ICE when using Matching, Async and Indexing

[VincentWo]

Code

enum Status {
    SystemOutage { issue_id: u32 },
}

#[tokio::main]
async fn main() {
    let issues: tokio::sync::RwLock<Vec<bool>> = Default::default();

    let closure = |status: Status| {
            async move {
                match status {
                    Status::SystemOutage { issue_id }
                        if issues.read().await[issue_id as usize] => {}
                    _ => {
                        // Do nothing;
                    }
                }
            }
        };
    closure(Status::SystemOutage { issue_id: 1 }).await;
}

Meta

rustc --version --verbose:

rustc 1.49.0-nightly (ffa2e7ae8 2020-10-24)
binary: rustc
commit-hash: ffa2e7ae8fbf9badc035740db949b9dae271c29f
commit-date: 2020-10-24
host: x86_64-unknown-linux-gnu
release: 1.49.0-nightly
LLVM version: 11.0

Error output

   Compiling system_change v0.1.0 (/home/perikles/programming/system_change_ice)
error: internal compiler error: compiler/rustc_mir/src/transform/generator.rs:751:13: Broken MIR: generator contains type &u32 in MIR, but typeck only knows about for<'r, 's, 't0> {ResumeTy, Status, u32, &'r tokio::sync::RwLock<Vec<bool>>, tokio::sync::RwLock<Vec<bool>>, impl std::future::Future, ()}
  --> src/main.rs:10:24
   |
10 |               async move {
   |  ________________________^
11 | |                 match status {
12 | |                     Status::SystemOutage { issue_id }
13 | |                         if issues.read().await[issue_id as usize] => {}
...  |
17 | |                 }
18 | |             }
   | |_____________^

thread 'rustc' panicked at 'Box<Any>', /rustc/ffa2e7ae8fbf9badc035740db949b9dae271c29f/compiler/rustc_errors/src/lib.rs:891:9
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

note: the compiler unexpectedly panicked. this is a bug.

note: we would appreciate a bug report: https://github.com/rust-lang/rust/issues/new?labels=C-bug%2C+I-ICE%2C+T-compiler&template=ice.md

note: rustc 1.49.0-nightly (ffa2e7ae8 2020-10-24) running on x86_64-unknown-linux-gnu

note: compiler flags: -C embed-bitcode=no -C debuginfo=2 -C incremental --crate-type bin

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

query stack during panic:
#0 [optimized_mir] optimizing MIR for `main::{closure#0}::{closure#0}::{closure#0}`
#1 [layout_raw] computing layout of `[static generator@src/main.rs:10:24: 18:14 for<'r, 's> {std::future::ResumeTy, Status, u32, &'r tokio::sync::RwLock<std::vec::Vec<bool>>, tokio::sync::RwLock<std::vec::Vec<bool>>, std::future::from_generator::GenFuture<[static generator@tokio::sync::RwLock::<T>::read::{closure#0} for<'t0, 't1> {std::future::ResumeTy, &'t0 tokio::sync::RwLock<std::vec::Vec<bool>>, u16, std::future::from_generator::GenFuture<[static generator@tokio::sync::rwlock::ReleasingPermit::<'a, T>::acquire::{closure#0} for<'t2, 't3, 't4> {std::future::ResumeTy, &'t2 tokio::sync::RwLock<std::vec::Vec<bool>>, u16, tokio::sync::RwLock<std::vec::Vec<bool>>, &'t3 tokio::sync::batch_semaphore::Semaphore, tokio::sync::batch_semaphore::Semaphore, u32, tokio::sync::batch_semaphore::Acquire<'t4>, ()}]>, ()}]>, ()}]`
end of query stack
error: aborting due to previous error

error: could not compile `system_change`

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

Backtrace

   Compiling system_change v0.1.0 (/home/perikles/programming/system_change_ice)
error: internal compiler error: compiler/rustc_mir/src/transform/generator.rs:751:13: Broken MIR: generator contains type &u32 in MIR, but typeck only knows about for<'r, 's, 't0> {ResumeTy, Status, u32, &'r tokio::sync::RwLock<Vec<bool>>, tokio::sync::RwLock<Vec<bool>>, impl std::future::Future, ()}
  --> src/main.rs:10:24
   |
10 |               async move {
   |  ________________________^
11 | |                 match status {
12 | |                     Status::SystemOutage { issue_id }
13 | |                         if issues.read().await[issue_id as usize] => {}
...  |
17 | |                 }
18 | |             }
   | |_____________^

