rust: enable Clippy's check-private-items

In Rust 1.76.0, Clippy added the `check-private-items` lint configuration
option. When turned on (the default is off), it makes several lints
check private items as well.

In our case, it affects two lints we have enabled [1]:
`missing_safety_doc` and `unnecessary_safety_doc`.

It also seems to affect the new `too_long_first_doc_paragraph` lint [2],
even though the documentation does not mention it.

Thus allow the few instances remaining we currently hit and enable
the lint.

Link: https://doc.rust-lang.org/nightly/clippy/lint_configuration.html#check-private-items [1]
Link: https://rust-lang.github.io/rust-clippy/master/index.html#/too_long_first_doc_paragraph [2]
Reviewed-by: Trevor Gross <[email protected]>
Reviewed-by: Alice Ryhl <[email protected]>
Tested-by: Gary Guo <[email protected]>
Reviewed-by: Gary Guo <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Miguel Ojeda <[email protected]>
(cherry picked from commit 624063b9ac97f40cadca32a896aafeb28b1220fd)
Signed-off-by: Paolo Bonzini <[email protected]>

Author: ojeda

.clippy.toml

@@ -0,0 +1,3 @@
+# SPDX-License-Identifier: GPL-2.0
+
+check-private-items = true

examples/mutex.rs

@@ -1,5 +1,6 @@
 #![allow(clippy::undocumented_unsafe_blocks)]
 #![cfg_attr(feature = "alloc", feature(allocator_api))]
+#![allow(clippy::missing_safety_doc)]
 
 use core::{
     cell::{Cell, UnsafeCell},

src/__internal.rs

@@ -61,6 +61,7 @@ where
 pub unsafe trait HasPinData {
     type PinData: PinData;
 
+    #[allow(clippy::missing_safety_doc)]
     unsafe fn __pin_data() -> Self::PinData;
 }
 
@@ -90,6 +91,7 @@ pub unsafe trait PinData: Copy {
 pub unsafe trait HasInitData {
     type InitData: InitData;
 
+    #[allow(clippy::missing_safety_doc)]
     unsafe fn __init_data() -> Self::InitData;
 }
 

src/macros.rs

@@ -989,6 +989,7 @@ macro_rules! __pin_data {
         //
         // The functions are `unsafe` to prevent accidentally calling them.
         #[allow(dead_code)]
+        #[allow(clippy::missing_safety_doc)]
         impl<$($impl_generics)*> $pin_data<$($ty_generics)*>
         where $($whr)*
         {