Using const value from trait to construct array produces error

[Bert-Proesmans]

Playground code

use std::u32::MAX;

trait RPCService {
    type Method;
    const MAX_METHODS: usize = 4;
    
    // RPCService::MAX_METHODS -> ERROR
    // Self::MAX_METHODS -> ERROR
    // MAX_METHODS -> ERROR
    fn get_methods() -> [(&'static str, u32); Self::MAX_METHODS];
}

#[repr(u32)]
enum ConnectMethods {
    Bind = 0,
    Connect = 1,
}

struct ConnectService {}
impl ConnectService {
    pub const METHOD_BIND: ConnectMethods = ConnectMethods::Bind;
    pub const METHOD_CONNECT: ConnectMethods = ConnectMethods::Connect;
}

impl RPCService for ConnectService {
    type Method = ConnectMethods;
    
    fn get_methods() -> [(&'static str, u32); Self::MAX_METHODS] {
        [
        ("Bind", ConnectMethods::Bind as u32),
        ("Connect", ConnectMethods::Connect as u32),
        ("", MAX),
        ("", MAX),
        ]
    }
}


fn main() {
    let bind_id = ConnectService::METHOD_BIND;
}

(Playground)

Errors:

   Compiling playground v0.0.1 (file:///playground)
error[E0599]: no associated item named `MAX_METHODS` found for type `Self` in the current scope
  --> src/main.rs:10:47
   |
10 |     fn get_methods() -> [(&'static str, u32); Self::MAX_METHODS];
   |                                               ^^^^^^^^^^^^^^^^^ associated item not found in `Self`
   |
   = help: items from traits can only be used if the trait is implemented and in scope
   = note: the following trait defines an item `MAX_METHODS`, perhaps you need to implement it:
           candidate #1: `RPCService`

error: aborting due to previous error

For more information about this error, try `rustc --explain E0599`.
error: Could not compile `playground`.

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

Like it shows above, the compiler is confused by the MAX_METHODS item within the trait that declared it. I suppose the trait impl resolves fine, because no error is produced for that span.
Within my own crate i even get an ICE, but i'm unsure if it's the same error or caused by it. This ICE is what made me build the playground example.

My crate's ICE

error[E0599]: no associated item named `MAX_METHODS` found for type `Self` in the current scope
   --> src\service.rs:141:47
    |
141 |     fn get_methods() -> [(&'static str, u32); Self::MAX_METHODS];
    |                                               ^^^^^^^^^^^^^^^^^ associated item not found in `Self`
    |
    = help: items from traits can only be used if the trait is implemented and in scope
    = note: the following trait defines an item `MAX_METHODS`, perhaps you need to implement it:
            candidate #1: `service::RPCService`

error: internal compiler error: librustc\traits\codegen\mod.rs:63: Encountered ambiguity selecting `Binder(<[type error] as service::RPCService>)` during codegen, presuming due to overflow

