[Const generics] thread 'rustc' panicked at 'no errors encountered even though delay_span_bug issued'

[mcserv]

The code simply does "not" compile, because compiler crashes.

I tried this code:

#![feature(const_generics)]

fn test<const A: &'static str, const B: &'static str>() {
    println!("{} {}", A, B);
}

fn main() {
    test::<"Hello", "World">();
}

Which is expected to compile without errors and execute the binary, which prints out "Hello World".

It's internal checks seem to fail while it produces seemingly working binary.

I say so because trying to run it again after the failure, it does work with no errors and it... prints "Hello World".

Meta

rustc --version --verbose:

rustc 1.39.0-nightly (bea0372a1 2019-08-20)
binary: rustc
commit-hash: bea0372a1a7a31b81f28cc4d9a83a2dc9a79d008
commit-date: 2019-08-20
host: x86_64-unknown-linux-gnu
release: 1.39.0-nightly
LLVM version: 9.0

Backtrace (RUST_BACKTRACE=full cargo run):

warning: the feature `const_generics` is incomplete and may cause the compiler to crash
 --> src/main.rs:1:12
  |
1 | #![feature(const_generics)]
  |            ^^^^^^^^^^^^^^
  |
  = note: `#[warn(incomplete_features)]` on by default

error: internal compiler error: broken MIR in DefId(0:15 ~ testbug[7665]::main[0]) (CanonicalUserTypeAnnotation { user_ty: Canonical { max_universe: U0, variables: [], value: TypeOf(DefId(0:12 ~ testbug[7665]::test[0]), UserSubsts { substs: [Const { ty: &'static str, val: Unevaluated(DefId(0:16 ~ testbug[7665]::main[0]::{{constant}}[0]), []) }, Const { ty: &'static str, val: Unevaluated(DefId(0:17 ~ testbug[7665]::main[0]::{{constant}}[1]), []) }], user_self_ty: None }) }, span: src/main.rs:8:5: 8:29, inferred_ty: fn() {test::<"Hello", "World">} }): bad user type AscribeUserType(fn() {test::<"Hello", "World">}, DefId(0:12 ~ testbug[7665]::test[0]) UserSubsts { substs: [Const { ty: &'static str, val: Unevaluated(DefId(0:16 ~ testbug[7665]::main[0]::{{constant}}[0]), []) }, Const { ty: &'static str, val: Unevaluated(DefId(0:17 ~ testbug[7665]::main[0]::{{constant}}[1]), []) }], user_self_ty: None }): NoSolution

error: internal compiler error: broken MIR in DefId(0:15 ~ testbug[7665]::main[0]) (const test::<"Hello", "World">): bad constant user type CanonicalUserTypeAnnotation { user_ty: Canonical { max_universe: U0, variables: [], value: TypeOf(DefId(0:12 ~ testbug[7665]::test[0]), UserSubsts { substs: [Const { ty: &'static str, val: Unevaluated(DefId(0:16 ~ testbug[7665]::main[0]::{{constant}}[0]), []) }, Const { ty: &'static str, val: Unevaluated(DefId(0:17 ~ testbug[7665]::main[0]::{{constant}}[1]), []) }], user_self_ty: None }) }, span: src/main.rs:8:5: 8:29, inferred_ty: fn() {test::<"Hello", "World">} } vs fn() {test::<"Hello", "World">}: NoSolution
 --> src/main.rs:8:5
  |
8 |     test::<"Hello", "World">();
  |     ^^^^^^^^^^^^^^^^^^^^^^^^

