Merge #7888: prevector: fix 2 bugs in currently unreached code paths

a7af72a prevector::swap: fix (unreached) data corruption (Kaz Wesley)
4ed41a2 test prevector::swap (Kaz Wesley)
1e2c29f prevector: destroy elements only via erase() (Kaz Wesley)

src/prevector.h

@@ -298,9 +298,8 @@ public:
     }
 
     void resize(size_type new_size) {
-        while (size() > new_size) {
-            item_ptr(size() - 1)->~T();
-            _size--;
+        if (size() > new_size) {
+            erase(item_ptr(new_size), end());
         }
         if (new_size > capacity()) {
             change_capacity(new_size);
@@ -368,10 +367,7 @@ public:
     }
 
     iterator erase(iterator pos) {
-        (*pos).~T();
-        memmove(&(*pos), &(*pos) + 1, ((char*)&(*end())) - ((char*)(1 + &(*pos))));
-        _size--;
-        return pos;
+        return erase(pos, pos + 1);
     }
 
     iterator erase(iterator first, iterator last) {
@@ -396,7 +392,7 @@ public:
     }
 
     void pop_back() {
-        _size--;
+        erase(end() - 1, end());
     }
 
     T& front() {
@@ -416,12 +412,7 @@ public:
     }
 
     void swap(prevector<N, T, Size, Diff>& other) {
-        if (_size & other._size & 1) {
-            std::swap(_union.capacity, other._union.capacity);
-            std::swap(_union.indirect, other._union.indirect);
-        } else {
         std::swap(_union, other._union);
-        }
         std::swap(_size, other._size);
     }
 

src/test/prevector_tests.cpp

@@ -19,9 +19,11 @@ template<unsigned int N, typename T>
 class prevector_tester {
     typedef std::vector<T> realtype;
     realtype real_vector;
+    realtype real_vector_alt;
 
     typedef prevector<N, T> pretype;
     pretype pre_vector;
+    pretype pre_vector_alt;
 
     typedef typename pretype::size_type Size;
 
@@ -149,6 +151,12 @@ public:
         pre_vector.shrink_to_fit();
         test();
     }
+
+    void swap() {
+        real_vector.swap(real_vector_alt);
+        pre_vector.swap(pre_vector_alt);
+        test();
+    }
 };
 
 BOOST_AUTO_TEST_CASE(PrevectorTestInt)
@@ -204,12 +212,15 @@ BOOST_AUTO_TEST_CASE(PrevectorTestInt)
             if (test.size() > 0) {
                 test.update(insecure_rand() % test.size(), insecure_rand());
             }
-            if (((r >> 11) & 1024) == 11) {
+            if (((r >> 11) % 1024) == 11) {
                 test.clear();
             }
-            if (((r >> 21) & 512) == 12) {
+            if (((r >> 21) % 512) == 12) {
                 test.assign(insecure_rand() % 32, insecure_rand());
             }
+            if (((r >> 15) % 64) == 3) {
+                test.swap();
+            }
         }
     }
 }