ICE: cannot convert `ReEarlyBound(0, 'a)` to a region vid

[95th]

I got an internal compiler error at commit 95th/btrs@f2eb533 . I dont know how to minimize it.

Relevant code is:

impl<'a> Handshake<'a> {
    const LEN: usize = 68;

    pub fn new(info_hash: &'a InfoHash, peer_id: &'a str) -> Self {
        Self {
            peer_id,
            info_hash,
            extensions: Default::default(),
        }
    }

    pub async fn send(&self, peer: &Peer) -> crate::Result<()> {
        let mut tcp = TcpStream::connect(peer.addr()).await?;
        self.write_bytes(&mut tcp).await?;

        let mut v = [0; Self::LEN];
        tcp.read_exact(&mut v).await?;

        println!("{:?}", v);
        Ok(())
    }
  ...

If I remove the const field and directly put the array size like below, the ICE goes away and I get the expected compilation error that [u8; 68] is not Debug.

       let mut v = [0; 68];
       ...

Backtrace:

~/btrs$ RUST_BACKTRACE=1 cargo check
    Checking btrs v0.1.0 (/home/95th/btrs)
error: internal compiler error: src/librustc_mir/borrow_check/nll/universal_regions.rs:764: cannot convert `ReEarlyBound(0, 'a)` to a region vid

