ICE: error from fully_perform, with HRTB on GAT

Code

Minimal example below, with rust playground link. This may be related to #130797, as both involve type inference when there is a HRTB over a GAT, though that bug specifically involves usage with trait objects, where this bug did not occur when using trait objects.

trait FunctionLikeTrait {}

impl<Func> FunctionLikeTrait for Func where Func: Fn() {}

trait ArgTrait {
    type Unwrapped<'a>;
}

impl<'t> ArgTrait for &'t () {
    type Unwrapped<'a> = &'a ();
}

struct FunctionWrapper<Func, Arg> {
    _phantom: std::marker::PhantomData<(Func, Arg)>,
}

impl<Func, Arg> FunctionLikeTrait for FunctionWrapper<Func, Arg>
where
    Func: Fn(Arg),
    for<'a> Arg: ArgTrait<Unwrapped<'a> = Arg>,
{
}

fn apply_func<Func, Arg>(_: Func)
where
    FunctionWrapper<Func, Arg>: FunctionLikeTrait,
{
}

fn main() {
    apply_func(|_: &()| {});
}

Error output

<output>
   Compiling bug_mwe v0.1.0 (/home/username/bug_mwe)
note: no errors encountered even though delayed bugs were created

note: those delayed bugs will now be shown as internal compiler errors

error: internal compiler error: error performing operation: fully_perform
  --> src/main.rs:31:5
   |
31 |     apply_func(|_: &()| {});
   |     ^^^^^^^^^^^^^^^^^^^^^^^
   |
note: delayed at /rustc/a9730c3b5f84a001c052c60c97ed0765e9ceac04/compiler/rustc_trait_selection/src/traits/query/type_op/custom.rs:87:25 - disabled backtrace
  --> src/main.rs:31:5
   |
31 |     apply_func(|_: &()| {});
   |     ^^^^^^^^^^^^^^^^^^^^^^^

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/username/bug_mwe/rustc-ice-2025-02-06T15_08_40-780362.txt` to your bug report

note: compiler flags: --crate-type bin -C embed-bitcode=no -C debuginfo=2 -C link-arg=-B/usr/local/libexec/mold

note: some of the compiler flags provided by cargo are hidden

query stack during panic:
end of query stack
error: could not compile `bug_mwe` (bin "bug_mwe")

Caused by:
  process didn't exit successfully: `/home/username/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/rustc --crate-name bug_mwe --edition=2021 src/main.rs --error-format=json --json=diagnostic-rendered-ansi,artifacts,future-incompat --crate-type bin --emit=dep-info,link -C embed-bitcode=no -C debuginfo=2 --check-cfg 'cfg(docsrs,test)' --check-cfg 'cfg(feature, values())' -C metadata=81c7c60b51af13e3 -C extra-filename=-bca91fa17f684345 --out-dir /home/username/bug_mwe/target/debug/deps -L dependency=/home/username/bug_mwe/target/debug/deps -C link-arg=-B/usr/local/libexec/mold` (exit status: 101)