thread 'rustc' panicked at 'Box<Any>', /rustc/ffa2e7ae8fbf9badc035740db949b9dae271c29f/compiler/rustc_errors/src/lib.rs:891:9
stack backtrace:
   0: std::panicking::begin_panic
   1: rustc_errors::HandlerInner::span_bug
   2: rustc_errors::Handler::span_bug
   3: rustc_middle::util::bug::opt_span_bug_fmt::{{closure}}
   4: rustc_middle::ty::context::tls::with_opt::{{closure}}
   5: rustc_middle::ty::context::tls::with_opt
   6: rustc_middle::util::bug::opt_span_bug_fmt
   7: rustc_middle::util::bug::span_bug_fmt
   8: <rustc_mir::transform::generator::StateTransform as rustc_mir::transform::MirPass>::run_pass
   9: rustc_mir::transform::run_passes
  10: rustc_mir::transform::run_optimization_passes
  11: rustc_mir::transform::optimized_mir
  12: rustc_middle::dep_graph::<impl rustc_query_system::dep_graph::DepKind for rustc_middle::dep_graph::dep_node::DepKind>::with_deps
  13: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  14: rustc_data_structures::stack::ensure_sufficient_stack
  15: rustc_query_system::query::plumbing::get_query_impl
  16: rustc_middle::ty::layout::LayoutCx<rustc_middle::ty::context::TyCtxt>::layout_raw_uncached
  17: rustc_middle::ty::layout::layout_raw
  18: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::layout_raw>::compute
  19: rustc_middle::dep_graph::<impl rustc_query_system::dep_graph::DepKind for rustc_middle::dep_graph::dep_node::DepKind>::with_deps
  20: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  21: rustc_data_structures::stack::ensure_sufficient_stack
  22: rustc_query_system::query::plumbing::get_query_impl
  23: <rustc_middle::ty::layout::LayoutCx<rustc_middle::ty::context::TyCtxt> as rustc_target::abi::LayoutOf>::layout_of
  24: <alloc::vec::Vec<T> as alloc::vec::SpecFromIter<T,I>>::from_iter
  25: <core::iter::adapters::ResultShunt<I,E> as core::iter::traits::iterator::Iterator>::next
  26: <alloc::vec::Vec<T> as alloc::vec::SpecFromIter<T,I>>::from_iter
  27: rustc_middle::ty::layout::LayoutCx<rustc_middle::ty::context::TyCtxt>::layout_raw_uncached
  28: rustc_middle::ty::layout::layout_raw
  29: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::layout_raw>::compute
  30: rustc_middle::dep_graph::<impl rustc_query_system::dep_graph::DepKind for rustc_middle::dep_graph::dep_node::DepKind>::with_deps
  31: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  32: rustc_data_structures::stack::ensure_sufficient_stack
  33: rustc_query_system::query::plumbing::get_query_impl
  34: <rustc_middle::ty::layout::LayoutCx<rustc_middle::ty::context::TyCtxt> as rustc_target::abi::LayoutOf>::layout_of
  35: <alloc::vec::Vec<T> as alloc::vec::SpecFromIter<T,I>>::from_iter
  36: <core::iter::adapters::ResultShunt<I,E> as core::iter::traits::iterator::Iterator>::next
  37: <alloc::vec::Vec<T> as alloc::vec::SpecFromIter<T,I>>::from_iter
  38: rustc_middle::ty::layout::LayoutCx<rustc_middle::ty::context::TyCtxt>::layout_raw_uncached
  39: rustc_middle::ty::layout::layout_raw
  40: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::layout_raw>::compute
  41: rustc_middle::dep_graph::<impl rustc_query_system::dep_graph::DepKind for rustc_middle::dep_graph::dep_node::DepKind>::with_deps
  42: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  43: rustc_data_structures::stack::ensure_sufficient_stack
  44: rustc_query_system::query::plumbing::get_query_impl
  45: <rustc_middle::ty::layout::LayoutCx<rustc_middle::ty::context::TyCtxt> as rustc_target::abi::LayoutOf>::layout_of
  46: <alloc::vec::Vec<T> as alloc::vec::SpecFromIter<T,I>>::from_iter
  47: <core::iter::adapters::ResultShunt<I,E> as core::iter::traits::iterator::Iterator>::next
  48: <alloc::vec::Vec<T> as alloc::vec::SpecFromIter<T,I>>::from_iter
  49: rustc_middle::ty::layout::LayoutCx<rustc_middle::ty::context::TyCtxt>::layout_raw_uncached
  50: rustc_middle::ty::layout::layout_raw
  51: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::layout_raw>::compute
  52: rustc_middle::dep_graph::<impl rustc_query_system::dep_graph::DepKind for rustc_middle::dep_graph::dep_node::DepKind>::with_deps
  53: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  54: rustc_data_structures::stack::ensure_sufficient_stack
  55: rustc_query_system::query::plumbing::get_query_impl
  56: <rustc_middle::ty::layout::LayoutCx<rustc_middle::ty::context::TyCtxt> as rustc_target::abi::LayoutOf>::layout_of
  57: <core::iter::adapters::Map<I,F> as core::iter::traits::iterator::Iterator>::try_fold
  58: <core::iter::adapters::chain::Chain<A,B> as core::iter::traits::iterator::Iterator>::try_fold
  59: <alloc::vec::Vec<T> as alloc::vec::SpecFromIter<T,I>>::from_iter
  60: rustc_middle::ty::layout::LayoutCx<rustc_middle::ty::context::TyCtxt>::layout_raw_uncached
  61: rustc_middle::ty::layout::layout_raw
  62: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::layout_raw>::compute
  63: rustc_middle::dep_graph::<impl rustc_query_system::dep_graph::DepKind for rustc_middle::dep_graph::dep_node::DepKind>::with_deps
  64: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  65: rustc_data_structures::stack::ensure_sufficient_stack
  66: rustc_query_system::query::plumbing::get_query_impl
  67: <rustc_middle::ty::layout::LayoutCx<rustc_middle::ty::context::TyCtxt> as rustc_target::abi::LayoutOf>::layout_of
  68: <alloc::vec::Vec<T> as alloc::vec::SpecFromIter<T,I>>::from_iter
  69: <core::iter::adapters::ResultShunt<I,E> as core::iter::traits::iterator::Iterator>::next
  70: <alloc::vec::Vec<T> as alloc::vec::SpecFromIter<T,I>>::from_iter
  71: rustc_middle::ty::layout::LayoutCx<rustc_middle::ty::context::TyCtxt>::layout_raw_uncached
  72: rustc_middle::ty::layout::layout_raw
  73: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::layout_raw>::compute
  74: rustc_middle::dep_graph::<impl rustc_query_system::dep_graph::DepKind for rustc_middle::dep_graph::dep_node::DepKind>::with_deps
  75: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  76: rustc_data_structures::stack::ensure_sufficient_stack
  77: rustc_query_system::query::plumbing::get_query_impl
  78: <rustc_middle::ty::layout::LayoutCx<rustc_middle::ty::context::TyCtxt> as rustc_target::abi::LayoutOf>::layout_of
  79: <rustc_mir::transform::const_prop::ConstProp as rustc_mir::transform::MirPass>::run_pass
  80: rustc_mir::transform::run_passes
  81: rustc_mir::transform::run_optimization_passes
  82: rustc_mir::transform::optimized_mir
  83: rustc_middle::dep_graph::<impl rustc_query_system::dep_graph::DepKind for rustc_middle::dep_graph::dep_node::DepKind>::with_deps
  84: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  85: rustc_data_structures::stack::ensure_sufficient_stack
  86: rustc_query_system::query::plumbing::get_query_impl
  87: rustc_middle::ty::<impl rustc_middle::ty::context::TyCtxt>::instance_mir
  88: rustc_mir::monomorphize::collector::collect_neighbours
  89: rustc_mir::monomorphize::collector::collect_items_rec
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

