MIR: End-user description not implemented for field access on TyGenerator....

[thedodd]

Using nightly. Decent number of features enabled. Using futures-await. Attempting to use map_err on the result coming out of a call to await! seems to cause a panic.

code

Working code:

    #[async]
    fn _post(mut state: State) -> Result<(State, Response), (State, HandlerError)> {
        let body_res = await!(Body::take_from(&mut state).concat2());
        let body = match body_res {
            Ok(body) => body.to_vec(),
            Err(err) => {
                return Err((state, err.into_handler_error()));
            }
        };

        let res = create_response(&state, StatusCode::Ok, Some((body, mime::APPLICATION_JSON)));
        Ok((state, res))
    }

Broken code:

    #[async]
    fn _post(mut state: State) -> Result<(State, Response), (State, HandlerError)> {
        let body = await!(Body::take_from(&mut state).concat2())
            .map(|chunks| chunks.to_vec())
            .map_err(|err| (state, err.into_handler_error()))?;

        let res = create_response(&state, StatusCode::Ok, Some((body, mime::APPLICATION_JSON)));
        Ok((state, res))
    }

Let me know if adding any additional type info here would be helpful.

expectations

I expected to have the code successfully compile and be the same as the working code block.

Instead, got a panic during compilation.

meta

Nightly features:

#![feature(conservative_impl_trait, generators, nll, proc_macro, universal_impl_trait, use_nested_groups)]

rustc info:

$ rustc --version --verbose
rustc 1.25.0-nightly (a0dcecff9 2018-01-24)
binary: rustc
commit-hash: a0dcecff90c45ad5d4eb60859e22bb3f1b03842a
commit-date: 2018-01-24
host: x86_64-apple-darwin
release: 1.25.0-nightly
LLVM version: 4.0

Backtrace:

error: internal compiler error: librustc_mir/borrow_check/error_reporting.rs:762: End-user description not implemented for field access on `TyGenerator(DefId(0/1:49 ~ gateway_service[ace7]::service[0]::{{impl}}[0]::_post[0]::{{closure}}[0]), ClosureSubsts { substs: Slice([futures::Async<futures::__rt::Mu>, std::result::Result<(gotham::state::State, hyper::Response), (gotham::state::State, gotham::handler::HandlerError)>, gotham::state::State]) }, GeneratorInterior { witness: {futures::stream::Concat2<hyper::Body>, futures::Async<futures::__rt::Mu>, (), std::vec::Vec<u8>, std::result::Result<(gotham::state::State, hyper::Response), (gotham::state::State, gotham::handler::HandlerError)>}, movable: true })`

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 1.25.0-nightly (a0dcecff9 2018-01-24) running on x86_64-apple-darwin

