const generic ICE on *stable*

[DutchGhost]

I tried this code on stable:

trait Trait<const S: &'static str> {}

struct Bug<T>
where
    T: Trait<{std::intrinsics::type_name::<T>()}>
{
    t: T
}

I expected to see this happen: For one, report an error that Im using const generics without a feature flag. For two, report an error Im uising an intrinsic without a feature flag.

Instead, this happened: The above code crashed the compiler.

Meta

rustc --version --verbose:

1.41.0

A quick check in godbolt gives that the ICE's started in 1.35 and onwards. This also includes the current nightly and beta.

Backtrace

 Compiling playground v0.0.1 (/playground)
error[E0658]: const generics are unstable
 --> src/lib.rs:1:19
  |
1 | trait Trait<const S: &'static str> {}
  |                   ^
  |
  = note: for more information, see https://github.com/rust-lang/rust/issues/44580

error[E0658]: use of unstable library feature 'core_intrinsics': intrinsics are unlikely to ever be stabilized, instead they should be used through stabilized interfaces in the rest of the standard library
 --> src/lib.rs:5:15
  |
5 |     T: Trait<{std::intrinsics::type_name::<T>()}>
  |               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: internal compiler error: src/librustc/ty/subst.rs:610: type parameter `T/#0` (T/0) out of range when substituting (root type=Some(extern "rust-intrinsic" fn() -> &'static str {std::intrinsics::type_name::<T>})) substs=[]

thread 'rustc' panicked at 'Box<Any>', src/librustc_errors/lib.rs:864:9
stack backtrace:
   0: backtrace::backtrace::libunwind::trace
             at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.40/src/backtrace/libunwind.rs:88
   1: backtrace::backtrace::trace_unsynchronized
             at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.40/src/backtrace/mod.rs:66
   2: std::sys_common::backtrace::_print_fmt
             at src/libstd/sys_common/backtrace.rs:84
   3: <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt
             at src/libstd/sys_common/backtrace.rs:61
   4: core::fmt::write
             at src/libcore/fmt/mod.rs:1025
   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:65
   7: std::sys_common::backtrace::print
             at src/libstd/sys_common/backtrace.rs:50
   8: std::panicking::default_hook::{{closure}}
             at src/libstd/panicking.rs:193
   9: std::panicking::default_hook
             at src/libstd/panicking.rs:210
  10: rustc_driver::report_ice
  11: std::panicking::rust_panic_with_hook
             at src/libstd/panicking.rs:475
  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_ty
  21: rustc::ty::fold::TypeFoldable::fold_with
  22: rustc::ty::structural_impls::<impl rustc::ty::fold::TypeFoldable for &rustc::ty::TyS>::super_fold_with
  23: <rustc::ty::subst::SubstFolder as rustc::ty::fold::TypeFolder>::fold_ty
  24: rustc::ty::structural_impls::<impl rustc::ty::fold::TypeFoldable for &rustc::ty::sty::Const>::super_fold_with
  25: <rustc::ty::subst::SubstFolder as rustc::ty::fold::TypeFolder>::fold_const
  26: rustc::traits::codegen::<impl rustc::ty::context::TyCtxt>::subst_and_normalize_erasing_regions
  27: rustc_mir::interpret::operand::<impl rustc_mir::interpret::eval_context::InterpCx<M>>::eval_operand
  28: rustc_mir::interpret::step::<impl rustc_mir::interpret::eval_context::InterpCx<M>>::step
  29: rustc_mir::const_eval::const_eval_raw_provider
  30: rustc::ty::query::__query_compute::const_eval_raw
  31: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::const_eval_raw>::compute
  32: rustc::dep_graph::graph::DepGraph::with_task_impl
  33: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  34: rustc_mir::const_eval::const_eval_provider
  35: rustc::ty::query::__query_compute::const_eval
  36: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::const_eval>::compute
  37: rustc::dep_graph::graph::DepGraph::with_task_impl
  38: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  39: rustc_mir::const_eval::const_eval_provider
  40: rustc::ty::query::__query_compute::const_eval
  41: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::const_eval>::compute
  42: rustc::dep_graph::graph::DepGraph::with_task_impl
  43: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  44: rustc::ty::sty::Const::eval::{{closure}}
  45: rustc::ty::sty::Const::eval
  46: rustc::ty::fold::TypeFoldable::fold_with
  47: rustc::ty::fold::TypeFoldable::fold_with
  48: rustc::ty::fold::TypeFoldable::fold_with
  49: rustc::traits::project::normalize
  50: rustc::traits::fully_normalize
  51: rustc::ty::context::tls::with_context::{{closure}}
  52: rustc::ty::context::GlobalCtxt::enter_local
  53: rustc::traits::do_normalize_predicates
  54: rustc::traits::normalize_param_env_or_error
  55: rustc::ty::param_env
  56: rustc::ty::query::__query_compute::param_env
  57: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::param_env>::compute
  58: rustc::dep_graph::graph::DepGraph::with_task_impl
  59: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  60: rustc_typeck::check::wfcheck::check_item_well_formed
  61: rustc::ty::query::__query_compute::check_item_well_formed
  62: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::check_item_well_formed>::compute
  63: rustc::dep_graph::graph::DepGraph::with_task_impl
  64: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  65: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::ensure_query
  66: __rust_maybe_catch_panic
             at src/libpanic_unwind/lib.rs:78
  67: rustc_data_structures::sync::par_for_each_in
  68: __rust_maybe_catch_panic
             at src/libpanic_unwind/lib.rs:78
  69: rustc::hir::Crate::par_visit_all_item_likes
  70: rustc::util::common::time
  71: rustc_typeck::check_crate
  72: rustc_interface::passes::analysis
  73: rustc::ty::query::__query_compute::analysis
  74: rustc::dep_graph::graph::DepGraph::with_task_impl
  75: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  76: rustc::ty::context::tls::enter_global
  77: rustc_interface::interface::run_compiler_in_existing_thread_pool
  78: std::thread::local::LocalKey<T>::with
  79: scoped_tls::ScopedKey<T>::set
  80: syntax::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 1.41.0 (5e1a79984 2020-01-27) 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 `Bug::{{constant}}#0`
#1 [const_eval] const-evaluating + checking `Bug::{{constant}}#0`
#2 [const_eval] const-evaluating + checking `Bug::{{constant}}#0`
#3 [param_env] processing `Bug`
#4 [check_item_well_formed] processing `Bug`
#5 [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: https://play.rust-lang.org/?version=nightly&mode=debug&edition=2018&gist=357ac33432915dc13f0339771b264fe7