note: the compiler unexpectedly panicked. this is a bug.

note: we would appreciate a bug report: https://github.com/rust-lang/rust/issues/new?labels=C-bug%2C+I-ICE%2C+T-compiler&template=ice.md

note: rustc 1.49.0-nightly (ffa2e7ae8 2020-10-24) running on x86_64-unknown-linux-gnu

note: compiler flags: -C embed-bitcode=no -C debuginfo=2 -C incremental --crate-type bin

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

query stack during panic:
#0 [optimized_mir] optimizing MIR for `main::{closure#0}::{closure#0}::{closure#0}`
#1 [layout_raw] computing layout of `[static generator@src/main.rs:10:24: 18:14 for<'r, 's> {std::future::ResumeTy, Status, u32, &'r tokio::sync::RwLock<std::vec::Vec<bool>>, tokio::sync::RwLock<std::vec::Vec<bool>>, std::future::from_generator::GenFuture<[static generator@tokio::sync::RwLock::<T>::read::{closure#0} for<'t0, 't1> {std::future::ResumeTy, &'t0 tokio::sync::RwLock<std::vec::Vec<bool>>, u16, std::future::from_generator::GenFuture<[static generator@tokio::sync::rwlock::ReleasingPermit::<'a, T>::acquire::{closure#0} for<'t2, 't3, 't4> {std::future::ResumeTy, &'t2 tokio::sync::RwLock<std::vec::Vec<bool>>, u16, tokio::sync::RwLock<std::vec::Vec<bool>>, &'t3 tokio::sync::batch_semaphore::Semaphore, tokio::sync::batch_semaphore::Semaphore, u32, tokio::sync::batch_semaphore::Acquire<'t4>, ()}]>, ()}]>, ()}]`
#2 [layout_raw] computing layout of `std::future::from_generator::GenFuture<[static generator@src/main.rs:10:24: 18:14 for<'r, 's> {std::future::ResumeTy, Status, u32, &'r tokio::sync::RwLock<std::vec::Vec<bool>>, tokio::sync::RwLock<std::vec::Vec<bool>>, std::future::from_generator::GenFuture<[static generator@tokio::sync::RwLock::<T>::read::{closure#0} for<'t0, 't1> {std::future::ResumeTy, &'t0 tokio::sync::RwLock<std::vec::Vec<bool>>, u16, std::future::from_generator::GenFuture<[static generator@tokio::sync::rwlock::ReleasingPermit::<'a, T>::acquire::{closure#0} for<'t2, 't3, 't4> {std::future::ResumeTy, &'t2 tokio::sync::RwLock<std::vec::Vec<bool>>, u16, tokio::sync::RwLock<std::vec::Vec<bool>>, &'t3 tokio::sync::batch_semaphore::Semaphore, tokio::sync::batch_semaphore::Semaphore, u32, tokio::sync::batch_semaphore::Acquire<'t4>, ()}]>, ()}]>, ()}]>`
#3 [layout_raw] computing layout of `std::mem::ManuallyDrop<std::future::from_generator::GenFuture<[static generator@src/main.rs:10:24: 18:14 for<'r, 's> {std::future::ResumeTy, Status, u32, &'r tokio::sync::RwLock<std::vec::Vec<bool>>, tokio::sync::RwLock<std::vec::Vec<bool>>, std::future::from_generator::GenFuture<[static generator@tokio::sync::RwLock::<T>::read::{closure#0} for<'t0, 't1> {std::future::ResumeTy, &'t0 tokio::sync::RwLock<std::vec::Vec<bool>>, u16, std::future::from_generator::GenFuture<[static generator@tokio::sync::rwlock::ReleasingPermit::<'a, T>::acquire::{closure#0} for<'t2, 't3, 't4> {std::future::ResumeTy, &'t2 tokio::sync::RwLock<std::vec::Vec<bool>>, u16, tokio::sync::RwLock<std::vec::Vec<bool>>, &'t3 tokio::sync::batch_semaphore::Semaphore, tokio::sync::batch_semaphore::Semaphore, u32, tokio::sync::batch_semaphore::Acquire<'t4>, ()}]>, ()}]>, ()}]>>`
