linux-kernel - Re: [PATCH v2 5/5] rust: enable `clippy::as

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Message-ID: <CAJ-ks9k1gZ=tLSe6OjuKFgg6=QE5R_Ajo0ZJwZJp08_1LMiODw@mail.gmail.com>
Date: Wed, 12 Mar 2025 18:24:48 -0400
From: Tamir Duberstein <tamird@...il.com>
To: Benno Lossin <benno.lossin@...ton.me>
Cc: Masahiro Yamada <masahiroy@...nel.org>, Nathan Chancellor <nathan@...nel.org>, 
	Nicolas Schier <nicolas@...sle.eu>, Miguel Ojeda <ojeda@...nel.org>, 
	Alex Gaynor <alex.gaynor@...il.com>, Boqun Feng <boqun.feng@...il.com>, 
	Gary Guo <gary@...yguo.net>, Björn Roy Baron <bjorn3_gh@...tonmail.com>, 
	Andreas Hindborg <a.hindborg@...nel.org>, Alice Ryhl <aliceryhl@...gle.com>, 
	Trevor Gross <tmgross@...ch.edu>, Danilo Krummrich <dakr@...nel.org>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, "Rafael J. Wysocki" <rafael@...nel.org>, 
	Brendan Higgins <brendan.higgins@...ux.dev>, David Gow <davidgow@...gle.com>, 
	Rae Moar <rmoar@...gle.com>, Bjorn Helgaas <bhelgaas@...gle.com>, 
	Luis Chamberlain <mcgrof@...nel.org>, Russ Weight <russ.weight@...ux.dev>, Rob Herring <robh@...nel.org>, 
	Saravana Kannan <saravanak@...gle.com>, linux-kbuild@...r.kernel.org, 
	linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org, 
	linux-kselftest@...r.kernel.org, kunit-dev@...glegroups.com, 
	linux-pci@...r.kernel.org, linux-block@...r.kernel.org, 
	devicetree@...r.kernel.org
Subject: Re: [PATCH v2 5/5] rust: enable `clippy::as_underscore` lint

On Wed, Mar 12, 2025 at 5:30 PM Benno Lossin <benno.lossin@...ton.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@...il.com> wrote:
> >>
> >> On Wed, Mar 12, 2025 at 5:01 PM Benno Lossin <benno.lossin@...ton.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