Fix empty nested class properties not being cleaned up (#3998)

src/libtiled/object.cpp

@@ -123,7 +123,15 @@ QVariantMap Object::inheritedProperties() const
 
 bool Object::setProperty(const PropertyPath &path, const QVariant &value)
 {
-    return setPropertyMemberValue(mProperties, path, value);
+    // Allow removing an empty top-level class property only when it is defined
+    // in the object's class, so that manually added properties are preserved.
+    bool allowTopLevelReset = false;
+    if (path.size() > 1) {
+        const auto &topKey = std::get<QString>(path.first());
+        if (const ClassPropertyType *type = classType())
+            allowTopLevelReset = type->members.contains(topKey);
+    }
+    return setPropertyMemberValue(mProperties, path, value, allowTopLevelReset);
 }
 
 void Object::setPropertyTypes(const SharedPropertyTypes &propertyTypes)

src/libtiled/properties.cpp

@@ -173,7 +173,8 @@ bool setNestedPropertyValue(QVariant &compoundValue,
 
 bool setPropertyMemberValue(Properties &properties,
                             const PropertyPath &path,
-                            const QVariant &value)
+                            const QVariant &value,
+                            bool allowTopLevelReset)
 {
     Q_ASSERT(!path.isEmpty());
 
@@ -184,9 +185,12 @@ bool setPropertyMemberValue(Properties &properties,
 
     if (path.size() > 1) {
         auto topLevelValue = properties.value(topLevelName);
-        if (!setNestedPropertyValue(topLevelValue, 1, path, value, false))
+        if (!setNestedPropertyValue(topLevelValue, 1, path, value, allowTopLevelReset))
             return false;
-        properties.insert(topLevelName, topLevelValue);
+        if (!topLevelValue.isValid() && allowTopLevelReset)
+            properties.remove(topLevelName);
+        else
+            properties.insert(topLevelName, topLevelValue);
     } else {
         properties.insert(topLevelName, value);
     }

src/libtiled/properties.h

@@ -191,7 +191,8 @@ TILEDSHARED_EXPORT bool setNestedPropertyValue(QVariant &compoundValue,
 
 TILEDSHARED_EXPORT bool setPropertyMemberValue(Properties &properties,
                                                const PropertyPath &path,
-                                               const QVariant &value);
+                                               const QVariant &value,
+                                               bool allowTopLevelReset = false);
 
 TILEDSHARED_EXPORT void aggregateProperties(AggregatedProperties &aggregated, const Properties &properties);
 TILEDSHARED_EXPORT void mergeProperties(Properties &target, const Properties &source);