ICE: error with disjoint closure returned as impl FnMut

[ehuss]

The following ICE was found migrating openvpn-parser 0.5.0 to 2021 during the latest crater run: https://crater-reports.s3.amazonaws.com/pr-87190-3/try%23a7a572ce3edd6d476191fbfe92c9c1986e009b34/reg/openvpn-parser-0.5.0/log.txt. Error was in this closure.

cc #87988 which was very similar, but has been fixed.

Also found in:

• https://github.com/rodolpheche/couchdb-purge - https://crater-reports.s3.amazonaws.com/pr-87190-3/try%23a7a572ce3edd6d476191fbfe92c9c1986e009b34/gh/rodolpheche.couchdb-purge/log.txt

Code

#![feature(capture_disjoint_fields)]

#[derive(Copy, Clone, PartialEq, Eq)]
pub struct Opcode(pub u8);

impl Opcode {
    pub const OP1: Opcode = Opcode(0x1);
}

pub fn example(msg_type: Opcode) -> impl FnMut(&[u8]) {
    move |i| match msg_type {
        Opcode::OP1 => unimplemented!(),
    }
}

Meta

rustc --version --verbose:

rustc 1.56.0-nightly (b03ccace5 2021-08-24)
binary: rustc
commit-hash: b03ccace573bb91e27625c190a0f7807045a1012
commit-date: 2021-08-24
host: x86_64-apple-darwin
release: 1.56.0-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:1765:53

Backtrace

thread 'rustc' panicked at 'called `Option::unwrap()` on a `None` value', compiler/rustc_mir_build/src/build/matches/mod.rs:1765:53
stack backtrace:
   0: _rust_begin_unwind
   1: core::panicking::panic_fmt
   2: core::panicking::panic
   3: rustc_mir_build::build::matches::<impl rustc_mir_build::build::Builder>::bind_and_guard_matched_candidate
   4: rustc_mir_build::build::matches::<impl rustc_mir_build::build::Builder>::bind_pattern
   5: rustc_mir_build::build::scope::<impl rustc_mir_build::build::Builder>::in_scope
   6: <core::iter::adapters::map::Map<I,F> as core::iter::traits::iterator::Iterator>::fold
   7: alloc::vec::source_iter_marker::<impl alloc::vec::spec_from_iter::SpecFromIter<T,I> for alloc::vec::Vec<T>>::from_iter
   8: rustc_mir_build::build::expr::into::<impl rustc_mir_build::build::Builder>::expr_into_dest
   9: rustc_mir_build::build::scope::<impl rustc_mir_build::build::Builder>::in_scope
  10: rustc_data_structures::stack::ensure_sufficient_stack
  11: rustc_mir_build::build::expr::into::<impl rustc_mir_build::build::Builder>::expr_into_dest
  12: rustc_mir_build::build::scope::<impl rustc_mir_build::build::Builder>::in_scope
  13: rustc_data_structures::stack::ensure_sufficient_stack
  14: rustc_mir_build::build::expr::into::<impl rustc_mir_build::build::Builder>::expr_into_dest
  15: rustc_mir_build::build::construct_fn
  16: rustc_infer::infer::InferCtxtBuilder::enter
  17: rustc_mir_build::build::mir_built
  18: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  19: rustc_data_structures::stack::ensure_sufficient_stack
  20: rustc_query_system::query::plumbing::get_query_impl
  21: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::mir_built
  22: rustc_mir::transform::check_unsafety::unsafety_check_result
  23: core::ops::function::FnOnce::call_once
  24: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  25: rustc_data_structures::stack::ensure_sufficient_stack
  26: rustc_query_system::query::plumbing::force_query_with_job
  27: rustc_query_system::query::plumbing::get_query_impl
  28: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::unsafety_check_result
  29: <rustc_mir::transform::check_unsafety::UnsafetyChecker as rustc_middle::mir::visit::Visitor>::visit_rvalue
  30: rustc_mir::transform::check_unsafety::unsafety_check_result
  31: core::ops::function::FnOnce::call_once
  32: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  33: rustc_data_structures::stack::ensure_sufficient_stack
  34: rustc_query_system::query::plumbing::force_query_with_job
  35: rustc_query_system::query::plumbing::get_query_impl
  36: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::unsafety_check_result
  37: rustc_mir::transform::mir_const
  38: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  39: rustc_data_structures::stack::ensure_sufficient_stack
  40: rustc_query_system::query::plumbing::get_query_impl
  41: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::mir_const
  42: rustc_mir::transform::mir_promoted
  43: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  44: rustc_data_structures::stack::ensure_sufficient_stack
  45: rustc_query_system::query::plumbing::get_query_impl
  46: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::mir_promoted
  47: rustc_mir::borrow_check::mir_borrowck
  48: core::ops::function::FnOnce::call_once
  49: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  50: rustc_data_structures::stack::ensure_sufficient_stack
  51: rustc_query_system::query::plumbing::force_query_with_job
  52: rustc_query_system::query::plumbing::get_query_impl
  53: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::mir_borrowck
  54: rustc_typeck::collect::type_of::type_of
  55: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  56: rustc_data_structures::stack::ensure_sufficient_stack
  57: rustc_query_system::query::plumbing::force_query_with_job
  58: rustc_query_system::query::plumbing::get_query_impl
  59: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::type_of
  60: rustc_typeck::check::check::check_item_type
  61: rustc_middle::hir::map::Map::visit_item_likes_in_module
  62: rustc_typeck::check::check::check_mod_item_types
  63: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  64: rustc_data_structures::stack::ensure_sufficient_stack
  65: rustc_query_system::query::plumbing::force_query_with_job
  66: rustc_query_system::query::plumbing::get_query_impl
  67: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::check_mod_item_types
  68: rustc_session::utils::<impl rustc_session::session::Session>::time
  69: rustc_typeck::check_crate
  70: rustc_interface::passes::analysis
  71: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  72: rustc_data_structures::stack::ensure_sufficient_stack
  73: rustc_query_system::query::plumbing::force_query_with_job
  74: rustc_query_system::query::plumbing::get_query_impl
  75: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::analysis
  76: rustc_interface::queries::<impl rustc_interface::interface::Compiler>::enter
  77: rustc_span::with_source_map
  78: scoped_tls::ScopedKey<T>::set
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 1.56.0-nightly (b03ccace5 2021-08-24) running on x86_64-apple-darwin

note: compiler flags: -C embed-bitcode=no -C split-debuginfo=unpacked -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 `example::{closure#0}`
#1 [unsafety_check_result] unsafety-checking `example::{closure#0}`
#2 [unsafety_check_result] unsafety-checking `example`
#3 [mir_const] processing MIR for `example`
#4 [mir_promoted] processing `example`
#5 [mir_borrowck] borrow-checking `example`
#6 [type_of] computing type of `example::{opaque#0}`
#7 [check_mod_item_types] checking item types in top-level module
#8 [analysis] running analysis passes on this crate
end of query stack
warning: `foo` (lib) generated 1 warning
error: could not compile `foo`; 1 warning emitted```

</p>
</details>



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[ehuss]

cc @rust-lang/wg-rfc-2229

[roxelo]

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