Fixed crash when changing file member of custom class

This crash was caused by an infinite recursion happening when changing
top-level FilePath values. It only affected Qt 6 builds, because two
QVariant values that both hold a FilePath value always compared as
unequal due to FilePath not defining a comparision operator.

In addition to adding the comparison operator, I've also added a
condition to the updating of the property value. It should only be
necessary to update the top-level value when a nested value was changed.
Further more, it now sets mUpdatingDetails as another protection against
recursive calls.

For completeness I've also added the comparision operator to
PropertyValue and ObjectRef, though they would not have caused problems
in this context since they're not used as property display values.

Closes #3783

NEWS.md

@@ -6,6 +6,7 @@
 * Scripting: Added API for editing tile layers using terrain sets (with a-morphous, #3758)
 * Scripting: Support erasing tiles in Tool.preview and TileMap.merge
 * Scripting: Added WangSet.effectiveTypeForColor
+* Fixed crash when changing file property of custom class (#3783)
 * Fixed object preview position with parallax factor on group layer (#3669)
 * Fixed hover highlight rendering with active parallax factor (#3669)
 * Fixed updating of object selection outlines when changing parallax factor (#3669)

src/libtiled/properties.h

@@ -60,6 +60,9 @@ class TILEDSHARED_EXPORT PropertyValue
 
     const PropertyType *type() const;
     QString typeName() const;
+
+    bool operator==(const PropertyValue &o) const
+    { return typeId == o.typeId && value == o.value; }
 };
 
 class TILEDSHARED_EXPORT FilePath
@@ -70,6 +73,9 @@ class TILEDSHARED_EXPORT FilePath
 public:
     QUrl url;
 
+    bool operator==(const FilePath &o) const
+    { return url == o.url; }
+
     static QString toString(const FilePath &path);
     static FilePath fromString(const QString &string);
 };
@@ -82,6 +88,9 @@ class TILEDSHARED_EXPORT ObjectRef
 public:
     int id;
 
+    bool operator==(const ObjectRef &o) const
+    { return id == o.id; }
+
     static int toInt(const ObjectRef &ref) { return ref.id; }
     static ObjectRef fromInt(int id) { return ObjectRef { id }; }
 };

src/tiled/propertytypeseditor.cpp

@@ -1133,13 +1133,18 @@ void PropertyTypesEditor::memberValueChanged(const QStringList &path, const QVar
     if (!classType)
         return;
 
-    auto &topLevelName = path.first();
-
     if (!setPropertyMemberValue(classType->members, path, value))
         return;
 
-    if (auto property = mPropertiesHelper->property(topLevelName))
-        property->setValue(mPropertiesHelper->toDisplayValue(classType->members.value(topLevelName)));
+    // When a nested property was changed, we need to update the value of the
+    // top-level property to match.
+    if (path.size() > 1) {
+        auto &topLevelName = path.first();
+        if (auto property = mPropertiesHelper->property(topLevelName)) {
+            QScopedValueRollback<bool> updatingDetails(mUpdatingDetails, true);
+            property->setValue(mPropertiesHelper->toDisplayValue(classType->members.value(topLevelName)));
+        }
+    }
 
     applyPropertyTypes();
 }