Regression/ICE: moving both a Copy type and a !Copy type into async move || { ... } (async_closure)

[finnbear]

Code

I tried this code (minimized):

#![feature(async_closure)]

fn foo() {
    // no ICE if removed or made !Copy
    let bar = 0u8;
    // no ICE if removed or made Copy
    let baz = "".to_owned();
    async move || {
        let _ = (bar, baz);
    };
}

fn main() {}

I expected to see this happen: Compiles

Instead, this happened (nightly-2024-02-09):

error[E0597]: `bar` does not live long enough
 --> src/main.rs:7:18
  |
6 |       async move || {
  |  ___________________-
7 | |         let _ = (bar, baz);
  | |                  ^^^ borrowed value does not live long enough
8 | |     };
  | |     -- borrow later used here
  | |     |
  | |_____`bar` dropped here while still borrowed
  |       value captured here by coroutine

Instead, this happened (latest nightly): ICE

   Compiling playground v0.0.1 (/playground)
thread 'rustc' panicked at compiler/rustc_mir_transform/src/coroutine/by_move_body.rs:140:21:
assertion `left != right` failed: `FnOnce` coroutine-closures return coroutines that capture from their body; it will always result in a borrowck error!
  left: FnOnce
 right: FnOnce

Versions

working -> error

searched nightlies: from nightly-2023-04-25 to nightly-2024-04-20
regressed nightly: nightly-2024-02-07
searched commit range: https://github.com/rust-lang/rust/compare/f067fd6084d750f3797f54b71771c5dbc149726f...256b6fb19a2c018eaad4806d2369d1f6a71fc6ec
regressed commit: https://github.com/rust-lang/rust/commit/4a2fe4491ea616983a0cf0cbbd145a39768f4e7a

<details>
<summary>bisected with <a href='https://github.com/rust-lang/cargo-bisect-rustc'>cargo-bisect-rustc</a> v0.6.6</summary>

Related: #120361
Mentioning @compiler-errors 😉

error -> ICE

********************************************************************************
Regression in 1921968cc5403892739b43bdefe793a130badd15
********************************************************************************

