Refactor to use `debug_struct` in several Debug impls

Fixes #44771.

4 files changed, 25 insertions, 43 deletions

diff --git a/src/libstd/sync/mpsc/mod.rs b/src/libstd/sync/mpsc/mod.rs
index dcd4c8dfdf5..ce1a07b31b2 100644
--- a/src/libstd/sync/mpsc/mod.rs
+++ b/src/libstd/sync/mpsc/mod.rs
@@ -919,7 +919,7 @@ impl<T> Drop for Sender<T> {
 #[stable(feature = "mpsc_debug", since = "1.8.0")]
 impl<T> fmt::Debug for Sender<T> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        write!(f, "Sender {{ .. }}")
+        f.debug_struct("Sender").finish()
     }
 }
 
@@ -1049,7 +1049,7 @@ impl<T> Drop for SyncSender<T> {
 #[stable(feature = "mpsc_debug", since = "1.8.0")]
 impl<T> fmt::Debug for SyncSender<T> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        write!(f, "SyncSender {{ .. }}")
+        f.debug_struct("SyncSender").finish()
     }
 }
 
@@ -1551,7 +1551,7 @@ impl<T> Drop for Receiver<T> {
 #[stable(feature = "mpsc_debug", since = "1.8.0")]
 impl<T> fmt::Debug for Receiver<T> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        write!(f, "Receiver {{ .. }}")
+        f.debug_struct("Receiver").finish()
     }
 }
 
@@ -3009,22 +3009,4 @@ mod sync_tests {
             repro()
         }
     }
-
-    #[test]
-    fn fmt_debug_sender() {
-        let (tx, _) = channel::<i32>();
-        assert_eq!(format!("{:?}", tx), "Sender { .. }");
-    }
-
-    #[test]
-    fn fmt_debug_recv() {
-        let (_, rx) = channel::<i32>();
-        assert_eq!(format!("{:?}", rx), "Receiver { .. }");
-    }
-
-    #[test]
-    fn fmt_debug_sync_sender() {
-        let (tx, _) = sync_channel::<i32>(1);
-        assert_eq!(format!("{:?}", tx), "SyncSender { .. }");
-    }
 }
diff --git a/src/libstd/sync/mpsc/select.rs b/src/libstd/sync/mpsc/select.rs
index e49f4cff024..a9f3cea243f 100644
--- a/src/libstd/sync/mpsc/select.rs
+++ b/src/libstd/sync/mpsc/select.rs
@@ -354,13 +354,13 @@ impl Iterator for Packets {
 
 impl fmt::Debug for Select {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        write!(f, "Select {{ .. }}")
+        f.debug_struct("Select").finish()
     }
 }
 
 impl<'rx, T:Send+'rx> fmt::Debug for Handle<'rx, T> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        write!(f, "Handle {{ .. }}")
+        f.debug_struct("Handle").finish()
     }
 }
 
@@ -774,18 +774,4 @@ mod tests {
             }
         }
     }
-
-    #[test]
-    fn fmt_debug_select() {
-        let sel = Select::new();
-        assert_eq!(format!("{:?}", sel), "Select { .. }");
-    }
-
-    #[test]
-    fn fmt_debug_handle() {
-        let (_, rx) = channel::<i32>();
-        let sel = Select::new();
-        let handle = sel.handle(&rx);
-        assert_eq!(format!("{:?}", handle), "Handle { .. }");
-    }
 }
diff --git a/src/libstd/sync/mutex.rs b/src/libstd/sync/mutex.rs
index 62d8de18f4b..a0349fe9d8b 100644
--- a/src/libstd/sync/mutex.rs
+++ b/src/libstd/sync/mutex.rs
@@ -384,11 +384,18 @@ impl<T: ?Sized + Default> Default for Mutex<T> {
 impl<T: ?Sized + fmt::Debug> fmt::Debug for Mutex<T> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match self.try_lock() {
-            Ok(guard) => write!(f, "Mutex {{ data: {:?} }}", &*guard),
+            Ok(guard) => f.debug_struct("Mutex").field("data", &&*guard).finish(),
             Err(TryLockError::Poisoned(err)) => {
-                write!(f, "Mutex {{ data: Poisoned({:?}) }}", &**err.get_ref())
+                f.debug_struct("Mutex").field("data", &&**err.get_ref()).finish()
             },
-            Err(TryLockError::WouldBlock) => write!(f, "Mutex {{ <locked> }}")
+            Err(TryLockError::WouldBlock) => {
+                struct LockedPlaceholder;
+                impl fmt::Debug for LockedPlaceholder {
+                    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { f.write_str("<locked>") }
+                }
+
+                f.debug_struct("Mutex").field("data", &LockedPlaceholder).finish()
+            }
         }
     }
 }
diff --git a/src/libstd/sync/rwlock.rs b/src/libstd/sync/rwlock.rs
index 4757faabfb8..5c49d6b5845 100644
--- a/src/libstd/sync/rwlock.rs
+++ b/src/libstd/sync/rwlock.rs
@@ -428,11 +428,18 @@ unsafe impl<#[may_dangle] T: ?Sized> Drop for RwLock<T> {
 impl<T: ?Sized + fmt::Debug> fmt::Debug for RwLock<T> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match self.try_read() {
-            Ok(guard) => write!(f, "RwLock {{ data: {:?} }}", &*guard),
+            Ok(guard) => f.debug_struct("RwLock").field("data", &&*guard).finish(),
             Err(TryLockError::Poisoned(err)) => {
-                write!(f, "RwLock {{ data: Poisoned({:?}) }}", &**err.get_ref())
+                f.debug_struct("RwLock").field("data", &&**err.get_ref()).finish()
             },
-            Err(TryLockError::WouldBlock) => write!(f, "RwLock {{ <locked> }}")
+            Err(TryLockError::WouldBlock) => {
+                struct LockedPlaceholder;
+                impl fmt::Debug for LockedPlaceholder {
+                    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { f.write_str("<locked>") }
+                }
+
+                f.debug_struct("RwLock").field("data", &LockedPlaceholder).finish()
+            }
         }
     }
 }