core/scriptmodel: structurally compare model entries

Comparisons regressed to being identity based when the values list was
changed from being a `QList<QVariant>` to `QList<QJSValue>`.

src/core/scriptmodel.cpp

@@ -5,6 +5,7 @@
 #include <qabstractitemmodel.h>
 #include <qcontainerfwd.h>
 #include <qjsvalue.h>
+#include <qjsvalueiterator.h>
 #include <qlist.h>
 #include <qnamespace.h>
 #include <qobject.h>
@@ -13,6 +14,55 @@
 #include <qtypes.h>
 #include <qvariant.h>
 
+namespace {
+struct RecursionPair {
+	const QJSValue* a;
+	const QJSValue* b;
+	const RecursionPair* previous;
+};
+
+bool qjsValueStructuralEq(
+    const QJSValue& a,
+    const QJSValue& b,
+    const RecursionPair* activePair = nullptr
+) {
+	if (a.strictlyEquals(b)) return true;
+	if (!a.isObject() || !b.isObject() || a.isArray() != b.isArray()) return false;
+
+	for (const auto* pair = activePair; pair != nullptr; pair = pair->previous) {
+		if (a.strictlyEquals(*pair->a) || b.strictlyEquals(*pair->b)) return false;
+	}
+
+	const auto nextActivePair = RecursionPair {.a = &a, .b = &b, .previous = activePair};
+
+	auto aIter = QJSValueIterator(a);
+	auto bIter = QJSValueIterator(b);
+
+	while (aIter.hasNext()) {
+		if (!bIter.hasNext()) return false;
+
+		aIter.next();
+		bIter.next();
+
+		const auto aName = aIter.name();
+		const auto bName = bIter.name();
+		const auto aValue = aIter.value();
+
+		if (aName == bName) {
+			const auto bValue = bIter.value();
+			if (!qjsValueStructuralEq(aValue, bValue, &nextActivePair)) return false;
+		} else {
+			if (!b.hasOwnProperty(aName)) return false;
+
+			const auto bValue = b.property(aName);
+			if (!qjsValueStructuralEq(aValue, bValue, &nextActivePair)) return false;
+		}
+	}
+
+	return !bIter.hasNext();
+}
+} // namespace
+
 bool ScriptModel::updateValuesUnique(const QList<QJSValue>& newValues) {
 	auto anyChanges = false;
 
@@ -22,14 +72,23 @@ bool ScriptModel::updateValuesUnique(const QList<QJSValue>& newValues) {
 	auto iter = this->mValues.begin();
 	auto newIter = newValues.begin();
 
-	auto getCmpKey = [this](const QJSValue& v) {
-		if (v.hasProperty(this->cmpKey)) return v.property(this->cmpKey);
-		else return v;
+	auto comparisonValue = [this](const QJSValue& value) {
+		if (value.hasProperty(this->cmpKey)) return value.property(this->cmpKey);
+
+		return value;
 	};
 
 	auto valueCmp = [&, this](const QJSValue& a, const QJSValue& b) {
-		if (!this->cmpKey.isEmpty()) return getCmpKey(a).strictlyEquals(getCmpKey(b));
-		return a.strictlyEquals(b);
+		if (a.strictlyEquals(b)) return true;
+
+		const auto aValue = this->cmpKey.isEmpty() ? a : comparisonValue(a);
+		const auto bValue = this->cmpKey.isEmpty() ? b : comparisonValue(b);
+
+		if (this->mComparisonMode == ObjectComparison::Identity) {
+			return aValue.strictlyEquals(bValue);
+		} else {
+			return qjsValueStructuralEq(aValue, bValue);
+		}
 	};
 
 	auto eqPredicate = [&](const QJSValue& b) {
@@ -187,6 +246,12 @@ void ScriptModel::setObjectProp(const QString& objectProp) {
 	emit this->objectPropChanged();
 }
 
+void ScriptModel::setComparisonMode(ObjectComparison::Enum comparisonMode) {
+	if (comparisonMode == this->mComparisonMode) return;
+	this->mComparisonMode = comparisonMode;
+	emit this->comparisonModeChanged();
+}
+
 qint32 ScriptModel::rowCount(const QModelIndex& parent) const {
 	if (parent != QModelIndex()) return 0;
 	return static_cast<qint32>(this->mValues.length());

src/core/scriptmodel.hpp

@@ -1,5 +1,7 @@
 #pragma once
 
+#include <optional>
+
 #include <qabstractitemmodel.h>
 #include <qcontainerfwd.h>
 #include <qjsvalue.h>
@@ -10,6 +12,21 @@
 #include <qtmetamacros.h>
 #include <qtypes.h>
 
