Never derive a uuid the file already carries

A symbol keeps its derived uuid once saved, even when it is moved. A
symbol saved without a uuid that later turns up on the spot it left -- a
hand edit, an older version, another tool writing the file -- derived the
same uuid, and the project had two symbols with one identity.

readDiagramsXml() now collects every symbol and wire uuid the file
carries, on any folio, before a folio loads; derivedItemUuid() moves to
the next counter value while a candidate is among them. The result still
depends on the file alone. Renamed from derivedUuid(), which QETProject
already has for the project's own uuid.

tst_derivedsymboluuid: newcomerOnAMovedSymbolsSpotGetsAnotherUuid fails
with the check switched off.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

sources/diagram.cpp

@@ -1685,7 +1685,7 @@ bool Diagram::fromXml(QDomElement &document,
 				//uuids anyway.
 			if (consider_informations && m_project
 				&& QUuid(element_xml.attribute(QStringLiteral("uuid"))).isNull()) {
-				nvel_elmt->setUuid(m_project->derivedUuid(
+				nvel_elmt->setUuid(m_project->derivedItemUuid(
 									   QStringLiteral("element"),
 									   QStringList{type_id,
 												   element_xml.attribute(QStringLiteral("x")),

sources/qetproject.cpp

@@ -276,7 +276,7 @@ QUuid QETProject::uuid() const
 }
 
 /**
-	@brief QETProject::derivedUuid
+	@brief QETProject::derivedItemUuid
 	A uuid for an item of this project that was saved without one, the same
 	on every load of the same file.
 	@p key describes the item by what it is, never by its place in the file
@@ -284,16 +284,31 @@ QUuid QETProject::uuid() const
 	Items with the same @p kind and @p key anywhere in the project (a copied
 	folio, two identical symbols stacked on one spot) are told apart by a
 	counter, in load order among those items alone.
+
+	A derived uuid is never one the file already carries: an item saved with
+	a derived uuid and then moved or re-connected keeps it, so a newcomer
+	later taking its old place or ends would otherwise derive the same one.
+	The file's saved uuids are collected before any folio loads
+	(readDiagramsXml()), so the result still depends on the file alone.
+
+	uuids are unique within one project; copies of a project share them, as
+	they share every saved uuid. Anything bringing items in from another
+	project must renew them, as paste does.
 	@return a UUID v5, which cannot collide with the v4 uuids given to new
 	items
 */
-QUuid QETProject::derivedUuid(const QString &kind, const QString &key)
+QUuid QETProject::derivedItemUuid(const QString &kind, const QString &key)
 {
 	static const QUuid derived_ns(QStringLiteral("{7d1e9c3a-5b2f-4e8a-9c61-2f4b8d0e6a17}"));
 	const QString full = kind + QLatin1Char('\n') + key;
-	const int n = m_derived_uuid_keys[full]++;
-	return QUuid::createUuidV5(derived_ns,
-							   n ? full + QLatin1Char('\n') + QString::number(n) : full);
+	int &n = m_derived_uuid_keys[full];
+	QUuid uuid;
+	do {
+		uuid = QUuid::createUuidV5(derived_ns,
+								   n ? full + QLatin1Char('\n') + QString::number(n) : full);
+		++n;
+	} while (m_saved_item_uuids.contains(uuid));
+	return uuid;
 }
 
 /**
@@ -1909,6 +1924,18 @@ void QETProject::readDiagramsXml(QDomDocument &xml_project)
 	//Search the diagrams in the project
 	QDomNodeList diagram_nodes = xml_project.elementsByTagName(QStringLiteral("diagram"));
 
+		//Every symbol and wire uuid the file already carries, on any folio,
+		//before a folio derives one for an item saved without: see
+		//derivedItemUuid().
+	for (const QString &tag : {QStringLiteral("element"), QStringLiteral("conductor")}) {
+		const QDomNodeList nodes = xml_project.elementsByTagName(tag);
+		for (int i = 0; i < nodes.size(); ++i) {
+			const QUuid saved(nodes.at(i).toElement().attribute(QStringLiteral("uuid")));
+			if (!saved.isNull())
+				m_saved_item_uuids.insert(saved);
+		}
+	}
+
 	if(dlgWaiting)
 		dlgWaiting->setProgressBarRange(0, diagram_nodes.length()*3);
 

sources/qetproject.h

@@ -36,6 +36,7 @@
 #endif
 
 #include <QHash>
+#include <QSet>
 #include <QFuture>
 
 class Diagram;
@@ -107,7 +108,7 @@ class QETProject : public QObject
 		ProjectPropertiesHandler& projectPropertiesHandler();
 		projectDataBase *dataBase();
 		QUuid uuid() const;
-		QUuid derivedUuid(const QString &kind, const QString &key);
+		QUuid derivedItemUuid(const QString &kind, const QString &key);
 		ProjectState state() const;
 		QList<Diagram *> diagrams() const;
 		int folioIndex(const Diagram *) const;
@@ -367,6 +368,7 @@ class QETProject : public QObject
 		KAutoSaveFile m_backup_file;
 		QUuid m_uuid = QUuid::createUuid();
 		QHash<QString, int> m_derived_uuid_keys;
+		QSet<QUuid> m_saved_item_uuids;	//symbol and wire uuids the file carries, see derivedItemUuid()
 		projectDataBase m_data_base;
 		QVector<TerminalStrip *> m_terminal_strip_vector;
 

tests/qttest/tst_derivedsymboluuid.cpp

@@ -156,6 +156,28 @@ private slots:
 		QCOMPARE(symbolUuids(resave(doc)), symbolUuids(doc));
 	}
 
+	// A symbol keeps its derived uuid once saved, even when moved. A symbol
+	// saved without a uuid that later turns up on the spot it left (a hand
+	// edit, an older version, another tool) would derive the same uuid: it
+	// must get another one instead.
+	void newcomerOnAMovedSymbolsSpotGetsAnotherUuid()
+	{
+		QDomDocument doc = resave(fixture());
+		QDomElement moved = symbols(diagrams(doc).first()).first();
+		QVERIFY(!QUuid(moved.attribute(QStringLiteral("uuid"))).isNull());
+		QDomElement newcomer = moved.cloneNode(true).toElement();
+		newcomer.removeAttribute(QStringLiteral("uuid"));
+		const QDomNodeList terminals = newcomer.elementsByTagName(QStringLiteral("terminal"));
+		for (int i = 0; i < terminals.size(); ++i)
+			terminals.at(i).toElement().setAttribute(QStringLiteral("id"), 90000 + i);
+		moved.setAttribute(QStringLiteral("x"), moved.attribute(QStringLiteral("x")).toInt() + 500);
+		moved.parentNode().appendChild(newcomer);
+
+		const QMultiHash<QString, QString> after = symbolUuids(resave(doc));
+		QCOMPARE(after.size(), 10);
+		QCOMPARE(QSet<QString>(after.begin(), after.end()).size(), 10);
+	}
+
 	void stackedIdenticalSymbolsDiffer()
 	{
 		QDomDocument doc = fixture();