Write a PDF's cross-reference links in the same order in every run

injectCrossRefLinks() drew each link as it found it: the contacts of a
cross-reference come from a QMultiMap keyed by Element pointer, and the
scene's items in stacking order. Both change from run to run, so the same
project exported twice gave two different PDFs whose only difference was
the order of the link annotations.

The links are now collected and drawn sorted by their rectangle on the
page (top, left, bottom, right), with the target as the tie-break. The
links themselves are unchanged. The print window's PDF export goes
through the same function.

tst_pdflinkorder exports examples/industrial.qet five times in separate
processes and requires the same links in the same order. It fails on
the old code (lists differ at index 2).

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

sources/pdf_links.cpp

@@ -35,6 +35,8 @@
 #include <QUrl>
 #include <QVector>
 
+#include <algorithm>
+
 namespace PdfLinks {
 
 void injectCrossRefLinks(QPdfEngine *engine, Diagram *diagram,
@@ -83,6 +85,14 @@ void injectCrossRefLinks(QPdfEngine *engine, Diagram *diagram,
 					  QPointF(qMax(a.x(), b.x()), qMax(a.y(), b.y())));
 	};
 
+	// The links are collected first and drawn sorted, not in the order the
+	// loop below finds them: a cross-reference's contacts are keyed by
+	// Element pointer and the scene's items come in stacking order, so that
+	// order changes from run to run and the same project gave a different
+	// PDF each time it was exported.
+	struct Link { QRectF rect; QUrl url; };
+	QList<Link> links;
+
 	auto injectLink = [&](const QRectF &sceneRect, Element *targetElmt) {
 		if (!targetElmt || !targetElmt->diagram()) return;
 		const int targetPage = pageMap.value(targetElmt->diagram(), -1);
@@ -99,7 +109,7 @@ void injectCrossRefLinks(QPdfEngine *engine, Diagram *diagram,
 
 		QUrl url = QUrl::fromLocalFile(outputFileName);
 		url.setFragment(frag);
-		engine->drawHyperlink(devRect, url);
+		links.append({devRect, url});
 	};
 
 	for (auto *item : diagram->items()) {
@@ -165,6 +175,22 @@ void injectCrossRefLinks(QPdfEngine *engine, Diagram *diagram,
 			continue;
 		}
 	}
+
+	// Top to bottom, then left to right; the target breaks a tie between
+	// two links on the same spot.
+	std::sort(links.begin(), links.end(), [](const Link &a, const Link &b) {
+		if (a.rect.top() != b.rect.top())
+			return a.rect.top() < b.rect.top();
+		if (a.rect.left() != b.rect.left())
+			return a.rect.left() < b.rect.left();
+		if (a.rect.bottom() != b.rect.bottom())
+			return a.rect.bottom() < b.rect.bottom();
+		if (a.rect.right() != b.rect.right())
+			return a.rect.right() < b.rect.right();
+		return a.url.fragment() < b.url.fragment();
+	});
+	for (const Link &link : std::as_const(links))
+		engine->drawHyperlink(link.rect, link.url);
 }
 
 void convertUriToGoTo(const QString &pdfPath)

tests/qttest/CMakeLists.txt

@@ -407,6 +407,19 @@ target_link_libraries(tst_pdfpagesize PRIVATE Qt::Test Qt::Gui)
 target_compile_definitions(tst_pdfpagesize PRIVATE
   "QET_TEST_BINARY_PATH=\"$<TARGET_FILE:qelectrotech>\"")
 
