[PATCH v4] rust: sync: add #[must_use] to Lock::try_lock

[Jason Devers <dev.json2@gmail.com>]

The `Lock::try_lock` function returns an `Option<Guard<...>>`, but it
currently does not issue a warning if the return value is unused.
To avoid potential bugs, the `#[must_use]` annotation is added to ensure proper usage.

Note that `T` is `#[must_use]` but `Option<T>` is not.
For more context, see: https://github.com/rust-lang/rust/issues/71368.

Suggested-by: Alice Ryhl <aliceryhl@google.com>
Link: https://github.com/Rust-for-Linux/linux/issues/1133
Signed-off-by: Jason Devers <dev.json2@gmail.com>
---
 rust/kernel/sync/lock.rs | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/rust/kernel/sync/lock.rs b/rust/kernel/sync/lock.rs
index 41dcddac69e2..39f8c07d2287 100644
--- a/rust/kernel/sync/lock.rs
+++ b/rust/kernel/sync/lock.rs
@@ -147,6 +147,8 @@ pub fn lock(&self) -> Guard<'_, T, B> {
     /// Tries to acquire the lock.
     ///
     /// Returns a guard that can be used to access the data protected by the lock if successful.
+    /// Note that `T` is `#[must_use]` but `Option<T>` is not.
+    #[must_use = "if unused, leads to an empty critical section"]
     pub fn try_lock(&self) -> Option<Guard<'_, T, B>> {
         // SAFETY: The constructor of the type calls `init`, so the existence of the object proves
         // that `init` was called.
-- 
2.44.2