Async/Await rustc assertion panic

[Proximyst]

When trying to pass on my server functionality to the API instead of the binary, rustc panics with assertion failed: target_offset >= offset found in src/librustc_codegen_llvm/type_of.rs:130:9.

I tried this code:

There is no small piece of code for this, sadly.
The source is here: https://gitlab.com/Moscovium/moscovium/blob/f295a097860af31be68c8374eed05cf6a58ab93e/impl/main.rs#L61-63

I expected to see this happen: flawless execution, or at least just a good ol' rustc error with a trillion futures generics

Instead, this happened: rustc panicked about LLVM code gen

Meta

$ rustc --version --verbose
rustc 1.37.0-nightly (0e4a56b4b 2019-06-13)
binary: rustc
commit-hash: 0e4a56b4b04ea98bb16caada30cb2418dd06e250
commit-date: 2019-06-13
host: x86_64-unknown-linux-gnu
release: 1.37.0-nightly
LLVM version: 8.0

$ RUST_BACKTRACE=full cargo run            
   Compiling moscovium v0.1.0 (/hdd1/Work/minecraft/moscovium)
warning: Hard linking files in the incremental compilation cache failed. Copying files instead. Consider moving the cache directory to a file system which supports hard linking in session dir `/hdd1/Work/minecraft/moscovium/target/debug/incremental/moscovium-15d9p06c5csz7/s-fdfx9m9gza-s7b2sh-working`

warning: unused import: `event::Cancellable as _`
 --> impl/main.rs:5:11
  |
5 | use api::{event::Cancellable as _, prelude::*};
  |           ^^^^^^^^^^^^^^^^^^^^^^^
  |
  = note: #[warn(unused_imports)] on by default

