Fix qsort to not skip the right side when the pivot element gets put at index 0.

Closes #705.

src/lib/sort.rs

@@ -63,8 +63,10 @@ fn qsort[T](lteq[T] compare_func, vec[mutable T] arr, uint left, uint right) {
     if (right > left) {
         auto pivot = (left + right) / 2u;
         auto new_pivot = part[T](compare_func, arr, left, right, pivot);
-        if (new_pivot == 0u) { ret; }
-        qsort[T](compare_func, arr, left, new_pivot - 1u);
+        if (new_pivot != 0u) {
+            // Need to do this check before recursing due to overflow
+            qsort[T](compare_func, arr, left, new_pivot - 1u);
+        }
         qsort[T](compare_func, arr, new_pivot + 1u, right);
     }
 }
@@ -194,8 +196,10 @@ fn qsort[T](lteq[T] compare_func, &T[mutable] arr, uint left,
         if (right > left) {
             auto pivot = (left + right) / 2u;
             auto new_pivot = part[T](compare_func, arr, left, right, pivot);
-            if (new_pivot == 0u) { ret; }
-            qsort[T](compare_func, arr, left, new_pivot - 1u);
+            if (new_pivot != 0u) {
+                // Need to do this check before recursing due to overflow
+                qsort[T](compare_func, arr, left, new_pivot - 1u);
+            }
             qsort[T](compare_func, arr, new_pivot + 1u, right);
         }
     }

src/test/run-pass/simple-qsort.rs

@@ -0,0 +1,23 @@
+use std;
+import std::ivec;
+import std::int;
+import std::sort;
+
+fn test_qsort() {
+    auto names = ~[mutable 2, 1, 3];
+
+    auto expected = ~[1, 2, 3];
+
+    fn lteq(&int a, &int b) -> bool { int::le(a, b) }
+    sort::ivector::quick_sort(lteq, names);
+
+    auto pairs = ivec::zip(expected, ivec::from_mut(names));
+    for (tup(int, int) p in pairs) {
+        log_err #fmt("%d %d", p._0, p._1);
+        assert p._0 == p._1;
+    }
+}
+
+fn main() {
+    test_qsort();
+}