Compiler Panic (min_const_generics?)

[npmccallum]

Code

I am unfortunately not able to make a reproducing example. This error only arises when writing a test for a method. Nothing is particularly strange about the method invocation. However, I am using min_const_generics.

Meta

rustc --version --verbose:

$ rustc --version --verbose
rustc 1.51.0-beta.4 (4d25f4607 2021-03-05)
binary: rustc
commit-hash: 4d25f4607015a56d18d7c6c649441608a9298845
commit-date: 2021-03-05
host: x86_64-unknown-linux-gnu
release: 1.51.0-beta.4
LLVM version: 11.0.1

Error output

thread 'rustc' panicked at 'index out of bounds: the len is 0 but the index is 0', /cargo/registry/src/github.com-1e
cc6299db9ec823/ena-0.14.0/src/snapshot_vec.rs:199:10
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

error: internal compiler error: unexpected panic

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-comp
iler&template=ice.md

note: rustc 1.51.0-beta.4 (4d25f4607 2021-03-05) 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::Try` fulfills its obligations
#1 [resolve_instance] resolving instance `<std::result::Result<[u8; 512], quoin_device::Error<quoin_device::Error<quoin_device::Error<_>>>> as std::ops::Try>::into_result`
end of query stack

Backtrace

stack backtrace:
   0: rust_begin_unwind
             at /rustc/4d25f4607015a56d18d7c6c649441608a9298845/library/std/src/panicking.rs:493:5
   1: core::panicking::panic_fmt
             at /rustc/4d25f4607015a56d18d7c6c649441608a9298845/library/core/src/panicking.rs:92:14
   2: core::panicking::panic_bounds_check
             at /rustc/4d25f4607015a56d18d7c6c649441608a9298845/library/core/src/panicking.rs:69:5
   3: <rustc_infer::infer::freshen::TypeFreshener as rustc_middle::ty::fold::TypeFolder>::fold_ty
   4: rustc_middle::ty::fold::TypeFoldable::fold_with
   5: rustc_middle::ty::structural_impls::<impl rustc_middle::ty::fold::TypeFoldable for &rustc_middle::ty::TyS>::su
per_fold_with
   6: <rustc_infer::infer::freshen::TypeFreshener as rustc_middle::ty::fold::TypeFolder>::fold_ty
   7: rustc_middle::ty::fold::TypeFoldable::fold_with
   8: rustc_middle::ty::structural_impls::<impl rustc_middle::ty::fold::TypeFoldable for &rustc_middle::ty::TyS>::su
per_fold_with
   9: <rustc_infer::infer::freshen::TypeFreshener as rustc_middle::ty::fold::TypeFolder>::fold_ty
  10: rustc_middle::ty::fold::TypeFoldable::fold_with
  11: rustc_middle::ty::structural_impls::<impl rustc_middle::ty::fold::TypeFoldable for &rustc_middle::ty::TyS>::super_fold_with
  12: <rustc_infer::infer::freshen::TypeFreshener as rustc_middle::ty::fold::TypeFolder>::fold_ty
  13: rustc_middle::ty::fold::TypeFoldable::fold_with
  14: rustc_middle::ty::structural_impls::<impl rustc_middle::ty::fold::TypeFoldable for &rustc_middle::ty::TyS>::super_fold_with
  15: <rustc_infer::infer::freshen::TypeFreshener as rustc_middle::ty::fold::TypeFolder>::fold_ty
  16: rustc_middle::ty::fold::TypeFoldable::fold_with
  17: rustc_trait_selection::traits::select::SelectionContext::select
  18: rustc_infer::infer::InferCtxtBuilder::enter
  19: rustc_trait_selection::traits::codegen::codegen_fulfill_obligation
  20: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::codegen_fulfill_obligation>::compute
  21: rustc_middle::dep_graph::<impl rustc_query_system::dep_graph::DepKind for rustc_middle::dep_graph::dep_node::DepKind>::with_deps
  22: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  23: rustc_data_structures::stack::ensure_sufficient_stack
  24: rustc_query_system::query::plumbing::force_query_with_job
  25: rustc_query_system::query::plumbing::get_query_impl
  26: rustc_ty_utils::instance::inner_resolve_instance
  27: rustc_ty_utils::instance::resolve_instance
  28: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::resolve_instance>::compute
  29: rustc_middle::dep_graph::<impl rustc_query_system::dep_graph::DepKind for rustc_middle::dep_graph::dep_node::DepKind>::with_deps
  30: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  31: rustc_data_structures::stack::ensure_sufficient_stack
  32: rustc_query_system::query::plumbing::force_query_with_job
  33: rustc_query_system::query::plumbing::get_query_impl
  34: rustc_middle::ty::instance::Instance::resolve_opt_const_arg
  35: rustc_middle::ty::instance::Instance::resolve
  36: <rustc_mir::monomorphize::collector::MirNeighborCollector as rustc_middle::mir::visit::Visitor>::visit_terminator
  37: rustc_mir::monomorphize::collector::collect_neighbours
  38: rustc_mir::monomorphize::collector::collect_items_rec
  39: rustc_mir::monomorphize::collector::collect_items_rec
  40: rustc_mir::monomorphize::collector::collect_items_rec
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  78: rustc_mir::monomorphize::collector::collect_items_rec
  79: rustc_mir::monomorphize::collector::collect_items_rec
  80: rustc_mir::monomorphize::collector::collect_items_rec
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  88: rustc_mir::monomorphize::collector::collect_items_rec
  89: rustc_mir::monomorphize::collector::collect_items_rec

[memoryruins]

http://blog.pnkfx.org/blog/2019/11/18/rust-bug-minimization-patterns/ contains many helpful tactics for minimizing code in bug reports.

[npmccallum]

I was able to figure out that this happens from infinite type recursion when using generics.

[memoryruins]

#83120 also hit a panic inside of ena-0.14.0/src/snapshot_vec.rs while using const generics, though it could be for a different reason.

[Enselic]

Triage: Without a way for others to reproduce the ICE, not much can be done at this point. Closing.