Add API to learn about QQmlBinding's dependencies

Adds a method `dependencies()` to QQmlBinding, that returns a
QVector<QQmlProperty> of all properties the binding depends on. The API is
meant to be used in debugging tools (e.g. in GammaRay).
Also adds a public method subBindings() to QQmlValueTypeProxyBinding in
order to be able to access their dependencies.

Change-Id: Ib833703ec9e632661626c4532b8d73997f38e62b
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

6 files changed, 57 insertions, 9 deletions

diff --git a/src/qml/qml/qqmlbinding.cpp b/src/qml/qml/qqmlbinding.cpp
index 84f30af066..566fbb86ac 100644
--- a/src/qml/qml/qqmlbinding.cpp
+++ b/src/qml/qml/qqmlbinding.cpp
@@ -54,6 +54,7 @@
 
 #include <QVariant>
 #include <QtCore/qdebug.h>
+#include <QVector>
 
 QT_BEGIN_NAMESPACE
 
@@ -579,6 +580,37 @@ void QQmlBinding::getPropertyData(QQmlPropertyData **propertyData, QQmlPropertyD
     }
 }
 
+QVector<QQmlProperty> QQmlBinding::dependencies() const
+{
+    QVector<QQmlProperty> dependencies;
+    if (!m_target.data())
+        return dependencies;
+
+    for (const auto &guardList : { permanentGuards, activeGuards }) {
+        for (QQmlJavaScriptExpressionGuard *guard = guardList.first(); guard; guard = guardList.next(guard)) {
+            if (guard->signalIndex() == -1) // guard's sender is a QQmlNotifier, not a QObject*.
+                continue;
+
+            QObject *senderObject = guard->senderAsObject();
+            if (!senderObject)
+                continue;
+
+            const QMetaObject *senderMeta = senderObject->metaObject();
+            if (!senderMeta)
+                continue;
+
+            for (int i = 0; i < senderMeta->propertyCount(); i++) {
+                QMetaProperty property = senderMeta->property(i);
+                if (property.notifySignalIndex() == QMetaObjectPrivate::signal(senderMeta, guard->signalIndex()).methodIndex()) {
+                    dependencies.push_back(QQmlProperty(senderObject, QString::fromUtf8(senderObject->metaObject()->property(i).name())));
+                }
+            }
+        }
+    }
+
+    return dependencies;
+}
+
 class QObjectPointerBinding: public QQmlNonbindingBinding
 {
     QQmlMetaObject targetMetaObject;
diff --git a/src/qml/qml/qqmlbinding_p.h b/src/qml/qml/qqmlbinding_p.h
index 1c894148e4..38d59a8919 100644
--- a/src/qml/qml/qqmlbinding_p.h
+++ b/src/qml/qml/qqmlbinding_p.h
@@ -102,6 +102,15 @@ public:
     QString expressionIdentifier() const override;
     void expressionChanged() override;
 
+    /**
+     * This method returns a snapshot of the currently tracked dependencies of
+     * this binding. The dependencies can change upon reevaluation. This method is
+     * used in GammaRay to visualize binding hierarchies.
+     *
+     * Call this method from the UI thread.
+     */
+    QVector<QQmlProperty> dependencies() const;
+
 protected:
     virtual void doUpdate(const DeleteWatcher &watcher,
                           QQmlPropertyData::WriteFlags flags, QV4::Scope &scope) = 0;
diff --git a/src/qml/qml/qqmljavascriptexpression_p.h b/src/qml/qml/qqmljavascriptexpression_p.h
index 8b4b64f4d2..e9a9f4feee 100644
--- a/src/qml/qml/qqmljavascriptexpression_p.h
+++ b/src/qml/qml/qqmljavascriptexpression_p.h
@@ -162,6 +162,13 @@ protected:
     void setupFunction(QV4::ExecutionContext *qmlContext, QV4::Function *f);
     void setCompilationUnit(QV4::CompiledData::CompilationUnit *compilationUnit);
 
