[escher] ScrollView: fix Decorators contructor/destructors

escher/include/escher/scroll_view.h

@@ -33,6 +33,9 @@ public:
       Bars,
       Arrows
     };
+    /* We want (Decorator *)->~Decorator() to call ~BarDecorator() or ~ArrowDecorator()
+     * when required. */
+    virtual ~Decorator() = default;
     virtual int numberOfIndicators() const { return 0; }
     virtual View * indicatorAtIndex(int index) { assert(false); return nullptr; }
     virtual KDRect layoutIndicators(KDSize content, KDPoint offset, KDRect frame) { return frame; }
@@ -132,9 +135,8 @@ private:
   Decorator::Type m_decoratorType;
   union Decorators {
   public:
-    /* Enforce trivial constructor and destructor that just leaves the memory unmodified. */
-    Decorators() {}
-    ~Decorators() {}
+    Decorators();
+    ~Decorators();
     Decorator * activeDecorator() { return &m_none; }
     void setActiveDecorator(Decorator::Type t);
   private:

escher/src/scroll_view.cpp

@@ -198,8 +198,20 @@ void ScrollView::ArrowDecorator::setBackgroundColor(KDColor c) {
   }
 }
 
+ScrollView::Decorators::Decorators() {
+  /* We need to initiate the Union at construction to avoid destructing an
+   * uninitialized object when changing the decorator type. */
+  new (this) Decorator();
+}
+
+ScrollView::Decorators::~Decorators() {
+  activeDecorator()->~Decorator();
+}
+
 void ScrollView::Decorators::setActiveDecorator(Decorator::Type t) {
-  /* We do NOT need to destroy the previous decorator because they don't have a destructor */
+  /* Decorator destructor is virtual so calling ~Decorator() on a Decorator
+   * pointer will call the appropriate destructor. */
+  activeDecorator()->~Decorator();
   switch (t) {
     case Decorator::Type::Bars:
       new (&m_bars) BarDecorator();