ICE with const generics with disabled feature flag

[Patryk27]

Hi,

Following code ICEs on stable (1.41.1), beta (1.42.0-beta.6) and nightly (2020-03-10):

fn foo<const A: usize, const B: usize>(bar: [usize; A + B]) {
    //
}

(playground)

The issue arises when:

• an expression in used in place of array size ([usize; A + B] in this case),
• and code generics are not enabled explicitly (notice missing feature attribute),

Backtrace

   Compiling playground v0.0.1 (/playground)
error[E0658]: const generics are unstable
 --> src/lib.rs:1:14
  |
1 | fn foo<const A: usize, const B: usize>(bar: [usize; A + B]) {
  |              ^
  |
  = note: see issue #44580 <https://github.com/rust-lang/rust/issues/44580> for more information
  = help: add `#![feature(const_generics)]` to the crate attributes to enable

error[E0658]: const generics are unstable
 --> src/lib.rs:1:30
  |
1 | fn foo<const A: usize, const B: usize>(bar: [usize; A + B]) {
  |                              ^
  |
  = note: see issue #44580 <https://github.com/rust-lang/rust/issues/44580> for more information
  = help: add `#![feature(const_generics)]` to the crate attributes to enable

error: internal compiler error: src/librustc/ty/subst.rs:605: const parameter `A/#0` (Const { ty: usize, val: Param(A/#0) }/0) out of range when substituting substs=[]

thread 'rustc' panicked at 'Box<Any>', src/librustc/lib.rs:1:1
stack backtrace:
   0: backtrace::backtrace::libunwind::trace
             at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.44/src/backtrace/libunwind.rs:86
   1: backtrace::backtrace::trace_unsynchronized
             at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.44/src/backtrace/mod.rs:66
   2: std::sys_common::backtrace::_print_fmt
             at src/libstd/sys_common/backtrace.rs:78
   3: <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt
             at src/libstd/sys_common/backtrace.rs:59
   4: core::fmt::write
             at src/libcore/fmt/mod.rs:1063
   5: std::io::Write::write_fmt
             at src/libstd/io/mod.rs:1426
   6: std::sys_common::backtrace::_print
             at src/libstd/sys_common/backtrace.rs:62
   7: std::sys_common::backtrace::print
             at src/libstd/sys_common/backtrace.rs:49
   8: std::panicking::default_hook::{{closure}}
             at src/libstd/panicking.rs:204
   9: std::panicking::default_hook
             at src/libstd/panicking.rs:224
  10: rustc_driver::report_ice
  11: std::panicking::rust_panic_with_hook
             at src/libstd/panicking.rs:474
  12: std::panicking::begin_panic
  13: rustc_errors::HandlerInner::span_bug
  14: rustc_errors::Handler::span_bug
  15: rustc::util::bug::opt_span_bug_fmt::{{closure}}
  16: rustc::ty::context::tls::with_opt::{{closure}}
  17: rustc::ty::context::tls::with_opt
  18: rustc::util::bug::opt_span_bug_fmt
  19: rustc::util::bug::span_bug_fmt
  20: <rustc::ty::subst::SubstFolder as rustc::ty::fold::TypeFolder>::fold_const
  21: rustc::ty::normalize_erasing_regions::<impl rustc::ty::context::TyCtxt>::subst_and_normalize_erasing_regions
  22: rustc_mir::interpret::operand::<impl rustc_mir::interpret::eval_context::InterpCx<M>>::eval_operand
  23: rustc_mir::interpret::step::<impl rustc_mir::interpret::eval_context::InterpCx<M>>::eval_rvalue_into_place
  24: rustc_mir::interpret::step::<impl rustc_mir::interpret::eval_context::InterpCx<M>>::run
  25: rustc_mir::const_eval::eval_queries::const_eval_raw_provider
  26: rustc::ty::query::__query_compute::const_eval_raw
  27: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::const_eval_raw>::compute
  28: rustc::dep_graph::graph::DepGraph::with_task_impl
  29: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  30: rustc_mir::const_eval::eval_queries::const_eval_validated_provider
  31: rustc::ty::query::__query_compute::const_eval_validated
  32: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::const_eval_validated>::compute
  33: rustc::dep_graph::graph::DepGraph::with_task_impl
  34: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  35: rustc_mir::const_eval::eval_queries::const_eval_validated_provider
  36: rustc::ty::query::__query_compute::const_eval_validated
  37: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::const_eval_validated>::compute
  38: rustc::dep_graph::graph::DepGraph::with_task_impl
  39: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  40: rustc::mir::interpret::queries::<impl rustc::ty::context::TyCtxt>::const_eval_resolve
  41: rustc::ty::sty::Const::eval::{{closure}}
  42: rustc::ty::sty::Const::eval
  43: rustc::ty::structural_impls::<impl rustc::ty::fold::TypeFoldable for &rustc::ty::TyS>::super_fold_with
  44: <rustc_infer::traits::project::AssocTypeNormalizer as rustc::ty::fold::TypeFolder>::fold_ty
  45: rustc::ty::structural_impls::fold_list
  46: rustc_infer::traits::project::normalize
  47: rustc_infer::infer::InferCtxt::partially_normalize_associated_types_in
  48: rustc::ty::context::GlobalCtxt::enter_local
  49: rustc_typeck::check::wfcheck::check_item_well_formed
  50: rustc::ty::query::__query_compute::check_item_well_formed
  51: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::check_item_well_formed>::compute
  52: rustc::dep_graph::graph::DepGraph::with_task_impl
  53: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  54: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::ensure_query
  55: __rust_maybe_catch_panic
             at src/libpanic_unwind/lib.rs:86
  56: <std::panic::AssertUnwindSafe<F> as core::ops::function::FnOnce<()>>::call_once
  57: __rust_maybe_catch_panic
             at src/libpanic_unwind/lib.rs:86
  58: rustc_hir::hir::Crate::par_visit_all_item_likes
  59: rustc_typeck::check_crate
  60: rustc_interface::passes::analysis
  61: rustc::ty::query::__query_compute::analysis
  62: rustc::dep_graph::graph::DepGraph::with_task_impl
  63: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  64: rustc::ty::context::tls::enter_global
  65: rustc_interface::interface::run_compiler_in_existing_thread_pool
  66: scoped_tls::ScopedKey<T>::set
  67: rustc_ast::attr::with_globals
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/blob/master/CONTRIBUTING.md#bug-reports

