Fix access to bar sets instantiated inside the module

The QBarModelMapper allocates QBarSet instances during initialization.
While this works for pure C++ applications, on the QML side these need
to be of type DeclarativeBarSet to be accessible, but also expose
additional properties.
The C++ module is not aware of QML, also the QBarModelMapper cannot
expose a dynamic allocator without breaking binary compatibility.

Hence, the approach is to create a custom allocator function and export
it from the C++ module. In case a declarative chart is created, the
allocator is replaced with the QML one.

Fixes: QTBUG-71013
Change-Id: I1864d637df37f8cd38d28fdba75da0c5608a612c
Reviewed-by: hjk <hjk@qt.io>
Reviewed-by: Maurice Kalinowski <maurice.kalinowski@qt.io>

2 files changed, 29 insertions, 1 deletions

diff --git a/src/charts/barchart/qbarmodelmapper.cpp b/src/charts/barchart/qbarmodelmapper.cpp
index 966d719f..6a7e18d7 100644
--- a/src/charts/barchart/qbarmodelmapper.cpp
+++ b/src/charts/barchart/qbarmodelmapper.cpp
@@ -540,6 +540,13 @@ void QBarModelMapperPrivate::barValueChanged(int index)
     initializeBarFromModel();
 }
 
+QBarSet *qt_allocate_bar_set_cpp(const QString &label)
+{
+    return new QBarSet(label);
+}
+
+QT_CHARTS_EXPORT QBarSet *(*qt_allocate_bar_set)(const QString &label) = &qt_allocate_bar_set_cpp;
+
 void QBarModelMapperPrivate::initializeBarFromModel()
 {
     if (m_model == 0 || m_series == 0)
@@ -556,7 +563,7 @@ void QBarModelMapperPrivate::initializeBarFromModel()
         QModelIndex barIndex = barModelIndex(i, posInBar);
         // check if there is such model index
         if (barIndex.isValid()) {
-            QBarSet *barSet = new QBarSet(m_model->headerData(i, m_orientation == Qt::Vertical ? Qt::Horizontal : Qt::Vertical).toString());
+            QBarSet *barSet = qt_allocate_bar_set(m_model->headerData(i, m_orientation == Qt::Vertical ? Qt::Horizontal : Qt::Vertical).toString());
             while (barIndex.isValid()) {
                 barSet->append(m_model->data(barIndex, Qt::DisplayRole).toDouble());
                 posInBar++;
diff --git a/src/chartsqml2/declarativechart.cpp b/src/chartsqml2/declarativechart.cpp
index 11677667..2437d4d5 100644
--- a/src/chartsqml2/declarativechart.cpp
+++ b/src/chartsqml2/declarativechart.cpp
@@ -441,6 +441,23 @@ DeclarativeChart::DeclarativeChart(QChart::ChartType type, QQuickItem *parent)
     initChart(type);
 }
 
+// QTBUG-71013
+// The symbol resides in qbarmodelmapper.cpp#548 in the C++ module.
+// Here, it gets imported and reset to the DeclarativeBarSet allocator
+#ifdef Q_OS_WIN
+QT_CHARTS_EXPORT
+#else
+extern
+#endif
+QBarSet *(*qt_allocate_bar_set)(const QString &label);
+
+QBarSet *qt_allocate_bar_set_qml(const QString &label)
+{
+    auto bar = new DeclarativeBarSet();
+    bar->setLabel(label);
+    return bar;
+}
+
 void DeclarativeChart::initChart(QChart::ChartType type)
 {
     m_sceneImage = 0;
@@ -452,6 +469,10 @@ void DeclarativeChart::initChart(QChart::ChartType type)
 
     setFlag(ItemHasContents, true);
 
+    // Reset allocator for QBarSet to create
+    // Declarative BarSets by default
+    qt_allocate_bar_set = &qt_allocate_bar_set_qml;
+
     if (type == QChart::ChartTypePolar)
         m_chart = new QPolarChart();
     else