From 189ccf20a21b367507447a8563d055f1d0b57ffb Mon Sep 17 00:00:00 2001
From: Jonas Schievink <jonasschievink@gmail.com>
Date: Wed, 11 Dec 2019 19:38:45 +0100
Subject: [PATCH 1/2] VecDeque: drop remaining items on destructor panic

---
 src/liballoc/collections/vec_deque.rs | 12 +++++++++-
 src/liballoc/tests/vec_deque.rs       | 34 +++++++++++++++++++++++++++
 2 files changed, 45 insertions(+), 1 deletion(-)

diff --git a/src/liballoc/collections/vec_deque.rs b/src/liballoc/collections/vec_deque.rs
index 7795083e0580c..6e644dced163f 100644
--- a/src/liballoc/collections/vec_deque.rs
+++ b/src/liballoc/collections/vec_deque.rs
@@ -144,11 +144,21 @@ impl<T: Clone> Clone for VecDeque<T> {
 #[stable(feature = "rust1", since = "1.0.0")]
 unsafe impl<#[may_dangle] T> Drop for VecDeque<T> {
     fn drop(&mut self) {
+        struct Dropper<'a, T>(&'a mut [T]);
+
+        impl<'a, T> Drop for Dropper<'a, T> {
+            fn drop(&mut self) {
+                unsafe {
+                    ptr::drop_in_place(self.0);
+                }
+            }
+        }
+
         let (front, back) = self.as_mut_slices();
         unsafe {
+            let _back_dropper = Dropper(back);
             // use drop for [T]
             ptr::drop_in_place(front);
-            ptr::drop_in_place(back);
         }
         // RawVec handles deallocation
     }
diff --git a/src/liballoc/tests/vec_deque.rs b/src/liballoc/tests/vec_deque.rs
index ebcc832017172..1ab3694a3ca61 100644
--- a/src/liballoc/tests/vec_deque.rs
+++ b/src/liballoc/tests/vec_deque.rs
@@ -2,6 +2,7 @@ use std::collections::TryReserveError::*;
 use std::collections::{vec_deque::Drain, VecDeque};
 use std::fmt::Debug;
 use std::mem::size_of;
+use std::panic::catch_unwind;
 use std::{isize, usize};
 
 use crate::hash;
@@ -709,6 +710,39 @@ fn test_drop_clear() {
     assert_eq!(unsafe { DROPS }, 4);
 }
 
+#[test]
+fn test_drop_panic() {
+    static mut DROPS: i32 = 0;
+
+    struct D(bool);
+
+    impl Drop for D {
+        fn drop(&mut self) {
+            unsafe {
+                DROPS += 1;
+            }
+
+            if self.0 {
+                panic!("panic in `drop`");
+            }
+        }
+    }
+
+    let mut q = VecDeque::new();
+    q.push_back(D(false));
+    q.push_back(D(false));
+    q.push_back(D(false));
+    q.push_back(D(false));
+    q.push_back(D(false));
+    q.push_front(D(false));
+    q.push_front(D(false));
+    q.push_front(D(true));
+
+    catch_unwind(move || drop(q)).ok();
+
+    assert_eq!(unsafe { DROPS }, 8);
+}
+
 #[test]
 fn test_reserve_grow() {
     // test growth path A

From 82c09b75d7fef78db2d485793cfa8bf5583ff7cf Mon Sep 17 00:00:00 2001
From: Jonas Schievink <jonasschievink@gmail.com>
Date: Thu, 12 Dec 2019 00:39:29 +0100
Subject: [PATCH 2/2] Add comment to `Dropper`

---
 src/liballoc/collections/vec_deque.rs | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/src/liballoc/collections/vec_deque.rs b/src/liballoc/collections/vec_deque.rs
index 6e644dced163f..5ec69f73740c3 100644
--- a/src/liballoc/collections/vec_deque.rs
+++ b/src/liballoc/collections/vec_deque.rs
@@ -144,6 +144,8 @@ impl<T: Clone> Clone for VecDeque<T> {
 #[stable(feature = "rust1", since = "1.0.0")]
 unsafe impl<#[may_dangle] T> Drop for VecDeque<T> {
     fn drop(&mut self) {
+        /// Runs the destructor for all items in the slice when it gets dropped (normally or
+        /// during unwinding).
         struct Dropper<'a, T>(&'a mut [T]);
 
         impl<'a, T> Drop for Dropper<'a, T> {