2 files changed, 8 insertions, 18 deletions
diff --git a/library/core/src/fmt/builders.rs b/library/core/src/fmt/builders.rs
index 36f49d51c..d2c9f9800 100644
--- a/library/core/src/fmt/builders.rs
+++ b/library/core/src/fmt/builders.rs
@@ -518,7 +518,7 @@ impl<'a, 'b: 'a> DebugSet<'a, 'b> {
     ///     fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
     ///         fmt.debug_set()
     ///            .entries(self.0.iter())
-    ///            .finish() // Ends the struct formatting.
+    ///            .finish() // Ends the set formatting.
     ///     }
     /// }
     ///
@@ -648,7 +648,7 @@ impl<'a, 'b: 'a> DebugList<'a, 'b> {
     ///     fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
     ///         fmt.debug_list()
     ///            .entries(self.0.iter())
-    ///            .finish() // Ends the struct formatting.
+    ///            .finish() // Ends the list formatting.
     ///     }
     /// }
     ///
@@ -905,7 +905,7 @@ impl<'a, 'b: 'a> DebugMap<'a, 'b> {
     ///     fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
     ///         fmt.debug_map()
     ///            .entries(self.0.iter().map(|&(ref k, ref v)| (k, v)))
-    ///            .finish() // Ends the struct formatting.
+    ///            .finish() // Ends the map formatting.
     ///     }
     /// }
     ///
diff --git a/library/core/src/fmt/mod.rs b/library/core/src/fmt/mod.rs
index 1786b309c..9ce6093f1 100644
--- a/library/core/src/fmt/mod.rs
+++ b/library/core/src/fmt/mod.rs
@@ -2521,22 +2521,12 @@ impl<T: Copy + Debug> Debug for Cell<T> {
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T: ?Sized + Debug> Debug for RefCell<T> {
     fn fmt(&self, f: &mut Formatter<'_>) -> Result {
+        let mut d = f.debug_struct("RefCell");
         match self.try_borrow() {
-            Ok(borrow) => f.debug_struct("RefCell").field("value", &borrow).finish(),
-            Err(_) => {
-                // The RefCell is mutably borrowed so we can't look at its value
-                // here. Show a placeholder instead.
-                struct BorrowedPlaceholder;
-
-                impl Debug for BorrowedPlaceholder {
-                    fn fmt(&self, f: &mut Formatter<'_>) -> Result {
-                        f.write_str("<borrowed>")
-                    }
-                }
-
-                f.debug_struct("RefCell").field("value", &BorrowedPlaceholder).finish()
-            }
-        }
+            Ok(borrow) => d.field("value", &borrow),
+            Err(_) => d.field("value", &format_args!("<borrowed>")),
+        };
+        d.finish()
     }
 }