ICE

[hellow554]

Discovered by cheblin: https://users.rust-lang.org/t/23968

#![feature(unboxed_closures)]
#![feature(const_vec_new)]
#![feature(fn_traits)]

pub struct PackBytes;
static mut HANDLERS: Vec<Box<dyn for<'a> FnMut<&'a mut PackBytes, Output=()>>> = Vec::new();

fn main() {
    let mut pack = PackBytes;
    unsafe { HANDLERS[0].as_mut().call_mut(&mut pack); }
}

(Playground)

Errors:

   Compiling playground v0.0.1 (/playground)
error: internal compiler error: src/librustc_codegen_llvm/abi.rs:433: argument to function with "rust-call" ABI is not a tuple

thread 'rustc' panicked at 'Box<Any>', src/librustc_errors/lib.rs:590:9
stack backtrace:
   0: std::sys::unix::backtrace::tracing::imp::unwind_backtrace
             at src/libstd/sys/unix/backtrace/tracing/gcc_s.rs:39
   1: std::sys_common::backtrace::_print
             at src/libstd/sys_common/backtrace.rs:70
   2: std::panicking::default_hook::{{closure}}
             at src/libstd/sys_common/backtrace.rs:58
             at src/libstd/panicking.rs:200
   3: std::panicking::default_hook
             at src/libstd/panicking.rs:215
   4: rustc::util::common::panic_hook
   5: std::panicking::rust_panic_with_hook
             at src/libstd/panicking.rs:482
   6: std::panicking::begin_panic
   7: rustc_errors::Handler::bug
   8: rustc::util::bug::opt_span_bug_fmt::{{closure}}
   9: rustc::ty::context::tls::with_opt::{{closure}}
  10: rustc::ty::context::tls::with_context_opt
  11: rustc::ty::context::tls::with_opt
  12: rustc::util::bug::opt_span_bug_fmt
  13: rustc::util::bug::bug_fmt
  14: <rustc_target::abi::call::FnType<'tcx, &'tcx rustc::ty::TyS<'tcx>> as rustc_codegen_llvm::abi::FnTypeExt<'tcx>>::new_vtable
  15: rustc_codegen_ssa::mir::block::<impl rustc_codegen_ssa::mir::FunctionCx<'a, 'tcx, Bx>>::codegen_terminator
  16: rustc_codegen_ssa::mir::codegen_mir
  17: rustc_codegen_ssa::base::codegen_instance
  18: rustc_codegen_ssa::mono_item::MonoItemExt::define
  19: rustc_codegen_llvm::base::compile_codegen_unit::module_codegen
  20: rustc::dep_graph::graph::DepGraph::with_task
  21: <rustc_codegen_llvm::LlvmCodegenBackend as rustc_codegen_ssa::traits::backend::ExtraBackendMethods>::compile_codegen_unit
  22: rustc_codegen_ssa::base::codegen_crate
  23: <rustc_codegen_llvm::LlvmCodegenBackend as rustc_codegen_utils::codegen_backend::CodegenBackend>::codegen_crate
  24: rustc_driver::driver::phase_4_codegen
  25: rustc_driver::driver::compile_input::{{closure}}
  26: <std::thread::local::LocalKey<T>>::with
  27: rustc::ty::context::TyCtxt::create_and_enter
  28: rustc_driver::driver::compile_input
  29: rustc_driver::run_compiler_with_pool
  30: <scoped_tls::ScopedKey<T>>::set
  31: rustc_driver::run_compiler
  32: <scoped_tls::ScopedKey<T>>::set
  33: syntax::with_globals
  34: __rust_maybe_catch_panic
             at src/libpanic_unwind/lib.rs:92
  35: <F as alloc::boxed::FnBox<A>>::call_box
  36: std::sys::unix::thread::Thread::new::thread_start
             at /rustc/b92552d5578e4544006da0dd5e793a19c2149321/src/liballoc/boxed.rs:744
             at src/libstd/sys_common/thread.rs:14
             at src/libstd/sys/unix/thread.rs:81
  37: start_thread
  38: __clone
query stack during panic:
end of query stack
error: aborting due to previous error


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 1.33.0-nightly (b92552d55 2019-01-06) 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

error: Could not compile `playground`.

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

[hellow554]

Reduced example

#![feature(unboxed_closures)]
#![feature(fn_traits)]

fn main() {
    let handlers: Option<Box<dyn for<'a> FnMut<&'a mut (), Output=()>>> = None;
    handlers.unwrap().as_mut().call_mut(&mut ());
}

[awaitlink]

Hmm, it seems like @cheblin has already filed this issue in #57404...

[hellow554]

Sorry :/