ICE: attrs: `error was constructed but not emitted`

[matthiaskrgr]

snippet:

fn outer() -> u8 {
    #[cfg(foo)]
    cfg(foo)

    #[]
    fn
}

Version information

rustc 1.76.0-nightly (d5fab3376 2023-12-02)
binary: rustc
commit-hash: d5fab33766917085588d9bb4fb9477776695d98b
commit-date: 2023-12-02
host: x86_64-unknown-linux-gnu
release: 1.76.0-nightly
LLVM version: 17.0.5

but still crashes with

rustc 1.76.0-nightly (8b6a4a93e 2023-12-03)
binary: rustc
commit-hash: 8b6a4a93ed1bf637718e28ed266a5f6d70c2776d
commit-date: 2023-12-03
host: x86_64-unknown-linux-gnu
release: 1.76.0-nightly
LLVM version: 17.0.5

Command:
/home/matthias/.rustup/toolchains/master/bin/rustc

Program output

error: internal compiler error: the following error was constructed but not emitted

error: expected identifier, found `]`
 --> /tmp/icemaker_global_tempdir.E5kp2dgcGyxl/rustc_testrunner_tmpdir_reporting.LJKdvhI9GKUw/mvce.rs:5:7
  |
5 |     #[]
  |       ^ expected identifier