thread 'rustc' panicked at 'assertion failed: target_offset >= offset', src/librustc_codegen_llvm/type_of.rs:130:9
stack backtrace:
   0:     0x7f589a54918b - backtrace::backtrace::libunwind::trace::h41595b2657878dbc
                               at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.29/src/backtrace/libunwind.rs:88
   1:     0x7f589a54918b - backtrace::backtrace::trace_unsynchronized::h4efe511900bf5e12
                               at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.29/src/backtrace/mod.rs:66
   2:     0x7f589a54918b - std::sys_common::backtrace::_print::h7275b63687b21f98
                               at src/libstd/sys_common/backtrace.rs:47
   3:     0x7f589a54918b - std::sys_common::backtrace::print::h790c12384440cac4
                               at src/libstd/sys_common/backtrace.rs:36
   4:     0x7f589a54918b - std::panicking::default_hook::{{closure}}::he6cba1bdf748f1c3
                               at src/libstd/panicking.rs:198
   5:     0x7f589a548e8c - std::panicking::default_hook::h1296d9a476e7a9c2
                               at src/libstd/panicking.rs:212
   6:     0x7f589829b3f1 - rustc::util::common::panic_hook::ha2e96a0b919e5a1a
   7:     0x7f589a5499e9 - std::panicking::rust_panic_with_hook::h8d2408723e9a2bd4
                               at src/libstd/panicking.rs:479
   8:     0x7f58902f44b5 - std::panicking::begin_panic::h74637358fcbcf49a
   9:     0x7f589043919c - rustc_codegen_llvm::type_of::struct_llfields::h61dc16133d19abaa
  10:     0x7f5890418895 - <rustc_target::abi::TyLayout<&rustc::ty::TyS> as rustc_codegen_llvm::type_of::LayoutLlvmExt>::llvm_type::hd0eea50cae39777c
  11:     0x7f5890438dd9 - rustc_codegen_llvm::type_of::struct_llfields::h61dc16133d19abaa
  12:     0x7f5890418895 - <rustc_target::abi::TyLayout<&rustc::ty::TyS> as rustc_codegen_llvm::type_of::LayoutLlvmExt>::llvm_type::hd0eea50cae39777c
  13:     0x7f58902da58f - <rustc_target::abi::call::FnType<&rustc::ty::TyS> as rustc_codegen_llvm::abi::FnTypeLlvmExt>::llvm_type::h0d0aa59294abb94c
  14:     0x7f5890327a26 - rustc_codegen_llvm::declare::<impl rustc_codegen_ssa::traits::declare::DeclareMethods for rustc_codegen_llvm::context::CodegenCx>::declare_fn::hfd002e9de8564d19
  15:     0x7f589032807f - rustc_codegen_llvm::mono_item::<impl rustc_codegen_ssa::traits::declare::PreDefineMethods for rustc_codegen_llvm::context::CodegenCx>::predefine_fn::h158b31f162921281
  16:     0x7f589034e5d6 - <rustc::mir::mono::MonoItem as rustc_codegen_ssa::mono_item::MonoItemExt>::predefine::hf5e95d5c0693b901
  17:     0x7f58902dba8b - rustc_codegen_llvm::base::compile_codegen_unit::module_codegen::h3dfd41b76a21d604
  18:     0x7f589031a28c - rustc::dep_graph::graph::DepGraph::with_task::h9223b093287413d7
  19:     0x7f58902db8b2 - rustc_codegen_llvm::base::compile_codegen_unit::h84cbcc9f84ef685b
  20:     0x7f58904203d3 - rustc_codegen_ssa::base::codegen_crate::h74b58a2ac9b23913
  21:     0x7f589041cc8a - <rustc_codegen_llvm::LlvmCodegenBackend as rustc_codegen_utils::codegen_backend::CodegenBackend>::codegen_crate::h50e9412946ee1e63
  22:     0x7f5899f7bd67 - rustc::util::common::time::haa32cafeeb3d54cb
  23:     0x7f5899f2713b - rustc_interface::passes::start_codegen::hcdb1e9299570ccd1
  24:     0x7f5899f0e317 - rustc::ty::context::tls::enter_global::h5d834d2634f7fc92
  25:     0x7f5899f27941 - rustc_interface::passes::BoxedGlobalCtxt::access::{{closure}}::h10a967fa77f2b087
  26:     0x7f5899f83b05 - rustc_interface::passes::create_global_ctxt::{{closure}}::h7a059b6cf199597d
  27:     0x7f5899f26496 - rustc_interface::passes::BoxedGlobalCtxt::enter::h4a247e90412a9579
  28:     0x7f5899f10740 - rustc_interface::queries::Query<T>::compute::h595d6a8dccab9742
  29:     0x7f5899ffa7e4 - rustc_interface::queries::<impl rustc_interface::interface::Compiler>::ongoing_codegen::h93f94310b1d268e6
  30:     0x7f589a83d840 - rustc_interface::interface::run_compiler_in_existing_thread_pool::h35eddbfcfbbe0eb4
  31:     0x7f589a8af5f6 - std::thread::local::LocalKey<T>::with::hea85159711765771
  32:     0x7f589a847fb5 - scoped_tls::ScopedKey<T>::set::he08d6211f459724f
  33:     0x7f589a87aad4 - syntax::with_globals::h2c63be024f0c1f38
  34:     0x7f589a89989d - std::sys_common::backtrace::__rust_begin_short_backtrace::hfc7fb053a9ed90ec
  35:     0x7f589a55a8da - __rust_maybe_catch_panic
                               at src/libpanic_unwind/lib.rs:82
  36:     0x7f589a8256d9 - core::ops::function::FnOnce::call_once{{vtable.shim}}::h0cd7d8fc1b0a39a3
  37:     0x7f589a52ceef - <alloc::boxed::Box<F> as core::ops::function::FnOnce<A>>::call_once::he71721d2d956d451
                               at /rustc/0e4a56b4b04ea98bb16caada30cb2418dd06e250/src/liballoc/boxed.rs:746
  38:     0x7f589a5595b0 - <alloc::boxed::Box<F> as core::ops::function::FnOnce<A>>::call_once::he520045b8d28ce5c
                               at /rustc/0e4a56b4b04ea98bb16caada30cb2418dd06e250/src/liballoc/boxed.rs:746
  39:     0x7f589a5595b0 - std::sys_common::thread::start_thread::h2e98d1272dc6d74b
                               at src/libstd/sys_common/thread.rs:13
  40:     0x7f589a5595b0 - std::sys::unix::thread::Thread::new::thread_start::h18485805666ccd3c
                               at src/libstd/sys/unix/thread.rs:79
  41:     0x7f589a49d57f - start_thread
  42:     0x7f589a3bcf13 - __clone
  43:                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 1.37.0-nightly (0e4a56b4b 2019-06-13) 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 `moscovium`.

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

[Proximyst]

I've narrowed down the issue to this:

            match &packet {
                Packet::HSBHandshake(ref _handshake) => {
                    // handle here when implemented
                }
                Packet::HSBLegacyStatusPing(ref _ping) => {
// the line under here causes the ICE;
// I don't know why, but that's all I've gotten so far
//
// Leaving it out (commenting it away) gets rid of the issue
                    packet.handle(self).await?;
                }
                _ => unreachable!(
                    "only a handshake or a legacy packet should
                be possible here. any other packet should have returned an
                error of ProtocolError::UnknownPacket."
                ),
            }```

https://gitlab.com/Moscovium/moscovium/blob/f295a097860af31be68c8374eed05cf6a58ab93e/src/network/stream.rs#L282-294

[Proximyst]

So I further narrowed down the issue till it wrapped back around in ServerboundLegacyStatus (src/network/protocol/packet/handshake/serverbound/legacy). Here it wraps around to the MoscoviumStream's write_packet.

This call, no matter the contents of write_packet, creates an ICE.

Call to write_packet: https://gitlab.com/Moscovium/moscovium/blob/f295a097860af31be68c8374eed05cf6a58ab93e/src/network/protocol/packet/handshake/serverbound/legacy.rs#L12

write_packet: https://gitlab.com/Moscovium/moscovium/blob/f295a097860af31be68c8374eed05cf6a58ab93e/src/network/stream.rs#L233

[Proximyst]

It seems as if this is a duplicate of #61793 and will be fixed by #62011.