ICE OutputTypeParameterMismatch

[HellButcher]

Code

use std::{cell::{Ref, RefCell}, marker::PhantomData};

trait Query<'a> {
  type Fetch: for<'b> Fetch<'a, 'b>;
}
trait Fetch<'a,'b>{
  type Item: 'b;
  fn borrow(source: &'a A) -> Self;
  fn get(&'b self, index: usize) -> Self::Item;
}

struct A(RefCell<Vec<u32>>);
struct ARef<'a>(Ref<'a, Vec<u32>>);

impl<'a,'b> Fetch<'a,'b> for ARef<'a> {
  type Item = &'b u32;
  fn borrow(source: &'a A) -> Self {
    ARef(source.0.borrow())
  }
  fn get(&'b self, index: usize) -> Self::Item {
    &self.0[index]
  }
}

impl<'a> Query<'a> for &'_ u32 {
  type Fetch = ARef<'a>;
}

struct Qry<Q>(PhantomData<Q>);

impl<'a, Q> Qry<Q>
  where Q: Query<'a>
{
  fn new() -> Self { Self(PhantomData) }
  fn with_fn<F,R>(&self, source: &'a A, index: usize, f: F) -> R
    where for<'b> F: FnOnce(<Q::Fetch as Fetch<'a, 'b>>::Item) -> R
  {
    let b = Q::Fetch::borrow(source);
    let item = b.get(index);
    f(item)
  }
}

pub fn test() {
  let a = A(RefCell::new(vec![1,2,3]));
  let qry = Qry::<&u32>::new();
  assert_eq!(9, qry.with_fn(&a, 2, |v| *v * 3));
}

Meta

rustc --version --verbose:

rustc 1.54.0 (a178d0322 2021-07-26)
binary: rustc
commit-hash: a178d0322ce20e33eac124758e837cbd80a6f633
commit-date: 2021-07-26
host: x86_64-unknown-linux-gnu
release: 1.54.0
LLVM version: 12.0.1

Error output

error: internal compiler error: compiler/rustc_trait_selection/src/traits/codegen.rs:78:17: Encountered error `OutputTypeParameterMismatch(Binder(<[closure@crates/ice/src/lib.rs:47:36: 47:46] as std::ops::FnOnce<(<ARef as Fetch<'_, '_>>::Item,)>>, [Region(BrAnon(0))]), Binder(<[closure@crates/ice/src/lib.rs:47:36: 47:46] as std::ops::FnOnce<(&u32,)>>, []), Sorts(ExpectedFound { expected: &u32, found: <ARef as Fetch<'_, '_>>::Item }))` selecting `Binder(<[closure@crates/ice/src/lib.rs:47:36: 47:46] as std::ops::FnOnce<(&u32,)>>, [])` during codegen

thread 'rustc' panicked at 'Box<dyn Any>', compiler/rustc_errors/src/lib.rs:1007:9
stack 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 1.54.0 (a178d0322 2021-07-26) running on x86_64-unknown-linux-gnu

note: compiler flags: -C embed-bitcode=no -C debuginfo=2 -C incremental

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

query stack during panic:
#0 [codegen_fulfill_obligation] checking if `std::ops::FnOnce` fulfills its obligations
#1 [resolve_instance] resolving instance `<[closure@crates/ice/src/lib.rs:48:36: 48:46] as std::ops::FnOnce<(&u32,)>>::call_once`
#2 [collect_and_partition_mono_items] collect_and_partition_mono_items
end of query stack
error: aborting due to previous error

Backtrace

thread 'rustc' panicked at 'Box<dyn Any>', compiler/rustc_errors/src/lib.rs:1007:9
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_impl::<impl rustc_query_system::query::config::QueryAccessors<rustc_query_impl::plumbing::QueryCtxt> for rustc_query_impl::queries::codegen_fulfill_obligation>::compute
  10: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  11: rustc_data_structures::stack::ensure_sufficient_stack
  12: rustc_query_system::query::plumbing::get_query_impl
  13: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::codegen_fulfill_obligation
  14: rustc_ty_utils::instance::inner_resolve_instance
  15: rustc_ty_utils::instance::resolve_instance
  16: rustc_query_impl::<impl rustc_query_system::query::config::QueryAccessors<rustc_query_impl::plumbing::QueryCtxt> for rustc_query_impl::queries::resolve_instance>::compute
  17: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  18: rustc_data_structures::stack::ensure_sufficient_stack
  19: rustc_query_system::query::plumbing::get_query_impl
  20: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::resolve_instance
  21: rustc_middle::ty::instance::Instance::resolve_opt_const_arg
  22: rustc_middle::ty::instance::Instance::resolve
  23: <rustc_mir::monomorphize::collector::MirNeighborCollector as rustc_middle::mir::visit::Visitor>::visit_terminator
  24: rustc_mir::monomorphize::collector::collect_neighbours
  25: rustc_mir::monomorphize::collector::collect_items_rec
  26: rustc_mir::monomorphize::collector::collect_items_rec
  27: rustc_mir::monomorphize::collector::collect_items_rec
  28: rustc_mir::monomorphize::collector::collect_items_rec
  29: rustc_session::utils::<impl rustc_session::session::Session>::time
  30: rustc_mir::monomorphize::collector::collect_crate_mono_items
  31: rustc_mir::monomorphize::partitioning::collect_and_partition_mono_items
  32: rustc_query_impl::<impl rustc_query_system::query::config::QueryAccessors<rustc_query_impl::plumbing::QueryCtxt> for rustc_query_impl::queries::collect_and_partition_mono_items>::compute
  33: rustc_middle::dep_graph::<impl rustc_query_system::dep_graph::DepKind for rustc_middle::dep_graph::dep_node::DepKind>::with_deps
  34: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  35: rustc_data_structures::stack::ensure_sufficient_stack
  36: rustc_query_system::query::plumbing::force_query_with_job
  37: rustc_query_system::query::plumbing::get_query_impl
  38: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::collect_and_partition_mono_items
  39: <rustc_codegen_llvm::LlvmCodegenBackend as rustc_codegen_ssa::traits::backend::CodegenBackend>::codegen_crate
  40: rustc_interface::passes::QueryContext::enter
  41: rustc_interface::queries::Queries::ongoing_codegen
  42: rustc_interface::queries::<impl rustc_interface::interface::Compiler>::enter
  43: rustc_span::with_source_map
  44: rustc_interface::interface::create_compiler_and_run
  45: scoped_tls::ScopedKey<T>::set
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

[jackh726]

Closing as duplicate of #62529 (see #85499 for likely fix)