(nightly) internal compiler error: union fields that need dropping should be impossible

[papricasix]

While compiling rlua using a nightly build of rust, I triggered the following bug (in https://github.com/amethyst/rlua/blob/10c95b7ffa8ad1a64f755a05c7cf806211f3f27f/src/util.rs#L129):

Code

    unsafe extern "C" fn do_call<F, R>(state: *mut ffi::lua_State) -> c_int
    where
        R: Copy,
        F: Fn(*mut ffi::lua_State) -> R,
    {
        let params = ffi::lua_touserdata(state, -1) as *mut Params<F, R>;
        ffi::lua_pop(state, 1);

        (*params).result.init = ((*params).function)(state);

        if (*params).nresults == ffi::LUA_MULTRET {
            ffi::lua_gettop(state)
        } else {
            (*params).nresults
        }
    }

Meta

rustc --version --verbose:

rustc 1.64.0-nightly (d5e7f4782 2022-07-16)
binary: rustc
commit-hash: d5e7f4782e4b699728d0a08200ecd1a54d56a85d
commit-date: 2022-07-16
host: x86_64-unknown-linux-gnu
release: 1.64.0-nightly
LLVM version: 14.0.6

Error output

error: internal compiler error: no errors encountered even though `delay_span_bug` issued

error: internal compiler error: union fields that need dropping should be impossible
   --> /home/micha/.cargo/registry/src/github.com-1ecc6299db9ec823/rlua-0.19.2/src/util.rs:129:9
    |
129 |         (*params).result.init = ((*params).function)(state);
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = note: delayed at compiler/rustc_mir_transform/src/check_unsafety.rs:227:39

thread 'rustc' panicked at 'Box<dyn Any>', compiler/rustc_errors/src/lib.rs:1425:13