thread 'rustc' panicked at 'Box<Any>', src/librustc_errors/lib.rs:931:9
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:77
   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:1028
   5: std::io::Write::write_fmt
             at src/libstd/io/mod.rs:1412
   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:188
   9: std::panicking::default_hook
             at src/libstd/panicking.rs:205
  10: rustc_driver::report_ice
  11: std::panicking::rust_panic_with_hook
             at src/libstd/panicking.rs:468
  12: std::panicking::begin_panic
  13: rustc_errors::HandlerInner::bug
  14: rustc_errors::Handler::bug
  15: rustc::util::bug::opt_span_bug_fmt::{{closure}}
  16: rustc::ty::context::tls::with_opt::{{closure}}
  17: rustc::ty::context::tls::with_context_opt
  18: rustc::ty::context::tls::with_opt
  19: rustc::util::bug::opt_span_bug_fmt
  20: rustc::util::bug::bug_fmt
  21: rustc_mir::borrow_check::nll::universal_regions::UniversalRegionIndices::to_region_vid::{{closure}}
  22: rustc_mir::borrow_check::nll::universal_regions::UniversalRegionIndices::to_region_vid
  23: rustc_mir::borrow_check::nll::type_check::constraint_conversion::ConstraintConversion::convert_all
  24: rustc_mir::borrow_check::nll::type_check::TypeChecker::fully_perform_op
  25: rustc_mir::borrow_check::nll::type_check::type_check
  26: rustc_mir::borrow_check::nll::compute_regions
  27: rustc_mir::borrow_check::do_mir_borrowck
  28: rustc::ty::context::GlobalCtxt::enter_local
  29: rustc_mir::borrow_check::mir_borrowck
  30: rustc::ty::query::__query_compute::mir_borrowck
  31: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::mir_borrowck>::compute
  32: rustc::dep_graph::graph::DepGraph::with_task_impl
  33: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  34: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::ensure_query
  35: rustc_mir::transform::optimized_mir
  36: rustc::ty::query::__query_compute::optimized_mir
  37: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::optimized_mir>::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::eval_context::InterpCx<M>::load_mir
  41: rustc_mir::const_eval::const_eval_raw_provider
  42: rustc::ty::query::__query_compute::const_eval_raw
  43: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::const_eval_raw>::compute
  44: rustc::dep_graph::graph::DepGraph::with_task_impl
  45: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  46: rustc_mir::const_eval::const_eval_provider
  47: rustc::ty::query::__query_compute::const_eval
  48: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::const_eval>::compute
  49: rustc::dep_graph::graph::DepGraph::with_task_impl
  50: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  51: rustc_typeck::check::expr::<impl rustc_typeck::check::FnCtxt>::check_expr_kind
  52: rustc_typeck::check::expr::<impl rustc_typeck::check::FnCtxt>::check_expr_with_expectation_and_needs
  53: rustc_typeck::check::FnCtxt::check_decl_initializer
  54: rustc_typeck::check::FnCtxt::check_decl_local
  55: rustc_typeck::check::FnCtxt::check_stmt
  56: rustc_typeck::check::FnCtxt::check_block_with_expected
  57: rustc_typeck::check::expr::<impl rustc_typeck::check::FnCtxt>::check_expr_kind
  58: rustc_typeck::check::expr::<impl rustc_typeck::check::FnCtxt>::check_expr_with_expectation_and_needs
  59: rustc_typeck::check::expr::<impl rustc_typeck::check::FnCtxt>::check_expr_kind
  60: rustc_typeck::check::expr::<impl rustc_typeck::check::FnCtxt>::check_expr_with_expectation_and_needs
  61: rustc_typeck::check::FnCtxt::check_block_with_expected
  62: rustc_typeck::check::expr::<impl rustc_typeck::check::FnCtxt>::check_expr_kind
  63: rustc_typeck::check::expr::<impl rustc_typeck::check::FnCtxt>::check_expr_with_expectation_and_needs
  64: rustc_typeck::check::expr::<impl rustc_typeck::check::FnCtxt>::check_return_expr
  65: rustc_typeck::check::check_fn
  66: rustc_typeck::check::closure::<impl rustc_typeck::check::FnCtxt>::check_expr_closure
  67: rustc_typeck::check::expr::<impl rustc_typeck::check::FnCtxt>::check_expr_kind
  68: rustc_typeck::check::expr::<impl rustc_typeck::check::FnCtxt>::check_expr_with_expectation_and_needs
  69: rustc_typeck::check::FnCtxt::check_argument_types
  70: rustc_typeck::check::callee::<impl rustc_typeck::check::FnCtxt>::confirm_builtin_call
  71: rustc_typeck::check::callee::<impl rustc_typeck::check::FnCtxt>::check_call
  72: rustc_typeck::check::expr::<impl rustc_typeck::check::FnCtxt>::check_expr_kind
  73: rustc_typeck::check::expr::<impl rustc_typeck::check::FnCtxt>::check_expr_with_expectation_and_needs
  74: rustc_typeck::check::expr::<impl rustc_typeck::check::FnCtxt>::check_return_expr
  75: rustc_typeck::check::check_fn
  76: rustc::ty::context::tls::with_context::{{closure}}
  77: rustc_typeck::check::typeck_tables_of
  78: rustc::ty::query::__query_compute::typeck_tables_of
  79: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::typeck_tables_of>::compute
  80: rustc::dep_graph::graph::DepGraph::with_task_impl
  81: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  82: rustc::ty::query::__query_compute::typeck_tables_of
  83: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::typeck_tables_of>::compute
  84: rustc::dep_graph::graph::DepGraph::with_task_impl
  85: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  86: rustc_typeck::collect::checked_type_of
  87: rustc_typeck::collect::type_of
  88: rustc::ty::query::__query_compute::type_of
  89: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::type_of>::compute
  90: rustc::dep_graph::graph::DepGraph::with_task_impl
  91: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  92: rustc::hir::intravisit::walk_expr
  93: rustc::hir::intravisit::Visitor::visit_fn
  94: rustc::hir::intravisit::walk_impl_item
  95: rustc::hir::map::Map::visit_item_likes_in_module
  96: rustc_typeck::collect::collect_mod_item_types
  97: rustc::ty::query::__query_compute::collect_mod_item_types
  98: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::collect_mod_item_types>::compute
  99: rustc::dep_graph::graph::DepGraph::with_task_impl
 100: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
 101: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::ensure_query
 102: rustc_typeck::check_crate::{{closure}}::{{closure}}
 103: rustc::util::common::time
 104: rustc_typeck::check_crate
 105: rustc_interface::passes::analysis
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 1.40.0 (73528e339 2019-12-16) running on x86_64-unknown-linux-gnu

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

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

query stack during panic:
#0 [mir_borrowck] processing `conn::Handshake::<'a>::send::{{closure}}#0::{{constant}}#0`
#1 [optimized_mir] processing `conn::Handshake::<'a>::send::{{closure}}#0::{{constant}}#0`
#2 [const_eval_raw] const-evaluating `conn::Handshake::<'a>::send::{{closure}}#0::{{constant}}#0`
#3 [const_eval] const-evaluating + checking `conn::Handshake::<'a>::send::{{closure}}#0::{{constant}}#0`
#4 [typeck_tables_of] processing `conn::Handshake::<'a>::send`
#5 [typeck_tables_of] processing `conn::Handshake::<'a>::send::{{closure}}#0`
#6 [type_of] processing `conn::Handshake::<'a>::send::{{closure}}#0`
#7 [collect_mod_item_types] collecting item types in module `conn`
#8 [analysis] running analysis passes on this crate
end of query stack
error: aborting due to previous error

error: could not compile `btrs`.