thread 'rustc' panicked at 'no errors encountered even though `delay_span_bug` issued', src/librustc_errors/lib.rs:360:17
stack backtrace:
   0:     0x7fafb0591742 - backtrace::backtrace::libunwind::trace::h1358d2edf0666fdd
                               at /cargo/registry/src/git.luolix.top-1ecc6299db9ec823/backtrace-0.3.35/src/backtrace/libunwind.rs:88
   1:     0x7fafb0591742 - backtrace::backtrace::trace_unsynchronized::hef042fe061eb4c23
                               at /cargo/registry/src/git.luolix.top-1ecc6299db9ec823/backtrace-0.3.35/src/backtrace/mod.rs:66
   2:     0x7fafb0591742 - std::sys_common::backtrace::_print::h9179b6bace739ad8
                               at src/libstd/sys_common/backtrace.rs:47
   3:     0x7fafb0591742 - std::sys_common::backtrace::print::hcf88edef7e09a883
                               at src/libstd/sys_common/backtrace.rs:36
   4:     0x7fafb0591742 - std::panicking::default_hook::{{closure}}::h8dc0d8684e782a7d
                               at src/libstd/panicking.rs:200
   5:     0x7fafb0591426 - std::panicking::default_hook::hf9f03712ee0993e3
                               at src/libstd/panicking.rs:214
   6:     0x7fafb24516a1 - rustc::util::common::panic_hook::h6a42bef1376a73bb
   7:     0x7fafb0591f7c - std::panicking::rust_panic_with_hook::h0ea1022fc447fb64
                               at src/libstd/panicking.rs:481
   8:     0x7fafb2837a25 - std::panicking::begin_panic::h4b303d0c24f0718d
   9:     0x7fafb2852015 - <rustc_errors::Handler as core::ops::drop::Drop>::drop::h412b37825c03be8d
  10:     0x7fafb0ac6a62 - core::ptr::real_drop_in_place::hd04278cb61ac8aea
  11:     0x7fafb0acae16 - <alloc::rc::Rc<T> as core::ops::drop::Drop>::drop::hd91d31ba89a5839f
  12:     0x7fafb0a7f09c - core::ptr::real_drop_in_place::h59844e5d47f4e573
  13:     0x7fafb0a7aae1 - rustc_interface::interface::run_compiler_in_existing_thread_pool::hdc75fb0fd8463a42
  14:     0x7fafb0ab34b2 - std::thread::local::LocalKey<T>::with::h8b398dfa59f49869
  15:     0x7fafb0abb45e - scoped_tls::ScopedKey<T>::set::hfc35056456681111
  16:     0x7fafb0aec9b2 - syntax::with_globals::habacbfaab82229eb
  17:     0x7fafb0a4b832 - std::sys_common::backtrace::__rust_begin_short_backtrace::h4741bd6aafe31c7e
  18:     0x7fafb05a283a - __rust_maybe_catch_panic
                               at src/libpanic_unwind/lib.rs:80
  19:     0x7fafb0a7ce89 - core::ops::function::FnOnce::call_once{{vtable.shim}}::hdf6a2a83fa760424
  20:     0x7fafb057540f - <alloc::boxed::Box<F> as core::ops::function::FnOnce<A>>::call_once::h0ccaf38361ac89de
                               at /rustc/bea0372a1a7a31b81f28cc4d9a83a2dc9a79d008/src/liballoc/boxed.rs:922
  21:     0x7fafb05a14c0 - <alloc::boxed::Box<F> as core::ops::function::FnOnce<A>>::call_once::h6bdddc9c647146b9
                               at /rustc/bea0372a1a7a31b81f28cc4d9a83a2dc9a79d008/src/liballoc/boxed.rs:922
  22:     0x7fafb05a14c0 - std::sys_common::thread::start_thread::hff9f2bb3b7a58e8c
                               at src/libstd/sys_common/thread.rs:13
  23:     0x7fafb05a14c0 - std::sys::unix::thread::Thread::new::thread_start::h88f38d807be79b1c
                               at src/libstd/sys/unix/thread.rs:79
  24:     0x7fafb03116db - start_thread
  25:     0x7fafafc2e88f - __clone
  26:                0x0 - <unknown>
query stack during panic:
end of query stack

error: internal compiler error: unexpected panic

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 1.39.0-nightly (bea0372a1 2019-08-20) running on x86_64-unknown-linux-gnu

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

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

error: Could not compile `testbug`.

As a note, I'm completely oblivious to what's wrong, I only searched if there's any similar issue that mentions 'no errors encountered even though delay_span_bug issued', and I didn't seem to find anything related, so sorry if this is duplicate. #60619 for example may point to identical issue as this, but I'll put this here just to be safe.

[yodaldevoid]

This is most likely related to #60813.