#4 [layout_raw] computing layout of `std::mem::MaybeUninit<std::future::from_generator::GenFuture<[static generator@src/main.rs:10:24: 18:14 for<'r, 's> {std::future::ResumeTy, Status, u32, &'r tokio::sync::RwLock<std::vec::Vec<bool>>, tokio::sync::RwLock<std::vec::Vec<bool>>, std::future::from_generator::GenFuture<[static generator@tokio::sync::RwLock::<T>::read::{closure#0} for<'t0, 't1> {std::future::ResumeTy, &'t0 tokio::sync::RwLock<std::vec::Vec<bool>>, u16, std::future::from_generator::GenFuture<[static generator@tokio::sync::rwlock::ReleasingPermit::<'a, T>::acquire::{closure#0} for<'t2, 't3, 't4> {std::future::ResumeTy, &'t2 tokio::sync::RwLock<std::vec::Vec<bool>>, u16, tokio::sync::RwLock<std::vec::Vec<bool>>, &'t3 tokio::sync::batch_semaphore::Semaphore, tokio::sync::batch_semaphore::Semaphore, u32, tokio::sync::batch_semaphore::Acquire<'t4>, ()}]>, ()}]>, ()}]>>`
#5 [layout_raw] computing layout of `[static generator@src/main.rs:5:1: 5:15 {std::future::ResumeTy, tokio::sync::RwLock<std::vec::Vec<bool>>, [closure@src/main.rs:9:19: 19:10], u32, Status, std::future::from_generator::GenFuture<[static generator@src/main.rs:10:24: 18:14 for<'r, 's> {std::future::ResumeTy, Status, u32, &'r tokio::sync::RwLock<std::vec::Vec<bool>>, tokio::sync::RwLock<std::vec::Vec<bool>>, std::future::from_generator::GenFuture<[static generator@tokio::sync::RwLock::<T>::read::{closure#0} for<'t0, 't1> {std::future::ResumeTy, &'t0 tokio::sync::RwLock<std::vec::Vec<bool>>, u16, std::future::from_generator::GenFuture<[static generator@tokio::sync::rwlock::ReleasingPermit::<'a, T>::acquire::{closure#0} for<'t2, 't3, 't4> {std::future::ResumeTy, &'t2 tokio::sync::RwLock<std::vec::Vec<bool>>, u16, tokio::sync::RwLock<std::vec::Vec<bool>>, &'t3 tokio::sync::batch_semaphore::Semaphore, tokio::sync::batch_semaphore::Semaphore, u32, tokio::sync::batch_semaphore::Acquire<'t4>, ()}]>, ()}]>, ()}]>, ()}]`
#6 [layout_raw] computing layout of `std::future::from_generator::GenFuture<[static generator@src/main.rs:5:1: 5:15 {std::future::ResumeTy, tokio::sync::RwLock<std::vec::Vec<bool>>, [closure@src/main.rs:9:19: 19:10], u32, Status, std::future::from_generator::GenFuture<[static generator@src/main.rs:10:24: 18:14 for<'r, 's> {std::future::ResumeTy, Status, u32, &'r tokio::sync::RwLock<std::vec::Vec<bool>>, tokio::sync::RwLock<std::vec::Vec<bool>>, std::future::from_generator::GenFuture<[static generator@tokio::sync::RwLock::<T>::read::{closure#0} for<'t0, 't1> {std::future::ResumeTy, &'t0 tokio::sync::RwLock<std::vec::Vec<bool>>, u16, std::future::from_generator::GenFuture<[static generator@tokio::sync::rwlock::ReleasingPermit::<'a, T>::acquire::{closure#0} for<'t2, 't3, 't4> {std::future::ResumeTy, &'t2 tokio::sync::RwLock<std::vec::Vec<bool>>, u16, tokio::sync::RwLock<std::vec::Vec<bool>>, &'t3 tokio::sync::batch_semaphore::Semaphore, tokio::sync::batch_semaphore::Semaphore, u32, tokio::sync::batch_semaphore::Acquire<'t4>, ()}]>, ()}]>, ()}]>, ()}]>`
#7 [optimized_mir] optimizing MIR for `main`
#8 [collect_and_partition_mono_items] collect_and_partition_mono_items
end of query stack
error: aborting due to previous error

