Panic on arithmetic overflow in drain

Fixes #258.

Author: mbrubeck

src/lib.rs

@@ -725,11 +725,11 @@ impl<A: Array> SmallVec<A> {
         let len = self.len();
         let start = match range.start_bound() {
             Included(&n) => n,
-            Excluded(&n) => n + 1,
+            Excluded(&n) => n.checked_add(1).expect("Range start out of bounds"),
             Unbounded => 0,
         };
         let end = match range.end_bound() {
-            Included(&n) => n + 1,
+            Included(&n) => n.checked_add(1).expect("Range end out of bounds"),
             Excluded(&n) => n,
             Unbounded => len,
         };

src/tests.rs

@@ -423,6 +423,13 @@ fn test_invalid_grow() {
     v.grow(5);
 }
 
+#[test]
+#[should_panic]
+fn drain_overflow() {
+    let mut v: SmallVec<[u8; 8]> = smallvec![0];
+    v.drain(..=std::usize::MAX);
+}
+
 #[test]
 fn test_insert_from_slice() {
     let mut v: SmallVec<[u8; 8]> = SmallVec::new();