[PATCH] rust: error: allow `useless_conversion` for 32-bit builds

[Miguel Ojeda <ojeda@kernel.org>]

For the new Rust support for 32-bit arm [1], Clippy warns:

    error: useless conversion to the same type: `i32`
       --> rust/kernel/error.rs:139:36
        |
    139 |         unsafe { bindings::ERR_PTR(self.0.into()) as *mut _ }
        |                                    ^^^^^^^^^^^^^ help: consider removing `.into()`: `self.0`
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#useless_conversion
        = note: `-D clippy::useless-conversion` implied by `-D warnings`
        = help: to override `-D warnings` add `#[allow(clippy::useless_conversion)]`

The `self.0.into()` converts an `c_int` into `ERR_PTR`'s parameter
which is a `c_long`. Thus, both types are `i32` in 32-bit. Therefore,
allow it for those architectures.

Link: https://lore.kernel.org/rust-for-linux/2dbd1491-149d-443c-9802-75786a6a3b73@gmail.com/ [1]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
---
 rust/kernel/error.rs | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/rust/kernel/error.rs b/rust/kernel/error.rs
index 145f5c397009..6f1587a2524e 100644
--- a/rust/kernel/error.rs
+++ b/rust/kernel/error.rs
@@ -135,8 +135,11 @@ pub(crate) fn to_blk_status(self) -> bindings::blk_status_t {
     /// Returns the error encoded as a pointer.
     #[allow(dead_code)]
     pub(crate) fn to_ptr<T>(self) -> *mut T {
+        #[cfg_attr(target_pointer_width = "32", allow(clippy::useless_conversion))]
         // SAFETY: `self.0` is a valid error due to its invariant.
-        unsafe { bindings::ERR_PTR(self.0.into()) as *mut _ }
+        unsafe {
+            bindings::ERR_PTR(self.0.into()) as *mut _
+        }
     }
 
     /// Returns a string representing the error, if one exists.

base-commit: 8400291e289ee6b2bf9779ff1c83a291501f017b
-- 
2.46.0