+///! @@ScriptModel value comparison mode.
+namespace ObjectComparison { // NOLINT
+Q_NAMESPACE;
+QML_ELEMENT;
+
+enum Enum : quint8 {
+	/// Compare values using strict JavaScript equality.
+	Identity = 0,
+	/// Compare records and arrays structurally.
+	Structure = 1,
+};
+Q_ENUM_NS(Enum);
+
+} // namespace ObjectComparison
+
 ///! QML model reflecting a javascript expression
 /// ScriptModel is a QML [Data Model] that generates model operations based on changes
 /// to a javascript expression attached to @@values.
@@ -44,6 +61,7 @@
 /// [Data Model]: https://doc.qt.io/qt-6/qtquick-modelviewsdata-modelview.html#qml-data-models
 class ScriptModel: public QAbstractListModel {
 	Q_OBJECT;
+	// clang-format off
 	/// The list of values to reflect in the model.
 	/// > [!WARNING] ScriptModel currently only works with lists of *unique* values.
 	/// > There must not be any duplicates in the given list, or behavior of the model is undefined.
@@ -79,6 +97,12 @@ class ScriptModel: public QAbstractListModel {
 	///
 	/// Defaults to `""`, meaning no key.
 	Q_PROPERTY(QString objectProp READ objectProp WRITE setObjectProp NOTIFY objectPropChanged);
+	/// How values should be compared. Defaults to `ObjectComparison.Structure`.
+	///
+	/// Identity based comparison is faster if usable for a given model, and often
+  /// achievable with @@objectProp.
+	Q_PROPERTY(ObjectComparison::Enum comparisonMode READ comparisonMode WRITE setComparisonMode NOTIFY comparisonModeChanged);
+	// clang-format on
 	QML_ELEMENT;
 
 public:
@@ -94,6 +118,9 @@ public:
 	[[nodiscard]] QString objectProp() const { return this->cmpKey; }
 	void setObjectProp(const QString& objectProp);
 
+	[[nodiscard]] ObjectComparison::Enum comparisonMode() const { return this->mComparisonMode; }
+	void setComparisonMode(ObjectComparison::Enum comparisonMode);
+
 	[[nodiscard]] qint32 rowCount(const QModelIndex& parent) const override;
 	[[nodiscard]] QVariant data(const QModelIndex& index, qint32 role) const override;
 	[[nodiscard]] QHash<int, QByteArray> roleNames() const override;
@@ -101,10 +128,12 @@ public:
 signals:
 	void valuesChanged();
 	void objectPropChanged();
+	void comparisonModeChanged();
 
 private:
 	QList<QJSValue> mValues;
 	QString cmpKey;
+	ObjectComparison::Enum mComparisonMode = ObjectComparison::Structure;
 	bool isModifying = false;
 	std::optional<QList<QJSValue>> stagedValues;
 

src/core/test/scriptmodel.cpp

@@ -4,6 +4,7 @@
 #include <qabstractitemmodeltester.h>
 #include <qcontainerfwd.h>
 #include <qdebug.h>
+#include <qjsengine.h>
 #include <qjsvalue.h>
 #include <qlist.h>
 #include <qlogging.h>
@@ -15,8 +16,6 @@
 
 #include "../scriptmodel.hpp"
 
-using OpList = QList<ModelOperation>;
-
 bool ModelOperation::operator==(const ModelOperation& other) const {
 	return other.operation == this->operation && other.index == this->index
 	    && other.length == this->length && other.destIndex == this->destIndex;
@@ -44,9 +43,38 @@ QDebug& operator<<(QDebug& debug, const ModelOperation& op) {
 	return debug;
 }
 