Best guess: #123350

Backtrace

 Compiling playground v0.0.1 (/playground)
thread 'rustc' panicked at compiler/rustc_mir_transform/src/coroutine/by_move_body.rs:140:21:
assertion `left != right` failed: `FnOnce` coroutine-closures return coroutines that capture from their body; it will always result in a borrowck error!
  left: FnOnce
 right: FnOnce
stack backtrace:
   0:     0x7f5b0babe015 - std::backtrace_rs::backtrace::libunwind::trace::h202d45d8fd20a824
                               at /rustc/aed2187d53b8789e3a37f50ae36f894a2a679077/library/std/src/../../backtrace/src/backtrace/libunwind.rs:105:5
   1:     0x7f5b0babe015 - std::backtrace_rs::backtrace::trace_unsynchronized::h1daee13ebb59eeb4
                               at /rustc/aed2187d53b8789e3a37f50ae36f894a2a679077/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x7f5b0babe015 - std::sys_common::backtrace::_print_fmt::hf1c1d6c712400d1b
                               at /rustc/aed2187d53b8789e3a37f50ae36f894a2a679077/library/std/src/sys_common/backtrace.rs:68:5
   3:     0x7f5b0babe015 - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::ha6cb3dac0d776969
                               at /rustc/aed2187d53b8789e3a37f50ae36f894a2a679077/library/std/src/sys_common/backtrace.rs:44:22
   4:     0x7f5b0bb0d27b - core::fmt::rt::Argument::fmt::hb86c5e5f8ba90810
                               at /rustc/aed2187d53b8789e3a37f50ae36f894a2a679077/library/core/src/fmt/rt.rs:165:63
   5:     0x7f5b0bb0d27b - core::fmt::write::h5b057186bbc5fec2
                               at /rustc/aed2187d53b8789e3a37f50ae36f894a2a679077/library/core/src/fmt/mod.rs:1157:21
   6:     0x7f5b0bab2bbf - std::io::Write::write_fmt::h62aa7b9115cec986
                               at /rustc/aed2187d53b8789e3a37f50ae36f894a2a679077/library/std/src/io/mod.rs:1832:15
   7:     0x7f5b0babddee - std::sys_common::backtrace::_print::hdfcedaa64cb5957c
                               at /rustc/aed2187d53b8789e3a37f50ae36f894a2a679077/library/std/src/sys_common/backtrace.rs:47:5
   8:     0x7f5b0babddee - std::sys_common::backtrace::print::h128dd53d70614027
                               at /rustc/aed2187d53b8789e3a37f50ae36f894a2a679077/library/std/src/sys_common/backtrace.rs:34:9
   9:     0x7f5b0bac0759 - std::panicking::default_hook::{{closure}}::h25cd5b2272122564
  10:     0x7f5b0bac049d - std::panicking::default_hook::h3f62a662b49f346a
                               at /rustc/aed2187d53b8789e3a37f50ae36f894a2a679077/library/std/src/panicking.rs:298:9
  11:     0x7f5b0eb62d0c - std[f6dbfb092428beee]::panicking::update_hook::<alloc[1dedc0b6462c0e58]::boxed::Box<rustc_driver_impl[a06908b56a08a5f3]::install_ice_hook::{closure#0}>>::{closure#0}
  12:     0x7f5b0bac0e56 - <alloc::boxed::Box<F,A> as core::ops::function::Fn<Args>>::call::h195b48b24ae880e2
                               at /rustc/aed2187d53b8789e3a37f50ae36f894a2a679077/library/alloc/src/boxed.rs:2036:9
  13:     0x7f5b0bac0e56 - std::panicking::rust_panic_with_hook::h906fa2f149cd991b
                               at /rustc/aed2187d53b8789e3a37f50ae36f894a2a679077/library/std/src/panicking.rs:799:13
  14:     0x7f5b0bac0c04 - std::panicking::begin_panic_handler::{{closure}}::hf5f40df14bc3ecc3
                               at /rustc/aed2187d53b8789e3a37f50ae36f894a2a679077/library/std/src/panicking.rs:664:13
  15:     0x7f5b0babe4d9 - std::sys_common::backtrace::__rust_end_short_backtrace::h6caf7624fbbe1a8f
                               at /rustc/aed2187d53b8789e3a37f50ae36f894a2a679077/library/std/src/sys_common/backtrace.rs:171:18
  16:     0x7f5b0bac0937 - rust_begin_unwind
                               at /rustc/aed2187d53b8789e3a37f50ae36f894a2a679077/library/std/src/panicking.rs:652:5
  17:     0x7f5b0bb09743 - core::panicking::panic_fmt::h24ccdca200c3cead
                               at /rustc/aed2187d53b8789e3a37f50ae36f894a2a679077/library/core/src/panicking.rs:72:14