thread 'main' panicked at 'Box<Any>', librustc_errors\lib.rs:554:9
stack backtrace:
   0: <std::sys::windows::args::Args as core::ops::drop::Drop>::drop
   1: <std::sync::condvar::Condvar as core::ops::drop::Drop>::drop
   2: std::panicking::take_hook
   3: std::panicking::take_hook
   4: <rustc::ty::SymbolName as core::fmt::Display>::fmt
   5: std::panicking::rust_panic_with_hook
   6: <rustc_errors::emitter::ColorConfig as core::fmt::Debug>::fmt
   7: rustc_errors::Handler::bug
   8: rustc::session::config::OutputTypes::values
   9: rustc::ty::context::tls::track_diagnostic
  10: rustc::ty::context::tls::track_diagnostic
  11: rustc::ty::context::tls::track_diagnostic
  12: rustc::session::bug_fmt
  13: rustc::session::bug_fmt
  14: rustc::ty::context::tls::track_diagnostic
  15: rustc::traits::codegen::codegen_fulfill_obligation
  16: rustc::ty::query::on_disk_cache::__ty_decoder_impl::<impl serialize::serialize::Decoder for rustc::ty::query::on_disk_cache::CacheDecoder<'a, 'tcx, 'x>>::read_str
  17: rustc::ty::context::tls::track_diagnostic
  18: rustc::ty::context::tls::track_diagnostic
  19: rustc::dep_graph::graph::DepGraph::assert_ignored
  20: rustc::ty::context::tls::track_diagnostic
  21: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::try_print_query_stack
  22: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::try_print_query_stack
  23: rustc::ty::instance::Instance::resolve
  24: <rustc_mir::interpret::eval_context::Frame<'mir, 'tcx> as core::cmp::PartialEq>::eq
  25: <rustc_mir::interpret::eval_context::Frame<'mir, 'tcx> as core::cmp::PartialEq>::eq
  26: <&'a rustc_mir::transform::const_prop::ConstPropagator<'a, 'b, 'tcx> as rustc_target::abi::LayoutOf>::layout_of
  27: <rustc_mir::transform::const_prop::ConstPropagator<'b, 'a, 'tcx> as rustc::mir::visit::Visitor<'tcx>>::visit_statement
  28: <rustc_mir::transform::const_prop::ConstProp as rustc_mir::transform::MirPass>::run_pass
  29: <rustc_mir::transform::MirSource as core::fmt::Debug>::fmt
  30: rustc_mir::transform::optimized_mir
  31: rustc::ty::query::on_disk_cache::__ty_decoder_impl::<impl serialize::serialize::Decoder for rustc::ty::query::on_disk_cache::CacheDecoder<'a, 'tcx, 'x>>::read_str
  32: rustc::ty::context::tls::track_diagnostic
  33: rustc::ty::context::tls::track_diagnostic
  34: rustc::dep_graph::graph::DepGraph::assert_ignored
  35: rustc::ty::context::tls::track_diagnostic
  36: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::try_print_query_stack
  37: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::try_print_query_stack
  38: rustc::ty::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::maybe_optimized_mir
  39: <rustc_mir::interpret::eval_context::Frame<'mir, 'tcx> as core::cmp::PartialEq>::eq
  40: rustc_mir::interpret::const_eval::value_to_const_value
  41: rustc_mir::interpret::const_eval::const_eval_provider
  42: rustc::ty::query::on_disk_cache::__ty_decoder_impl::<impl serialize::serialize::Decoder for rustc::ty::query::on_disk_cache::CacheDecoder<'a, 'tcx, 'x>>::read_str
  43: rustc::ty::context::tls::track_diagnostic
  44: rustc::ty::context::tls::track_diagnostic
  45: rustc::dep_graph::graph::DepGraph::assert_ignored
  46: rustc::ty::context::tls::track_diagnostic
  47: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::try_print_query_stack
  48: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::try_print_query_stack
  49: <rustc::traits::project::AssociatedTypeNormalizer<'a, 'b, 'gcx, 'tcx> as rustc::ty::fold::TypeFolder<'gcx, 'tcx>>::fold_const
  50: rustc::ty::structural_impls::<impl rustc::ty::context::Lift<'tcx> for rustc::ty::sty::FnSig<'a>>::lift_to_tcx
  51: <rustc::traits::project::AssociatedTypeNormalizer<'a, 'b, 'gcx, 'tcx> as rustc::ty::fold::TypeFolder<'gcx, 'tcx>>::fold_ty
  52: <rustc_typeck::outlives::implicit_infer::InferVisitor<'cx, 'tcx> as rustc::hir::itemlikevisit::ItemLikeVisitor<'tcx>>::visit_item