+ChangeObserver::ChangeObserver(QAbstractItemModel* model) {
+	QObject::connect(model, &QAbstractItemModel::rowsInserted, this, &ChangeObserver::onInsert);
+	QObject::connect(model, &QAbstractItemModel::rowsRemoved, this, &ChangeObserver::onRemove);
+	QObject::connect(model, &QAbstractItemModel::rowsMoved, this, &ChangeObserver::onMove);
+}
+
+void ChangeObserver::onInsert(const QModelIndex& parent, int first, int last) {
+	QCOMPARE(parent, QModelIndex());
+	this->mOperations.emplaceBack(ModelOperation::Insert, first, last - first + 1);
+}
+
+void ChangeObserver::onRemove(const QModelIndex& parent, int first, int last) {
+	QCOMPARE(parent, QModelIndex());
+	this->mOperations.emplaceBack(ModelOperation::Remove, first, last - first + 1);
+}
+
+void ChangeObserver::onMove(
+    const QModelIndex& sourceParent,
+    int sourceStart,
+    int sourceEnd,
+    const QModelIndex& destParent,
+    int destStart
+) {
+	QCOMPARE(sourceParent, QModelIndex());
+	QCOMPARE(destParent, QModelIndex());
+	this->mOperations
+	    .emplaceBack(ModelOperation::Move, sourceStart, sourceEnd - sourceStart + 1, destStart);
+}
+
 // NOLINTNEXTLINE(misc-use-internal-linkage)
 QDebug& operator<<(QDebug& debug, const QJSValueList& list) {
-	auto str = QString();
+	QString str;
 
 	for (const auto& var: list) {
 		if (var.isString()) {
@@ -139,55 +167,117 @@ void TestScriptModel::unique() {
 		return list;
 	};
 
-	auto oldlist = strToJsValueList(oldstr);
-	auto newlist = strToJsValueList(newstr);
+	auto oldList = strToJsValueList(oldstr);
+	auto newList = strToJsValueList(newstr);
 
-	auto model = ScriptModel();
+	ScriptModel model;
 	auto modelTester = QAbstractItemModelTester(&model);
+	auto observer = ChangeObserver(&model);
 
-	OpList actualOperations;
-
-	auto onInsert = [&](const QModelIndex& parent, int first, int last) {
-		QCOMPARE(parent, QModelIndex());
-		actualOperations << ModelOperation(ModelOperation::Insert, first, last - first + 1);
-	};
-
-	auto onRemove = [&](const QModelIndex& parent, int first, int last) {
-		QCOMPARE(parent, QModelIndex());
-		actualOperations << ModelOperation(ModelOperation::Remove, first, last - first + 1);
-	};
-
-	auto onMove = [&](const QModelIndex& sourceParent,
-	                  int sourceStart,
-	                  int sourceEnd,
-	                  const QModelIndex& destParent,
-	                  int destStart) {
-		QCOMPARE(sourceParent, QModelIndex());
-		QCOMPARE(destParent, QModelIndex());
-		actualOperations << ModelOperation(
-		    ModelOperation::Move,
-		    sourceStart,
-		    sourceEnd - sourceStart + 1,
-		    destStart
-		);
-	};
-
-	QObject::connect(&model, &QAbstractItemModel::rowsInserted, &model, onInsert);
-	QObject::connect(&model, &QAbstractItemModel::rowsRemoved, &model, onRemove);
-	QObject::connect(&model, &QAbstractItemModel::rowsMoved, &model, onMove);
-
-	model.setValues(oldlist);
-	QVERIFY(qjsValueListsEqual(model.values(), oldlist));
+	model.setValues(oldList);
+	QVERIFY(qjsValueListsEqual(model.values(), oldList));
 	QCOMPARE_EQ(
-	    actualOperations,
-	    OpList({{ModelOperation::Insert, 0, static_cast<qint32>(oldlist.length())}})
+	    observer.operations(),
+	    OpList({{ModelOperation::Insert, 0, static_cast<qint32>(oldList.length())}})
 	);
 
-	actualOperations.clear();
+	observer.clear();
 
