Remember the expanded state of custom class properties

The expanded state is now remembered for each "path", meaning you can
select different objects, and when they happen to have the same
properties the expanded state applies to all of them.

For now the state is lost when Tiled is closed. It might be nice to
store the list of expanded property paths in the session.

src/tiled/propertieswidget.cpp

@@ -517,6 +517,7 @@ class VariantMapProperty : public GroupProperty
     QVariantMap mValue;
     QVariantMap mSuggestions;
     QHash<QString, Property*> mPropertyMap;
+    QSet<QStringList> mExpandedProperties;
 };
 
 
@@ -2576,6 +2577,15 @@ Property *VariantMapProperty::createProperty(const QStringList &path,
 
                 createClassMembers(path, groupProperty, classType, std::move(get));
 
+                groupProperty->setExpanded(mExpandedProperties.contains(path));
+
+                connect(groupProperty, &GroupProperty::expandedChanged, this, [=](bool expanded) {
+                    if (expanded)
+                        mExpandedProperties.insert(path);
+                    else
+                        mExpandedProperties.remove(path);
+                });
+
                 property = groupProperty;
                 break;
             }

src/tiled/varianteditor.cpp

@@ -73,6 +73,14 @@ void Property::setActions(Actions actions)
     }
 }
 
+void GroupProperty::setExpanded(bool expanded)
+{
+    if (m_expanded != expanded) {
+        m_expanded = expanded;
+        emit expandedChanged(expanded);
+    }
+}
+
 void StringProperty::setPlaceholderText(const QString &placeholderText)
 {
     if (m_placeholderText != placeholderText) {
@@ -664,12 +672,14 @@ QLayout *VariantEditor::createPropertyLayout(Property *property)
         widgets.childrenLayout->addLayout(rowLayout);
         widgets.layout = widgets.childrenLayout;
 
+        connect(groupProperty, &GroupProperty::expandedChanged, widgets.label, &PropertyLabel::setExpanded);
         connect(widgets.label, &PropertyLabel::toggled, this, [=](bool expanded) {
             setPropertyChildrenExpanded(groupProperty, expanded);
+            groupProperty->setExpanded(expanded);
         });
 
         widgets.label->setExpandable(true);
-        widgets.label->setExpanded(widgets.label->isHeader());
+        widgets.label->setExpanded(groupProperty->isExpanded());
     }
 
     updatePropertyEnabled(widgets, property->isEnabled());

src/tiled/varianteditor.h

@@ -128,6 +128,7 @@ class Separator final : public Property
 class GroupProperty : public Property
 {
     Q_OBJECT
+    Q_PROPERTY(bool expanded READ isExpanded WRITE setExpanded NOTIFY expandedChanged)
 
 public:
     GroupProperty(const QString &name, QObject *parent = nullptr)
@@ -143,6 +144,9 @@ class GroupProperty : public Property
 
     void setHeader(bool header) { m_header = header; }
 
+    bool isExpanded() const { return m_expanded; }
+    void setExpanded(bool expanded);
+
     void clear()
     {
         qDeleteAll(m_subProperties);
@@ -176,10 +180,12 @@ class GroupProperty : public Property
     const QList<Property*> &subProperties() const { return m_subProperties; }
 
 signals:
+    void expandedChanged(bool expanded);
     void propertyAdded(int index, Property *property);
 
 private:
     bool m_header = true;
+    bool m_expanded = true;
     QList<Property*> m_subProperties;
 };