Re: [PATCH v2 5/5] rust: enable `clippy::as_underscore` lint

[Benno Lossin <benno.lossin@proton.me>]

On Wed Mar 12, 2025 at 11:24 PM CET, Tamir Duberstein wrote:
> On Wed, Mar 12, 2025 at 5:30 PM Benno Lossin <benno.lossin@proton.me> wrote:
>>
>> On Wed Mar 12, 2025 at 10:10 PM CET, Tamir Duberstein wrote:
>> > On Wed, Mar 12, 2025 at 5:04 PM Tamir Duberstein <tamird@gmail.com> wrote:
>> >>
>> >> On Wed, Mar 12, 2025 at 5:01 PM Benno Lossin <benno.lossin@proton.me> wrote:
>> >> > Always enable the features, we have `allow(stable_features)` for this
>> >> > reason (then you don't have to do this dance with checking if it's
>> >> > already stable or not :)
>> >>
>> >> It's not so simple. In rustc < 1.84.0 the lints *and* the strict
>> >> provenance APIs are behind `feature(strict_provenance)`. In rustc >=
>> >> 1.84.0 the lints are behind `feature(strict_provenance_lints)`. So you
>> >> need to read the config to learn that you need to enable
>> >> `feature(strict_provenance_lints)`.
>>
>> I see... And `strict_provenance_lints` doesn't exist in <1.84? That's a
>> bit of a bummer...
>>
>> But I guess we could have this config option (in `init/Kconfig`):
>>
>>     config RUSTC_HAS_STRICT_PROVENANCE
>>             def_bool RUSTC_VERSION >= 108400
>>
>> and then do this in `lib.rs`:
>>
>>     #![cfg_attr(CONFIG_RUSTC_HAS_STRICT_PROVENANCE, feature(strict_provenance_lints))]
>
> Yep! That's exactly what I did, but as I mentioned up-thread, the
> result is that we only cover the `kernel` crate.

Ah I see, can't we just have the above line in the other crate roots?

>> > Actually this isn't even the only problem. It seems that
>> > `-Astable_features` doesn't affect features enabled on the command
>> > line at all:
>> >
>> > error[E0725]: the feature `strict_provenance` is not in the list of
>> > allowed features
>> >  --> <crate attribute>:1:9
>> >   |
>> > 1 | feature(strict_provenance)
>> >   |         ^^^^^^^^^^^^^^^^^
>>
>> That's because you need to append the feature to `rust_allowed_features`
>> in `scripts/Makefile.build` (AFAIK).
>
> Thanks, that's a helpful pointer, and it solves some problems but not
> all. The root Makefile contains this bit:
>
>> KBUILD_HOSTRUSTFLAGS := $(rust_common_flags) -O -Cstrip=debuginfo \
>> -Zallow-features= $(HOSTRUSTFLAGS)
>
> which means we can't use the provenance lints against these host
> targets (including e.g. `rustdoc_test_gen`). We can't remove this
> -Zallow-features= either because then core fails to compile.
>
> I'm at the point where I think I need more involved help. Want to take
> a look at my attempt? It's here:
> https://github.com/tamird/linux/tree/b4/ptr-as-ptr.

I'll take a look tomorrow, you're testing my knowledge of the build
system a lot here :)

---
Cheers,
Benno