Update std_detect support for AArch64 Darwin

[pthariensflame]

This makes it current as of late September, 2026.

No part of this was done using LLMs in any capacity.

[rustbot]

Some changes occurred in std_detect

cc @Amanieu, @folkertdev, @sayantn

[rustbot]

r? @Darksonn

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[Darksonn]

This doesn't match the Linux check:

rust/library/std_detect/src/detect/os/linux/aarch64.rs

Lines 372 to 373 in c1bf6e1

	let fp8 = self.f8cvt && self.faminmax && self.lut && self.bf16;
	enable_feature(Feature::fp8, fp8);

Note that the fp8 feature was changed in LLVM to depend on just neon rather than FeatureFAMINMAX, FeatureLUT, FeatureBF16 in llvm/llvm-project#125874. But rustc still lists those three features. Should this also be updated to match LLVM?

View changes since the review

[pthariensflame]

We have no idea; who would be the best person to consult for this?

[Darksonn]

Hopefully one of the people cc'd above by the bot can help.

[folkertdev]

cc @davidtwco @adamgemmell (target maintainers), but seems to me that we should follow LLVM here?

[adamgemmell]

Unfortunately it's a breaking change to do so as this example would require an unsafe context on the call:

#[target_feature(enable="fp8")]
fn fp8() {
    bf16();
}

#[target_feature(enable="bf16")]
fn bf16() {}

[pthariensflame]

Unfortunately it's a breaking change to do so as this example would require an unsafe context on the call

Would that be potentially solvable by use of a new feature (fp8cvt, name subject to bikeshedding) to represent the actual FEAT_FP8 and then redefining fp8 retroactively to imply fp8cvt+lut+bf16+faminmax?

Or is it okay to do this breaking change as fp8 is currently unstable anyway?

[adamgemmell]

Oh, if fp8 is still unstable then we can just make that change :)