  18:     0x7f5b0bb09d0f - core::panicking::assert_failed_inner::h154a63e2b6258de7
                               at /rustc/aed2187d53b8789e3a37f50ae36f894a2a679077/library/core/src/panicking.rs:404:23
  19:     0x7f5b0f161938 - core[3cc7221ca1340ad0]::panicking::assert_failed::<rustc_type_ir[f35b0a68110f4e13]::ClosureKind, rustc_type_ir[f35b0a68110f4e13]::ClosureKind>
  20:     0x7f5b0e383740 - <rustc_mir_transform[2378a63253b3ac0c]::coroutine::by_move_body::ByMoveBody as rustc_middle[fb5dda08dce04472]::mir::MirPass>::run_pass
  21:     0x7f5b0ff3394d - rustc_mir_transform[2378a63253b3ac0c]::pass_manager::run_passes_inner
  22:     0x7f5b102521a8 - rustc_query_impl[ffc1dc643be498fd]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[ffc1dc643be498fd]::query_impl::mir_built::dynamic_query::{closure#2}::{closure#0}, rustc_middle[fb5dda08dce04472]::query::erase::Erased<[u8; 8usize]>>
  23:     0x7f5b10348771 - rustc_query_system[6eb3337d20c14267]::query::plumbing::try_execute_query::<rustc_query_impl[ffc1dc643be498fd]::DynamicConfig<rustc_query_system[6eb3337d20c14267]::query::caches::VecCache<rustc_span[413b5bd4996aee21]::def_id::LocalDefId, rustc_middle[fb5dda08dce04472]::query::erase::Erased<[u8; 8usize]>>, false, false, false>, rustc_query_impl[ffc1dc643be498fd]::plumbing::QueryCtxt, false>
  24:     0x7f5b1034828c - rustc_query_impl[ffc1dc643be498fd]::query_impl::mir_built::get_query_non_incr::__rust_end_short_backtrace
  25:     0x7f5b103340b0 - <rustc_mir_build[a31e700f633e9780]::check_unsafety::UnsafetyVisitor>::visit_inner_body
  26:     0x7f5b0d506cd4 - <rustc_mir_build[a31e700f633e9780]::check_unsafety::UnsafetyVisitor as rustc_middle[fb5dda08dce04472]::thir::visit::Visitor>::visit_expr
  27:     0x7f5b103341c1 - <rustc_mir_build[a31e700f633e9780]::check_unsafety::UnsafetyVisitor>::visit_inner_body
  28:     0x7f5b0d506cd4 - <rustc_mir_build[a31e700f633e9780]::check_unsafety::UnsafetyVisitor as rustc_middle[fb5dda08dce04472]::thir::visit::Visitor>::visit_expr
  29:     0x7f5b1077d119 - <rustc_mir_build[a31e700f633e9780]::check_unsafety::UnsafetyVisitor as rustc_middle[fb5dda08dce04472]::thir::visit::Visitor>::visit_block
  30:     0x7f5b0d507fd0 - <rustc_mir_build[a31e700f633e9780]::check_unsafety::UnsafetyVisitor as rustc_middle[fb5dda08dce04472]::thir::visit::Visitor>::visit_expr
  31:     0x7f5b0d506cd4 - <rustc_mir_build[a31e700f633e9780]::check_unsafety::UnsafetyVisitor as rustc_middle[fb5dda08dce04472]::thir::visit::Visitor>::visit_expr
  32:     0x7f5b10331324 - rustc_mir_build[a31e700f633e9780]::check_unsafety::check_unsafety
  33:     0x7f5b10330dd1 - rustc_query_impl[ffc1dc643be498fd]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[ffc1dc643be498fd]::query_impl::check_unsafety::dynamic_query::{closure#2}::{closure#0}, rustc_middle[fb5dda08dce04472]::query::erase::Erased<[u8; 0usize]>>
  34:     0x7f5b1032fe4d - rustc_query_system[6eb3337d20c14267]::query::plumbing::try_execute_query::<rustc_query_impl[ffc1dc643be498fd]::DynamicConfig<rustc_query_system[6eb3337d20c14267]::query::caches::VecCache<rustc_span[413b5bd4996aee21]::def_id::LocalDefId, rustc_middle[fb5dda08dce04472]::query::erase::Erased<[u8; 0usize]>>, false, false, false>, rustc_query_impl[ffc1dc643be498fd]::plumbing::QueryCtxt, false>
  35:     0x7f5b1032faff - rustc_query_impl[ffc1dc643be498fd]::query_impl::check_unsafety::get_query_non_incr::__rust_end_short_backtrace
  36:     0x7f5b103282e5 - rustc_interface[7ce95aec19cf85e]::passes::analysis
  37:     0x7f5b103273d5 - rustc_query_impl[ffc1dc643be498fd]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[ffc1dc643be498fd]::query_impl::analysis::dynamic_query::{closure#2}::{closure#0}, rustc_middle[fb5dda08dce04472]::query::erase::Erased<[u8; 1usize]>>
