[PATCH v2 3/3] rust: ptr: allow clippy::incompatible_msrv for slice_ptr_len

[John Hubbard <jhubbard@nvidia.com>]

Clippy reports four warnings when building with CLIPPY=1:

  warning: current MSRV (Minimum Supported Rust Version) is `1.78.0` but this item is stable since `1.79.0`
    --> rust/kernel/ptr/projection.rs:79:26
     |
  79 |         if self >= slice.len() {
     |                          ^^^^^

  warning: current MSRV (Minimum Supported Rust Version) is `1.78.0` but this item is stable since `1.79.0`
    --> rust/kernel/ptr/projection.rs:95:29
     |
  95 |         if self.end > slice.len() {
     |                             ^^^^^

  warning: current MSRV (Minimum Supported Rust Version) is `1.78.0` but this item is stable since `1.79.0`
     --> rust/kernel/ptr/projection.rs:121:28
      |
  121 |         (self.start..slice.len()).get(slice)
      |                            ^^^^^

  warning: current MSRV (Minimum Supported Rust Version) is `1.78.0` but this item is stable since `1.79.0`
     --> rust/kernel/ptr.rs:253:11
      |
  253 |         p.len() * size_of::<T>()
      |           ^^^^^

These are false positives. The <*mut [T]>::len() and <*const [T]>::len()
methods are available because the kernel enables #![feature(slice_ptr_len)]
in lib.rs. Clippy does not account for feature gates when checking MSRV
compatibility.

Silence these false positive via #[allow(clippy::incompatible_msrv)].

Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
 rust/kernel/ptr.rs            | 1 +
 rust/kernel/ptr/projection.rs | 3 +++
 2 files changed, 4 insertions(+)

diff --git a/rust/kernel/ptr.rs b/rust/kernel/ptr.rs
index bdc2d79ff669..7482653ef160 100644
--- a/rust/kernel/ptr.rs
+++ b/rust/kernel/ptr.rs
@@ -248,6 +248,7 @@ fn size(_: *const Self) -> usize {
 }
 
 impl<T> KnownSize for [T] {
+    #[allow(clippy::incompatible_msrv)]
     #[inline(always)]
     fn size(p: *const Self) -> usize {
         p.len() * size_of::<T>()
diff --git a/rust/kernel/ptr/projection.rs b/rust/kernel/ptr/projection.rs
index 140ea8e21617..7d1c878b3116 100644
--- a/rust/kernel/ptr/projection.rs
+++ b/rust/kernel/ptr/projection.rs
@@ -74,6 +74,7 @@ fn index(self, slice: *mut T) -> *mut Self::Output {
 unsafe impl<T> ProjectIndex<[T]> for usize {
     type Output = T;
 
+    #[allow(clippy::incompatible_msrv)]
     #[inline(always)]
     fn get(self, slice: *mut [T]) -> Option<*mut T> {
         if self >= slice.len() {
@@ -89,6 +90,7 @@ fn get(self, slice: *mut [T]) -> Option<*mut T> {
 unsafe impl<T> ProjectIndex<[T]> for core::ops::Range<usize> {
     type Output = [T];
 
+    #[allow(clippy::incompatible_msrv)]
     #[inline(always)]
     fn get(self, slice: *mut [T]) -> Option<*mut [T]> {
         let new_len = self.end.checked_sub(self.start)?;
@@ -116,6 +118,7 @@ fn get(self, slice: *mut [T]) -> Option<*mut [T]> {
 unsafe impl<T> ProjectIndex<[T]> for core::ops::RangeFrom<usize> {
     type Output = [T];
 
+    #[allow(clippy::incompatible_msrv)]
     #[inline(always)]
     fn get(self, slice: *mut [T]) -> Option<*mut [T]> {
         (self.start..slice.len()).get(slice)
-- 
2.53.0