note: rustc 1.43.0-nightly (158127853 2020-03-10) running on x86_64-unknown-linux-gnu

note: compiler flags: -C codegen-units=1 -C debuginfo=2 --crate-type lib

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

query stack during panic:
#0 [const_eval_raw] const-evaluating `foo::{{constant}}#0`
#1 [const_eval_validated] const-evaluating + checking `foo::{{constant}}#0`
#2 [const_eval_validated] const-evaluating + checking `foo::{{constant}}#0`
#3 [check_item_well_formed] processing `foo`
#4 [analysis] running analysis passes on this crate
end of query stack
error: aborting due to 3 previous errors

For more information about this error, try `rustc --explain E0658`.
error: could not compile `playground`.

To learn more, run the command again with --verbose.

[chrissimpkins]

Source:

fn foo<const A: usize, const B: usize>(bar: [usize; A + B]) {
    //
}

Godbolt shows that the ICE occurs in 1.39.0 and not in 1.38.0.

cargo bisect-rustc indicates that the regression is in nightly-2019-08-21. We're outside of the 167 day CI date range window to bisect at the commit level with the tool.

Here is the commit dump:

commit[0] 2019-08-19UTC: Auto merge of #63579 - alexcrichton:new-lockfile, r=Mark-Simulacrum
commit[1] 2019-08-19UTC: Auto merge of #63715 - Centril:rollup-dga8qtp, r=Centril
commit[2] 2019-08-20UTC: Auto merge of #62727 - SimonSapin:plugins-tls-dylib, r=petrochenkov
commit[3] 2019-08-20UTC: Auto merge of #63497 - eddyb:miri-subst, r=oli-obk
commit[4] 2019-08-20UTC: Auto merge of #63709 - matklad:decomposed-tokens, r=petrochenkov
commit[5] 2019-08-20UTC: Auto merge of #63587 - flip1995:clippyup, r=flip1995
commit[6] 2019-08-20UTC: Auto merge of #63744 - Centril:rollup-g4l3ra9, r=Centril
commit[7] 2019-08-20UTC: Auto merge of #63752 - Centril:rollup-nlxwety, r=Centril

[lcnr]

@rustbot claim

[lcnr]

will be fixed by lazy normalization.
@rustbot release-assignment