ICE for async block containing match on empty slice and wildcard

[jix]

Code

pub async fn something(path: &[usize]) -> usize {
    // Without this async block it doesn't ICE
    async {
        match path {
            [] => 0,
            // Adding the following match arm makes it not ICE, thankfully that makes this not a
            // blocker for me :)

            // [1] => 2,
            _ => 1,
        }
    }
    .await
}

playground (nightly)

Meta

rustc --version --verbose:

% rustc --version --verbose
rustc 1.58.1 (db9d1b20b 2022-01-20)
binary: rustc
commit-hash: db9d1b20bba1968c1ec1fc49616d4742c1725b4b
commit-date: 2022-01-20
host: x86_64-unknown-linux-gnu
release: 1.58.1
LLVM version: 13.0.0

% rustc +nightly --version --verbose
rustc 1.60.0-nightly (777bb86bc 2022-01-20)
binary: rustc
commit-hash: 777bb86bcdbc568be7cff6eeeaaf81a89b4aa50b
commit-date: 2022-01-20
host: x86_64-unknown-linux-gnu
release: 1.60.0-nightly
LLVM version: 13.0.0

Error output

thread 'rustc' panicked at 'called `Option::unwrap()` on a `None` value', compiler/rustc_mir_build/src/build/matches/mod.rs:1825:53