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

thread 'rustc' panicked at 'Box<Any>', librustc_errors/lib.rs:509:9
stack backtrace:
   0:        0x10a383eab - std::sys::unix::backtrace::tracing::imp::unwind_backtrace::ha9efc95a1760cacd
   1:        0x10a390044 - std::sys_common::backtrace::print::hf5c8aa5eb53db16a
   2:        0x10a3836e0 - std::panicking::default_hook::{{closure}}::hdce9608c60053b8f
   3:        0x10a3833e3 - std::panicking::default_hook::hba09553cc28730a2
   4:        0x10a383b66 - std::panicking::rust_panic_with_hook::h3639511a0c7cb848
   5:        0x1063bcbfa - std::panicking::begin_panic::h635ae642d665c620
   6:        0x1063d287c - rustc_errors::Handler::bug::hbe64a18383da6dc4
   7:        0x1091c39cb - <std::thread::local::LocalKey<T>>::with::h541fcea574b37332
   8:        0x109665bd5 - rustc::ty::context::tls::with_opt::hcf7b444f3a2040d7
   9:        0x109248f37 - rustc::session::opt_span_bug_fmt::h78c03a1ab5eaf5a1
  10:        0x109248e01 - rustc::session::bug_fmt::h3fe1e243a47291cd
  11:        0x1055c8ea1 - rustc_mir::borrow_check::error_reporting::<impl rustc_mir::borrow_check::MirBorrowckCtxt<'cx, 'gcx, 'tcx>>::describe_field_from_ty::h49a8c174a0cb9b6c
  12:        0x1055c8a2a - rustc_mir::borrow_check::error_reporting::<impl rustc_mir::borrow_check::MirBorrowckCtxt<'cx, 'gcx, 'tcx>>::describe_field::h78965fd178f95d79
  13:        0x1055c8404 - rustc_mir::borrow_check::error_reporting::<impl rustc_mir::borrow_check::MirBorrowckCtxt<'cx, 'gcx, 'tcx>>::append_place_to_string::h8f79ea72234925a0
  14:        0x1055c5c7c - rustc_mir::borrow_check::error_reporting::<impl rustc_mir::borrow_check::MirBorrowckCtxt<'cx, 'gcx, 'tcx>>::report_use_of_moved_or_uninitialized::hc1998dae45d582c0
  15:        0x1055d12b4 - rustc_mir::borrow_check::MirBorrowckCtxt::check_if_path_is_moved::h6b5e4bc029599395
  16:        0x1055ce35f - <rustc_mir::borrow_check::MirBorrowckCtxt<'cx, 'gcx, 'tcx> as rustc_mir::dataflow::DataflowResultsConsumer<'cx, 'tcx>>::visit_statement_entry::h62ebb1b4fffdcc55
  17:        0x1055cd67d - rustc_mir::borrow_check::do_mir_borrowck::hc1e7f5ca4c20578f
  18:        0x1055efc9b - rustc::ty::context::tls::enter::h1443e4f51080c1ab
  19:        0x10567c795 - rustc::infer::InferCtxtBuilder::enter::h3665c5dd412e5fd6
  20:        0x1055cc726 - rustc_mir::borrow_check::mir_borrowck::h5a5cf133637a758c
  21:        0x10942b303 - rustc::ty::maps::<impl rustc::ty::maps::queries::mir_borrowck<'tcx>>::compute_result::h8ce26d29167e8c3d
  22:        0x109500e96 - rustc::dep_graph::graph::DepGraph::with_task_impl::h92c13dbcd115d438
  23:        0x1091aa3be - rustc_errors::Handler::track_diagnostics::hc789be56ee0e16d2
  24:        0x109059cc3 - rustc::ty::maps::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::cycle_check::h62b3bfc64dcc5416
  25:        0x10942b394 - rustc::ty::maps::<impl rustc::ty::maps::queries::mir_borrowck<'tcx>>::force::h8f25e18a8c999fcc
  26:        0x109145fd9 - rustc::ty::maps::plumbing::force_from_dep_node::hd09e3b3c2deab39c
  27:        0x10952885f - rustc::dep_graph::graph::DepGraph::try_mark_green::hd9972ee6c4efc24b
  28:        0x109090eb2 - rustc::ty::maps::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::try_mark_green_and_read::ha976c0deb96cdb31
  29:        0x10941c4df - rustc::ty::maps::<impl rustc::ty::maps::queries::optimized_mir<'tcx>>::try_get::h74325177e7bc3dde
  30:        0x1095935e0 - rustc::ty::maps::TyCtxtAt::optimized_mir::he2f762eeb346da9e
  31:        0x109585033 - rustc::ty::sty::ClosureSubsts::field_tys::ha48451c7a027a51d
  32:        0x1056db3ea - rustc_mir::borrow_check::nll::type_check::TypeChecker::typeck_mir::hc7ad7a734db20202
  33:        0x1056d180d - rustc_mir::borrow_check::nll::type_check::type_check_internal::h518be4c3ad2ff3e9
  34:        0x1055f0faf - rustc::ty::context::tls::enter::h4236a27145a73016
  35:        0x10567c87f - rustc::infer::InferCtxtBuilder::enter::h600f468bc4789a28
