src/librustc_mir/transform/generator.rs:715: Broken MIR

[gila]

The minimal code that reproduces the issue:

#![feature(async_await)]
use futures::{executor::LocalPool, future, task::LocalSpawnExt};

async fn do_something(s: String) -> Result<String, String> {
    Ok(s)
}

async fn do_it() {
    for i in 0 ..= 3 {
        let s = format!("test-{}", i);
        let result = do_something(s).await;
        // when removing the dbg!() the code compiles 
        dbg!(result);
    }
}

#[test]
fn mir_error() {
    let mut p = LocalPool::new();
    let mut s = p.spawner();
    s.spawn_local(do_it()).unwrap();
    p.run_until_stalled();
}

Getting the following error:

  --> spdk-rs/tests/for.rs:8:18
   |
8  |   async fn do_it() {
   |  __________________^
9  | |     for i in 0 ..= 3 {
10 | |         let s = format!("test-{}", i);
11 | |         let result = do_something(s).await;
12 | |         dbg!(result);
13 | |     }
14 | | }
   | |_^

thread 'rustc' panicked at 'Box<Any>', src/librustc_errors/lib.rs:578:9
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>::force_query
  24: rustc::ty::query::plumbing::force_from_dep_node
  25: rustc::dep_graph::graph::DepGraph::try_mark_previous_green
  26: rustc::dep_graph::graph::DepGraph::try_mark_green
  27: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  28: <rustc::ty::layout::LayoutCx<rustc::ty::context::TyCtxt> as rustc_target::abi::LayoutOf>::layout_of
  29: <rustc_mir::transform::const_prop::ConstPropagator as rustc::mir::visit::MutVisitor>::visit_statement
  30: <rustc_mir::transform::const_prop::ConstProp as rustc_mir::transform::MirPass>::run_pass
  31: rustc_mir::transform::run_passes::{{closure}}
  32: rustc_mir::transform::run_passes
  33: rustc_mir::transform::optimized_mir
  34: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::optimized_mir>::compute
  35: rustc::dep_graph::graph::DepGraph::with_task_impl
  36: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  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_crate_mono_items::{{closure}}
  42: rustc::util::common::time
  43: rustc_mir::monomorphize::collector::collect_crate_mono_items
  44: rustc::util::common::time
  45: rustc_mir::monomorphize::partitioning::collect_and_partition_mono_items
  46: rustc::ty::query::__query_compute::collect_and_partition_mono_items
  47: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::collect_and_partition_mono_items>::compute
  48: rustc::dep_graph::graph::DepGraph::with_task_impl
  49: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  50: rustc_codegen_ssa::base::codegen_crate
  51: <rustc_codegen_llvm::LlvmCodegenBackend as rustc_codegen_utils::codegen_backend::CodegenBackend>::codegen_crate
  52: rustc::util::common::time
  53: rustc_interface::passes::start_codegen
  54: rustc::ty::context::tls::enter_global
  55: rustc_interface::passes::BoxedGlobalCtxt::access::{{closure}}
  56: rustc_interface::passes::create_global_ctxt::{{closure}}
  57: rustc_interface::passes::BoxedGlobalCtxt::enter
  58: rustc_interface::queries::Query<T>::compute
  59: rustc_interface::queries::<impl rustc_interface::interface::Compiler>::ongoing_codegen
  60: rustc_interface::interface::run_compiler_in_existing_thread_pool
  61: std::thread::local::LocalKey<T>::with
  62: scoped_tls::ScopedKey<T>::set
  63: 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 `do_it::{{closure}}#0`
#1 [layout_raw] computing layout of `[static generator@spdk-rs/tests/for.rs:8:18: 14:2 {fn(std::ops::RangeInclusive<i32>) -> <std::ops::RangeInclusive<i32> as std::iter::IntoIterator>::IntoIter {<std::ops::RangeInclusive<i32> as std::iter::IntoIterator>::into_iter}, fn(i32, i32) -> std::ops::RangeInclusive<i32> {std::ops::RangeInclusive::<i32>::new}, i32, std::ops::RangeInclusive<i32>, std::string::String, std::future::GenFuture<[static generator@spdk-rs/tests/for.rs:4:60: 6:2 s:std::string::String {}]>, ()}]`
#2 [optimized_mir] processing `do_it`
#3 [collect_and_partition_mono_items] collect_and_partition_mono_items
end of query stack

Meta

rustc 1.37.0-nightly (8aa42ed7c 2019-06-24)
binary: rustc
commit-hash: 8aa42ed7c2adb9f37faa6eb905f890f6199e1db9
commit-date: 2019-06-24
host: x86_64-unknown-linux-gnu
release: 1.37.0-nightly
LLVM version: 8.0

I think this might be somewhat related to #62025 and perhaps #61442 but i'll leave that to the experts.

[cramertj]

Fixed in #61872