thread 'rustc' panicked at compiler/rustc_errors/src/diagnostic_builder.rs:768:21:
error was constructed but not emitted
stack backtrace:
   0:     0x7fb1bd9cb50c - std::backtrace_rs::backtrace::libunwind::trace::h479849121ff49a5d
                               at /rustc/d5fab33766917085588d9bb4fb9477776695d98b/library/std/src/../../backtrace/src/backtrace/libunwind.rs:104:5
   1:     0x7fb1bd9cb50c - std::backtrace_rs::backtrace::trace_unsynchronized::hc9644f16de94df45
                               at /rustc/d5fab33766917085588d9bb4fb9477776695d98b/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x7fb1bd9cb50c - std::sys_common::backtrace::_print_fmt::h10290334532192e1
                               at /rustc/d5fab33766917085588d9bb4fb9477776695d98b/library/std/src/sys_common/backtrace.rs:68:5
   3:     0x7fb1bd9cb50c - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::h1f3df53d81057b3e
                               at /rustc/d5fab33766917085588d9bb4fb9477776695d98b/library/std/src/sys_common/backtrace.rs:44:22
   4:     0x7fb1bda1e540 - core::fmt::rt::Argument::fmt::hb8e319fcddae9a31
                               at /rustc/d5fab33766917085588d9bb4fb9477776695d98b/library/core/src/fmt/rt.rs:142:9
   5:     0x7fb1bda1e540 - core::fmt::write::h80be9ea7045f640f
                               at /rustc/d5fab33766917085588d9bb4fb9477776695d98b/library/core/src/fmt/mod.rs:1120:17
   6:     0x7fb1bd9bf36f - std::io::Write::write_fmt::h0522d22623a1843b
                               at /rustc/d5fab33766917085588d9bb4fb9477776695d98b/library/std/src/io/mod.rs:1810:15
   7:     0x7fb1bd9cb2f4 - std::sys_common::backtrace::_print::h11954509d6d4a59e
                               at /rustc/d5fab33766917085588d9bb4fb9477776695d98b/library/std/src/sys_common/backtrace.rs:47:5
   8:     0x7fb1bd9cb2f4 - std::sys_common::backtrace::print::h89028ceab4fa2c56
                               at /rustc/d5fab33766917085588d9bb4fb9477776695d98b/library/std/src/sys_common/backtrace.rs:34:9
   9:     0x7fb1bd9cdf87 - std::panicking::default_hook::{{closure}}::ha828cf6bd2b63731
  10:     0x7fb1bd9cdcef - std::panicking::default_hook::h85bef85bc0f3798a
                               at /rustc/d5fab33766917085588d9bb4fb9477776695d98b/library/std/src/panicking.rs:292:9
  11:     0x7fb1ba6f9490 - std[be0bda08bb484463]::panicking::update_hook::<alloc[5e2c4fa57d45c172]::boxed::Box<rustc_driver_impl[7a73365881d43582]::install_ice_hook::{closure#0}>>::{closure#0}
  12:     0x7fb1bd9ce6c8 - <alloc::boxed::Box<F,A> as core::ops::function::Fn<Args>>::call::he0dee972ea8e9cc9
                               at /rustc/d5fab33766917085588d9bb4fb9477776695d98b/library/alloc/src/boxed.rs:2021:9
  13:     0x7fb1bd9ce6c8 - std::panicking::rust_panic_with_hook::he9727088864fdef9
                               at /rustc/d5fab33766917085588d9bb4fb9477776695d98b/library/std/src/panicking.rs:783:13
  14:     0x7fb1bd9ce3e9 - std::panicking::begin_panic_handler::{{closure}}::h80b7e677079c8e55
                               at /rustc/d5fab33766917085588d9bb4fb9477776695d98b/library/std/src/panicking.rs:649:13
  15:     0x7fb1bd9cb9d6 - std::sys_common::backtrace::__rust_end_short_backtrace::hd9049e8056407812
                               at /rustc/d5fab33766917085588d9bb4fb9477776695d98b/library/std/src/sys_common/backtrace.rs:171:18
  16:     0x7fb1bd9ce182 - rust_begin_unwind
                               at /rustc/d5fab33766917085588d9bb4fb9477776695d98b/library/std/src/panicking.rs:645:5
  17:     0x7fb1bda1ac15 - core::panicking::panic_fmt::h97f53bcafbf77918
                               at /rustc/d5fab33766917085588d9bb4fb9477776695d98b/library/core/src/panicking.rs:72:14
  18:     0x7fb1bc0129e9 - <rustc_errors[d85cd907ae34f40d]::diagnostic_builder::DiagnosticBuilderInner as core[9199d425737c1d72]::ops::drop::Drop>::drop
  19:     0x7fb1bc012a16 - core[9199d425737c1d72]::ptr::drop_in_place::<rustc_errors[d85cd907ae34f40d]::diagnostic_builder::DiagnosticBuilderInner>
  20:     0x7fb1b9424157 - <rustc_parse[e3a3cb118eb68122]::parser::Parser>::attr_on_non_tail_expr
  21:     0x7fb1bc0c6cb0 - <rustc_parse[e3a3cb118eb68122]::parser::Parser>::parse_block_tail
  22:     0x7fb1bbde159f - <rustc_parse[e3a3cb118eb68122]::parser::Parser>::parse_fn
