ICE: 'index out of bounds: the len is 0 but the index is 0'

[DianaNites]

Code

Minimized code

pub fn encode_num<Writer: ExampleWriter>(n: u32, mut writer: Writer) -> Result<(), Writer::Error> {
    if n > 15 {
        encode_num(n / 16, &mut writer)?;
    }
    Ok(())
}

pub trait ExampleWriter {
    type Error;
}

impl<'a, T: ExampleWriter> ExampleWriter for &'a mut T {
    type Error = T::Error;
}

struct EmptyWriter;

impl ExampleWriter for EmptyWriter {
    type Error = ();
}

fn main() {
    encode_num(69, &mut EmptyWriter).unwrap();
}

Meta

rustc --version --verbose:

rustc 1.61.0-nightly (8d60bf427 2022-03-19)
binary: rustc
commit-hash: 8d60bf427a4b055f464122062e76b3ec34d4f8ba
commit-date: 2022-03-19
host: x86_64-unknown-linux-gnu
release: 1.61.0-nightly
LLVM version: 14.0.0

Error output

thread 'rustc' panicked at 'index out of bounds: the len is 0 but the index is 0', /cargo/registry/src/github.heygears.com-1ecc6299db9ec823/ena-0.14.0/src/snapshot_vec.rs:199:10

<backtrace>

query stack during panic:
#0 [codegen_fulfill_obligation] checking if `core::ops::try_trait::Try` fulfills its obligations
#1 [resolve_instance] resolving instance `<core::result::Result<(), _> as core::ops::try_trait::Try>::branch`
#2 [collect_and_partition_mono_items] collect_and_partition_mono_items
end of query stack

Backtrace

stack backtrace:
   0: rust_begin_unwind
             at /rustc/8d60bf427a4b055f464122062e76b3ec34d4f8ba/library/std/src/panicking.rs:584:5
   1: core::panicking::panic_fmt
             at /rustc/8d60bf427a4b055f464122062e76b3ec34d4f8ba/library/core/src/panicking.rs:143:14
   2: core::panicking::panic_bounds_check
             at /rustc/8d60bf427a4b055f464122062e76b3ec34d4f8ba/library/core/src/panicking.rs:84:5
   3: <rustc_middle::ty::Ty as rustc_middle::ty::fold::TypeFoldable>::try_fold_with::<rustc_infer::infer::freshen::TypeFreshener>
   4: <rustc_infer::infer::freshen::TypeFreshener as rustc_middle::ty::fold::TypeFolder>::fold_ty
   5: <rustc_trait_selection::traits::select::SelectionContext>::select
   6: <rustc_infer::infer::InferCtxtBuilder>::enter::<core::result::Result<&rustc_middle::traits::ImplSource<()>, rustc_errors::ErrorGuaranteed>, rustc_trait_selection::traits::codegen::codegen_fulfill_obligation::{closure#0}>
   7: rustc_trait_selection::traits::codegen::codegen_fulfill_obligation
   8: <rustc_query_system::dep_graph::graph::DepGraph<rustc_middle::dep_graph::dep_node::DepKind>>::with_task::<rustc_middle::ty::context::TyCtxt, (rustc_middle::ty::ParamEnv, rustc_middle::ty::sty::Binder<rustc_middle::ty::sty::TraitRef>), core::result::Result<&rustc_middle::traits::ImplSource<()>, rustc_errors::ErrorGuaranteed>>
   9: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::plumbing::QueryCtxt, rustc_query_system::query::caches::DefaultCache<(rustc_middle::ty::ParamEnv, rustc_middle::ty::sty::Binder<rustc_middle::ty::sty::TraitRef>), core::result::Result<&rustc_middle::traits::ImplSource<()>, rustc_errors::ErrorGuaranteed>>>
  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::dep_graph::graph::DepGraph<rustc_middle::dep_graph::dep_node::DepKind>>::with_task::<rustc_middle::ty::context::TyCtxt, rustc_middle::ty::ParamEnvAnd<(rustc_span::def_id::DefId, &rustc_middle::ty::list::List<rustc_middle::ty::subst::GenericArg>)>, core::result::Result<core::option::Option<rustc_middle::ty::instance::Instance>, rustc_errors::ErrorGuaranteed>>
  14: rustc_query_system::query::plumbing::get_query::<rustc_query_impl::queries::resolve_instance, rustc_query_impl::plumbing::QueryCtxt>
  15: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::resolve_instance
  16: <rustc_middle::ty::instance::Instance>::resolve
  17: rustc_monomorphize::collector::collect_neighbours
  18: rustc_monomorphize::collector::collect_items_rec
  19: rustc_monomorphize::collector::collect_items_rec
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note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

[WaffleLapkin]

A bit more minified example:

fn encode_num<W: ExampleWriter>(writer: W) -> W::Error {
    encode_num(&writer);
    loop {}
}

trait ExampleWriter {
    type Error;
}

impl<T: ExampleWriter> ExampleWriter for &T {
    type Error = T::Error;
}

impl ExampleWriter for () {
    type Error = ();
}

fn main() {
    encode_num(&());
}

[compiler-errors]

Reopened by #104610