[RFC 4/5] rust: sync: impl Debug for {Unique,}Arc

[Boqun Feng <boqun.feng@gmail.com>]

This allows printing macros to print the data and the refcount nubmer
of these struct for debugging purposes.

Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
---
 rust/kernel/sync/arc.rs | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/rust/kernel/sync/arc.rs b/rust/kernel/sync/arc.rs
index 4d8de20c996f..f143d8305c36 100644
--- a/rust/kernel/sync/arc.rs
+++ b/rust/kernel/sync/arc.rs
@@ -474,6 +474,7 @@ impl<T: ?Sized> Deref for ArcBorrow<'_, T> {
 ///
 /// # test().unwrap();
 /// ```
+#[derive(Debug)]
 pub struct UniqueArc<T: ?Sized> {
     inner: Arc<T>,
 }
@@ -545,3 +546,15 @@ impl<T: fmt::Display + ?Sized> fmt::Display for Arc<T> {
         fmt::Display::fmt(self.deref(), f)
     }
 }
+
+impl<T: fmt::Debug + ?Sized> fmt::Debug for Arc<T> {
+    /// Formats debug output for [`Arc`].
+    ///
+    /// Refcount is also printed for debugging purpose.
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("Arc")
+            .field("refcount", &self.get_inner().count())
+            .field("data", &self.deref())
+            .finish()
+    }
+}
-- 
2.39.1