linux-kernel - Re: [PATCH v6 6/6] rust: enable `clippy::cast

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Message-ID: <D8PA773W07SS.3T2SZUIJH4HOH@proton.me>
Date: Tue, 25 Mar 2025 10:39:54 +0000
From: Benno Lossin <benno.lossin@...ton.me>
To: Tamir Duberstein <tamird@...il.com>, 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>, Abdiel Janulgue <abdiel.janulgue@...il.com>, Daniel Almeida <daniel.almeida@...labora.com>, Robin Murphy
	<robin.murphy@....com>, Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, FUJITA Tomonori <fujita.tomonori@...il.com>
Cc: 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, dri-devel@...ts.freedesktop.org, netdev@...r.kernel.org
Subject: Re: [PATCH v6 6/6] rust: enable `clippy::cast_lossless` lint

On Mon Mar 24, 2025 at 11:01 PM CET, Tamir Duberstein wrote:
> Before Rust 1.29.0, Clippy introduced the `cast_lossless` lint [1]:
>
>> Rust’s `as` keyword will perform many kinds of conversions, including
>> silently lossy conversions. Conversion functions such as `i32::from`
>> will only perform lossless conversions. Using the conversion functions
>> prevents conversions from becoming silently lossy if the input types
>> ever change, and makes it clear for people reading the code that the
>> conversion is lossless.
>
> While this doesn't eliminate unchecked `as` conversions, it makes such
> conversions easier to scrutinize.  It also has the slight benefit of
> removing a degree of freedom on which to bikeshed. Thus apply the
> changes and enable the lint -- no functional change intended.
>
> Link: https://rust-lang.github.io/rust-clippy/master/index.html#cast_lossless [1]
> Suggested-by: Benno Lossin <benno.lossin@...ton.me>
> Link: https://lore.kernel.org/all/D8ORTXSUTKGL.1KOJAGBM8F8TN@proton.me/
> Signed-off-by: Tamir Duberstein <tamird@...il.com>

One nit below, but you may add:

Reviewed-by: Benno Lossin <benno.lossin@...ton.me>

> ---
>  Makefile                        |  1 +
>  drivers/gpu/drm/drm_panic_qr.rs | 10 +++++-----
>  rust/bindings/lib.rs            |  2 +-
>  rust/kernel/net/phy.rs          |  4 ++--
>  4 files changed, 9 insertions(+), 8 deletions(-)

> diff --git a/rust/bindings/lib.rs b/rust/bindings/lib.rs
> index 0486a32ed314..591e4ca9bc54 100644
> --- a/rust/bindings/lib.rs
> +++ b/rust/bindings/lib.rs
> @@ -25,7 +25,7 @@
>  )]
>  
>  #[allow(dead_code)]
> -#[allow(clippy::ptr_as_ptr)]
> +#[allow(clippy::cast_lossless, clippy::ptr_as_ptr)]

Not sure if we instead want this in a separate attribute, ultimately it
doesn't really matter, but why should `undocumented_unsafe_blocks` be
special?

---
Cheers,
Benno

>  #[allow(clippy::undocumented_unsafe_blocks)]
>  mod bindings_raw {
>      // Manual definition for blocklisted types.