  36:        0x1056de262 - <rustc_mir::borrow_check::nll::type_check::TypeckMir as rustc_mir::transform::MirPass>::run_pass::hadea65a31f93be35
  37:        0x1055e6c29 - rustc_mir::transform::mir_const::{{closure}}::h02e1b3b2b7d7b18f
  38:        0x1055e3fe8 - rustc_mir::transform::mir_const::hcc025ad467878db2
  39:        0x10941958b - rustc::ty::maps::<impl rustc::ty::maps::queries::mir_const<'tcx>>::compute_result::hbd8b9fd9e305d39f
  40:        0x1095146d7 - rustc::dep_graph::graph::DepGraph::with_task_impl::hee66bf436686dd4d
  41:        0x1091a72a9 - rustc_errors::Handler::track_diagnostics::hb5f11d2f9ffb02ae
  42:        0x109081070 - rustc::ty::maps::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::cycle_check::hd8ac9f49c4833a46
  43:        0x109419617 - rustc::ty::maps::<impl rustc::ty::maps::queries::mir_const<'tcx>>::force::h9d74c11776eebafb
  44:        0x109419d3c - rustc::ty::maps::<impl rustc::ty::maps::queries::mir_const<'tcx>>::try_get::h04568e10b15c7ebb
  45:        0x109593400 - rustc::ty::maps::TyCtxtAt::mir_const::hd2755156a7dbf95d
  46:        0x1090a10a3 - rustc::ty::maps::<impl rustc::ty::context::TyCtxt<'a, 'tcx, 'lcx>>::mir_const::h927c411a4f7efbe1
  47:        0x1055e41c2 - rustc_mir::transform::mir_validated::h94b6df5bcb6c3001
  48:        0x10941aa6b - rustc::ty::maps::<impl rustc::ty::maps::queries::mir_validated<'tcx>>::compute_result::hfe06032d6b01c5d6
  49:        0x1095146d7 - rustc::dep_graph::graph::DepGraph::with_task_impl::hee66bf436686dd4d
  50:        0x109194709 - rustc_errors::Handler::track_diagnostics::h6906f37a714bb65d
  51:        0x109063140 - rustc::ty::maps::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::cycle_check::h82a8367f44bba970
  52:        0x10941aaf7 - rustc::ty::maps::<impl rustc::ty::maps::queries::mir_validated<'tcx>>::force::ha7aa7d5f7e14a50f
  53:        0x10941b21c - rustc::ty::maps::<impl rustc::ty::maps::queries::mir_validated<'tcx>>::try_get::h1ac5c2c13a2a5e42
  54:        0x1095934f0 - rustc::ty::maps::TyCtxtAt::mir_validated::hab2b7cdf300d8bf0
  55:        0x1090a10d3 - rustc::ty::maps::<impl rustc::ty::context::TyCtxt<'a, 'tcx, 'lcx>>::mir_validated::he7d8147885139b09
  56:        0x1054b0e4b - rustc_borrowck::borrowck::borrowck::hb6f9751697f3d9f3
  57:        0x10950d7e7 - rustc::dep_graph::graph::DepGraph::with_task_impl::hc5e17307633b35cd
  58:        0x109181f09 - rustc_errors::Handler::track_diagnostics::h1a92dd5f67bcfba5
  59:        0x10906cbb0 - rustc::ty::maps::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::cycle_check::h9ecc5cf53eea6ba4
  60:        0x109429bc7 - rustc::ty::maps::<impl rustc::ty::maps::queries::borrowck<'tcx>>::force::h903403cccee498b4
  61:        0x10942a2ba - rustc::ty::maps::<impl rustc::ty::maps::queries::borrowck<'tcx>>::try_get::h576007b4b6c14f04
  62:        0x109593f42 - rustc::ty::maps::TyCtxtAt::borrowck::hd0c291eb8466ca41
  63:        0x1090a1313 - rustc::ty::maps::<impl rustc::ty::context::TyCtxt<'a, 'tcx, 'lcx>>::borrowck::h5cd5e26d06dfab2e
  64:        0x1054b0bc1 - rustc_borrowck::borrowck::check_crate::h000dc470c6e4e6db
  65:        0x103f6fb98 - <std::thread::local::LocalKey<T>>::with::hc97c0f695fc47a37
  66:        0x103f6d1ec - <std::thread::local::LocalKey<T>>::with::h5232c8db13d095a5
  67:        0x103f9b3e3 - rustc_driver::driver::compile_input::h13c6388277ea77a3
  68:        0x103fac17c - rustc_driver::run_compiler::hebc5d6e3e17d092c
  69:        0x103f2a2d1 - std::sys_common::backtrace::__rust_begin_short_backtrace::he16271a6bff11c29
  70:        0x10a3b2fbe - __rust_maybe_catch_panic
  71:        0x103ededdd - <F as alloc::boxed::FnBox<A>>::call_box::h838126c6997c937c
  72:        0x10a392a67 - std::sys_common::thread::start_thread::hee6a12d8ac7037fd
  73:        0x10a39eda8 - std::sys::unix::thread::Thread::new::thread_start::hca6ddd0e0fdf932d
  74:     0x7fff6b51d6c0 - _pthread_body
  75:     0x7fff6b51d56c - _pthread_start