compiler/rustc_mir_build/src/build/matches/mod.rs:1825

Backtrace

    Checking repro v0.1.0 (/tmp/tmpproj/repro)
thread 'rustc' panicked at 'called `Option::unwrap()` on a `None` value', compiler/rustc_mir_build/src/build/matches/mod.rs:1825:53
stack backtrace:
   0: rust_begin_unwind
             at /rustc/db9d1b20bba1968c1ec1fc49616d4742c1725b4b/library/std/src/panicking.rs:498:5
   1: core::panicking::panic_fmt
             at /rustc/db9d1b20bba1968c1ec1fc49616d4742c1725b4b/library/core/src/panicking.rs:107:14
   2: core::panicking::panic
             at /rustc/db9d1b20bba1968c1ec1fc49616d4742c1725b4b/library/core/src/panicking.rs:48:5
   3: <rustc_mir_build::build::Builder>::bind_and_guard_matched_candidate
   4: <rustc_mir_build::build::Builder>::bind_pattern
   5: <rustc_mir_build::build::Builder>::in_scope::<<rustc_mir_build::build::Builder>::lower_match_arms::{closure#0}::{closure#0}, ()>
   6: <core::iter::adapters::map::Map<alloc::vec::into_iter::IntoIter<(&rustc_middle::thir::Arm, rustc_mir_build::build::matches::Candidate)>, <rustc_mir_build::build::Builder>::lower_match_arms::{closure#0}> as core::iter::traits::iterator::Iterator>::fold::<(), core::iter::traits::iterator::Iterator::for_each::call<rustc_mir_build::build::BlockAnd<()>, <alloc::vec::Vec<rustc_mir_build::build::BlockAnd<()>> as alloc::vec::spec_extend::SpecExtend<rustc_mir_build::build::BlockAnd<()>, core::iter::adapters::map::Map<alloc::vec::into_iter::IntoIter<(&rustc_middle::thir::Arm, rustc_mir_build::build::matches::Candidate)>, <rustc_mir_build::build::Builder>::lower_match_arms::{closure#0}>>>::spec_extend::{closure#0}>::{closure#0}>
   7: <alloc::vec::Vec<rustc_mir_build::build::BlockAnd<()>> as alloc::vec::spec_from_iter::SpecFromIter<rustc_mir_build::build::BlockAnd<()>, core::iter::adapters::map::Map<alloc::vec::into_iter::IntoIter<(&rustc_middle::thir::Arm, rustc_mir_build::build::matches::Candidate)>, <rustc_mir_build::build::Builder>::lower_match_arms::{closure#0}>>>::from_iter
   8: <rustc_mir_build::build::Builder>::expr_into_dest
   9: <rustc_mir_build::build::Builder>::in_scope::<<rustc_mir_build::build::Builder>::expr_into_dest::{closure#0}::{closure#0}, ()>
  10: <rustc_mir_build::build::Builder>::expr_into_dest
  11: <rustc_mir_build::build::Builder>::ast_block_stmts
  12: <rustc_mir_build::build::Builder>::in_scope::<<rustc_mir_build::build::Builder>::ast_block::{closure#2}::{closure#0}, ()>
  13: <rustc_mir_build::build::Builder>::expr_into_dest
  14: <rustc_mir_build::build::Builder>::in_scope::<<rustc_mir_build::build::Builder>::expr_into_dest::{closure#0}::{closure#0}, ()>
  15: <rustc_mir_build::build::Builder>::expr_into_dest
  16: <rustc_mir_build::build::Builder>::in_scope::<<rustc_mir_build::build::Builder>::expr_into_dest::{closure#0}::{closure#0}, ()>
  17: <rustc_mir_build::build::Builder>::expr_into_dest
  18: rustc_mir_build::build::construct_fn::<core::iter::adapters::chain::Chain<alloc::vec::into_iter::IntoIter<rustc_mir_build::build::ArgInfo>, core::iter::adapters::map::Map<core::iter::adapters::enumerate::Enumerate<core::slice::iter::Iter<rustc_hir::hir::Param>>, rustc_mir_build::build::mir_build::{closure#1}::{closure#0}>>>
  19: <rustc_infer::infer::InferCtxtBuilder>::enter::<rustc_middle::mir::Body, rustc_mir_build::build::mir_build::{closure#1}>
  20: rustc_mir_build::build::mir_built
  21: <rustc_query_system::dep_graph::graph::DepGraph<rustc_middle::dep_graph::dep_node::DepKind>>::with_task::<rustc_middle::ty::context::TyCtxt, rustc_middle::ty::WithOptConstParam<rustc_span::def_id::LocalDefId>, &rustc_data_structures::steal::Steal<rustc_middle::mir::Body>>
  22: rustc_data_structures::stack::ensure_sufficient_stack::<(&rustc_data_structures::steal::Steal<rustc_middle::mir::Body>, rustc_query_system::dep_graph::graph::DepNodeIndex), rustc_query_system::query::plumbing::execute_job<rustc_query_impl::plumbing::QueryCtxt, rustc_middle::ty::WithOptConstParam<rustc_span::def_id::LocalDefId>, &rustc_data_structures::steal::Steal<rustc_middle::mir::Body>>::{closure#3}>
  23: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::plumbing::QueryCtxt, rustc_query_system::query::caches::DefaultCache<rustc_middle::ty::WithOptConstParam<rustc_span::def_id::LocalDefId>, &rustc_data_structures::steal::Steal<rustc_middle::mir::Body>>>
  24: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::mir_built
  25: rustc_mir_transform::check_unsafety::unsafety_check_result
  26: <rustc_mir_transform::check_unsafety::provide::{closure#0} as core::ops::function::FnOnce<(rustc_middle::ty::context::TyCtxt, rustc_span::def_id::LocalDefId)>>::call_once
  27: <rustc_query_system::dep_graph::graph::DepGraph<rustc_middle::dep_graph::dep_node::DepKind>>::with_task::<rustc_middle::ty::context::TyCtxt, rustc_span::def_id::LocalDefId, &rustc_middle::mir::query::UnsafetyCheckResult>
  28: rustc_data_structures::stack::ensure_sufficient_stack::<(&rustc_middle::mir::query::UnsafetyCheckResult, rustc_query_system::dep_graph::graph::DepNodeIndex), rustc_query_system::query::plumbing::execute_job<rustc_query_impl::plumbing::QueryCtxt, rustc_span::def_id::LocalDefId, &rustc_middle::mir::query::UnsafetyCheckResult>::{closure#3}>
