ProjectExplorer: Add a mechanism to access fixed data in ProjectNodes

To be used in CMakeTargetNode for Android-specific items, but possibly
useful for other combinations, too, at the price of (only) one empty hash
per _Project_Node.

Change-Id: I4ced56a6ddfa54a00f96be0507a556fa7b20b552
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>

src/plugins/projectexplorer/projectnodes.cpp

@@ -944,8 +944,7 @@ ProjectNode *ProjectNode::projectNode(const Utils::FilePath &file) const
 
 QVariant ProjectNode::data(Core::Id role) const
 {
-    Q_UNUSED(role)
-    return QVariant();
+    return m_fallbackData.value(role);
 }
 
 bool ProjectNode::setData(Core::Id role, const QVariant &value) const
@@ -955,6 +954,11 @@ bool ProjectNode::setData(Core::Id role, const QVariant &value) const
     return false;
 }
 
+void ProjectNode::setFallbackData(Core::Id key, const QVariant &value)
+{
+    m_fallbackData.insert(key, value);
+}
+
 bool FolderNode::isEmpty() const
 {
     return m_nodes.size() == 0;

src/plugins/projectexplorer/projectnodes.h

@@ -388,6 +388,8 @@ public:
     //       "build single file" case.
     virtual void build() {}
 
+    void setFallbackData(Core::Id key, const QVariant &value);
+
 protected:
     void setIsProduct() { m_isProduct = true; }
 
@@ -395,6 +397,7 @@ protected:
 
 private:
     bool m_isProduct = false;
+    QHash<Core::Id, QVariant> m_fallbackData; // Used in data(), unless overridden.
 };
 
 class PROJECTEXPLORER_EXPORT ContainerNode : public FolderNode