Version info

~/btrs$ rustc --version --verbose
rustc 1.40.0 (73528e339 2019-12-16)
binary: rustc
commit-hash: 73528e339aae0f17a15ffa49a8ac608f50c6cf14
commit-date: 2019-12-16
host: x86_64-unknown-linux-gnu
release: 1.40.0
LLVM version: 9.0

[95th]

The ICE also goes away if I change [0; Self::LEN] to vec![0; Self::LEN]

[95th]

Ok. I minimized it to just:

fn main() {}

struct A<'a>(&'a ());

impl<'a> A<'a> {
    const N: usize = 68;

    fn foo(&self) {
        let mut b = [0; Self::N];
    }
}

It ICEs on latest nightly: https://play.rust-lang.org/?version=nightly&mode=debug&edition=2018&gist=7cc81a6eead5acb39f6a3ca58131ed0f

[pnkfelix]

triage: P-high, assiging to self, removing nomination label

[95th]

Following example fails to compile:

pub struct A<T>(T);

impl<T> A<T> {
    pub const N: usize = 68;

    pub fn foo(&self) {
        let b = [0; Self::N];
        println!("{}", b.len());
    }
}

Error

error[E0277]: the size for values of type `T` cannot be known at compilation time
 --> src/main.rs:9:21
  |
3 | pub struct A<T>(T);
  | ------------------- required by `A`
4 | 
5 | impl<T> A<T> {
  |      - this type parameter needs to be `std::marker::Sized`
...
9 |         let b = [0; Self::N];
  |                     ^^^^^^^ doesn't have a size known at compile-time
  |
  = help: the trait `std::marker::Sized` is not implemented for `T`
  = note: to learn more, visit <https://doc.rust-lang.org/book/ch19-04-advanced-types.html#dynamically-sized-types-and-the-sized-trait>

Even if I add T: Sized, still issue:

    pub fn foo(&self) where T: Sized {
        let b = [0; Self::N];
        println!("{}", b.len());
    }

or

impl<T: Sized> A<T> {
    pub const N: usize = 68;

    pub fn foo(&self) {
        let b = [0; Self::N];
        println!("{}", b.len());
    }
}

Error

error[E0277]: the size for values of type `T` cannot be known at compilation time
 --> src/main.rs:9:21
  |
3 | pub struct A<T>(T);
  | ------------------- required by `A`
4 | 
5 | impl<T> A<T> {
  |      - this type parameter needs to be `std::marker::Sized`
...
9 |         let b = [0; Self::N];
  |                     ^^^^^^^ doesn't have a size known at compile-time
  |
  = help: the trait `std::marker::Sized` is not implemented for `T`
  = note: to learn more, visit <https://doc.rust-lang.org/book/ch19-04-advanced-types.html#dynamically-sized-types-and-the-sized-trait>

But this works:

pub struct A<T>(T);

impl<T> A<T> {
    pub const N: usize = 68;

    pub fn foo(&self) {
        let b = Self::N;
        println!("{}", b);
    }
}

[stormmq]

Also just got this; no idea how to minimize it and the trace doesn't seem useful:-

error: internal compiler error: src/librustc_mir/borrow_check/universal_regions.rs:754: cannot convert `ReEarlyBound(0, 'a)` to a region vid

