Broken MIR: generator contains type std::vec::Vec<()>

[shiewa]

I tried this code:

#![feature(await_macro, async_await)]
#![recursion_limit = "128"]
pub const LIMIT: usize = 50;

#[runtime::main(runtime_tokio::Tokio)]
async fn main() {
            let text = "123\n456\n789";
            let lines = text.lines();

            for i in 0..(lines.size_hint().0 / LIMIT) {
                let mut futures = Vec::new();

                let ids = lines.clone().skip(i * LIMIT).take(LIMIT);
                for id in ids {
                    futures.push(scrape(id.to_string()));
                }

                futures::future::join_all(futures).await;
            }
}

async fn scrape(_line: String) {
    // do something
}

I get the following error:

error: internal compiler error: src/librustc_mir/transform/generator.rs:715: Broken MIR: generator contains type std::vec::Vec<()> in MIR, but typeck only knows about for<'r, 's, 't0, 't1, 't2> {&'r str, std::str::Lines<'s>, fn(std::ops::Range<usize>) -> <std::ops::Range<usize> as std::iter::IntoIterator>::IntoIter {<std::ops::Range<usize> as std::iter::IntoIterator>::into_iter}, usize, &'t0 std::str::Lines<'t1>, (usize, std::option::Option<usize>), std::ops::Range<usize>, std::vec::Vec<impl core::future::future::Future>, std::iter::Take<std::iter::Skip<std::str::Lines<'t2>>>, futures_util::future::join_all::JoinAll<impl core::future::future::Future>, ()}
 --> src/main.rs:5:1
  |
5 | #[runtime::main(runtime_tokio::Tokio)]
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

thread 'rustc' panicked at 'Box<Any>', src/librustc_errors/lib.rs:578:9
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace.
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 1.37.0-nightly (1d9981f04 2019-06-20) running on x86_64-unknown-linux-gnu

note: compiler flags: -C debuginfo=2 -C incremental --crate-type bin

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

error: Could not compile `example`.

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

Meta

Installed crates:

• runtime v0.3.0-alpha.5
• runtime-tokio v0.3.0-alpha.5
• futures-preview v0.3.0-alpha.16

rustc --version --verbose;

rustc 1.37.0-nightly (1d9981f04 2019-06-20)
binary: rustc
commit-hash: 1d9981f04e8957345205c07adc2742886420ac37
commit-date: 2019-06-20
host: x86_64-unknown-linux-gnu
release: 1.37.0-nightly
LLVM version: 8.0

Backtrace:

