffa611636c8e5b]::plumbing::QueryCtxt, false>
  23:     0x7f6ecb05dca6 - rustc_query_impl[efffa611636c8e5b]::query_impl::check_well_formed::get_query_non_incr::__rust_end_short_backtrace
  24:     0x7f6ecb05b225 - rustc_hir_analysis[2ff1991ffb30aa1a]::check::wfcheck::check_mod_type_wf
  25:     0x7f6ecb05b01f - rustc_query_impl[efffa611636c8e5b]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[efffa611636c8e5b]::query_impl::check_mod_type_wf::dynamic_query::{closure#2}::{closure#0}, rustc_middle[3cba1f9493d37f78]::query::erase::Erased<[u8; 1usize]>>
  26:     0x7f6ecb7fc284 - rustc_query_system[194713339954f907]::query::plumbing::try_execute_query::<rustc_query_impl[efffa611636c8e5b]::DynamicConfig<rustc_query_system[194713339954f907]::query::caches::DefaultCache<rustc_span[10508ddd74bd9d4e]::def_id::LocalModDefId, rustc_middle[3cba1f9493d37f78]::query::erase::Erased<[u8; 1usize]>>, false, false, false>, rustc_query_impl[efffa611636c8e5b]::plumbing::QueryCtxt, false>
  27:     0x7f6ecb7fc011 - rustc_query_impl[efffa611636c8e5b]::query_impl::check_mod_type_wf::get_query_non_incr::__rust_end_short_backtrace
  28:     0x7f6ecaae36ae - rustc_hir_analysis[2ff1991ffb30aa1a]::check_crate
  29:     0x7f6ecac41245 - rustc_interface[88f95fb9e776d181]::passes::run_required_analyses
  30:     0x7f6ecb6f8ade - rustc_interface[88f95fb9e776d181]::passes::analysis
  31:     0x7f6ecb6f8ab5 - rustc_query_impl[efffa611636c8e5b]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[efffa611636c8e5b]::query_impl::analysis::dynamic_query::{closure#2}::{closure#0}, rustc_middle[3cba1f9493d37f78]::query::erase::Erased<[u8; 0usize]>>
  32:     0x7f6ecb6fabba - rustc_query_system[194713339954f907]::query::plumbing::try_execute_query::<rustc_query_impl[efffa611636c8e5b]::DynamicConfig<rustc_query_system[194713339954f907]::query::caches::SingleCache<rustc_middle[3cba1f9493d37f78]::query::erase::Erased<[u8; 0usize]>>, false, false, false>, rustc_query_impl[efffa611636c8e5b]::plumbing::QueryCtxt, false>
  33:     0x7f6ecb6fa88f - rustc_query_impl[efffa611636c8e5b]::query_impl::analysis::get_query_non_incr::__rust_end_short_backtrace
  34:     0x7f6ecb926607 - rustc_interface[88f95fb9e776d181]::passes::create_and_enter_global_ctxt::<core[64e60dbc053b37]::option::Option<rustc_interface[88f95fb9e776d181]::queries::Linker>, rustc_driver_impl[c8796dbdb0a790d0]::run_compiler::{closure#0}::{closure#2}>::{closure#2}::{closure#0}
  35:     0x7f6ecb879ba6 - rustc_interface[88f95fb9e776d181]::interface::run_compiler::<(), rustc_driver_impl[c8796dbdb0a790d0]::run_compiler::{closure#0}>::{closure#1}
  36:     0x7f6ecb8528be - std[23b1014898398f3a]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[88f95fb9e776d181]::util::run_in_thread_with_globals<rustc_interface[88f95fb9e776d181]::util::run_in_thread_pool_with_globals<rustc_interface[88f95fb9e776d181]::interface::run_compiler<(), rustc_driver_impl[c8796dbdb0a790d0]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
  37:     0x7f6ecb852d2b - <<std[23b1014898398f3a]::thread::Builder>::spawn_unchecked_<rustc_interface[88f95fb9e776d181]::util::run_in_thread_with_globals<rustc_interface[88f95fb9e776d181]::util::run_in_thread_pool_with_globals<rustc_interface[88f95fb9e776d181]::interface::run_compiler<(), rustc_driver_impl[c8796dbdb0a790d0]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core[64e60dbc053b37]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  38:     0x7f6ecb85412b - std::sys::pal::unix::thread::Thread::new::thread_start::ha2537cf437130d92
  39:     0x7f6ec56a370a - <unknown>
  40:     0x7f6ec5727aac - <unknown>
  41:                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/matthias/vcs/github/CRED/rustc-ice-2025-05-17T12_23_23-1960773.txt` to your bug report

query stack during panic:
#0 [check_well_formed] checking that `<impl at code.rs:12:1: 12:23>` is well-formed
#1 [check_mod_type_wf] checking that types are well-formed in top-level module
... and 1 other queries... use `env RUST_BACKTRACE=1` to see the full query stack
error: aborting due to 2 previous errors; 5 warnings emitted

For more information about this error, try `rustc --explain E0275`.