error: could not compile `system_change`

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

This is the most minimal example I could find, it needs tokio with the features "macro" and "sync". While this error occured on Nightly I could also reproduce this on stable (as far back as on 1.39, didn't test beyond that because my build started failing because of other reasons)

[SNCPlay42]

This is very reminiscent of #72651 (await in if guard in match statement)

[SNCPlay42]

MCVE:

async fn bar() -> &'static [bool] {
    unimplemented!()
}

async fn foo(status: usize) {
    match status {
        x if bar().await[x] => {}
        _ => {}
    }
}

Yeah, very #72651.

[VincentWo]

Thank you for reducing this further. Totally forgot that I could just declare my own async function this way!

But I do understand correctly that the linked example is just related, not the same? (Since it's still occuring in latest nightly and the linked issue seemes to be already fixed)

[SNCPlay42]

Yeah, just related - my immediate guess is this is some case that was missed in the fix for that issue. The difference appears to be that x is used in a index expression after the await instead of some other way.

[SNCPlay42]

Another example:

async fn bar() -> usize {
    unimplemented!()
}

async fn foo(status: usize) {
    match status {
        x if bar().await == (x + 1) => {}
        _ => {}
    }
}

Any usage of x in the if guard after the await that does not cause x to be autorefed (like just == x from the #72651 MCVE would) appears to trigger the ICE.

[SNCPlay42]

@rustbot claim

[JohnTitor]

Assigning P-high as discussed as part of the Prioritization Working Group procedure and removing I-prioritize.