Backtrace

<backtrace>
note: delayed at /rustc/a9730c3b5f84a001c052c60c97ed0765e9ceac04/compiler/rustc_trait_selection/src/traits/query/type_op/custom.rs:87:25
         0: <rustc_errors::DiagCtxtInner>::emit_diagnostic
         1: <rustc_errors::DiagCtxtHandle>::emit_diagnostic
         2: <rustc_span::ErrorGuaranteed as rustc_errors::diagnostic::EmissionGuarantee>::emit_producing_guarantee
         3: <rustc_errors::DiagCtxtHandle>::span_delayed_bug::<rustc_span::span_encoding::Span, alloc::string::String>
         4: <rustc_borrowck::type_check::TypeChecker>::fully_perform_op::<(), rustc_middle::ty::ParamEnvAnd<rustc_middle::traits::query::type_op::ProvePredicate>>
         5: <rustc_borrowck::type_check::TypeChecker>::normalize_and_prove_instantiated_predicates
         6: <rustc_borrowck::type_check::TypeVerifier as rustc_middle::mir::visit::Visitor>::visit_const_operand
         7: <rustc_borrowck::type_check::TypeVerifier as rustc_middle::mir::visit::Visitor>::visit_body
         8: rustc_borrowck::type_check::type_check
         9: rustc_borrowck::nll::compute_regions
        10: rustc_borrowck::do_mir_borrowck
        11: rustc_query_impl::plumbing::__rust_begin_short_backtrace::<rustc_query_impl::query_impl::mir_borrowck::dynamic_query::{closure#2}::{closure#0}, rustc_middle::query::erase::Erased<[u8; 8]>>
        12: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::DynamicConfig<rustc_data_structures::vec_cache::VecCache<rustc_span::def_id::LocalDefId, rustc_middle::query::erase::Erased<[u8; 8]>, rustc_query_system::dep_graph::graph::DepNodeIndex>, false, false, false>, rustc_query_impl::plumbing::QueryCtxt, false>
        13: rustc_query_impl::query_impl::mir_borrowck::get_query_non_incr::__rust_end_short_backtrace
        14: rustc_interface::passes::run_required_analyses
        15: rustc_interface::passes::analysis
        16: rustc_query_impl::plumbing::__rust_begin_short_backtrace::<rustc_query_impl::query_impl::analysis::dynamic_query::{closure#2}::{closure#0}, rustc_middle::query::erase::Erased<[u8; 0]>>
        17: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::DynamicConfig<rustc_query_system::query::caches::SingleCache<rustc_middle::query::erase::Erased<[u8; 0]>>, false, false, false>, rustc_query_impl::plumbing::QueryCtxt, false>
        18: rustc_query_impl::query_impl::analysis::get_query_non_incr::__rust_end_short_backtrace
        19: rustc_interface::passes::create_and_enter_global_ctxt::<core::option::Option<rustc_interface::queries::Linker>, rustc_driver_impl::run_compiler::{closure#0}::{closure#2}>::{closure#2}::{closure#0}
        20: rustc_interface::interface::run_compiler::<(), rustc_driver_impl::run_compiler::{closure#0}>::{closure#1}
        21: std::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface::util::run_in_thread_with_globals<rustc_interface::util::run_in_thread_pool_with_globals<rustc_interface::interface::run_compiler<(), rustc_driver_impl::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
        22: <<std::thread::Builder>::spawn_unchecked_<rustc_interface::util::run_in_thread_with_globals<rustc_interface::util::run_in_thread_pool_with_globals<rustc_interface::interface::run_compiler<(), rustc_driver_impl::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
        23: std::sys::pal::unix::thread::Thread::new::thread_start
        24: start_thread
                   at ./nptl/pthread_create.c:447:8
        25: clone3
                   at ./misc/../sysdeps/unix/sysv/linux/x86_64/clone3.S:78:0

Slightly simplified and reorganized:

// Needed so that rust can infer that the A in what() is &()
trait IsRef<T> {}
struct Dummy;
impl<'a> IsRef<&'a ()> for Dummy {}

trait WithLifetime {
    type Output<'a>;
}
impl<'t> WithLifetime for &'t () {
    type Output<'a> = &'a ();
}

// Needed to prevent the two Foo impls from overlapping
struct Wrap<A>(A);

trait Unimplemented {}

trait Foo {}
impl<T> Foo for T where T: Unimplemented {}
impl<A> Foo for Wrap<A>
where
    Dummy: IsRef<A>,
    for<'a> A: WithLifetime<Output<'a> = A>,
{
}

fn what<A>()
where
    Wrap<A>: Foo,
{
}

fn main() {
    what();
}

duplicate of #124440. Will be fixed by next-solver

Rollup merge of rust-lang#163806 - lcnr:crashes-migration-cont, r=lqd

Unrolled build for #163806 in rollup 163957

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ICE: error from fully_perform, with HRTB on GAT #136666

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ICE: error from fully_perform, with HRTB on GAT #136666

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theemathas commented on Feb 7, 2025

lcnr commented on Oct 5, 2026

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