The KnownLayout macro has an issue with the latest nightly

[AaronKutch]

This is failing for me with nightly-2024-11-26

use zerocopy::{FromBytes, Immutable, IntoBytes, KnownLayout, Unaligned};

#[derive(
    Clone, Copy, Hash, PartialEq, Eq, FromBytes, IntoBytes, KnownLayout, Immutable, Unaligned,
)]
#[repr(C)]
pub struct Test(pub [u8; 32]);

running cargo +nightly-2024-11-26 clippy gives

warning: unexpected `cfg` condition name: `coverage_nightly`
 --> src/main.rs:5:61
  |
5 |     Clone, Copy, Hash, PartialEq, Eq, FromBytes, IntoBytes, KnownLayout, Immutable, Unaligned,
  |                                                             ^^^^^^^^^^^
  |
  = help: expected names are: `clippy`, `debug_assertions`, `doc`, `docsrs`, `doctest`, `feature`, `fmt_debug`, `miri`, `overflow_checks`, `panic`, `proc_macro`, `relocation_model`, `rustfmt`, `sanitize`, `sanitizer_cfi_generalize_pointers`, `sanitizer_cfi_normalize_integers`, `target_abi`, `target_arch`, `target_endian`, `target_env`, `target_family`, `target_feature`, `target_has_atomic`, `target_has_atomic_equal_alignment`, `target_has_atomic_load_store`, `target_os`, `target_pointer_width`, `target_thread_local`, `target_vendor`, `test`, `ub_checks`, `unix`, and `windows`
  = help: consider using a Cargo feature instead
  = help: or consider adding in `Cargo.toml` the `check-cfg` lint config for the lint:
           [lints.rust]
           unexpected_cfgs = { level = "warn", check-cfg = ['cfg(coverage_nightly)'] }
  = help: or consider adding `println!("cargo::rustc-check-cfg=cfg(coverage_nightly)");` to the top of the `build.rs`
  = note: see <https://doc.rust-lang.org/nightly/rustc/check-cfg/cargo-specifics.html> for more information about checking conditional configuration
  = note: `#[warn(unexpected_cfgs)]` on by default
  = note: this warning originates in the derive macro `KnownLayout` (in Nightly builds, run with -Z macro-backtrace for more info)

which is causing issues in my strict CI

[joshlf]

I am able to reproduce this locally using zerocopy 0.8.11. Confusingly, when I run cargo expand, I don't see the string coverage_nightly anywhere in the output. That makes me think that this might be a compiler bug.

What was the most recent nightly for which this code passed Clippy without issue?

EDIT: I bisected locally and determined that the regression was introduced in nightly-2024-11-20.

[joshlf]

I've filed an issue upstream: rust-lang/rust#133775

[joshlf]

Update: It's actually a zerocopy bug.

Fix pending: #2123

[joshlf]

Fixed by #2123.

[joshlf]

The fix is now released in 0.8.12.