struct containing array of size given in Self and slice causes compiler panic

[dbartussek]

A struct containing an array and a reference to a slice causes the compiler to panic if the array size is defined in the impl block.
The issue also occurs for smaller array sizes.

• Size in impl (panics): https://play.rust-lang.org/?version=stable&mode=release&edition=2018&gist=68c21606e452c40f2330402a9f4768e6
• Moving SIZE out of the impl resolves this: https://play.rust-lang.org/?version=stable&mode=release&edition=2018&gist=5b65fe2fcbc33b4436cbbfcc168276c7
• The same happens in constructors:
  • https://play.rust-lang.org/?version=stable&mode=release&edition=2018&gist=bc4ac0526a12e0fc8f6585c5ddf91369
  • https://play.rust-lang.org/?version=stable&mode=release&edition=2018&gist=32bcf1323d6484eeeba7d840a5730766

pub struct Memory<'rom> {
    rom: &'rom [u8],
    ram: [u8; Self::SIZE],
}

impl<'rom> Memory<'rom> {
    pub const SIZE: usize = 0x8000;
}

Backtrace for Playground:

   Compiling playground v0.0.1 (/playground)
error: internal compiler error: src/librustc_mir/borrow_check/nll/universal_regions.rs:741: cannot convert `ReEarlyBound(0, 'rom)` to a region vid

