[PATCH 6.12.y] rust: init: fix `clippy::undocumented_unsafe_blocks` warnings

[Miguel Ojeda <ojeda@kernel.org>]

The stable backport in commit acc105db0826 ("rust: pin-init:
add references to previously initialized fields") introduced some
`clippy::undocumented_unsafe_blocks` warnings [1], e.g.

    error: unsafe block missing a safety comment
        --> rust/kernel/init/macros.rs:1015:25

As well as:

    --> rust/kernel/init/macros.rs:1243:45
    --> rust/kernel/init/macros.rs:1286:22
    --> rust/kernel/init/macros.rs:1374:45

After discussing it with Benno and Gary, we decided to clean the build
log by doing a minimal targeted stable commit.

Thus, depending on the case:

  - Reorder the attributes so that the existing `// SAFETY:` comments
    may be seen by Clippy.

  - Add a placeholder `// SAFETY: TODO.` comment.

Cc: Benno Lossin <lossin@kernel.org>
Cc: Gary Guo <gary@garyguo.net>
Fixes: acc105db0826 ("rust: pin-init: add references to previously initialized fields")
Link: https://lore.kernel.org/stable/20260421111111.57059-1-ojeda@kernel.org/ [1]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
---
Greg/Sasha: please let Benno & Gary Acked-by the patch before picking it
up -- thanks!

 rust/kernel/init/macros.rs | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/rust/kernel/init/macros.rs b/rust/kernel/init/macros.rs
index e477e4de817b..d6e27c522115 100644
--- a/rust/kernel/init/macros.rs
+++ b/rust/kernel/init/macros.rs
@@ -1012,6 +1012,7 @@ impl<$($impl_generics)*> $pin_data<$($ty_generics)*>
                         self,
                         slot: &'__slot mut $p_type,
                     ) -> ::core::pin::Pin<&'__slot mut $p_type> {
+                        // SAFETY: TODO.
                         unsafe { ::core::pin::Pin::new_unchecked(slot) }
                     }
                 )*
@@ -1235,11 +1236,11 @@ fn assert_zeroable<T: $crate::init::Zeroable>(_: *mut T) {}
         // Unaligned fields will cause the compiler to emit E0793. We do not support
         // unaligned fields since `Init::__init` requires an aligned pointer; the call to
         // `ptr::write` below has the same requirement.
+        #[allow(unused_variables, unused_assignments)]
         // SAFETY:
         // - the project function does the correct field projection,
         // - the field has been initialized,
         // - the reference is only valid until the end of the initializer.
-        #[allow(unused_variables, unused_assignments)]
         let $field = $crate::macros::paste!(unsafe { $data.[< __project_ $field >](&mut (*$slot).$field) });

         // Create the drop guard:
@@ -1278,11 +1279,11 @@ fn assert_zeroable<T: $crate::init::Zeroable>(_: *mut T) {}
         // Unaligned fields will cause the compiler to emit E0793. We do not support
         // unaligned fields since `Init::__init` requires an aligned pointer; the call to
         // `ptr::write` below has the same requirement.
+        #[allow(unused_variables, unused_assignments)]
         // SAFETY:
         // - the field is not structurally pinned, since the line above must compile,
         // - the field has been initialized,
         // - the reference is only valid until the end of the initializer.
-        #[allow(unused_variables, unused_assignments)]
         let $field = unsafe { &mut (*$slot).$field };

         // Create the drop guard:
@@ -1366,11 +1367,11 @@ fn assert_zeroable<T: $crate::init::Zeroable>(_: *mut T) {}
         // Unaligned fields will cause the compiler to emit E0793. We do not support
         // unaligned fields since `Init::__init` requires an aligned pointer; the call to
         // `ptr::write` below has the same requirement.
+        #[allow(unused_variables, unused_assignments)]
         // SAFETY:
         // - the project function does the correct field projection,
         // - the field has been initialized,
         // - the reference is only valid until the end of the initializer.
-        #[allow(unused_variables, unused_assignments)]
         let $field = $crate::macros::paste!(unsafe { $data.[< __project_ $field >](&mut (*$slot).$field) });

         // Create the drop guard:

base-commit: 59f8529e78a2fc581c35fbed58169f5e8c79b8d7
--
2.53.0