  23:     0x7fb1bc0b4c2f - <rustc_parse[e3a3cb118eb68122]::parser::Parser>::parse_item_kind
  24:     0x7fb1bbdf993f - <rustc_parse[e3a3cb118eb68122]::parser::Parser>::parse_item_common
  25:     0x7fb1bbdf6fec - <rustc_parse[e3a3cb118eb68122]::parser::Parser>::parse_mod
  26:     0x7fb1bc972350 - rustc_interface[2959b8b48a60afbe]::passes::parse
  27:     0x7fb1bc9720ce - <rustc_interface[2959b8b48a60afbe]::queries::Queries>::parse
  28:     0x7fb1bc968de5 - rustc_interface[2959b8b48a60afbe]::interface::run_compiler::<core[9199d425737c1d72]::result::Result<(), rustc_span[baba122c7922aac3]::ErrorGuaranteed>, rustc_driver_impl[7a73365881d43582]::run_compiler::{closure#0}>::{closure#0}
  29:     0x7fb1bc95c411 - std[be0bda08bb484463]::sys_common::backtrace::__rust_begin_short_backtrace::<rustc_interface[2959b8b48a60afbe]::util::run_in_thread_with_globals<rustc_interface[2959b8b48a60afbe]::util::run_in_thread_pool_with_globals<rustc_interface[2959b8b48a60afbe]::interface::run_compiler<core[9199d425737c1d72]::result::Result<(), rustc_span[baba122c7922aac3]::ErrorGuaranteed>, rustc_driver_impl[7a73365881d43582]::run_compiler::{closure#0}>::{closure#0}, core[9199d425737c1d72]::result::Result<(), rustc_span[baba122c7922aac3]::ErrorGuaranteed>>::{closure#0}, core[9199d425737c1d72]::result::Result<(), rustc_span[baba122c7922aac3]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[9199d425737c1d72]::result::Result<(), rustc_span[baba122c7922aac3]::ErrorGuaranteed>>
  30:     0x7fb1bc95c23b - <<std[be0bda08bb484463]::thread::Builder>::spawn_unchecked_<rustc_interface[2959b8b48a60afbe]::util::run_in_thread_with_globals<rustc_interface[2959b8b48a60afbe]::util::run_in_thread_pool_with_globals<rustc_interface[2959b8b48a60afbe]::interface::run_compiler<core[9199d425737c1d72]::result::Result<(), rustc_span[baba122c7922aac3]::ErrorGuaranteed>, rustc_driver_impl[7a73365881d43582]::run_compiler::{closure#0}>::{closure#0}, core[9199d425737c1d72]::result::Result<(), rustc_span[baba122c7922aac3]::ErrorGuaranteed>>::{closure#0}, core[9199d425737c1d72]::result::Result<(), rustc_span[baba122c7922aac3]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[9199d425737c1d72]::result::Result<(), rustc_span[baba122c7922aac3]::ErrorGuaranteed>>::{closure#1} as core[9199d425737c1d72]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  31:     0x7fb1bd9d8555 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h97e5c9d6b1622657
                               at /rustc/d5fab33766917085588d9bb4fb9477776695d98b/library/alloc/src/boxed.rs:2007:9
  32:     0x7fb1bd9d8555 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::hb5f6014336ba501b
                               at /rustc/d5fab33766917085588d9bb4fb9477776695d98b/library/alloc/src/boxed.rs:2007:9
  33:     0x7fb1bd9d8555 - std::sys::unix::thread::Thread::new::thread_start::h758e18463c2780d9
                               at /rustc/d5fab33766917085588d9bb4fb9477776695d98b/library/std/src/sys/unix/thread.rs:108:17
  34:     0x7fb1b78aa9eb - <unknown>
  35:     0x7fb1b792e7cc - <unknown>
  36:                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: rustc 1.76.0-nightly (d5fab3376 2023-12-02) running on x86_64-unknown-linux-gnu

query stack during panic:
end of query stack
error: aborting due to 2 previous errors

[sjwang05]

Reduced further:

fn outer() -> u8 {
    #[cfg(foo)]
    cfg(foo)
    #[]
}

searched nightlies: from nightly-2023-11-17 to nightly-2023-12-02
regressed nightly: nightly-2023-11-21
searched commit range: 9a66e44...3a85a5c
regressed commit: 46ecc10

bisected with cargo-bisect-rustc v0.6.7

Host triple: x86_64-pc-windows-msvc
Reproduce with:

cargo bisect-rustc

Looks like #117988

[sjwang05]

This might be a duplicate of #118164, now that I've taken another look at it

[matthiaskrgr]

When I checked, 118164 was already fixed but this one wasn't

[sjwang05]

You're right--#118164 doesn't reproduce with the latest nightly, but this one does, which I find strange since I thought they have the same root cause, which #118182 should address. (Hence also why I closed #118582--it almost exactly duplicated the work in #118182.)

[bend-n]

Can be further reduced to

fn outer() {
    #[cfg(foo)]
    cfg
    #[]
}