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

[Benno Lossin]

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>

> ---
>  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.