tst_qvarlengtharray: fix MyBase trackers for swap()

I don't begin to understand the semantics of the trackers here, but
whatever they are, they break with the fallback std::swap() 3-moves
implementation and lose track of alive objects, so provide an ADL swap
that does the right thing.

Amends dd58ddd5d9 (I think).

Pick-to: 6.5 6.4 6.2 5.15
Change-Id: I1cd49c95dca2d103a26c2c7ac0a896929135a6c8
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

tests/auto/corelib/tools/qvarlengtharray/tst_qvarlengtharray.cpp

@@ -590,6 +590,12 @@ struct MyBase
     bool hasMoved() const { return !wasConstructedAt(this); }
 
 protected:
+    void swap(MyBase &other) {
+        using std::swap;
+        swap(data, other.data);
+        swap(isCopy, other.isCopy);
+    }
+
     MyBase(const MyBase *data, bool isCopy)
             : data(data), isCopy(isCopy) {}
 
@@ -664,6 +670,14 @@ struct MyMovable
         return *this;
     }
 
+    void swap(MyMovable &other) noexcept
+    {
+        MyBase::swap(other);
+        std::swap(i, other.i);
+    }
+
+    friend void swap(MyMovable &lhs, MyMovable &rhs) noexcept { lhs.swap(rhs); }
+
     bool operator==(const MyMovable &other) const
     {
         return i == other.i;
@@ -679,6 +693,15 @@ struct MyComplex
     {
         return i == other.i;
     }
+
+    void swap(MyComplex &other) noexcept
+    {
+        MyBase::swap(other);
+        std::swap(i, other.i);
+    }
+
+    friend void swap(MyComplex &lhs, MyComplex &rhs) noexcept { lhs.swap(rhs); }
+
     char i;
 };
 
@@ -1310,6 +1333,17 @@ void tst_QVarLengthArray::insertMove()
     QCOMPARE(MyBase::liveCount, 0);
     QCOMPARE(MyBase::copyCount, 0);
 
+    {
+        MyMovable m1, m2;
+        QCOMPARE(MyBase::liveCount, 2);
+        QCOMPARE(MyBase::copyCount, 0);
+        using std::swap;
+        swap(m1, m2);
+        QCOMPARE(MyBase::liveCount, 2);
+        QCOMPARE(MyBase::movedCount, 0);
+        QCOMPARE(MyBase::copyCount, 0);
+    }
+
     {
         QVarLengthArray<MyMovable, 6> vec;
         MyMovable m1;