  38:     0x7f5b10d2a9e5 - rustc_query_system[6eb3337d20c14267]::query::plumbing::try_execute_query::<rustc_query_impl[ffc1dc643be498fd]::DynamicConfig<rustc_query_system[6eb3337d20c14267]::query::caches::SingleCache<rustc_middle[fb5dda08dce04472]::query::erase::Erased<[u8; 1usize]>>, false, false, false>, rustc_query_impl[ffc1dc643be498fd]::plumbing::QueryCtxt, false>
  39:     0x7f5b10d2a749 - rustc_query_impl[ffc1dc643be498fd]::query_impl::analysis::get_query_non_incr::__rust_end_short_backtrace
  40:     0x7f5b10b8a98e - rustc_interface[7ce95aec19cf85e]::interface::run_compiler::<core[3cc7221ca1340ad0]::result::Result<(), rustc_span[413b5bd4996aee21]::ErrorGuaranteed>, rustc_driver_impl[a06908b56a08a5f3]::run_compiler::{closure#0}>::{closure#1}
  41:     0x7f5b10b77327 - std[f6dbfb092428beee]::sys_common::backtrace::__rust_begin_short_backtrace::<rustc_interface[7ce95aec19cf85e]::util::run_in_thread_with_globals<rustc_interface[7ce95aec19cf85e]::util::run_in_thread_pool_with_globals<rustc_interface[7ce95aec19cf85e]::interface::run_compiler<core[3cc7221ca1340ad0]::result::Result<(), rustc_span[413b5bd4996aee21]::ErrorGuaranteed>, rustc_driver_impl[a06908b56a08a5f3]::run_compiler::{closure#0}>::{closure#1}, core[3cc7221ca1340ad0]::result::Result<(), rustc_span[413b5bd4996aee21]::ErrorGuaranteed>>::{closure#0}, core[3cc7221ca1340ad0]::result::Result<(), rustc_span[413b5bd4996aee21]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[3cc7221ca1340ad0]::result::Result<(), rustc_span[413b5bd4996aee21]::ErrorGuaranteed>>
  42:     0x7f5b10b770ea - <<std[f6dbfb092428beee]::thread::Builder>::spawn_unchecked_<rustc_interface[7ce95aec19cf85e]::util::run_in_thread_with_globals<rustc_interface[7ce95aec19cf85e]::util::run_in_thread_pool_with_globals<rustc_interface[7ce95aec19cf85e]::interface::run_compiler<core[3cc7221ca1340ad0]::result::Result<(), rustc_span[413b5bd4996aee21]::ErrorGuaranteed>, rustc_driver_impl[a06908b56a08a5f3]::run_compiler::{closure#0}>::{closure#1}, core[3cc7221ca1340ad0]::result::Result<(), rustc_span[413b5bd4996aee21]::ErrorGuaranteed>>::{closure#0}, core[3cc7221ca1340ad0]::result::Result<(), rustc_span[413b5bd4996aee21]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[3cc7221ca1340ad0]::result::Result<(), rustc_span[413b5bd4996aee21]::ErrorGuaranteed>>::{closure#2} as core[3cc7221ca1340ad0]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  43:     0x7f5b0bacac8b - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h8f96bdbdef28286c
                               at /rustc/aed2187d53b8789e3a37f50ae36f894a2a679077/library/alloc/src/boxed.rs:2022:9
  44:     0x7f5b0bacac8b - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::hdc6d9d278290e1ae
                               at /rustc/aed2187d53b8789e3a37f50ae36f894a2a679077/library/alloc/src/boxed.rs:2022:9
  45:     0x7f5b0bacac8b - std::sys::pal::unix::thread::Thread::new::thread_start::hd8b6cbeea7b365c6
                               at /rustc/aed2187d53b8789e3a37f50ae36f894a2a679077/library/std/src/sys/pal/unix/thread.rs:108:17
  46:     0x7f5b0b9d8609 - start_thread
  47:     0x7f5b0b8fb353 - clone
  48:                0x0 - <unknown>

error: 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: please make sure that you have updated to the latest nightly

note: please attach the file at `/playground/rustc-ice-2024-04-28T18_30_30-119.txt` to your bug report

note: compiler flags: --crate-type bin -C embed-bitcode=no -C codegen-units=1 -C debuginfo=2

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

query stack during panic:
#0 [mir_built] building MIR for `foo::{closure#0}::{closure#0}`
#1 [check_unsafety] unsafety-checking `foo`
#2 [analysis] running analysis passes on this crate
end of query stack
error: could not compile `playground` (bin "playground")

@rustbot modify labels: +regression-from-nightly-to-nightly -regression-untriaged

Thanks for investigating!

Workaround

async move || { ... } -> move || async move { ... }

[compiler-errors]

Nightly-only features aren't typically regression triaged. I'll look into it soon.