  29: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::plumbing::QueryCtxt, rustc_query_system::query::caches::DefaultCache<rustc_span::def_id::LocalDefId, &rustc_middle::mir::query::UnsafetyCheckResult>>
  30: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::unsafety_check_result
  31: <rustc_mir_transform::check_unsafety::UnsafetyChecker as rustc_middle::mir::visit::Visitor>::visit_rvalue
  32: rustc_mir_transform::check_unsafety::unsafety_check_result
  33: <rustc_mir_transform::check_unsafety::provide::{closure#0} as core::ops::function::FnOnce<(rustc_middle::ty::context::TyCtxt, rustc_span::def_id::LocalDefId)>>::call_once
  34: <rustc_query_system::dep_graph::graph::DepGraph<rustc_middle::dep_graph::dep_node::DepKind>>::with_task::<rustc_middle::ty::context::TyCtxt, rustc_span::def_id::LocalDefId, &rustc_middle::mir::query::UnsafetyCheckResult>
  35: rustc_data_structures::stack::ensure_sufficient_stack::<(&rustc_middle::mir::query::UnsafetyCheckResult, rustc_query_system::dep_graph::graph::DepNodeIndex), rustc_query_system::query::plumbing::execute_job<rustc_query_impl::plumbing::QueryCtxt, rustc_span::def_id::LocalDefId, &rustc_middle::mir::query::UnsafetyCheckResult>::{closure#3}>
  36: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::plumbing::QueryCtxt, rustc_query_system::query::caches::DefaultCache<rustc_span::def_id::LocalDefId, &rustc_middle::mir::query::UnsafetyCheckResult>>
  37: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::unsafety_check_result
  38: <rustc_mir_transform::check_unsafety::UnsafetyChecker as rustc_middle::mir::visit::Visitor>::visit_rvalue
  39: rustc_mir_transform::check_unsafety::unsafety_check_result
  40: <rustc_mir_transform::check_unsafety::provide::{closure#0} as core::ops::function::FnOnce<(rustc_middle::ty::context::TyCtxt, rustc_span::def_id::LocalDefId)>>::call_once
  41: <rustc_query_system::dep_graph::graph::DepGraph<rustc_middle::dep_graph::dep_node::DepKind>>::with_task::<rustc_middle::ty::context::TyCtxt, rustc_span::def_id::LocalDefId, &rustc_middle::mir::query::UnsafetyCheckResult>
  42: rustc_data_structures::stack::ensure_sufficient_stack::<(&rustc_middle::mir::query::UnsafetyCheckResult, rustc_query_system::dep_graph::graph::DepNodeIndex), rustc_query_system::query::plumbing::execute_job<rustc_query_impl::plumbing::QueryCtxt, rustc_span::def_id::LocalDefId, &rustc_middle::mir::query::UnsafetyCheckResult>::{closure#3}>
  43: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::plumbing::QueryCtxt, rustc_query_system::query::caches::DefaultCache<rustc_span::def_id::LocalDefId, &rustc_middle::mir::query::UnsafetyCheckResult>>
  44: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::unsafety_check_result
  45: rustc_mir_transform::mir_const
  46: <rustc_query_system::dep_graph::graph::DepGraph<rustc_middle::dep_graph::dep_node::DepKind>>::with_task::<rustc_middle::ty::context::TyCtxt, rustc_middle::ty::WithOptConstParam<rustc_span::def_id::LocalDefId>, &rustc_data_structures::steal::Steal<rustc_middle::mir::Body>>
  47: rustc_data_structures::stack::ensure_sufficient_stack::<(&rustc_data_structures::steal::Steal<rustc_middle::mir::Body>, rustc_query_system::dep_graph::graph::DepNodeIndex), rustc_query_system::query::plumbing::execute_job<rustc_query_impl::plumbing::QueryCtxt, rustc_middle::ty::WithOptConstParam<rustc_span::def_id::LocalDefId>, &rustc_data_structures::steal::Steal<rustc_middle::mir::Body>>::{closure#3}>
  48: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::plumbing::QueryCtxt, rustc_query_system::query::caches::DefaultCache<rustc_middle::ty::WithOptConstParam<rustc_span::def_id::LocalDefId>, &rustc_data_structures::steal::Steal<rustc_middle::mir::Body>>>
  49: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::mir_const
  50: rustc_mir_transform::mir_promoted
  51: <rustc_query_system::dep_graph::graph::DepGraph<rustc_middle::dep_graph::dep_node::DepKind>>::with_task::<rustc_middle::ty::context::TyCtxt, rustc_middle::ty::WithOptConstParam<rustc_span::def_id::LocalDefId>, (&rustc_data_structures::steal::Steal<rustc_middle::mir::Body>, &rustc_data_structures::steal::Steal<rustc_index::vec::IndexVec<rustc_middle::mir::Promoted, rustc_middle::mir::Body>>)>
  52: rustc_data_structures::stack::ensure_sufficient_stack::<((&rustc_data_structures::steal::Steal<rustc_middle::mir::Body>, &rustc_data_structures::steal::Steal<rustc_index::vec::IndexVec<rustc_middle::mir::Promoted, rustc_middle::mir::Body>>), rustc_query_system::dep_graph::graph::DepNodeIndex), rustc_query_system::query::plumbing::execute_job<rustc_query_impl::plumbing::QueryCtxt, rustc_middle::ty::WithOptConstParam<rustc_span::def_id::LocalDefId>, (&rustc_data_structures::steal::Steal<rustc_middle::mir::Body>, &rustc_data_structures::steal::Steal<rustc_index::vec::IndexVec<rustc_middle::mir::Promoted, rustc_middle::mir::Body>>)>::{closure#3}>
  53: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::plumbing::QueryCtxt, rustc_query_system::query::caches::DefaultCache<rustc_middle::ty::WithOptConstParam<rustc_span::def_id::LocalDefId>, (&rustc_data_structures::steal::Steal<rustc_middle::mir::Body>, &rustc_data_structures::steal::Steal<rustc_index::vec::IndexVec<rustc_middle::mir::Promoted, rustc_middle::mir::Body>>)>>