[moxian]

not smaller, but with more conventional item names and fewer warnings:

struct S;
trait SimpleTrait {}
trait TraitAssoc {
    type Assoc;
}

impl<T> TraitAssoc for T
where
    T: SimpleTrait,
{
    type Assoc = <(T,) as TraitAssoc>::Assoc;
}
impl SimpleTrait for <S as TraitAssoc>::Assoc {}

pub fn main() {}

Bisection

Regression in nightly-2024-02-23. PRs in range:

 - #117658 (rename ptr::invalid -> ptr::without_provenance) by RalfJung
 - #121415 (Rollup of 8 pull requests) by matthiaskrgr
   - #121206 (Top level error handling)
   - #121261 (coverage: Remove `pending_dups` from the span refiner)
   - #121336 (triagebot: add queue notifications)
   - #121373 (Consistently refer to a test's `revision` instead of `cfg`)
   - #121391 (never patterns: Fix liveness analysis in the presence of never patterns)
   - #121392 (Unify dylib loading between proc macros and codegen backends)
   - #121399 (Solaris linker does not support --strip-debug)
   - #121406 (Add a couple tests)
 - #118634 (Remove useless `'static` bounds on `Box` allocator) by Jules-Bertholet
 - #121223 (intrinsics::simd: add missing functions, avoid UB-triggering fast-math) by RalfJung
 - #117174 (Improve UEFI stdio) by Ayush1325
 - #121129 (Improve codegen diagnostic handling) by nnethercote
 - #121225 (require simd_insert, simd_extract indices to be constants) by RalfJung
 - #121309 (Make intrinsic fallback bodies cross-crate inlineable) by Nilstrieb
 - #121372 (Make `x test tests` work) by clubby789
 - #121370 (Migrate compiletest to use `ui_test`-style `//@` directives) by jieyouxu
 - #121469 (Rollup of 8 pull requests) by matthiaskrgr
   - #120598 (No need to `validate_alias_bound_self_from_param_env` in `assemble_alias_bound_candidates`)
   - #121386 (test that we do not support higher-ranked regions in opaque type inference)
   - #121393 (match lowering: Introduce a `TestCase` enum to replace most matching on `PatKind`)
   - #121401 (Fix typo in serialized.rs)
   - #121427 (Fix panic when compiling `Rocket`.)
   - #121439 (Fix typo in metadata.rs doc comment)
   - #121441 (`DefId`  to `LocalDefId`)
   - #121452 (Add new maintainers to nto-qnx.md)
 - #119989 (remove `sub_relations` from the `InferCtxt`) by lcnr

Sounds like #119989 ?.. (or maybe #120598 / #121386 ?..)

Interestingly (academically speaking), this used to ICE even before that, and got fixed once in nightly-2022-03-31. Seemingly accidentally, by #94081

PRs in nightly-2022-03-31:

 - #95448 (Rollup of 4 pull requests) by Dylan-DPC
   - #93840 (Stabilize Termination and ExitCode)
   - #95256 (Ensure io::Error's bitpacked repr doesn't accidentally impl UnwindSafe)
   - #95386 (Suggest wrapping patterns in enum variants)
   - #95437 (diagnostics: regression test for derive bounds)
 - #95455 (update miri) by RalfJung
 - #94081 (Lazy type-alias-impl-trait take two) by oli-obk
 - #95466 (Rollup of 5 pull requests) by Dylan-DPC
   - #95294 (Document Linux kernel handoff in std::io::copy and std::fs::copy)
   - #95443 (Clarify how `src/tools/x` searches for python)
   - #95452 (fix since field version for termination stabilization)
   - #95460 (Spellchecking compiler code)
   - #95461 (Spellchecking some comments)
 - #95241 (Strict Provenance MVP) by Gankra
 - #94963 (allow arbitrary inherent impls for builtin types in core) by lcnr
 - #95458 (Sync rustfmt subtree) by calebcartwright
 - #95425 (Yet more `parse_tt` improvements) by nnethercote

doesn't ICE with -Znext-solver

@rustbot label: +S-has-mcve +S-has-bisection +T-types +A-trait-system +A-associated-items -T-compiler