From 71714edf8b8a0e710f4a17a120b86e07e279ccc7 Mon Sep 17 00:00:00 2001
From: David Spies <dnspies@gmail.com>
Date: Fri, 2 Apr 2021 08:34:43 -0700
Subject: [PATCH 1/2] Add drop_leak and drop_leak_mut

---
 library/core/src/cell.rs | 46 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 46 insertions(+)

diff --git a/library/core/src/cell.rs b/library/core/src/cell.rs
index 9a2908c275da8..68e839d1435e6 100644
--- a/library/core/src/cell.rs
+++ b/library/core/src/cell.rs
@@ -1034,6 +1034,52 @@ impl<T: ?Sized> RefCell<T> {
         self.get_mut()
     }
 
+    /// Assert that a single leaked immutable guard has been cleaned up.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(cell_leak)]
+    /// use std::cell::{RefCell, Ref};
+    ///
+    /// let mut c = RefCell::new(0);
+    /// Ref::leak(c.borrow());
+    ///
+    /// assert!(c.try_borrow_mut().is_err());
+    /// c.drop_leak();
+    /// assert!(c.try_borrow_mut().is_ok());
+    /// ```
+    #[unstable(feature = "cell_leak", issue = "69099")]
+    pub unsafe fn drop_leak(&self) {
+        self.borrow.update(|x| {
+            assert!(x > 0, "Cell not borrowed immutably");
+            x - 1
+        });
+    }
+
+    /// Assert that a single leaked mutable guard has been cleaned up.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(cell_leak)]
+    /// use std::cell::{RefCell, RefMut};
+    ///
+    /// let mut c = RefCell::new(0);
+    /// RefMut::leak(c.borrow_mut());
+    ///
+    /// assert!(c.try_borrow().is_err());
+    /// c.drop_leak_mut();
+    /// assert!(c.try_borrow().is_ok());
+    /// ```
+    #[unstable(feature = "cell_leak", issue = "69099")]
+    pub unsafe fn drop_leak_mut(&self) {
+        self.borrow.update(|x| {
+            assert!(x < 0, "Cell not borrowed mutably");
+            x + 1
+        });
+    }
+
     /// Immutably borrows the wrapped value, returning an error if the value is
     /// currently mutably borrowed.
     ///

From 2572f3b535101ed0bd1247b09a6658c48327413c Mon Sep 17 00:00:00 2001
From: David Spies <dnspies@gmail.com>
Date: Fri, 2 Apr 2021 09:07:33 -0700
Subject: [PATCH 2/2] Forgot the unsafe block in the doctest

---
 library/core/src/cell.rs | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/library/core/src/cell.rs b/library/core/src/cell.rs
index 68e839d1435e6..4ef41e974d5ec 100644
--- a/library/core/src/cell.rs
+++ b/library/core/src/cell.rs
@@ -1046,7 +1046,7 @@ impl<T: ?Sized> RefCell<T> {
     /// Ref::leak(c.borrow());
     ///
     /// assert!(c.try_borrow_mut().is_err());
-    /// c.drop_leak();
+    /// unsafe { c.drop_leak() };
     /// assert!(c.try_borrow_mut().is_ok());
     /// ```
     #[unstable(feature = "cell_leak", issue = "69099")]
@@ -1069,7 +1069,7 @@ impl<T: ?Sized> RefCell<T> {
     /// RefMut::leak(c.borrow_mut());
     ///
     /// assert!(c.try_borrow().is_err());
-    /// c.drop_leak_mut();
+    /// unsafe { c.drop_leak_mut() };
     /// assert!(c.try_borrow().is_ok());
     /// ```
     #[unstable(feature = "cell_leak", issue = "69099")]