Rustc bug:cannot convert `ReEmpty` to a region vid

[lispc]

When compiling my code, I saw cargo/rustc panicked.

I tried this code:

pub struct Data<A> {
    pub a: A,
}

impl<A> Data<A>
where
    A: 'static,
    &'static A: ,
{
    pub fn run() {
        let mut entries: Vec<A> = Vec::new();
        if !entries.is_empty() {}
    }
}

pub type DataA = Data<i32>;

fn main() {
    println!("Hello, world!");
}

The output is

 $ cargo build
   Compiling rustc-crash v0.1.0 (/Users/zhangzhuo/repos/personal/rustc-crash)
error: internal compiler error: src/librustc_mir/borrow_check/universal_regions.rs:729: cannot convert `ReEmpty` to a region vid

thread 'rustc' panicked at 'Box<Any>', src/librustc_errors/lib.rs:883:9
note: run with `RUST_BACKTRACE=1` environment variable to display a 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 1.42.0-nightly (6d3f4e0aa 2020-01-25) running on x86_64-apple-darwin

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

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

error: aborting due to previous error

error: could not compile `rustc-crash`.

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

Meta

rustc --version --verbose:

rustc 1.42.0-nightly (6d3f4e0aa 2020-01-25)
binary: rustc
commit-hash: 6d3f4e0aab3e36ceb8b83d1e9467514685f6b751
commit-date: 2020-01-25
host: x86_64-apple-darwin
release: 1.42.0-nightly
LLVM version: 9.0

[Centril]

Reduced:

fn run<'a, A>(x: A)
where
    A: 'static,
    &'static A: ,
{
    let _: &'a A = &x;
}

fn main() {}

backtrace:

   Compiling playground v0.0.1 (/playground)
error: internal compiler error: src/librustc_mir/borrow_check/universal_regions.rs:729: cannot convert `ReEmpty` to a region vid

thread 'rustc' panicked at 'Box<Any>', src/librustc_errors/lib.rs:883:9
stack backtrace:
   0: backtrace::backtrace::libunwind::trace
             at /cargo/registry/src/github.zerozr99.workers.dev-1ecc6299db9ec823/backtrace-0.3.40/src/backtrace/libunwind.rs:88
   1: backtrace::backtrace::trace_unsynchronized
             at /cargo/registry/src/github.zerozr99.workers.dev-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:59
   4: core::fmt::write
             at src/libcore/fmt/mod.rs:1052
   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:62
   7: std::sys_common::backtrace::print
             at src/libstd/sys_common/backtrace.rs:49
   8: std::panicking::default_hook::{{closure}}
             at src/libstd/panicking.rs:204
   9: std::panicking::default_hook
             at src/libstd/panicking.rs:224
  10: rustc_driver::report_ice
  11: std::panicking::rust_panic_with_hook
             at src/libstd/panicking.rs:476
  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_opt
  18: rustc::util::bug::opt_span_bug_fmt
  19: rustc::util::bug::bug_fmt
  20: rustc_mir::borrow_check::universal_regions::UniversalRegionIndices::to_region_vid::{{closure}}
  21: rustc_mir::borrow_check::universal_regions::UniversalRegionIndices::to_region_vid
  22: rustc_mir::borrow_check::region_infer::RegionInferenceContext::eval_verify_bound
  23: rustc_mir::borrow_check::region_infer::RegionInferenceContext::eval_verify_bound
  24: rustc_mir::borrow_check::nll::compute_regions
  25: rustc_mir::borrow_check::do_mir_borrowck
  26: rustc::ty::context::GlobalCtxt::enter_local
  27: rustc_mir::borrow_check::mir_borrowck
  28: rustc::ty::query::__query_compute::mir_borrowck
  29: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::mir_borrowck>::compute
  30: rustc::dep_graph::graph::DepGraph::with_task_impl
  31: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  32: rustc::ty::<impl rustc::ty::context::TyCtxt>::par_body_owners
  33: rustc_session::utils::<impl rustc_session::session::Session>::time
  34: rustc_interface::passes::analysis
  35: rustc::ty::query::__query_compute::analysis
  36: rustc::dep_graph::graph::DepGraph::with_task_impl
  37: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  38: rustc::ty::context::tls::enter_global
  39: rustc_interface::interface::run_compiler_in_existing_thread_pool
  40: scoped_tls::ScopedKey<T>::set
  41: 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 1.42.0-nightly (6d3f4e0aa 2020-01-25) running on x86_64-unknown-linux-gnu

note: compiler flags: -C codegen-units=1 -C debuginfo=2 --crate-type bin

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

query stack during panic:
#0 [mir_borrowck] processing `run`
#1 [analysis] running analysis passes on this crate
end of query stack
error: aborting due to previous error

error: could not compile `playground`.

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

Problem occurs in:

rust/src/librustc_mir/borrow_check/universal_regions.rs

Lines 722 to 731 in 698fcd3

	pub fn to_region_vid(&self, r: ty::Region<'tcx>) -> RegionVid {
	if let ty::ReVar(..) = r {
	r.to_region_vid()
	} else {
	*self
	.indices
	.get(&r)
	.unwrap_or_else(|| bug!("cannot convert `{:?}` to a region vid", r))
	}
	}

which does not account for ReEmpty (which it presumably shouldn't).

cc @matthewjasper

[pnkfelix]

triage: P-high, assigning to self, removing nomination label.

[pnkfelix]

@rustbot assign @nikomatsakis

reassigning to niko because they told me that they are doing work that should address the issue here.

[izik1]

Possibly interesting variant of this:

fn spawn<T: Send>(_: T) {}

async fn fetch(_: &()) {
    fn f<T>() {}
    spawn(f);
}

pub async fn spawn_fetch() {
    spawn(fetch(&()));
}

which outputs the following:
output.txt