  53: <rustc_typeck::constrained_type_params::Parameter as core::fmt::Debug>::fmt
  54: <rustc_typeck::outlives::implicit_infer::InferVisitor<'cx, 'tcx> as rustc::hir::itemlikevisit::ItemLikeVisitor<'tcx>>::visit_item
  55: <rustc_typeck::check::method::probe::ProbeScope as core::fmt::Debug>::fmt
  56: <rustc_typeck::collect::has_late_bound_regions::LateBoundRegionsDetector<'a, 'tcx> as rustc::hir::intravisit::Visitor<'tcx>>::visit_lifetime
  57: <rustc_typeck::check::Diverges as core::fmt::Debug>::fmt
  58: <rustc_typeck::check::writeback::Resolver<'cx, 'gcx, 'tcx> as rustc::ty::fold::TypeFolder<'gcx, 'tcx>>::fold_region
  59: <rustc_typeck::check::writeback::Resolver<'cx, 'gcx, 'tcx> as rustc::ty::fold::TypeFolder<'gcx, 'tcx>>::fold_region
  60: rustc::ty::context::tls::track_diagnostic
  61: rustc::ty::context::tls::track_diagnostic
  62: rustc::dep_graph::graph::DepGraph::assert_ignored
  63: rustc::ty::context::tls::track_diagnostic
  64: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::try_print_query_stack
  65: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::try_print_query_stack
  66: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::try_print_query_stack
  67: <rustc_typeck::check::method::probe::ProbeScope as core::fmt::Debug>::fmt
  68: <rustc_typeck::check::autoderef::AutoderefKind as core::fmt::Debug>::fmt
  69: rustc_typeck::check_crate
  70: <humantime::duration::Error as std::error::Error>::cause
  71: <rustc_driver::derive_registrar::Finder as rustc::hir::itemlikevisit::ItemLikeVisitor<'v>>::visit_item
  72: <rustc_driver::Compilation as core::fmt::Debug>::fmt
  73: rustc_driver::driver::compile_input
  74: rustc_driver::run_compiler
  75: rustc_driver::target_features::add_configuration
  76: <humantime::duration::Error as std::error::Error>::cause
  77: _rust_maybe_catch_panic
  78: rustc_driver::profile::dump
  79: rustc_driver::main
  80: <unknown>
  81: std::panicking::update_panic_count
  82: _rust_maybe_catch_panic
  83: std::rt::lang_start_internal
  84: <unknown>
  85: <unknown>
  86: BaseThreadInitThunk
  87: RtlUserThreadStart
query stack during panic:
#0 [codegen_fulfill_obligation] checking if `service::RPCService` fulfills its obligations
#1 [optimized_mir] processing `<services::bnet::connection_service::ConnectionService as service::RPCService>::get_methods::{{constant}}`
#2 [const_eval] const-evaluating `<services::bnet::connection_service::ConnectionService as service::RPCService>::get_methods::{{constant}}`
#3 [check_impl_item_well_formed] processing `<services::bnet::connection_service::ConnectionService as service::RPCService>::get_methods`
end of query stack
error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0599`.

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 1.29.0-nightly (1ecf6929d 2018-07-16) running on x86_64-pc-windows-msvc

note: compiler flags: -C debuginfo=2 -C incremental --crate-type lib

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

error: Could not compile `incite`.

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

[oli-obk]

Duplicate of #42863

The ICE is separate though

[Bert-Proesmans]

@oli-obk Hi, thanks for the info.
Do you need additional information regarding the ICE? I'm unsure myself which code is related, but currently experimenting to understand more about the cause.

[oli-obk]

I'm not sure how extensive your code is. Maybe it can easily be reduced by removing unrelated parts until it's just one small file without crate dependencies? It's always helpful to have a small example that reproduces the ICE.

[Bert-Proesmans]

It seems i cannot trigger the ICE without the error from the original post.

[estebank]

That is fine, as long as you can create a small enough repro case that causes the ICE, we can investigate the root cause.

[Bert-Proesmans]

Sorry, i can't reproduce. I guess this can be closed?

[oli-obk]

If it happens to you again, feel free to just place it in a branch and point us to it