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 <tmgross@umich.edu>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Tested-by: Gary Guo <gary@garyguo.net>
Reviewed-by: Gary Guo <gary@garyguo.net>
Link: https://lore.kernel.org/r/20240904204347.168520-16-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

.clippy.toml

@@ -1,5 +1,7 @@
 # SPDX-License-Identifier: GPL-2.0
 
+check-private-items = true
+
 disallowed-macros = [
     # The `clippy::dbg_macro` lint only works with `std::dbg!`, thus we simulate
     # it here, see: https://github.com/rust-lang/rust-clippy/issues/11303.

rust/kernel/init.rs

@@ -125,6 +125,7 @@
 //! use core::{ptr::addr_of_mut, marker::PhantomPinned, pin::Pin};
 //! # mod bindings {
 //! #     #![allow(non_camel_case_types)]
+//! #     #![allow(clippy::missing_safety_doc)]
 //! #     pub struct foo;
 //! #     pub unsafe fn init_foo(_ptr: *mut foo) {}
 //! #     pub unsafe fn destroy_foo(_ptr: *mut foo) {}

rust/kernel/init/__internal.rs

@@ -54,6 +54,7 @@ unsafe fn __pinned_init(self, slot: *mut T) -> Result<(), E> {
 pub unsafe trait HasPinData {
     type PinData: PinData;
 
+    #[allow(clippy::missing_safety_doc)]
     unsafe fn __pin_data() -> Self::PinData;
 }
 
@@ -83,6 +84,7 @@ fn make_closure<F, O, E>(self, f: F) -> F
 pub unsafe trait HasInitData {
     type InitData: InitData;
 
+    #[allow(clippy::missing_safety_doc)]
     unsafe fn __init_data() -> Self::InitData;
 }
 

rust/kernel/init/macros.rs

@@ -989,6 +989,7 @@ fn drop(&mut self) {
         //
         // 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)*
         {

rust/kernel/print.rs

@@ -14,6 +14,7 @@
 use crate::str::RawFormatter;
 
 // Called from `vsprintf` with format specifier `%pA`.
+#[allow(clippy::missing_safety_doc)]
 #[no_mangle]
 unsafe extern "C" fn rust_fmt_argument(
     buf: *mut c_char,