Backtrace

stack backtrace:
   0:     0x7fca884a3710 - std::backtrace_rs::backtrace::libunwind::trace::he2b7f064c6c8ebd8
                               at /rustc/d5e7f4782e4b699728d0a08200ecd1a54d56a85d/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   1:     0x7fca884a3710 - std::backtrace_rs::backtrace::trace_unsynchronized::h6c5848816085cb4d
                               at /rustc/d5e7f4782e4b699728d0a08200ecd1a54d56a85d/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x7fca884a3710 - std::sys_common::backtrace::_print_fmt::h05ef0be136010689
                               at /rustc/d5e7f4782e4b699728d0a08200ecd1a54d56a85d/library/std/src/sys_common/backtrace.rs:66:5
   3:     0x7fca884a3710 - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::h10c19668734af2a3
                               at /rustc/d5e7f4782e4b699728d0a08200ecd1a54d56a85d/library/std/src/sys_common/backtrace.rs:45:22
   4:     0x7fca884fd81c - core::fmt::write::hb483b6baf6f08a60
                               at /rustc/d5e7f4782e4b699728d0a08200ecd1a54d56a85d/library/core/src/fmt/mod.rs:1198:17
   5:     0x7fca88494b75 - std::io::Write::write_fmt::hf77bd6f7d58fef0e
                               at /rustc/d5e7f4782e4b699728d0a08200ecd1a54d56a85d/library/std/src/io/mod.rs:1672:15
   6:     0x7fca884a63e1 - std::sys_common::backtrace::_print::h03f34c62e5bfdc80
                               at /rustc/d5e7f4782e4b699728d0a08200ecd1a54d56a85d/library/std/src/sys_common/backtrace.rs:48:5
   7:     0x7fca884a63e1 - std::sys_common::backtrace::print::he0f61808579de256
                               at /rustc/d5e7f4782e4b699728d0a08200ecd1a54d56a85d/library/std/src/sys_common/backtrace.rs:35:9
   8:     0x7fca884a63e1 - std::panicking::default_hook::{{closure}}::h03e5cc363b5f6eb0
                               at /rustc/d5e7f4782e4b699728d0a08200ecd1a54d56a85d/library/std/src/panicking.rs:295:22
   9:     0x7fca884a60b3 - std::panicking::default_hook::h2bb8a9d1f237276a
                               at /rustc/d5e7f4782e4b699728d0a08200ecd1a54d56a85d/library/std/src/panicking.rs:314:9
  10:     0x7fca88d4f7f1 - rustc_driver[8f049ba7ec2fe4e]::DEFAULT_HOOK::{closure#0}::{closure#0}
  11:     0x7fca884a6bb6 - std::panicking::rust_panic_with_hook::h2b6418ec29aa433e
                               at /rustc/d5e7f4782e4b699728d0a08200ecd1a54d56a85d/library/std/src/panicking.rs:702:17
  12:     0x7fca89f27531 - std[c33fd1b84eff1e1b]::panicking::begin_panic::<rustc_errors[2e7ae59e55ccb0de]::ExplicitBug>::{closure#0}
  13:     0x7fca89f272c6 - std[c33fd1b84eff1e1b]::sys_common::backtrace::__rust_end_short_backtrace::<std[c33fd1b84eff1e1b]::panicking::begin_panic<rustc_errors[2e7ae59e55ccb0de]::ExplicitBug>::{closure#0}, !>
  14:     0x7fca89f210c6 - std[c33fd1b84eff1e1b]::panicking::begin_panic::<rustc_errors[2e7ae59e55ccb0de]::ExplicitBug>
  15:     0x7fca89f243b6 - std[c33fd1b84eff1e1b]::panic::panic_any::<rustc_errors[2e7ae59e55ccb0de]::ExplicitBug>
  16:     0x7fca8b81c0e3 - <rustc_errors[2e7ae59e55ccb0de]::HandlerInner as core[8559c76fbb49d2ec]::ops::drop::Drop>::drop
  17:     0x7fca8af46cab - core[8559c76fbb49d2ec]::ptr::drop_in_place::<rustc_session[f28dbaef20431e1d]::parse::ParseSess>
  18:     0x7fca8af491e3 - <alloc[34fcb9634b68b8d8]::rc::Rc<rustc_session[f28dbaef20431e1d]::session::Session> as core[8559c76fbb49d2ec]::ops::drop::Drop>::drop
  19:     0x7fca8af2b64d - core[8559c76fbb49d2ec]::ptr::drop_in_place::<rustc_interface[d0628200c9d01d52]::interface::Compiler>
  20:     0x7fca8af29804 - rustc_span[1b79d0b79e871695]::with_source_map::<core[8559c76fbb49d2ec]::result::Result<(), rustc_errors[2e7ae59e55ccb0de]::ErrorGuaranteed>, rustc_interface[d0628200c9d01d52]::interface::create_compiler_and_run<core[8559c76fbb49d2ec]::result::Result<(), rustc_errors[2e7ae59e55ccb0de]::ErrorGuaranteed>, rustc_driver[8f049ba7ec2fe4e]::run_compiler::{closure#1}>::{closure#1}>
  21:     0x7fca8af45aa0 - rustc_interface[d0628200c9d01d52]::interface::create_compiler_and_run::<core[8559c76fbb49d2ec]::result::Result<(), rustc_errors[2e7ae59e55ccb0de]::ErrorGuaranteed>, rustc_driver[8f049ba7ec2fe4e]::run_compiler::{closure#1}>
  22:     0x7fca8af59be2 - <scoped_tls[1595f96802d8f51d]::ScopedKey<rustc_span[1b79d0b79e871695]::SessionGlobals>>::set::<rustc_interface[d0628200c9d01d52]::interface::run_compiler<core[8559c76fbb49d2ec]::result::Result<(), rustc_errors[2e7ae59e55ccb0de]::ErrorGuaranteed>, rustc_driver[8f049ba7ec2fe4e]::run_compiler::{closure#1}>::{closure#0}, core[8559c76fbb49d2ec]::result::Result<(), rustc_errors[2e7ae59e55ccb0de]::ErrorGuaranteed>>
  23:     0x7fca8af2bbcf - std[c33fd1b84eff1e1b]::sys_common::backtrace::__rust_begin_short_backtrace::<rustc_interface[d0628200c9d01d52]::util::run_in_thread_pool_with_globals<rustc_interface[d0628200c9d01d52]::interface::run_compiler<core[8559c76fbb49d2ec]::result::Result<(), rustc_errors[2e7ae59e55ccb0de]::ErrorGuaranteed>, rustc_driver[8f049ba7ec2fe4e]::run_compiler::{closure#1}>::{closure#0}, core[8559c76fbb49d2ec]::result::Result<(), rustc_errors[2e7ae59e55ccb0de]::ErrorGuaranteed>>::{closure#0}, core[8559c76fbb49d2ec]::result::Result<(), rustc_errors[2e7ae59e55ccb0de]::ErrorGuaranteed>>
  24:     0x7fca8af45ef9 - <<std[c33fd1b84eff1e1b]::thread::Builder>::spawn_unchecked_<rustc_interface[d0628200c9d01d52]::util::run_in_thread_pool_with_globals<rustc_interface[d0628200c9d01d52]::interface::run_compiler<core[8559c76fbb49d2ec]::result::Result<(), rustc_errors[2e7ae59e55ccb0de]::ErrorGuaranteed>, rustc_driver[8f049ba7ec2fe4e]::run_compiler::{closure#1}>::{closure#0}, core[8559c76fbb49d2ec]::result::Result<(), rustc_errors[2e7ae59e55ccb0de]::ErrorGuaranteed>>::{closure#0}, core[8559c76fbb49d2ec]::result::Result<(), rustc_errors[2e7ae59e55ccb0de]::ErrorGuaranteed>>::{closure#1} as core[8559c76fbb49d2ec]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  25:     0x7fca884b0923 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h6d78f1dcc4e189b8
                               at /rustc/d5e7f4782e4b699728d0a08200ecd1a54d56a85d/library/alloc/src/boxed.rs:1935:9
  26:     0x7fca884b0923 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::hc462dd82c109fc34
                               at /rustc/d5e7f4782e4b699728d0a08200ecd1a54d56a85d/library/alloc/src/boxed.rs:1935:9
  27:     0x7fca884b0923 - std::sys::unix::thread::Thread::new::thread_start::h671a7ad89d56ef6e
                               at /rustc/d5e7f4782e4b699728d0a08200ecd1a54d56a85d/library/std/src/sys/unix/thread.rs:108:17
  28:     0x7fca8808c54d - <unknown>
  29:     0x7fca88111874 - clone
  30:                0x0 - <unknown>

note: the compiler unexpectedly panicked. this is a bug.

note: we would appreciate a bug report: https://github.com/rust-lang/rust/issues/new?labels=C-bug%2C+I-ICE%2C+T-compiler&template=ice.md

note: rustc 1.64.0-nightly (d5e7f4782 2022-07-16) running on x86_64-unknown-linux-gnu

note: compiler flags: --crate-type lib -C opt-level=3 -C embed-bitcode=no -C linker=clang -C link-arg=-fuse-ld=lld -Z share-generics=y -C link-arg=-Wl,--no-rosegment

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

query stack during panic:
end of query stack
error: could not compile `rlua`

[carbotaniuman]

This looks related to #97995.