-	model.setValues(newlist);
-	QVERIFY(qjsValueListsEqual(model.values(), newlist));
-	QCOMPARE_EQ(actualOperations, operations);
+	model.setValues(newList);
+	QVERIFY(qjsValueListsEqual(model.values(), newList));
+	QCOMPARE_EQ(observer.operations(), operations);
+}
+
+void TestScriptModel::structuralEquality() {
+	ScriptModel model;
+	QJSEngine engine;
+
+	auto object = engine.newObject();
+	object.setProperty("foo", "bar");
+	object.setProperty("bar", "baz");
+	object.setProperty("subobject", engine.newObject());
+
+	auto replacement = engine.newObject();
+	replacement.setProperty("subobject", engine.newObject());
+	replacement.setProperty("bar", "baz");
+	replacement.setProperty("foo", "bar");
+
+	auto oldList = QList<QJSValue> {object};
+
+	auto newList = QList<QJSValue> {replacement};
+
+	auto modelTester = QAbstractItemModelTester(&model);
+	auto observer = ChangeObserver(&model);
+
+	model.setValues(oldList);
+	QVERIFY(qjsValueListsEqual(model.values(), oldList));
+	QCOMPARE_EQ(
+	    observer.operations(),
+	    OpList({{ModelOperation::Insert, 0, static_cast<qint32>(oldList.length())}})
+	);
+
+	observer.clear();
+
+	model.setValues(newList);
+	QVERIFY(qjsValueListsEqual(model.values(), newList));
+	QCOMPARE_EQ(observer.operations(), OpList());
+
+	auto structurallyEquals = [](const QJSValue& a, const QJSValue& b) {
+		ScriptModel model;
+		model.setValues({a});
+
+		auto observer = ChangeObserver(&model);
+		model.setValues({b});
+		return observer.operations().isEmpty();
+	};
+
+	auto different = engine.newObject();
+	different.setProperty("foo", "bar");
+	different.setProperty("bar", "baz");
+	auto differentSubobject = engine.newObject();
+	differentSubobject.setProperty("value", 1);
+	different.setProperty("subobject", differentSubobject);
+	QVERIFY(!structurallyEquals(object, different));
+
+	auto cycleA = engine.newObject();
+	cycleA.setProperty("self", cycleA);
+	auto cycleB = engine.newObject();
+	cycleB.setProperty("self", cycleB);
+	QVERIFY(!structurallyEquals(cycleA, cycleB));
+
+	const auto arrayA = engine.evaluate("[1, { value: 'x' }]");
+	const auto arrayB = engine.evaluate("[1, { value: 'x' }]");
+	QVERIFY(structurallyEquals(arrayA, arrayB));
+
+	auto sparseArrayA = engine.newArray(1);
+	auto sparseArrayB = engine.newArray(2);
+	QVERIFY(!structurallyEquals(sparseArrayA, sparseArrayB));
+}
+
+void TestScriptModel::comparisonModes() {
+	QJSEngine engine;
+	auto makeValue = [&engine]() {
+		auto value = engine.newObject();
+		value.setProperty("nested", engine.newObject());
+		return value;
+	};
+
+	ScriptModel model;
+	QCOMPARE_EQ(model.comparisonMode(), ObjectComparison::Structure);
+
+	model.setValues({makeValue()});
+	model.setComparisonMode(ObjectComparison::Identity);
+	QCOMPARE_EQ(model.comparisonMode(), ObjectComparison::Identity);
+
+	auto observer = ChangeObserver(&model);
+	model.setValues({makeValue()});
+	QVERIFY(!observer.operations().isEmpty());
+
+	model.setComparisonMode(ObjectComparison::Structure);
+
+	observer.clear();
+	model.setValues({makeValue()});
+	QCOMPARE_EQ(observer.operations(), OpList());
 }
 
 QTEST_MAIN(TestScriptModel);

src/core/test/scriptmodel.hpp

@@ -1,6 +1,8 @@
 #pragma once
 
+#include <qabstractitemmodel.h>
 #include <qdebug.h>
+#include <qlist.h>
 #include <qobject.h>
 #include <qtmetamacros.h>
 #include <qtypes.h>
@@ -26,6 +28,29 @@ struct ModelOperation {
 	[[nodiscard]] bool operator==(const ModelOperation& other) const;
 };
 
+using OpList = QList<ModelOperation>;
+
+class ChangeObserver: public QObject {
+public:
+	explicit ChangeObserver(QAbstractItemModel* model);
+
+	[[nodiscard]] const OpList& operations() const { return this->mOperations; }
+	void clear() { this->mOperations.clear(); }
+
+private:
+	void onInsert(const QModelIndex& parent, int first, int last);
+	void onRemove(const QModelIndex& parent, int first, int last);
+	void onMove(
+	    const QModelIndex& sourceParent,
+	    int sourceStart,
+	    int sourceEnd,
+	    const QModelIndex& destParent,
+	    int destStart
+	);
+
+	OpList mOperations;
+};
+
 QDebug& operator<<(QDebug& debug, const ModelOperation& op);
 
 class TestScriptModel: public QObject {
@@ -34,4 +59,6 @@ class TestScriptModel: public QObject {
 private slots:
 	static void unique_data(); // NOLINT
 	static void unique();
+	static void structuralEquality();
+	static void comparisonModes();
 };