Re: [PATCH v6 6/6] rust: enable `clippy::cast_lossless` lint

[Tamir Duberstein]

On Tue, Mar 25, 2025 at 6:40 AM Benno Lossin <benno.lossin@xxxxxxxxx> 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@xxxxxxxxx>
> > Link: https://lore.kernel.org/all/D8ORTXSUTKGL.1KOJAGBM8F8TN@xxxxxxxxx/
> > Signed-off-by: Tamir Duberstein <tamird@xxxxxxxxx>
>
> One nit below, but you may add:
>
> Reviewed-by: Benno Lossin <benno.lossin@xxxxxxxxx>

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