ICE in generator MIR generated by async/await

[cramertj]

Attempting to get a minimal repro-- I'll update the issue when I've gotten one.

error: internal compiler error: librustc_mir/transform/generator.rs:495: Broken MIR: generator contains type std::result::Result<(), futures::channel::mpsc::SendError> in MIR, but typeck only knows about for<'r, 's, 't0, 't1, 't2, 't3, 't4> {fn(std::iter::Rev<std::ops::RangeInclusive<u32>>) -> <std::iter::Rev<std::ops::RangeInclusive<u32>> as std::iter::IntoIterator>::IntoIter {<std::iter::Rev<std::ops::RangeInclusive<u32>> as std::iter::IntoIterator>::into_iter}, fn(u32, u32) -> std::ops::RangeInclusive<u32> {<std::ops::RangeInclusive<Idx>><u32>::new}, u32, std::ops::RangeInclusive<u32>, std::iter::Rev<std::ops::RangeInclusive<u32>>, futures::sink::Send<'r, futures::channel::mpsc::Sender<u32>>, std::mem::PinMut<'s, futures::sink::Send<'t0, futures::channel::mpsc::Sender<u32>>>, for<'t5, 't6> fn(&'t5 mut std::mem::PinMut<'t6, futures::sink::Send<'t1, futures::channel::mpsc::Sender<u32>>>) -> futures::Poll<<futures::sink::Send<'t1, futures::channel::mpsc::Sender<u32>> as futures::Future>::Output> {std::future::poll_in_task_cx::<futures::sink::Send<'t1, futures::channel::mpsc::Sender<u32>>>}, &'t2 mut std::mem::PinMut<'t3, futures::sink::Send<'t4, futures::channel::mpsc::Sender<u32>>>, futures::Poll<std::result::Result<(), futures::channel::mpsc::SendError>>, ()}
   --> futures-channel/tests/mpsc.rs:410:78
    |
410 |   async fn stress_poll_ready_sender(mut sender: mpsc::Sender<u32>, count: u32) {
    |  ______________________________________________________________________________^
411 | |     for i in (1..=count).rev() {
412 | |         assert!(await!(sender.send(i)).is_ok());
413 | |     }
414 | | }
    | |_^

thread 'main' panicked at 'Box<Any>', librustc_errors/lib.rs:499:9
stack backtrace:
   0: std::sys::unix::backtrace::tracing::imp::unwind_backtrace
             at libstd/sys/unix/backtrace/tracing/gcc_s.rs:49
   1: std::sys_common::backtrace::print
             at libstd/sys_common/backtrace.rs:71
             at libstd/sys_common/backtrace.rs:59
   2: std::panicking::default_hook::{{closure}}
             at libstd/panicking.rs:211
   3: std::panicking::default_hook
             at libstd/panicking.rs:227
   4: rustc::util::common::panic_hook
   5: std::panicking::rust_panic_with_hook
             at libstd/panicking.rs:515
   6: std::panicking::begin_panic
   7: rustc_errors::Handler::span_bug
   8: rustc::session::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::session::opt_span_bug_fmt
  13: rustc::session::span_bug_fmt
  14: <rustc_mir::transform::generator::StateTransform as rustc_mir::transform::MirPass>::run_pass
  15: rustc_mir::transform::optimized_mir::{{closure}}
  16: rustc_mir::transform::optimized_mir
  17: rustc::ty::query::__query_compute::optimized_mir
  18: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors<'tcx> for rustc::ty::query::queries::optimized_mir<'tcx>>::compute
  19: rustc::ty::context::tls::with_context
  20: rustc::dep_graph::graph::DepGraph::with_task_impl
  21: rustc::ty::context::tls::with_related_context
  22: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::force_query_with_job
  23: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::try_get_query
  24: rustc::ty::query::<impl rustc::ty::context::TyCtxt<'a, 'tcx, 'lcx>>::optimized_mir
  25: rustc_mir::shim::make_shim
  26: rustc::ty::query::__query_compute::mir_shims
  27: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors<'tcx> for rustc::ty::query::queries::mir_shims<'tcx>>::compute
  28: rustc::ty::context::tls::with_context
  29: rustc::dep_graph::graph::DepGraph::with_task_impl
  30: rustc::ty::context::tls::with_related_context
  31: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::force_query_with_job
  32: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::get_query
  33: rustc::ty::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::instance_mir
  34: rustc_mir::monomorphize::collector::collect_items_rec
  35: rustc_mir::monomorphize::collector::collect_items_rec
  36: rustc_mir::monomorphize::collector::collect_items_rec
  37: rustc_mir::monomorphize::collector::collect_items_rec
  38: rustc_mir::monomorphize::collector::collect_items_rec
  39: rustc_mir::monomorphize::collector::collect_items_rec
  40: rustc_mir::monomorphize::collector::collect_items_rec
  41: rustc_mir::monomorphize::collector::collect_items_rec
  42: rustc_mir::monomorphize::collector::collect_items_rec
  43: rustc_mir::monomorphize::collector::collect_items_rec
  44: rustc_mir::monomorphize::collector::collect_items_rec
  45: rustc_mir::monomorphize::collector::collect_items_rec
  46: rustc_mir::monomorphize::collector::collect_items_rec
  47: rustc_mir::monomorphize::collector::collect_items_rec
  48: rustc_mir::monomorphize::collector::collect_items_rec
  49: rustc_mir::monomorphize::collector::collect_items_rec
  50: rustc_mir::monomorphize::collector::collect_items_rec
  51: rustc_mir::monomorphize::collector::collect_items_rec
  52: rustc_mir::monomorphize::collector::collect_items_rec
  53: rustc_mir::monomorphize::collector::collect_crate_mono_items::{{closure}}
  54: rustc_mir::monomorphize::collector::collect_crate_mono_items
  55: rustc::util::common::time
  56: rustc_codegen_llvm::base::collect_and_partition_mono_items
  57: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors<'tcx> for rustc::ty::query::queries::collect_and_partition_mono_items<'tcx>>::compute
  58: rustc::ty::context::tls::with_context
  59: rustc::dep_graph::graph::DepGraph::with_task_impl
  60: rustc::ty::context::tls::with_related_context
  61: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::force_query_with_job
  62: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::get_query
  63: rustc_codegen_llvm::base::codegen_crate
  64: <rustc_codegen_llvm::LlvmCodegenBackend as rustc_codegen_utils::codegen_backend::CodegenBackend>::codegen_crate
  65: rustc::util::common::time
  66: rustc_driver::driver::phase_4_codegen
  67: rustc_driver::driver::compile_input::{{closure}}
  68: rustc::ty::context::tls::enter_context
  69: <std::thread::local::LocalKey<T>>::with
  70: rustc::ty::context::TyCtxt::create_and_enter
  71: rustc_driver::driver::compile_input
  72: rustc_driver::run_compiler_with_pool
  73: <scoped_tls::ScopedKey<T>>::set
  74: syntax::with_globals
  75: <std::panic::AssertUnwindSafe<F> as core::ops::function::FnOnce<()>>::call_once
  76: __rust_maybe_catch_panic
             at libpanic_unwind/lib.rs:105
  77: rustc_driver::run
  78: rustc_driver::main
  79: std::rt::lang_start::{{closure}}
  80: std::panicking::try::do_call
             at libstd/rt.rs:59
             at libstd/panicking.rs:310
  81: __rust_maybe_catch_panic
             at libpanic_unwind/lib.rs:105
  82: std::rt::lang_start_internal
             at libstd/panicking.rs:289
             at libstd/panic.rs:392
             at libstd/rt.rs:58
  83: main
  84: __libc_start_main
  85: <unknown>
query stack during panic:
#0 [optimized_mir] processing `stress_poll_ready_sender::{{closure}}`
#1 [mir_shims] generating MIR shim for `std::intrinsics::drop_in_place`
#2 [collect_and_partition_mono_items] collect_and_partition_mono_items
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 1.28.0-nightly (84804c387 2018-06-26) running on x86_64-unknown-linux-gnu