+# --export-pdf writes the cross-reference links in the same order in every
+# run, rather than in Element pointer order. Exports examples/industrial.qet
+# several times, in separate processes.
+add_executable(
+  tst_pdflinkorder
+  tst_pdflinkorder.cpp)
+add_test(NAME tst_pdflinkorder COMMAND tst_pdflinkorder)
+add_dependencies(tst_pdflinkorder qelectrotech)
+target_link_libraries(tst_pdflinkorder PRIVATE Qt::Test)
+target_compile_definitions(tst_pdflinkorder PRIVATE
+  "QET_TEST_BINARY_PATH=\"$<TARGET_FILE:qelectrotech>\""
+  "QET_EXAMPLES_DIR=\"${QET_DIR}/examples\"")
+
 # One text per potential: the number goes on the same conductor in every
 # run when two conductors tie for longest. Exports
 # fixtures/one_text_per_potential_tie.qet through the real binary, several

tests/qttest/tst_pdflinkorder.cpp

@@ -0,0 +1,80 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+	--export-pdf writes a project's cross-reference links in the same order
+	every time. They used to come out in the order of Element pointers, so
+	the same project gave a different PDF in each run. Exported in separate
+	processes, since pointers only change between runs.
+*/
+#include <QDir>
+#include <QFile>
+#include <QProcess>
+#include <QRegularExpression>
+#include <QTemporaryDir>
+#include <QtTest>
+
+class tst_pdflinkorder : public QObject
+{
+	Q_OBJECT
+
+	QTemporaryDir m_dir;
+
+	// The link annotations' rectangles and destinations, in file order.
+	QStringList exportLinks(const QString &project, int run)
+	{
+		const QString home = m_dir.filePath(QStringLiteral("home%1").arg(run));
+		const QString tmp = m_dir.filePath(QStringLiteral("tmp%1").arg(run));
+		const QString out = m_dir.filePath(QStringLiteral("out%1.pdf").arg(run));
+		QDir().mkpath(home);
+		QDir().mkpath(tmp);
+		QProcessEnvironment env = QProcessEnvironment::systemEnvironment();
+		env.insert(QStringLiteral("QT_QPA_PLATFORM"), QStringLiteral("offscreen"));
+		env.insert(QStringLiteral("HOME"), home);
+		env.insert(QStringLiteral("XDG_CONFIG_HOME"), home + QStringLiteral("/.config"));
+		env.insert(QStringLiteral("XDG_DATA_HOME"), home + QStringLiteral("/.local/share"));
+		env.insert(QStringLiteral("TMPDIR"), tmp);
+
+		QProcess proc;
+		proc.setProcessEnvironment(env);
+		proc.start(QStringLiteral(QET_TEST_BINARY_PATH),
+				   {QStringLiteral("--export-pdf"), project, out});
+		if (!proc.waitForFinished(120000) || proc.exitCode() != 0)
+			return {};
+
+		QFile file(out);
+		if (!file.open(QIODevice::ReadOnly))
+			return {};
+		const QString pdf = QString::fromLatin1(file.readAll());
+		static const QRegularExpression link(QStringLiteral(
+			R"(/Subtype /Link\s*/Rect \[([^\]]*)\][\s\S]*?/D \[\d+ 0 R ([^\]]*)\])"));
+		QStringList links;
+		auto it = link.globalMatch(pdf);
+		while (it.hasNext()) {
+			const auto m = it.next();
+			links << m.captured(1).simplified() + QStringLiteral(" -> ")
+					 + m.captured(2).simplified();
+		}
+		return links;
+	}
+
+private slots:
+	void initTestCase()
+	{
+		QVERIFY(m_dir.isValid());
+		QVERIFY(QFile::exists(QStringLiteral(QET_TEST_BINARY_PATH)));
+	}
+
+	void sameOrderEveryRun()
+	{
+		const QString project =
+			QStringLiteral(QET_EXAMPLES_DIR) + QStringLiteral("/industrial.qet");
+		QVERIFY2(QFile::exists(project), "examples/industrial.qet not found");
+
+		const QStringList first = exportLinks(project, 0);
+		QVERIFY2(first.size() >= 2, "expected several cross-reference links");
+		for (int run = 1; run < 5; ++run)
+			QCOMPARE(exportLinks(project, run), first);
+	}
+};
+
+QTEST_MAIN(tst_pdflinkorder)
+#include "tst_pdflinkorder.moc"