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

Tamir Duberstein
2025-03-12T22:25:27Z

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.

>
> > 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.

Thanks!
Tamir