stack backtrace:
   0: backtrace::backtrace::libunwind::trace
             at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.29/src/backtrace/libunwind.rs:88
   1: backtrace::backtrace::trace_unsynchronized
             at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.29/src/backtrace/mod.rs:66
   2: std::sys_common::backtrace::_print
             at src/libstd/sys_common/backtrace.rs:47
   3: std::sys_common::backtrace::print
             at src/libstd/sys_common/backtrace.rs:36
   4: std::panicking::default_hook::{{closure}}
             at src/libstd/panicking.rs:198
   5: std::panicking::default_hook
             at src/libstd/panicking.rs:212
   6: rustc::util::common::panic_hook
   7: std::panicking::rust_panic_with_hook
             at src/libstd/panicking.rs:479
   8: std::panicking::begin_panic
   9: rustc_errors::Handler::span_bug
  10: rustc::util::bug::opt_span_bug_fmt::{{closure}}
  11: rustc::ty::context::tls::with_opt::{{closure}}
  12: rustc::ty::context::tls::with_context_opt
  13: rustc::ty::context::tls::with_opt
  14: rustc::util::bug::opt_span_bug_fmt
  15: rustc::util::bug::span_bug_fmt
  16: rustc_mir::transform::generator::compute_layout
  17: <rustc_mir::transform::generator::StateTransform as rustc_mir::transform::MirPass>::run_pass
  18: rustc_mir::transform::run_passes::{{closure}}
  19: rustc_mir::transform::run_passes
  20: rustc_mir::transform::optimized_mir
  21: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::optimized_mir>::compute
  22: rustc::dep_graph::graph::DepGraph::with_task_impl
  23: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  24: rustc::ty::layout::LayoutCx<rustc::ty::context::TyCtxt>::layout_raw_uncached
  25: rustc::ty::layout::layout_raw
  26: rustc::ty::query::__query_compute::layout_raw
  27: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::layout_raw>::compute
  28: rustc::dep_graph::graph::DepGraph::with_task_impl
  29: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  30: <rustc::ty::layout::LayoutCx<rustc::ty::context::TyCtxt> as rustc_target::abi::LayoutOf>::layout_of
  31: <&mut I as core::iter::traits::iterator::Iterator>::next
  32: <alloc::vec::Vec<T> as alloc::vec::SpecExtend<T,I>>::from_iter
  33: <alloc::vec::Vec<T> as alloc::vec::SpecExtend<T,I>>::from_iter
  34: rustc::ty::layout::LayoutCx<rustc::ty::context::TyCtxt>::layout_raw_uncached
  35: rustc::ty::layout::layout_raw
  36: rustc::ty::query::__query_compute::layout_raw
  37: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::layout_raw>::compute
  38: rustc::dep_graph::graph::DepGraph::with_task_impl
  39: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  40: <rustc::ty::layout::LayoutCx<rustc::ty::context::TyCtxt> as rustc_target::abi::LayoutOf>::layout_of
  41: <&mut I as core::iter::traits::iterator::Iterator>::next
  42: <alloc::vec::Vec<T> as alloc::vec::SpecExtend<T,I>>::from_iter
  43: <&mut I as core::iter::traits::iterator::Iterator>::next
  44: <alloc::vec::Vec<T> as alloc::vec::SpecExtend<T,I>>::from_iter
  45: rustc::ty::layout::LayoutCx<rustc::ty::context::TyCtxt>::layout_raw_uncached
  46: rustc::ty::layout::layout_raw
  47: rustc::ty::query::__query_compute::layout_raw
  48: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::layout_raw>::compute
  49: rustc::dep_graph::graph::DepGraph::with_task_impl
  50: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  51: <rustc::ty::layout::LayoutCx<rustc::ty::context::TyCtxt> as rustc_target::abi::LayoutOf>::layout_of
  52: <rustc_mir::transform::const_prop::ConstPropagator as rustc::mir::visit::MutVisitor>::visit_statement
  53: <rustc_mir::transform::const_prop::ConstProp as rustc_mir::transform::MirPass>::run_pass
  54: rustc_mir::transform::run_passes::{{closure}}
  55: rustc_mir::transform::run_passes
  56: rustc_mir::transform::optimized_mir
  57: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::optimized_mir>::compute
  58: rustc::dep_graph::graph::DepGraph::with_task_impl
  59: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  60: rustc_mir::monomorphize::collector::collect_items_rec
  61: rustc_mir::monomorphize::collector::collect_crate_mono_items::{{closure}}
  62: rustc::util::common::time
  63: rustc_mir::monomorphize::collector::collect_crate_mono_items
  64: rustc::util::common::time
  65: rustc_mir::monomorphize::partitioning::collect_and_partition_mono_items