cargo-bisect-rustc indicates a regression in nightly-2019-03-08 with tests that use a rustc shell script. I ran into a cargo bisect-rustc error and couldn't bisect at the commit level because there is a missing git commit sha hash for nightly-2019-03-07. It looks like commit 88f755f appeared around this time with this block that seems to be the site of the ICE error string.

[pnkfelix]

@jonas-schievink : I was under impression that the F-* flags were reserved for bugs that required (in actuality, not solely according to our current specification/desired behavior) the feature flag to occur? I.e. ones that hypothetically could be deprioritized on that basis?

Do I have an incorrect impression?

[jonas-schievink]

Hmm, to my knowledge we've usually applied them whenever the feature in question was involved. For things that only occur on nightly, we have the additional requires-nightly label.

[pnkfelix]

Oh, wait, it does print:

error[E0658]: const generics are unstable
 --> src/lib.rs:1:19
  |
1 | trait Trait<const S: &'static str> {}
  |                   ^
  |
  = note: for more information, see https://github.com/rust-lang/rust/issues/44580

in the first diagnostic it prints.

@DutchGhost we don't print anything about #!feature(flag) on the stable or beta channels. That suggestion is only emitted on nightly channel.

[pnkfelix]

Hmm, to my knowledge we've usually applied them whenever the feature in question was involved. For things that only occur on nightly, we have the additional requires-nightly label.

okay thanks; I indeed had the wrong impression.

[pnkfelix]

triage: P-medium, removing nomination label. Assigning to self. (Since this is leveraging a nightly-only feature, and we do emit the diagnostic saying so, this gets relatively lower priority.)