thread 'rustc' panicked at 'Box<Any>', src/librustc_errors/lib.rs:650:9
stack backtrace:
   0: backtrace::backtrace::libunwind::trace
             at /cargo/registry/src/git.luolix.top-1ecc6299db9ec823/backtrace-0.3.29/src/backtrace/libunwind.rs:88
   1: backtrace::backtrace::trace_unsynchronized
             at /cargo/registry/src/git.luolix.top-1ecc6299db9ec823/backtrace-0.3.29/src/backtrace/mod.rs:66
   2: std::sys_common::backtrace::_print
             at src/libstd/sys_common/backtrace.rs:47
   3: std::sys_common::backtrace::print
             at src/libstd/sys_common/backtrace.rs:36
   4: std::panicking::default_hook::{{closure}}
             at src/libstd/panicking.rs:200
   5: std::panicking::default_hook
             at src/libstd/panicking.rs:214
   6: rustc::util::common::panic_hook
   7: std::panicking::rust_panic_with_hook
             at src/libstd/panicking.rs:481
   8: std::panicking::begin_panic
   9: rustc_errors::Handler::bug
  10: rustc::util::bug::opt_span_bug_fmt::{{closure}}
  11: rustc::ty::context::tls::with_opt::{{closure}}
  12: rustc::ty::context::tls::with_context_opt
  13: rustc::ty::context::tls::with_opt
  14: rustc::util::bug::opt_span_bug_fmt
  15: rustc::util::bug::bug_fmt
  16: rustc_mir::borrow_check::nll::universal_regions::UniversalRegionIndices::to_region_vid::{{closure}}
  17: rustc_mir::borrow_check::nll::type_check::constraint_conversion::ConstraintConversion::to_region_vid
  18: rustc_mir::borrow_check::nll::type_check::constraint_conversion::ConstraintConversion::convert_all
  19: rustc_mir::borrow_check::nll::type_check::TypeChecker::fully_perform_op
  20: rustc_mir::borrow_check::nll::type_check::type_check
  21: rustc_mir::borrow_check::nll::compute_regions
  22: rustc_mir::borrow_check::do_mir_borrowck
  23: rustc::ty::context::GlobalCtxt::enter_local
  24: rustc_mir::borrow_check::mir_borrowck
  25: rustc::ty::query::__query_compute::mir_borrowck
  26: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::mir_borrowck>::compute
  27: rustc::dep_graph::graph::DepGraph::with_task_impl
  28: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  29: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::ensure_query
  30: rustc_mir::transform::optimized_mir
  31: rustc::ty::query::__query_compute::optimized_mir
  32: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::optimized_mir>::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::interpret::eval_context::InterpretCx<M>::load_mir
  36: rustc_mir::const_eval::const_eval_raw_provider
  37: rustc::ty::query::__query_compute::const_eval_raw
  38: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::const_eval_raw>::compute
  39: rustc::dep_graph::graph::DepGraph::with_task_impl
  40: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  41: rustc_mir::const_eval::const_eval_provider
  42: rustc::ty::query::__query_compute::const_eval
  43: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::const_eval>::compute
  44: rustc::dep_graph::graph::DepGraph::with_task_impl
  45: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  46: <rustc::traits::project::AssocTypeNormalizer as rustc::ty::fold::TypeFolder>::fold_const
  47: rustc::ty::structural_impls::<impl rustc::ty::fold::TypeFoldable for &rustc::ty::TyS>::super_fold_with
  48: <rustc::traits::project::AssocTypeNormalizer as rustc::ty::fold::TypeFolder>::fold_ty
  49: rustc::traits::project::normalize
  50: rustc_typeck::check::FnCtxt::normalize_associated_types_in
  51: <core::iter::adapters::Map<I,F> as core::iter::traits::iterator::Iterator>::fold
  52: rustc::ty::context::GlobalCtxt::enter_local
  53: rustc_typeck::check::wfcheck::check_item_well_formed
  54: rustc::ty::query::__query_compute::check_item_well_formed
  55: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::check_item_well_formed>::compute
  56: rustc::dep_graph::graph::DepGraph::with_task_impl
  57: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  58: <rustc_typeck::check::wfcheck::CheckTypeWellFormedVisitor as rustc::hir::itemlikevisit::ParItemLikeVisitor>::visit_item
  59: __rust_maybe_catch_panic
             at src/libpanic_unwind/lib.rs:82
  60: rustc_data_structures::sync::par_for_each_in
  61: __rust_maybe_catch_panic
             at src/libpanic_unwind/lib.rs:82
  62: rustc::hir::Crate::par_visit_all_item_likes
  63: rustc::util::common::time
  64: rustc_typeck::check_crate
  65: rustc_interface::passes::analysis
  66: rustc::ty::query::__query_compute::analysis
  67: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::analysis>::compute
  68: rustc::dep_graph::graph::DepGraph::with_task_impl
  69: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  70: rustc::ty::context::tls::enter_global
  71: rustc_interface::passes::BoxedGlobalCtxt::access::{{closure}}
  72: rustc_interface::passes::create_global_ctxt::{{closure}}
  73: rustc_interface::interface::run_compiler_in_existing_thread_pool
  74: std::thread::local::LocalKey<T>::with
  75: scoped_tls::ScopedKey<T>::set
  76: syntax::with_globals
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
query stack during panic:
#0 [mir_borrowck] processing `Memory::ram::{{constant}}#0`
#1 [optimized_mir] processing `Memory::ram::{{constant}}#0`
 --> src/lib.rs:3:15
  |
3 |     ram: [u8; Self::SIZE],
  |               ^^^^^^^^^^
#2 [const_eval_raw] const-evaluating `Memory::ram::{{constant}}#0`
#3 [const_eval] const-evaluating + checking `Memory::ram::{{constant}}#0`
#4 [check_item_well_formed] processing `Memory`
#5 [analysis] running analysis passes on this crate
end of query stack
error: aborting due to previous error


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 1.37.0 (eae3437df 2019-08-13) running on x86_64-unknown-linux-gnu

note: compiler flags: -C opt-level=3 -C codegen-units=1 --crate-type lib

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

error: Could not compile `playground`.

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

Warnings

No main function was detected, so your code was compiled
but not run. If you’d like to execute your code, please
add a main function.

[dbartussek]

I found this issue #56445. I think mine may be a duplicate.

[jonas-schievink]

Yup, closing as a duplicate, but thanks for the report!