Fix a deleted symbol's joining wire getting a random uuid on every run

Deleting a symbol whose terminal held several wires joins the wires
left behind with a new one. That wire got a random uuid, so the same
deletion saved a different file every time: a diff for nothing in a
project kept in git (discussion #1512), and two copies with the same
edit could not be compared.

Its uuid now comes from its two ends (each end's symbol and terminal,
sorted), the recipe a wire saved without a uuid already gets on load
(Diagram::fromXml(), derivedItemUuid()). Undo and redo keep the same
wire, so its uuid too.

tst_joinedwireuuid deletes the coil KA1 of examples/affuteuse_250h.qet
in two runs: both saves are identical and no wire has a random uuid.
Without the fix one wire has a random uuid.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XCdg2Er2vYhB8Vwa5G7fSR

tests/qttest/CMakeLists.txt

@@ -889,6 +889,19 @@ if(QET_HAS_SCRIPTING)
   target_compile_definitions(tst_scriptconductoruuid PRIVATE
     "QET_TEST_BINARY_PATH=\"$<TARGET_FILE:qelectrotech>\"")
 
+  # Deleting a symbol whose terminal held several wires joins them with a
+  # new wire; its uuid comes from its two ends, so the same deletion saves
+  # the same file every time (F115): examples/affuteuse_250h.qet.
+  add_executable(
+    tst_joinedwireuuid
+    tst_joinedwireuuid.cpp)
+  add_test(NAME tst_joinedwireuuid COMMAND tst_joinedwireuuid)
+  add_dependencies(tst_joinedwireuuid qelectrotech)
+  target_link_libraries(tst_joinedwireuuid PRIVATE Qt::Test)
+  target_compile_definitions(tst_joinedwireuuid PRIVATE
+    "QET_TEST_BINARY_PATH=\"$<TARGET_FILE:qelectrotech>\""
+    "QET_EXAMPLES_DIR=\"${QET_DIR}/examples\"")
+
   # qet.terminalPosition() and qet.conductorPath(), checked against each
   # other on a fixture's conductors.
   add_executable(

tests/qttest/tst_joinedwireuuid.cpp

@@ -0,0 +1,103 @@
+/*
+	Copyright 2006-2026 The QElectroTech Team
+	This file is part of QElectroTech.
+
+	QElectroTech is free software: you can redistribute it and/or modify
+	it under the terms of the GNU General Public License as published by
+	the Free Software Foundation, either version 2 of the License, or
+	(at your option) any later version.
+
+	QElectroTech is distributed in the hope that it will be useful,
+	but WITHOUT ANY WARRANTY; without even the implied warranty of
+	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+	GNU General Public License for more details.
+
+	You should have received a copy of the GNU General Public License
+	along with QElectroTech.  If not, see <http://www.gnu.org/licenses/>.
+*/
+#include <QtTest>
+#include <QProcess>
+#include <QRegularExpression>
+#include <QTemporaryDir>
+
+/**
+	Deleting a symbol whose terminal held several wires joins the wires
+	left behind with a new one. That wire got a random uuid, so the same
+	deletion saved a different file on every run (F115). Its uuid now
+	comes from its two ends, as a wire saved without a uuid gets on load.
+
+	Runs the real binary's --run on examples/affuteuse_250h.qet (wires
+	saved without uuids): the coil KA1 on folio 3 deleted, twice, in two
+	separate runs. Both saves must be identical, and no wire may carry a
+	random (version 4) uuid.
+*/
+class tst_joinedwireuuid : public QObject
+{
+	Q_OBJECT
+
+	QTemporaryDir m_dir;
+
+	QByteArray deleteAndSave(const QString &name)
+	{
+		const QString out = m_dir.filePath(name + QStringLiteral(".qet"));
+		const QString js = m_dir.filePath(name + QStringLiteral(".js"));
+		QFile script(js);
+		if (!script.open(QIODevice::WriteOnly)) return {};
+		script.write(QStringLiteral(
+			"qet.log('DELETED ' + qet.deleteElement(3, '{d8ba5ae4-c76f-4936-bb05-f719eec2be81}'));\n"
+			"qet.save('%1');\n").arg(out).toUtf8());
+		script.close();
+
+		QProcessEnvironment env = QProcessEnvironment::systemEnvironment();
+		env.insert(QStringLiteral("QT_QPA_PLATFORM"), QStringLiteral("offscreen"));
+			//Its own settings and single-instance socket: another test's
+			//QElectroTech running at the same time would otherwise be
+			//handed this run (SingleApplication)
+		const QString home = m_dir.filePath(QStringLiteral("home"));
+		QDir().mkpath(home);
+		env.insert(QStringLiteral("HOME"), home);
+		env.insert(QStringLiteral("XDG_CONFIG_HOME"), home + QStringLiteral("/config"));
+		env.insert(QStringLiteral("XDG_DATA_HOME"), home + QStringLiteral("/data"));
+		env.insert(QStringLiteral("TMPDIR"), m_dir.path());
+		env.insert(QStringLiteral("QET_ENABLE_SCRIPTING"), QStringLiteral("1"));
+		QProcess proc;
+		proc.setProcessEnvironment(env);
+		proc.setProcessChannelMode(QProcess::MergedChannels);
+		proc.start(QStringLiteral(QET_TEST_BINARY_PATH),
+				   {QStringLiteral("--run"), js,
+					QStringLiteral(QET_EXAMPLES_DIR "/affuteuse_250h.qet")});
+		if (!proc.waitForFinished(180000) || proc.exitCode() != 0
+				|| !proc.readAll().contains("DELETED true"))
+			return {};
+		QFile saved(out);
+		return saved.open(QIODevice::ReadOnly) ? saved.readAll() : QByteArray();
+	}
+
+private slots:
+	void initTestCase()
+	{
+		QVERIFY2(QFile::exists(QStringLiteral(QET_TEST_BINARY_PATH)), "qelectrotech binary not found");
+		QVERIFY(m_dir.isValid());
+	}
+
+	void sameDeletionSavesTheSameFile()
+	{
+		const QByteArray first = deleteAndSave(QStringLiteral("first"));
+		const QByteArray second = deleteAndSave(QStringLiteral("second"));
+		QVERIFY2(!first.isEmpty() && !second.isEmpty(), "the coil was not deleted and saved");
+
+			//No wire with a random uuid: every one is derived
+		const QRegularExpression wire(QStringLiteral(
+			"<conductor [^>]*\\buuid=\"\\{[0-9a-f]{8}-[0-9a-f]{4}-([0-9a-f])"));
+		int wires = 0, random = 0;
+		for (auto it = wire.globalMatch(QString::fromUtf8(first)); it.hasNext(); ++wires)
+			if (it.next().captured(1) == QLatin1String("4")) ++random;
+		QVERIFY(wires > 200);
+		QCOMPARE(random, 0);
+
+		QVERIFY(first == second);
+	}
+};
+
+QTEST_GUILESS_MAIN(tst_joinedwireuuid)
+#include "tst_joinedwireuuid.moc"