[cpufeatures] nightly warning: unexpected cfg condition value: ``

[DaniPopes]

cpufeatures::new!(cpuid_avx2, "avx2");

On nightly x86_64-unknown-linux-gnu + no rustflags generates:

warning: unexpected `cfg` condition value: ``
  --> src/arch/x86.rs:33:9
   |
33 |         cpufeatures::new!(cpuid_avx2, "avx2");
   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: expected values for `target_os` are: `aix`, `android`, `cuda`, `dragonfly`, `emscripten`, `espidf`, `freebsd`, `fuchsia`, `haiku`, `hermit`, `horizon`, `hurd`, `illumos`, `ios`, `l4re`, `linux`, `macos`, `netbsd`, `none`, `nto`, `nuttx`, `openbsd`, `psp`, `psx`, `redox`, `rtems`, `solaris`, `solid_asp3`, `teeos`, `trusty`, `tvos`, `uefi`, `unknown`, `visionos`, and `vita` and 6 more
   = note: see <https://doc.rust-lang.org/nightly/rustc/check-cfg/cargo-specifics.html> for more information about checking conditional configuration
   = note: this warning originates in the macro `$crate::__unless_target_features` which comes from the expansion of the macro `cpufeatures::new` (in Nightly builds, run with -Z macro-backtrace for more info)

Rust:

rustc 1.84.0-nightly (3fee0f12e 2024-11-20)
binary: rustc
commit-hash: 3fee0f12e4f595948f8f54f57c8b7a7a58127124
commit-date: 2024-11-20
host: x86_64-unknown-linux-gnu
release: 1.84.0-nightly
LLVM version: 19.1.3

Due to this line:

utils/cpufeatures/src/x86.rs

Line 17 in e74e578

#[cfg(not(any(target_env = "sgx", target_os = "", target_os = "uefi")))]

[newpavlov]

Hm, I guess we should use none instead of an empty line?

UPD: Yeap, the x86_64-unknown-none spec uses the default value for target_os, i.e. none.