Sync the folder after saving, and save from the command line through a temporary file

QSaveFile writes a new file, forces it to disk and renames it over the
old one, but does not force the folder to disk. On ext4 or XFS a power
cut soon after a save can then lose the rename: the previous file comes
back, or none. QET::syncFolderOf() now syncs the folder after every
project, symbol and title block save (QET::writeXmlText()) and every
.qetz save (QetZip::write()). Nothing to do on Windows.

--resave and --set-titleblock wrote a .qet straight over the output file
(QFile, truncate, write): a run stopped part-way left half a project.
They now write through QET::writeXmlText() like the GUI's save. On
Windows their .qet now has LF line ends, as the GUI writes.

Checked with strace on --resave: fdatasync of the new file, linkat into
place, fsync of the folder. The .qet written is byte-identical to before.
ctest 106/106.

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

cmake/qet_compilation_vars.cmake

@@ -941,6 +941,7 @@ set(QET_SRC_FILES
   ${QET_DIR}/sources/utils/qetsettings.h
   ${QET_DIR}/sources/utils/qetutils.cpp
   ${QET_DIR}/sources/utils/qetutils.h
+  ${QET_DIR}/sources/utils/syncfolder.h
 
   ${QET_DIR}/sources/materiallist/materialentrydialog.cpp
   ${QET_DIR}/sources/materiallist/materialentrydialog.h

sources/cli_export.cpp

@@ -885,14 +885,13 @@ int resaveProject(QETProject &project, const QString &output)
 		//what building them would write (QETProject::toXml())
 	QHash<int, QByteArray> kept_folios;
 	const QDomDocument doc = project.toXml(&kept_folios);
-	QFile file(output);
+		//Through a temporary file, as the GUI saves: a run stopped
-	if (!file.open(QIODevice::WriteOnly | QIODevice::Text)) {
+		//part-way leaves the previous file
-		err << "Cannot open '" << output << "' for writing.\n";
+	QString error;
+	if (!QET::writeXmlText(QETProject::spliceKeptFolios(doc.toString(4), kept_folios), output, &error)) {
+		err << "Cannot write '" << output << "': " << error << "\n";
 		return 1;
 	}
-	QTextStream fout(&file);
-	fout << QETProject::spliceKeptFolios(doc.toString(4), kept_folios);
-	file.close();
 	out << "Re-saved project -> " << output << "\n";
 	return 0;
 }
@@ -980,14 +979,11 @@ int setTitleBlock(QETProject &project, const QString &output,
 			//is what building them would write (QETProject::toXml())
 		QHash<int, QByteArray> kept_folios;
 		const QDomDocument doc = project.toXml(&kept_folios);
-		QFile file(output);
+		QString error;
-		if (!file.open(QIODevice::WriteOnly | QIODevice::Text)) {
+		if (!QET::writeXmlText(QETProject::spliceKeptFolios(doc.toString(4), kept_folios), output, &error)) {
-			err << "Cannot open '" << output << "' for writing.\n";
+			err << "Cannot write '" << output << "': " << error << "\n";
 			return 1;
 		}
-		QTextStream fout(&file);
-		fout << QETProject::spliceKeptFolios(doc.toString(4), kept_folios);
-		file.close();
 	}
 	out << "Stamped " << fields.size() << " field(s) on "
 		<< folios << " folio(s) -> " << output << "\n";

sources/container/qetzip.cpp

@@ -18,6 +18,7 @@
 #include "qetzip.h"
 
 #include "miniz/miniz.h"
+#include "../utils/syncfolder.h"
 
 #include <QFile>
 #include <QSaveFile>
@@ -152,6 +153,7 @@ bool QetZip::write(const QString &path, const QList<Entry> &entries, QString *er
 		setError(error, file.errorString());
 		return false;
 	}
+	QET::syncFolderOf(path);
 	return true;
 }
 

sources/qet.cpp

@@ -19,6 +19,7 @@
 #include "qetapp.h"
 #include "qeticons.h"
 #include "shortcutmanager.h"
+#include "utils/syncfolder.h"
 
 #include <cmath>
 #include <limits>
@@ -809,6 +810,7 @@ bool QET::writeXmlText(const QString &text, const QString &filepath, QString *er
 
 		return false;
 	}
+	syncFolderOf(filepath);
 
 	return(true);
 }

sources/utils/syncfolder.h

@@ -0,0 +1,54 @@
+/*
+	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/>.
+*/
+#ifndef SYNCFOLDER_H
+#define SYNCFOLDER_H
+
+#include <QFile>
+#include <QFileInfo>
+#include <QString>
+
+#ifndef Q_OS_WIN
+#include <fcntl.h>
+#include <unistd.h>
+#endif
+
+namespace QET {
+	/**
+		Force to disk the folder holding @p file_path, once
+		QSaveFile::commit() renamed a new file into it. QSaveFile syncs the
+		file it wrote but not the folder, and on some file systems (ext4,
+		XFS) a power cut soon after can then lose the rename: the previous
+		file comes back, or none. Does nothing on Windows, where a folder
+		cannot be synced this way.
+	*/
+	inline void syncFolderOf(const QString &file_path)
+	{
+#ifndef Q_OS_WIN
+		const QByteArray folder = QFile::encodeName(QFileInfo(file_path).absolutePath());
+		const int fd = ::open(folder.constData(), O_RDONLY | O_DIRECTORY | O_CLOEXEC);
+		if (fd >= 0) {
+			::fsync(fd);
+			::close(fd);
+		}
+#else
+		Q_UNUSED(file_path)
+#endif
+	}
+}
+
+#endif // SYNCFOLDER_H