  66: rustc::ty::query::__query_compute::collect_and_partition_mono_items
  67: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::collect_and_partition_mono_items>::compute
  68: rustc::dep_graph::graph::DepGraph::with_task_impl
  69: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  70: rustc_codegen_ssa::base::codegen_crate
  71: <rustc_codegen_llvm::LlvmCodegenBackend as rustc_codegen_utils::codegen_backend::CodegenBackend>::codegen_crate
  72: rustc::util::common::time
  73: rustc_interface::passes::start_codegen
  74: rustc::ty::context::tls::enter_global
  75: rustc_interface::passes::BoxedGlobalCtxt::access::{{closure}}
  76: rustc_interface::passes::create_global_ctxt::{{closure}}
  77: rustc_interface::passes::BoxedGlobalCtxt::enter
  78: rustc_interface::queries::Query<T>::compute
  79: rustc_interface::queries::<impl rustc_interface::interface::Compiler>::ongoing_codegen
  80: rustc_interface::interface::run_compiler_in_existing_thread_pool
  81: std::thread::local::LocalKey<T>::with
  82: scoped_tls::ScopedKey<T>::set
  83: syntax::with_globals
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
query stack during panic:
#0 [optimized_mir] processing `main::main::{{closure}}#0`
#1 [layout_raw] computing layout of `[static generator@src/main.rs:5:1: 5:39 for<'r, 's, 't0, 't1, 't2> {&'r str, std::str::Lines<'s>, fn(std::ops::Range<usize>) -> <std::ops::Range<usize> as std::iter::IntoIterator>::IntoIter {<std::ops::Range<usize> as std::iter::IntoIterator>::into_iter}, usize, &'t0 std::str::Lines<'t1>, (usize, std::option::Option<usize>), std::ops::Range<usize>, std::vec::Vec<std::future::GenFuture<[static generator@src/main.rs:22:32: 24:2 _line:std::string::String {}]>>, std::iter::Take<std::iter::Skip<std::str::Lines<'t2>>>, futures_util::future::join_all::JoinAll<std::future::GenFuture<[static generator@src/main.rs:22:32: 24:2 _line:std::string::String {}]>>, ()}]`
#2 [layout_raw] computing layout of `std::future::GenFuture<[static generator@src/main.rs:5:1: 5:39 for<'r, 's, 't0, 't1, 't2> {&'r str, std::str::Lines<'s>, fn(std::ops::Range<usize>) -> <std::ops::Range<usize> as std::iter::IntoIterator>::IntoIter {<std::ops::Range<usize> as std::iter::IntoIterator>::into_iter}, usize, &'t0 std::str::Lines<'t1>, (usize, std::option::Option<usize>), std::ops::Range<usize>, std::vec::Vec<std::future::GenFuture<[static generator@src/main.rs:22:32: 24:2 _line:std::string::String {}]>>, std::iter::Take<std::iter::Skip<std::str::Lines<'t2>>>, futures_util::future::join_all::JoinAll<std::future::GenFuture<[static generator@src/main.rs:22:32: 24:2 _line:std::string::String {}]>>, ()}]>`
#3 [layout_raw] computing layout of `[static generator@src/main.rs:5:1: 5:39 {std::future::GenFuture<[static generator@src/main.rs:5:1: 5:39 for<'r, 's, 't0, 't1, 't2> {&'r str, std::str::Lines<'s>, fn(std::ops::Range<usize>) -> <std::ops::Range<usize> as std::iter::IntoIterator>::IntoIter {<std::ops::Range<usize> as std::iter::IntoIterator>::into_iter}, usize, &'t0 std::str::Lines<'t1>, (usize, std::option::Option<usize>), std::ops::Range<usize>, std::vec::Vec<std::future::GenFuture<[static generator@src/main.rs:22:32: 24:2 _line:std::string::String {}]>>, std::iter::Take<std::iter::Skip<std::str::Lines<'t2>>>, futures_util::future::join_all::JoinAll<std::future::GenFuture<[static generator@src/main.rs:22:32: 24:2 _line:std::string::String {}]>>, ()}]>, ()}]`
#4 [optimized_mir] processing `main`
#5 [collect_and_partition_mono_items] collect_and_partition_mono_items
end of query stack```

[mati865]

Probably duplicate of #61442

[nikomatsakis]

Does this still reproduce?

[zimond]

Using 2019-06-25 after #61442 , still reproduce

[mati865]

@zimond the fix landed in 2019-06-26 nightly. Could you try that version?

[zimond]

@mati865 The latest nightly is 2019-06-25 with commit tag 5f9c044

[zimond]

and I just tested #62126, it's still broken.

[mati865]

@zimond it can be a bit confusing because when you install nightly-2019-06-25 you will get rustc 1.37.0-nightly (8aa42ed7c 2019-06-24). In parentheses you can see included commits date, not nightly version.
At the moment rustup toolchain install nightly is the same as rustup toolchain install nightly-2019-06-26.

Back to the issue, I confirm it has been fixed on the master by #61872. Fix will be available in tomorrows nightly.

[zimond]

Yeah.. I just saw the commit log after commenting this. It's indeed fixed, cheers.