thread 'rustc' panicked at 'Box<Any>', src/librustc_errors/lib.rs:880:9
stack backtrace:
   0:        0x10b21cf6f - <unknown>
   1:        0x10b251f5e - <unknown>
   2:        0x10b20e217 - <unknown>
   3:        0x10b22191a - <unknown>
   4:        0x10b22165c - <unknown>
   5:        0x10f9217f8 - <unknown>
   6:        0x10b222035 - <unknown>
   7:        0x1138bb5e6 - <unknown>
   8:        0x113576037 - <unknown>
   9:        0x113574cf7 - <unknown>
  10:        0x1132d71a0 - <unknown>
  11:        0x1132ccd66 - <unknown>
  12:        0x1132cccec - <unknown>
  13:        0x1132d70a8 - <unknown>
  14:        0x1138b473b - <unknown>
  15:        0x1122006ac - <unknown>
  16:        0x11220060a - <unknown>
  17:        0x1120bc13e - <unknown>
  18:        0x1124b6f24 - <unknown>
  19:        0x1121f0c88 - <unknown>
  20:        0x1123ef10e - <unknown>
  21:        0x1124aef9a - <unknown>
  22:        0x1123ec87a - <unknown>
  23:        0x1120b46ca - <unknown>
  24:        0x112449edb - <unknown>
  25:        0x112253042 - <unknown>
  26:        0x112477519 - <unknown>
  27:        0x11244a692 - <unknown>
  28:        0x1123fa81c - <unknown>
  29:        0x1120b4a8a - <unknown>
  30:        0x112449fcb - <unknown>
  31:        0x11225e0a2 - <unknown>
  32:        0x11244eca8 - <unknown>
  33:        0x1122c6593 - <unknown>
  34:        0x112431f70 - <unknown>
  35:        0x1120b4d46 - <unknown>
  36:        0x11244a098 - <unknown>
  37:        0x11225115b - <unknown>
  38:        0x11248e697 - <unknown>
  39:        0x112430eba - <unknown>
  40:        0x1120b5e26 - <unknown>
  41:        0x11244a458 - <unknown>
  42:        0x1122641e1 - <unknown>
  43:        0x112453853 - <unknown>
  44:        0x112430c2a - <unknown>
  45:        0x1131478ec - <unknown>
  46:        0x112f98608 - <unknown>
  47:        0x113316325 - <unknown>
  48:        0x112e81de4 - <unknown>
  49:        0x112e72cb2 - <unknown>
  50:        0x112c92577 - <unknown>
  51:        0x112c9a6fe - <unknown>
  52:        0x112bd1bf1 - <unknown>
  53:        0x112c9a18e - <unknown>
  54:        0x111c15ea1 - <unknown>
  55:        0x111c0014c - <unknown>
  56:        0x111d36462 - <unknown>
  57:        0x111cf789f - <unknown>
  58:        0x111c64518 - <unknown>
  59:        0x111c5932a - <unknown>
  60:        0x111c833db - <unknown>
  61:        0x111bed77f - <unknown>
  62:        0x111cd24ea - <unknown>
  63:        0x111c83850 - <unknown>
  64:        0x111bb6e98 - <unknown>
  65:        0x111d0e83d - <unknown>
  66:        0x111c13e91 - <unknown>
  67:        0x111d2be80 - <unknown>
  68:        0x10fb484ca - <unknown>
  69:        0x10f92b5c9 - <unknown>
  70:        0x10f985595 - <unknown>
  71:        0x10f961403 - <unknown>
  72:        0x10f993c3c - <unknown>
  73:        0x10f966068 - <unknown>
  74:        0x10f927e85 - <unknown>
  75:        0x10f968b7c - <unknown>
  76:        0x10b1fe56e - <unknown>
  77:        0x10b230376 - <unknown>
  78:     0x7fff71dcb2eb - <unknown>
  79:     0x7fff71dce249 - <unknown>

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 1.44.0-nightly (1057dc97a 2020-03-20) running on x86_64-apple-darwin

note: compiler flags: -C debuginfo=2 -C linker=x86_64-linux-musl-cc -C incremental --crate-type lib

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

query stack during panic:
#0 [mir_borrowck] borrow-checking `file_descriptors::directory::DirectoryEntryIterator::buffer::{{constant}}#0`
#1 [optimized_mir] processing `file_descriptors::directory::DirectoryEntryIterator::buffer::{{constant}}#0`
#2 [const_eval_raw] const-evaluating `file_descriptors::directory::DirectoryEntryIterator::buffer::{{constant}}#0`
#3 [const_eval_validated] const-evaluating + checking `file_descriptors::directory::DirectoryEntryIterator::buffer::{{constant}}#0`
#4 [const_eval_validated] const-evaluating + checking `file_descriptors::directory::DirectoryEntryIterator::buffer::{{constant}}#0`
#5 [check_item_well_formed] processing `file_descriptors::directory::DirectoryEntryIterator`
#6 [analysis] running analysis passes on this crate
end of query stack
error: aborting due to previous error

error: could not compile `linux-support`.

[stormmq]

If this is referring to the field buffer, it's defined as buffer: [u8; Self::BufferCapacity], where BufferCapacity is defined inside the impl as const BufferCapacity: usize = 2048;.