---

yaml
---
r: 114175
b: refs/heads/master
c: d547de9
h: refs/heads/master
i:
  114173: 780e3b0
  114171: 6143ab4
  114167: 66f9617
  114159: b14151e
  114143: 0400f43
  114111: 242db8a
  114047: 9c09d6a
  113919: 57f1f10
  113663: b73fc66
v: v3

Author: lilyball

[refs]

@@ -1,5 +1,5 @@
 ---
-refs/heads/master: 4bcc4d76a049a50474764383889e4ede9388da9f
+refs/heads/master: d547de998d33e5b688533f4159ea997c940d9431
 refs/heads/snap-stage1: e33de59e47c5076a89eadeb38f4934f58a3618a6
 refs/heads/snap-stage3: ec0258a381b88b5574e3f8ce72ae553ac3a574b7
 refs/heads/try: 7c6c492fb2af9a85f21ff952942df3523b22fd17

trunk/src/libstd/vec.rs

@@ -635,14 +635,14 @@ impl<T> Vec<T> {
     /// ```
     pub fn truncate(&mut self, len: uint) {
         unsafe {
-            let mut i = len;
             // drop any extra elements
-            while i < self.len {
-                ptr::read(self.as_slice().unsafe_ref(i));
-                i += 1;
+            while len < self.len {
+                // decrement len before the read(), so a failure on Drop doesn't
+                // re-drop the just-failed value.
+                self.len -= 1;
+                ptr::read(self.as_slice().unsafe_ref(self.len));
             }
         }
-        self.len = len;
     }
 
     /// Work with `self` as a mutable slice.
@@ -1862,4 +1862,39 @@ mod tests {
         assert_eq!(b[0].x, 42);
         assert_eq!(b[1].x, 84);
     }
+
+    #[test]
+    fn test_vec_truncate_drop() {
+        static mut drops: uint = 0;
+        struct Elem(int);
+        impl Drop for Elem {
+            fn drop(&mut self) {
+                unsafe { drops += 1; }
+            }
+        }
+
+        let mut v = vec![Elem(1), Elem(2), Elem(3), Elem(4), Elem(5)];
+        assert_eq!(unsafe { drops }, 0);
+        v.truncate(3);
+        assert_eq!(unsafe { drops }, 2);
+        v.truncate(0);
+        assert_eq!(unsafe { drops }, 5);
+    }
+
+    #[test]
+    #[should_fail]
+    fn test_vec_truncate_fail() {
+        struct BadElem(int);
+        impl Drop for BadElem {
+            fn drop(&mut self) {
+                let BadElem(ref mut x) = *self;
+                if *x == 0xbadbeef {
+                    fail!("BadElem failure: 0xbadbeef")
+                }
+            }
+        }
+
+        let mut v = vec![BadElem(1), BadElem(2), BadElem(0xbadbeef), BadElem(4)];
+        v.truncate(0);
+    }
 }