Crash using mlua crate.

[Emm54321]

Code

pub fn lua_touserdata() -> *mut () {
    unimplemented!()
}

pub union URes<R: Copy> {
    _uninit: (),
    init: R,
}

pub struct Params<F, R: Copy> {
    function: F,
    result: URes<R>,
}

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

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

Meta

rustc --version --verbose:

rustc 1.64.0-nightly (f8588549c 2022-07-18)
binary: rustc
commit-hash: f8588549c3c3d45c32b404210cada01e2a45def3
commit-date: 2022-07-18
host: x86_64-unknown-linux-gnu
release: 1.64.0-nightly
LLVM version: 14.0.6

Error output

    Checking yy v0.1.0 (/tmp/yy)
warning: Error finalizing incremental compilation session directory `/tmp/yy/target/debug/incremental/yy-uwxkiexch4q/s-gbv0o20hj6-12w3nk9-working`: No such file or directory (os error 2)

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
  --> src/lib.rs:22:5
   |
22 |     (*params).result.init = ((*params).function)();
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = 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

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 (f8588549c 2022-07-18) running on x86_64-unknown-linux-gnu

note: compiler flags: --crate-type lib -C embed-bitcode=no -C debuginfo=2 -C incremental -C target-feature=+aes

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

query stack during panic:
end of query stack
warning: `yy` (lib) generated 1 warning
error: could not compile `yy`; 1 warning emitted

Backtrace

stack backtrace:
   0: std::panicking::begin_panic::<rustc_errors::ExplicitBug>
   1: std::panic::panic_any::<rustc_errors::ExplicitBug>
   2: <rustc_errors::HandlerInner as core::ops::drop::Drop>::drop
   3: core::ptr::drop_in_place::<rustc_session::parse::ParseSess>
   4: <alloc::rc::Rc<rustc_session::session::Session> as core::ops::drop::Drop>::drop
   5: core::ptr::drop_in_place::<rustc_interface::interface::Compiler>
   6: rustc_span::with_source_map::<core::result::Result<(), rustc_errors::ErrorGuaranteed>, rustc_interface::interface::create_compiler_and_run<core::result::Result<(), rustc_errors::ErrorGuaranteed>, rustc_driver::run_compiler::{closure#1}>::{closure#1}>
   7: rustc_interface::interface::create_compiler_and_run::<core::result::Result<(), rustc_errors::ErrorGuaranteed>, rustc_driver::run_compiler::{closure#1}>
   8: <scoped_tls::ScopedKey<rustc_span::SessionGlobals>>::set::<rustc_interface::interface::run_compiler<core::result::Result<(), rustc_errors::ErrorGuaranteed>, rustc_driver::run_compiler::{closure#1}>::{closure#0}, core::result::Result<(), rustc_errors::ErrorGuaranteed>>
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

[5225225]

Looks like this was fixed by #99384 ? A bisection lead to the same regressed PR, and I can't reproduce this on the latest nightly (rustc 1.64.0-nightly (d68e7ebc3 2022-07-20)).

[Emm54321]

Indeed, it works with 2022-07-20.
I assumed 'rustup update' would give me the latest nightly version, but it gave me 2022-07-18.

[5225225]

I assumed 'rustup update' would give me the latest nightly version, but it gave me 2022-07-18.

rustup update will skip versions that don't have all the components you have, to avoid things not working. Do you have miri installed? Miri doesn't work in the latest versions.

[Emm54321]

Ah right, I have miri installed.
Anyway, thanks for your time.