btree: don't leak value if destructor of key panics

Author: Lukas Markeffsky

alloc/src/collections/btree/map/tests.rs

@@ -2270,6 +2270,54 @@ fn test_into_iter_drop_leak_height_0() {
     assert_eq!(e.dropped(), 1);
 }
 
+#[test]
+#[cfg_attr(not(panic = "unwind"), ignore = "test requires unwinding support")]
+fn test_into_iter_drop_leak_kv_panic_in_key() {
+    let a_k = CrashTestDummy::new(0);
+    let a_v = CrashTestDummy::new(1);
+    let b_k = CrashTestDummy::new(2);
+    let b_v = CrashTestDummy::new(3);
+    let c_k = CrashTestDummy::new(4);
+    let c_v = CrashTestDummy::new(5);
+    let mut map = BTreeMap::new();
+    map.insert(a_k.spawn(Panic::Never), a_v.spawn(Panic::Never));
+    map.insert(b_k.spawn(Panic::InDrop), b_v.spawn(Panic::Never));
+    map.insert(c_k.spawn(Panic::Never), c_v.spawn(Panic::Never));
+
+    catch_unwind(move || drop(map.into_iter())).unwrap_err();
+
+    assert_eq!(a_k.dropped(), 1);
+    assert_eq!(a_v.dropped(), 1);
+    assert_eq!(b_k.dropped(), 1);
+    assert_eq!(b_v.dropped(), 1);
+    assert_eq!(c_k.dropped(), 1);
+    assert_eq!(c_v.dropped(), 1);
+}
+
+#[test]
+#[cfg_attr(not(panic = "unwind"), ignore = "test requires unwinding support")]
+fn test_into_iter_drop_leak_kv_panic_in_val() {
+    let a_k = CrashTestDummy::new(0);
+    let a_v = CrashTestDummy::new(1);
+    let b_k = CrashTestDummy::new(2);
+    let b_v = CrashTestDummy::new(3);
+    let c_k = CrashTestDummy::new(4);
+    let c_v = CrashTestDummy::new(5);
+    let mut map = BTreeMap::new();
+    map.insert(a_k.spawn(Panic::Never), a_v.spawn(Panic::Never));
+    map.insert(b_k.spawn(Panic::Never), b_v.spawn(Panic::InDrop));
+    map.insert(c_k.spawn(Panic::Never), c_v.spawn(Panic::Never));
+
+    catch_unwind(move || drop(map.into_iter())).unwrap_err();
+
+    assert_eq!(a_k.dropped(), 1);
+    assert_eq!(a_v.dropped(), 1);
+    assert_eq!(b_k.dropped(), 1);
+    assert_eq!(b_v.dropped(), 1);
+    assert_eq!(c_k.dropped(), 1);
+    assert_eq!(c_v.dropped(), 1);
+}
+
 #[test]
 #[cfg_attr(not(panic = "unwind"), ignore = "test requires unwinding support")]
 fn test_into_iter_drop_leak_height_1() {

alloc/src/collections/btree/node.rs

@@ -1173,11 +1173,25 @@ impl<K, V, NodeType> Handle<NodeRef<marker::Dying, K, V, NodeType>, marker::KV>
     /// The node that the handle refers to must not yet have been deallocated.
     #[inline]
     pub unsafe fn drop_key_val(mut self) {
+        // Run the destructor of the value even if the destructor of the key panics.
+        struct Dropper<'a, T>(&'a mut MaybeUninit<T>);
+        impl<T> Drop for Dropper<'_, T> {
+            #[inline]
+            fn drop(&mut self) {
+                unsafe {
+                    self.0.assume_init_drop();
+                }
+            }
+        }
+
         debug_assert!(self.idx < self.node.len());
         let leaf = self.node.as_leaf_dying();
         unsafe {
-            leaf.keys.get_unchecked_mut(self.idx).assume_init_drop();
-            leaf.vals.get_unchecked_mut(self.idx).assume_init_drop();
+            let key = leaf.keys.get_unchecked_mut(self.idx);
+            let val = leaf.vals.get_unchecked_mut(self.idx);
+            let _guard = Dropper(val);
+            key.assume_init_drop();
+            // dropping the guard will drop the value
         }
     }
 }