From 5402abc4937e77c69d8a94eaec86cbc764564cf7 Mon Sep 17 00:00:00 2001
From: Mara Bos <m-ou.se@m-ou.se>
Date: Sat, 27 Mar 2021 13:47:11 +0100
Subject: [PATCH] Improve Debug implementations of Mutex and RwLock.

They now show the poison flag and use debug_non_exhaustive.
---
 library/std/src/sync/mutex.rs  | 12 ++++++++----
 library/std/src/sync/rwlock.rs | 12 ++++++++----
 2 files changed, 16 insertions(+), 8 deletions(-)

diff --git a/library/std/src/sync/mutex.rs b/library/std/src/sync/mutex.rs
index ab61618dc7d7b..98c34282e0c49 100644
--- a/library/std/src/sync/mutex.rs
+++ b/library/std/src/sync/mutex.rs
@@ -441,10 +441,13 @@ impl<T: ?Sized + Default> Default for Mutex<T> {
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T: ?Sized + fmt::Debug> fmt::Debug for Mutex<T> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let mut d = f.debug_struct("Mutex");
         match self.try_lock() {
-            Ok(guard) => f.debug_struct("Mutex").field("data", &&*guard).finish(),
+            Ok(guard) => {
+                d.field("data", &&*guard);
+            }
             Err(TryLockError::Poisoned(err)) => {
-                f.debug_struct("Mutex").field("data", &&**err.get_ref()).finish()
+                d.field("data", &&**err.get_ref());
             }
             Err(TryLockError::WouldBlock) => {
                 struct LockedPlaceholder;
@@ -453,10 +456,11 @@ impl<T: ?Sized + fmt::Debug> fmt::Debug for Mutex<T> {
                         f.write_str("<locked>")
                     }
                 }
-
-                f.debug_struct("Mutex").field("data", &LockedPlaceholder).finish()
+                d.field("data", &LockedPlaceholder);
             }
         }
+        d.field("poisoned", &self.poison.get());
+        d.finish_non_exhaustive()
     }
 }
 
diff --git a/library/std/src/sync/rwlock.rs b/library/std/src/sync/rwlock.rs
index 0298f59228cbe..ee5fe06ac1eff 100644
--- a/library/std/src/sync/rwlock.rs
+++ b/library/std/src/sync/rwlock.rs
@@ -422,10 +422,13 @@ unsafe impl<#[may_dangle] T: ?Sized> Drop for RwLock<T> {
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T: ?Sized + fmt::Debug> fmt::Debug for RwLock<T> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let mut d = f.debug_struct("RwLock");
         match self.try_read() {
-            Ok(guard) => f.debug_struct("RwLock").field("data", &&*guard).finish(),
+            Ok(guard) => {
+                d.field("data", &&*guard);
+            }
             Err(TryLockError::Poisoned(err)) => {
-                f.debug_struct("RwLock").field("data", &&**err.get_ref()).finish()
+                d.field("data", &&**err.get_ref());
             }
             Err(TryLockError::WouldBlock) => {
                 struct LockedPlaceholder;
@@ -434,10 +437,11 @@ impl<T: ?Sized + fmt::Debug> fmt::Debug for RwLock<T> {
                         f.write_str("<locked>")
                     }
                 }
-
-                f.debug_struct("RwLock").field("data", &LockedPlaceholder).finish()
+                d.field("data", &LockedPlaceholder);
             }
         }
+        d.field("poisoned", &self.poison.get());
+        d.finish_non_exhaustive()
     }
 }