  54: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::mir_promoted
  55: rustc_borrowck::mir_borrowck
  56: <rustc_borrowck::provide::{closure#0} as core::ops::function::FnOnce<(rustc_middle::ty::context::TyCtxt, rustc_span::def_id::LocalDefId)>>::call_once
  57: <rustc_query_system::dep_graph::graph::DepGraph<rustc_middle::dep_graph::dep_node::DepKind>>::with_task::<rustc_middle::ty::context::TyCtxt, rustc_span::def_id::LocalDefId, &rustc_middle::mir::query::BorrowCheckResult>
  58: rustc_data_structures::stack::ensure_sufficient_stack::<(&rustc_middle::mir::query::BorrowCheckResult, rustc_query_system::dep_graph::graph::DepNodeIndex), rustc_query_system::query::plumbing::execute_job<rustc_query_impl::plumbing::QueryCtxt, rustc_span::def_id::LocalDefId, &rustc_middle::mir::query::BorrowCheckResult>::{closure#3}>
  59: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::plumbing::QueryCtxt, rustc_query_system::query::caches::DefaultCache<rustc_span::def_id::LocalDefId, &rustc_middle::mir::query::BorrowCheckResult>>
  60: rustc_query_system::query::plumbing::get_query::<rustc_query_impl::queries::mir_borrowck, rustc_query_impl::plumbing::QueryCtxt>
  61: rustc_typeck::collect::type_of::type_of
  62: <rustc_query_system::dep_graph::graph::DepGraph<rustc_middle::dep_graph::dep_node::DepKind>>::with_task::<rustc_middle::ty::context::TyCtxt, rustc_span::def_id::DefId, &rustc_middle::ty::TyS>
  63: rustc_data_structures::stack::ensure_sufficient_stack::<(&rustc_middle::ty::TyS, rustc_query_system::dep_graph::graph::DepNodeIndex), rustc_query_system::query::plumbing::execute_job<rustc_query_impl::plumbing::QueryCtxt, rustc_span::def_id::DefId, &rustc_middle::ty::TyS>::{closure#3}>
  64: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::plumbing::QueryCtxt, rustc_query_system::query::caches::DefaultCache<rustc_span::def_id::DefId, &rustc_middle::ty::TyS>>
  65: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::type_of
  66: rustc_typeck::check::check::check_item_type
  67: <rustc_middle::hir::map::Map>::visit_item_likes_in_module::<rustc_typeck::check::CheckItemTypesVisitor>
  68: rustc_typeck::check::check::check_mod_item_types
  69: <rustc_query_system::dep_graph::graph::DepGraph<rustc_middle::dep_graph::dep_node::DepKind>>::with_task::<rustc_middle::ty::context::TyCtxt, rustc_span::def_id::LocalDefId, ()>
  70: rustc_data_structures::stack::ensure_sufficient_stack::<((), rustc_query_system::dep_graph::graph::DepNodeIndex), rustc_query_system::query::plumbing::execute_job<rustc_query_impl::plumbing::QueryCtxt, rustc_span::def_id::LocalDefId, ()>::{closure#3}>
  71: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::plumbing::QueryCtxt, rustc_query_system::query::caches::DefaultCache<rustc_span::def_id::LocalDefId, ()>>
  72: rustc_query_system::query::plumbing::get_query::<rustc_query_impl::queries::check_mod_item_types, rustc_query_impl::plumbing::QueryCtxt>
  73: <rustc_middle::hir::map::Map>::for_each_module::<rustc_typeck::check_crate::{closure#6}::{closure#0}>
  74: rustc_typeck::check_crate
  75: rustc_interface::passes::analysis
  76: <rustc_query_system::dep_graph::graph::DepGraph<rustc_middle::dep_graph::dep_node::DepKind>>::with_task::<rustc_middle::ty::context::TyCtxt, (), core::result::Result<(), rustc_errors::ErrorReported>>
  77: rustc_data_structures::stack::ensure_sufficient_stack::<(core::result::Result<(), rustc_errors::ErrorReported>, rustc_query_system::dep_graph::graph::DepNodeIndex), rustc_query_system::query::plumbing::execute_job<rustc_query_impl::plumbing::QueryCtxt, (), core::result::Result<(), rustc_errors::ErrorReported>>::{closure#3}>
  78: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::plumbing::QueryCtxt, rustc_query_system::query::caches::DefaultCache<(), core::result::Result<(), rustc_errors::ErrorReported>>>
  79: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::analysis
  80: <rustc_interface::passes::QueryContext>::enter::<rustc_driver::run_compiler::{closure#1}::{closure#2}::{closure#3}, core::result::Result<(), rustc_errors::ErrorReported>>
  81: <rustc_interface::interface::Compiler>::enter::<rustc_driver::run_compiler::{closure#1}::{closure#2}, core::result::Result<core::option::Option<rustc_interface::queries::Linker>, rustc_errors::ErrorReported>>
  82: rustc_span::with_source_map::<core::result::Result<(), rustc_errors::ErrorReported>, rustc_interface::interface::create_compiler_and_run<core::result::Result<(), rustc_errors::ErrorReported>, rustc_driver::run_compiler::{closure#1}>::{closure#1}>
  83: <scoped_tls::ScopedKey<rustc_span::SessionGlobals>>::set::<rustc_interface::util::setup_callbacks_and_run_in_thread_pool_with_globals<rustc_interface::interface::run_compiler<core::result::Result<(), rustc_errors::ErrorReported>, rustc_driver::run_compiler::{closure#1}>::{closure#0}, core::result::Result<(), rustc_errors::ErrorReported>>::{closure#0}::{closure#0}, core::result::Result<(), rustc_errors::ErrorReported>>
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

