Fix warnings in str.rs and binding_generated.rs

rust/kernel/str.rs

@@ -89,10 +89,14 @@ impl CStr {
  /// must not be mutated.
  #[inline]
  pub unsafe fn from_char_ptr<'a>(ptr: *const c_types::c_char) -> &'a Self {
+ // SAFETY: The safety precondition guarantees `ptr` is a valid pointer
+ // to a `NUL`-terminated C string.
  let len = unsafe { bindings::strlen(ptr) } + 1;
- unsafe {
- Self::from_bytes_with_nul_unchecked(core::slice::from_raw_parts(ptr as _, len as _))
- }
+ // SAFETY: Lifetime guaranteed by the safety precondition.
+ let bytes = unsafe { core::slice::from_raw_parts(ptr as _, len as _) };
+ // SAFETY: As `len` is returned by `strlen`, `bytes` does not contain interior `NUL`.
+ // As we have added 1 to `len`, the last byte is known to be `NUL`.
+ unsafe { Self::from_bytes_with_nul_unchecked(bytes) }
  }
 
  /// Creates a [`CStr`] from a `[u8]`.
@@ -146,6 +150,7 @@ impl CStr {
  // requires `ptr_metadata`).
  // While none of them are current stable, it is very likely that one of
  // them will eventually be.
+ // SAFETY: Properties of `bytes` guaranteed by the safety precondition.
  unsafe { &*(bytes as *const [u8] as *const Self) }
  }
 
@@ -188,11 +193,10 @@ impl Index<ops::RangeFrom<usize>> for CStr {
  type Output = CStr;
 
  #[inline]
- // Clippy false positive
- #[allow(clippy::unnecessary_operation)]
  fn index(&self, index: ops::RangeFrom<usize>) -> &Self::Output {
  // Delegate bounds checking to slice.
- &self.as_bytes()[index.start..];
+ // Assign to _ to mute clippy's unnecessary operation warning.
+ let _ = &self.as_bytes()[index.start..];
  // SAFETY: We just checked the bounds.
  unsafe { Self::from_bytes_with_nul_unchecked(&self.0[index.start..]) }
  }