note: compiler flags: -C debuginfo=2 -C incremental

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

error: Could not compile `futures-channel`.

Prettier:

Broken MIR: generator contains type
std::result::Result<(), futures::channel::mpsc::SendError> in MIR, but typeck only knows about
for<'r, 's, 't0, 't1, 't2, 't3, 't4> {
    fn(std::iter::Rev<std::ops::RangeInclusive<u32>>) -> <std::iter::Rev<std::ops::RangeInclusive<u32>> 
        as std::iter::IntoIterator>::IntoIter {
            <std::iter::Rev<std::ops::RangeInclusive<u32>> as std::iter::IntoIterator>::into_iter
        },
    fn(u32, u32) -> std::ops::RangeInclusive<u32> {
        <std::ops::RangeInclusive<Idx>><u32>::new
    },
    u32,
    std::ops::RangeInclusive<u32>,
    std::iter::Rev<std::ops::RangeInclusive<u32>>,
    futures::sink::Send<'r, futures::channel::mpsc::Sender<u32>>,
    std::mem::PinMut<'s, futures::sink::Send<'t0, futures::channel::mpsc::Sender<u32>>>,
    for<'t5, 't6> fn(
        &'t5 mut std::mem::PinMut<'t6, futures::sink::Send<'t1, futures::channel::mpsc::Sender<u32>>>) -> 
            futures::Poll<<futures::sink::Send<'t1, futures::channel::mpsc::Sender<u32>> as futures::Future>::Output> {
                std::future::poll_in_task_cx::<futures::sink::Send<'t1, futures::channel::mpsc::Sender<u32>>>
            }, &'t2 mut std::mem::PinMut<'t3, futures::sink::Send<'t4, futures::channel::mpsc::Sender<u32>>>,
            futures::Poll<std::result::Result<(), futures::channel::mpsc::SendError>>, ()
}

cc @Zoxc

[Zoxc]

Possibly related to #49232

[cramertj]

Removing the outer assert!(....is_ok()) fixes the issue (just .is_ok() also triggers the ICE, as does assigning the result of the await! expression to a local variable), so it does seem to have something to do with the lifetimes of temporaries.

[DutchGhost]

might also be related to #50878

[MajorBreakfast]

I since added unwrap() after await!(), so that we don't get a warning. Surprisingly it compiles in that case.

https://github.com/rust-lang-nursery/futures-rs/blob/844a9202bf5f40a292dbc54cafe359666678f9f9/futures-channel/tests/mpsc.rs#L409-L415

[nikomatsakis]

@cramertj feels like they have not gotten this ICE in a long time. The original code no longer exists or at minimum is awkward to test now. We're going to close for now but maybe we'll see duplicates later on.