error: internal compiler error: unexpected panic

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 1.58.1 (db9d1b20b 2022-01-20) running on x86_64-unknown-linux-gnu

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

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

query stack during panic:
#0 [mir_built] building MIR for `something::{closure#0}::{closure#0}`
#1 [unsafety_check_result] unsafety-checking `something::{closure#0}::{closure#0}`
#2 [unsafety_check_result] unsafety-checking `something::{closure#0}`
#3 [unsafety_check_result] unsafety-checking `something`
#4 [mir_const] processing MIR for `something`
#5 [mir_promoted] processing `something`
#6 [mir_borrowck] borrow-checking `something`
#7 [type_of] computing type of `something::{opaque#0}`
#8 [check_mod_item_types] checking item types in top-level module
#9 [analysis] running analysis passes on this crate
end of query stack
error: could not compile `repro`

[compiler-errors]

Interesting. Slightly minimized, seems not to do with async and instead to do with being in a closure. edit: Also it only crashes on edition 2021, so this also seems due to closure capture behavior changes between those editions? Strange.

pub fn something(path: &[usize]) -> impl Fn() -> usize {
    || match path {
        [] => 0,
        _ => 1,
    }
}

[compiler-errors]

So this definitely has to do with the fact that we only capture the second "length" field of the slice fat-pointer.

I'll see if I can come up with a fix!
@rustbot claim

[compiler-errors]

Actually not sure if I'm familiar enough with the pattern match code in MIR to come up with a good fix.

@rustbot release-assignment