sync: print MutexGuard inner value for debugging (#1961)

1 files changed, 6 insertions, 1 deletions

diff --git a/tokio/src/sync/mutex.rs b/tokio/src/sync/mutex.rs
index 35e13300..bee00df4 100644
--- a/tokio/src/sync/mutex.rs
+++ b/tokio/src/sync/mutex.rs
@@ -61,7 +61,6 @@ pub struct Mutex<T> {
 ///
 /// The lock is automatically released whenever the guard is dropped, at which point `lock`
 /// will succeed yet again.
-#[derive(Debug)]
 pub struct MutexGuard<'a, T> {
     lock: &'a Mutex<T>,
     permit: semaphore::Permit,
@@ -176,6 +175,12 @@ impl<'a, T> DerefMut for MutexGuard<'a, T> {
     }
 }
 
+impl<'a, T: fmt::Debug> fmt::Debug for MutexGuard<'a, T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Debug::fmt(&**self, f)
+    }
+}
+
 impl<'a, T: fmt::Display> fmt::Display for MutexGuard<'a, T> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         fmt::Display::fmt(&**self, f)