[PATCH] rust: transmute: use split_at_checked() and split_at_mut_checked()

[Albab Hasan]

Replace manual bounds checking followed by split_at() and split_at_mut()
calls with the checked variants split_at_checked() and
split_at_mut_checked(), which return None instead of panicking on
out-of-bounds indices.

These methods were stabilized in Rust 1.80.0, which is the current
minimum supported Rust version for the kernel.

This simplifies from_bytes_prefix(), from_bytes_mut_prefix(), and
from_bytes_copy_prefix() by removing the explicit bounds checks and
panic-avoidance comments that are no longer needed.

Signed-off-by: Albab Hasan <albabhasan276@xxxxxxxxx>
---
 rust/kernel/transmute.rs | 33 ++++++---------------------------
 1 file changed, 6 insertions(+), 27 deletions(-)

diff --git a/rust/kernel/transmute.rs b/rust/kernel/transmute.rs
index 5711580c9f9b..643b19406a24 100644
--- a/rust/kernel/transmute.rs
+++ b/rust/kernel/transmute.rs
@@ -67,16 +67,9 @@ fn from_bytes_prefix(bytes: &[u8]) -> Option<(&Self, &[u8])>
     where
         Self: Sized,
     {
-        if bytes.len() < size_of::<Self>() {
-            None
-        } else {
-            // PANIC: We checked that `bytes.len() >= size_of::<Self>`, thus `split_at` cannot
-            // panic.
-            // TODO: replace with `split_at_checked` once the MSRV is >= 1.80.
-            let (prefix, remainder) = bytes.split_at(size_of::<Self>());
+        let (prefix, remainder) = bytes.split_at_checked(size_of::<Self>())?;
 
-            Self::from_bytes(prefix).map(|s| (s, remainder))
-        }
+        Self::from_bytes(prefix).map(|s| (s, remainder))
     }
 
     /// Converts a mutable slice of bytes to a reference to `Self`.
@@ -110,16 +103,9 @@ fn from_bytes_mut_prefix(bytes: &mut [u8]) -> Option<(&mut Self, &mut [u8])>
     where
         Self: AsBytes + Sized,
     {
-        if bytes.len() < size_of::<Self>() {
-            None
-        } else {
-            // PANIC: We checked that `bytes.len() >= size_of::<Self>`, thus `split_at_mut` cannot
-            // panic.
-            // TODO: replace with `split_at_mut_checked` once the MSRV is >= 1.80.
-            let (prefix, remainder) = bytes.split_at_mut(size_of::<Self>());
+        let (prefix, remainder) = bytes.split_at_mut_checked(size_of::<Self>())?;
 
-            Self::from_bytes_mut(prefix).map(|s| (s, remainder))
-        }
+        Self::from_bytes_mut(prefix).map(|s| (s, remainder))
     }
 
     /// Creates an owned instance of `Self` by copying `bytes`.
@@ -149,16 +135,9 @@ fn from_bytes_copy_prefix(bytes: &[u8]) -> Option<(Self, &[u8])>
     where
         Self: Sized,
     {
-        if bytes.len() < size_of::<Self>() {
-            None
-        } else {
-            // PANIC: We checked that `bytes.len() >= size_of::<Self>`, thus `split_at` cannot
-            // panic.
-            // TODO: replace with `split_at_checked` once the MSRV is >= 1.80.
-            let (prefix, remainder) = bytes.split_at(size_of::<Self>());
+        let (prefix, remainder) = bytes.split_at_checked(size_of::<Self>())?;
 
-            Self::from_bytes_copy(prefix).map(|s| (s, remainder))
-        }
+        Self::from_bytes_copy(prefix).map(|s| (s, remainder))
     }
 }
 
-- 
2.43.0