ICE in codegen_fulfill_obligation

[TethysSvensson]

Code

trait AddLifetime<'a> {
    type Output: Apply;
}

impl<'a> AddLifetime<'a> for () {
    type Output = &'a ();
}

trait Apply {
    fn apply<F>(f: F)
    where
        for<'a> F: Fn(&'a mut Self);
}

impl<'a> Apply for &'a () {
    fn apply<F>(f: F)
    where
        for<'b> F: Fn(&'b mut &'a ()),
    {
        f(&mut &())
    }
}

fn crash<T, F>(f: F)
where
    for<'a> T: AddLifetime<'a>,
    for<'outer, 'inner> F: Fn(&'outer mut <T as AddLifetime<'inner>>::Output),
{
    <T as AddLifetime<'static>>::Output::apply(f);
}

fn main() {
    crash::<(), _>(|_| {});
}

Meta

I get an ICE on 1.21.0, 1.53.0 and current nightly:

rustc --version --verbose:

rustc 1.21.0 (3b72af97e 2017-10-09)
binary: rustc
commit-hash: 3b72af97e42989b2fe104d8edbaee123cdf7c58f
commit-date: 2017-10-09
host: x86_64-unknown-linux-gnu
release: 1.21.0
LLVM version: 4.0

rustc 1.53.0 (53cb7b09b 2021-06-17)
binary: rustc
commit-hash: 53cb7b09b00cbea8754ffb78e7e3cb521cb8af4b
commit-date: 2021-06-17
host: x86_64-unknown-linux-gnu
release: 1.53.0
LLVM version: 12.0.1

rustc 1.55.0-nightly (b3d11f95c 2021-07-04)
binary: rustc
commit-hash: b3d11f95cc5dd687fdd185ce91e02ebe40e6f46b
commit-date: 2021-07-04
host: x86_64-unknown-linux-gnu
release: 1.55.0-nightly
LLVM version: 12.0.1

I do not get an ICE on 1.20 (though it does not compile either).

Error output

error: internal compiler error: compiler/rustc_trait_selection/src/traits/codegen.rs:78:17: Encountered error `OutputTypeParameterMismatch(Binder(<[closure@src/main.rs:33:20: 33:26] as std::ops::Fn<(&mut <() as AddLifetime<'_>>::Output,)>>, [Region(BrAnon(0)), Region(BrAnon(1))]), Binder(<[closure@src/main.rs:33:20: 33:26] as std::ops::Fn<(&mut &(),)>>, []), Sorts(ExpectedFound { expected: &(), found: <() as AddLifetime<'_>>::Output }))` selecting `Binder(<[closure@src/main.rs:33:20: 33:26] as std::ops::Fn<(&mut &(),)>>, [])` during codegen

Backtrace

error: internal compiler error: compiler/rustc_trait_selection/src/traits/codegen.rs:78:17: Encountered error `OutputTypeParameterMismatch(Binder(<[closure@src/main.rs:33:20: 33:26] as std::ops::Fn<(&mut <() as AddLifetime<'_>>::Output,)>>, [Region(BrAnon(0)), Region(BrAnon(1))]), Binder(<[closure@src/main.rs:33:20: 33:26] as std::ops::Fn<(&mut &(),)>>, []), Sorts(ExpectedFound { expected: &(), found: <() as AddLifetime<'_>>::Output }))` selecting `Binder(<[closure@src/main.rs:33:20: 33:26] as std::ops::Fn<(&mut &(),)>>, [])` during codegen

thread 'rustc' panicked at 'Box<dyn Any>', compiler/rustc_errors/src/lib.rs:1006:9
stack backtrace:
   0: std::panicking::begin_panic
   1: std::panic::panic_any
   2: rustc_errors::HandlerInner::bug
   3: rustc_errors::Handler::bug
   4: rustc_middle::ty::context::tls::with_opt
   5: rustc_middle::util::bug::opt_span_bug_fmt
   6: rustc_middle::util::bug::bug_fmt
   7: rustc_infer::infer::InferCtxtBuilder::enter
   8: rustc_trait_selection::traits::codegen::codegen_fulfill_obligation
   9: rustc_query_system::query::plumbing::get_query_impl
  10: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::codegen_fulfill_obligation
  11: rustc_ty_utils::instance::inner_resolve_instance
  12: rustc_ty_utils::instance::resolve_instance
  13: rustc_query_system::query::plumbing::get_query_impl
  14: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::resolve_instance
  15: rustc_middle::ty::instance::Instance::resolve_opt_const_arg
  16: rustc_middle::ty::instance::Instance::resolve
  17: <rustc_mir::monomorphize::collector::MirNeighborCollector as rustc_middle::mir::visit::Visitor>::visit_terminator
  18: rustc_mir::monomorphize::collector::collect_neighbours
  19: rustc_mir::monomorphize::collector::collect_items_rec
  20: rustc_mir::monomorphize::collector::collect_items_rec
  21: rustc_mir::monomorphize::collector::collect_items_rec
  22: rustc_mir::monomorphize::collector::collect_crate_mono_items
  23: rustc_mir::monomorphize::partitioning::collect_and_partition_mono_items
  24: rustc_query_system::query::plumbing::get_query_impl
  25: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::collect_and_partition_mono_items
  26: <rustc_codegen_llvm::LlvmCodegenBackend as rustc_codegen_ssa::traits::backend::CodegenBackend>::codegen_crate
  27: rustc_interface::passes::QueryContext::enter
  28: rustc_interface::queries::Queries::ongoing_codegen
  29: rustc_interface::queries::<impl rustc_interface::interface::Compiler>::enter
  30: rustc_span::with_source_map
  31: rustc_interface::interface::create_compiler_and_run
  32: scoped_tls::ScopedKey<T>::set
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

note: the compiler unexpectedly panicked. this is a bug.

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: rustc 1.55.0-nightly (b3d11f95c 2021-07-04) running on x86_64-unknown-linux-gnu

query stack during panic:
#0 [codegen_fulfill_obligation] checking if `std::ops::Fn` fulfills its obligations
#1 [resolve_instance] resolving instance `<[closure@src/main.rs:33:20: 33:26] as std::ops::Fn<(&mut &(),)>>::call`
#2 [collect_and_partition_mono_items] collect_and_partition_mono_items
end of query stack
error: aborting due to previous error

[jonas-schievink]

This is probably #62529

[jackh726]

Yes, closing as duplicate of that issue. There are plenty of MCVEs.