Empty enum breaks --target=asmjs-unknown-emscripten

[therustmonk]

This code breaks compiler (when enum doesn't have any variant):

extern crate domafic;

use domafic::{DomNode, KeyIter};
use domafic::web_render::{run, JsIo};
use domafic::tags::*;

struct State { }

impl State {
    fn new() -> Self { State { } }
}

enum Msg {
    //RemoveItToGetCompilerFail,
}

fn main() {
    let update = |state: &mut State, msg: Msg, keys: KeyIter, _: &JsIo<Msg>| { };
    let render = |state: &State| {  div(())  };
    run("body", update, render, State::new());
}

https://github.com/DenisKolodin/emcc-fail/blob/master/src/main.rs#L17

error: internal compiler error: /checkout/src/librustc_trans/mir/block.rs:631: trans_argument: OperandRef(Immediate(({ %"domafic::web_render::private::JsIo<Msg>"*, {}* }:{ %"domafic::web_render::private::JsIo<Msg>"*, {}* } undef)) @ TyLayout { ty: &domafic::web_render::JsIo<Msg>, details: LayoutDetails { variants: Single { index: 0 }, fields: Arbitrary { offsets: [Size { raw: 0 }, Size { raw: 4 }], memory_index: [0, 1] }, abi: ScalarPair(Scalar { value: Pointer, valid_range: 1..=4294967295 }, Scalar { value: Pointer, valid_range: 1..=4294967295 }), align: Align { abi: 2, pref: 3 }, size: Size { raw: 8 } } }) invalid for pair arugment

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 1.24.0-nightly (f8af59d95 2017-12-13) running on x86_64-unknown-linux-gnu

note: run with `RUST_BACKTRACE=1` for a backtrace

thread 'rustc' panicked at 'Box<Any>', /checkout/src/librustc_errors/lib.rs:501:8
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
stack backtrace:
   0: std::sys::unix::backtrace::tracing::imp::unwind_backtrace
             at /checkout/src/libstd/sys/unix/backtrace/tracing/gcc_s.rs:49
   1: std::sys_common::backtrace::print
             at /checkout/src/libstd/sys_common/backtrace.rs:68
             at /checkout/src/libstd/sys_common/backtrace.rs:57
   2: std::panicking::default_hook::{{closure}}
             at /checkout/src/libstd/panicking.rs:381
   3: std::panicking::default_hook
             at /checkout/src/libstd/panicking.rs:391
   4: std::panicking::rust_panic_with_hook
             at /checkout/src/libstd/panicking.rs:577
   5: std::panicking::begin_panic
   6: rustc_errors::Handler::bug
   7: <std::thread::local::LocalKey<T>>::with
   8: rustc::ty::context::tls::with_opt
   9: rustc::session::opt_span_bug_fmt
  10: rustc::session::bug_fmt
  11: rustc_trans::mir::block::<impl rustc_trans::mir::MirContext<'a, 'tcx>>::trans_argument
  12: rustc_trans::mir::block::<impl rustc_trans::mir::MirContext<'a, 'tcx>>::trans_terminator
  13: rustc_trans::mir::trans_mir
  14: rustc_trans::base::trans_instance
  15: rustc_trans::trans_item::TransItemExt::define
  16: rustc_trans::base::compile_codegen_unit
  17: rustc::ty::maps::<impl rustc::ty::maps::queries::compile_codegen_unit<'tcx>>::compute_result
  18: rustc::dep_graph::graph::DepGraph::with_task_impl
  19: rustc_errors::Handler::track_diagnostics
  20: rustc::ty::maps::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::cycle_check
  21: rustc::ty::maps::<impl rustc::ty::maps::queries::compile_codegen_unit<'tcx>>::force
  22: rustc::ty::maps::<impl rustc::ty::maps::queries::compile_codegen_unit<'tcx>>::try_get
  23: rustc::ty::maps::TyCtxtAt::compile_codegen_unit
  24: rustc::ty::maps::<impl rustc::ty::context::TyCtxt<'a, 'tcx, 'lcx>>::compile_codegen_unit
  25: rustc_trans::base::trans_crate
  26: <rustc_trans::LlvmTransCrate as rustc_trans_utils::trans_crate::TransCrate>::trans_crate
  27: rustc::util::common::time
  28: rustc_driver::driver::phase_4_translate_to_llvm
  29: rustc_driver::driver::compile_input::{{closure}}
  30: <std::thread::local::LocalKey<T>>::with
  31: <std::thread::local::LocalKey<T>>::with
  32: rustc::ty::context::TyCtxt::create_and_enter
  33: rustc_driver::driver::compile_input
  34: rustc_driver::run_compiler

error: Could not compile `emcc-fail`.

I use:
latest nightly: rustc 1.24.0-nightly (f8af59d 2017-12-13) running on x86_64-unknown-linux-gnu
cargo web: cargo-web 0.3.4 (koute/cargo-web@2bd88e8)
Emscripten: system change: 1.37.21|/usr/bin|4.0 vs 1.37.21

[glandium]

I got a similar crash while targetting x86-64 linux (not emscripten) in #48873, that went away after I filled my empty enums.

[lqd]

As @glandium mentions, this issue is not limited to asmjs, it also happens in another non-emscripten "duplicate" issue #50153.

[eddyb]

This will hopefully go away when #49298 is fixed.

[tlively]

@alexcrichton It sounds like this was not an Emscripten-specific bug after all, so it should probably be closed, especially now that #49298 is closed.

[alexcrichton]

👍