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

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Message-ID: <CAJ-ks9=1BOsd-edBH-ZsDLzhtX=YfvZPMHebX=br4Wc1K1V-TA@mail.gmail.com>
Date: Tue, 25 Mar 2025 06:45:40 -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>, 
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	Luis Chamberlain <mcgrof@...nel.org>, Russ Weight <russ.weight@...ux.dev>, Rob Herring <robh@...nel.org>, 
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Subject: Re: [PATCH v6 6/6] rust: enable `clippy::cast_lossless` lint

On Tue, Mar 25, 2025 at 6:40 AM Benno Lossin <benno.lossin@...ton.me> wrote:
>
> 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>

Thanks!

>
> > ---
> >  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?

No reason. Moved it to a separate line. I won't respin just for this -
hopefully Miguel doesn't mind fixing when he takes it, if there's not
a v7 by then.

Tamir