+    // We store some flag bits in the following flag pointers.
+    //    activeGuards:flag1  - notifyOnValueChanged
+    //    activeGuards:flag2  - useSharedContext
+    QBiPointer<QObject, DeleteWatcher> m_scopeObject;
+    QForwardFieldList<QQmlJavaScriptExpressionGuard, &QQmlJavaScriptExpressionGuard::next> activeGuards;
+    QForwardFieldList<QQmlJavaScriptExpressionGuard, &QQmlJavaScriptExpressionGuard::next> permanentGuards;
+
 private:
     friend class QQmlContextData;
     friend class QQmlPropertyCapture;
@@ -170,13 +177,6 @@ private:
 
     QQmlDelayedError *m_error;
 
-    // We store some flag bits in the following flag pointers.
-    //    activeGuards:flag1  - notifyOnValueChanged
-    //    activeGuards:flag2  - useSharedContext
-    QBiPointer<QObject, DeleteWatcher> m_scopeObject;
-    QForwardFieldList<QQmlJavaScriptExpressionGuard, &QQmlJavaScriptExpressionGuard::next> activeGuards;
-    QForwardFieldList<QQmlJavaScriptExpressionGuard, &QQmlJavaScriptExpressionGuard::next> permanentGuards;
-
     QQmlContextData *m_context;
     QQmlJavaScriptExpression **m_prevExpression;
     QQmlJavaScriptExpression  *m_nextExpression;
diff --git a/src/qml/qml/qqmlnotifier_p.h b/src/qml/qml/qqmlnotifier_p.h
index 6e91369793..a99b13f155 100644
--- a/src/qml/qml/qqmlnotifier_p.h
+++ b/src/qml/qml/qqmlnotifier_p.h
@@ -109,6 +109,9 @@ public:
 
     inline int signalIndex() const { return sourceSignal; }
 
+    inline QObject *senderAsObject() const;
+    inline QQmlNotifier *senderAsNotifier() const;
+
 private:
     friend class QQmlData;
     friend class QQmlNotifier;
@@ -117,8 +120,6 @@ private:
     // endpoint is connected to.  While the endpoint is notifying, the
     // senderPtr points to another qintptr that contains this value.
     qintptr senderPtr;
-    inline QObject *senderAsObject() const;
-    inline QQmlNotifier *senderAsNotifier() const;
 
     Callback callback:4;
     int needsConnectNotify:1;
diff --git a/src/qml/qml/qqmlvaluetypeproxybinding.cpp b/src/qml/qml/qqmlvaluetypeproxybinding.cpp
index 4e2e7b06c7..7a3e4b2df4 100644
--- a/src/qml/qml/qqmlvaluetypeproxybinding.cpp
+++ b/src/qml/qml/qqmlvaluetypeproxybinding.cpp
@@ -72,6 +72,11 @@ bool QQmlValueTypeProxyBinding::isValueTypeProxy() const
     return true;
 }
 
+QQmlAbstractBinding *QQmlValueTypeProxyBinding::subBindings() const
+{
+    return m_bindings.data();
+}
+
 QQmlAbstractBinding *QQmlValueTypeProxyBinding::binding(QQmlPropertyIndex propertyIndex) const
 {
     QQmlAbstractBinding *binding = m_bindings.data();
diff --git a/src/qml/qml/qqmlvaluetypeproxybinding_p.h b/src/qml/qml/qqmlvaluetypeproxybinding_p.h
index 92b5470f39..ba0d305bd9 100644
--- a/src/qml/qml/qqmlvaluetypeproxybinding_p.h
+++ b/src/qml/qml/qqmlvaluetypeproxybinding_p.h
@@ -60,6 +60,7 @@ class QQmlValueTypeProxyBinding : public QQmlAbstractBinding
 public:
     QQmlValueTypeProxyBinding(QObject *o, QQmlPropertyIndex coreIndex);
 
+    QQmlAbstractBinding *subBindings() const;
     QQmlAbstractBinding *binding(QQmlPropertyIndex targetPropertyIndex) const;
     void removeBindings(quint32 mask);