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

I got an internal compiler error at commit https://github.com/95th/btrs/commit/f2eb5338fa5c865bdde110dfa21fba7d06f8de7e . I dont know how to minimize it.

Relevant code is:

```rust
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`.

```rust
       let mut v = [0; 68];
       ...
```
<details>
<summary>Backtrace:</summary>

```
~/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`.
```
</details>

<details>
<summary>Version info</summary>

```
~/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
```
</details>


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ICE: cannot convert `ReEarlyBound(0, 'a)` to a region vid #68532

95th
openedon Jan 25, 2020

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ICE: cannot convert ReEarlyBound(0, 'a) to a region vid #68532

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95thopenedon Jan 25, 2020

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