From e8a5d6aec0ee41605f08b81a480ea00b7c73fa91 Mon Sep 17 00:00:00 2001
From: ispyisail <shane.ringrose@gmail.com>
Date: Fri, 16 Oct 2026 12:17:21 +1300
Subject: [PATCH] Ask before saving over a project file someone else changed

Saving replaced the project file whatever had happened to it since it was
opened. If another user, another program or a second QET had saved the same
file in between (a shared drive, a copy synced from another PC), their work
was lost without a word.

QETProject now remembers the project file's size and modification time when
it reads it and after each save of its own. Before writing, write() compares
them with the file on disk and, if they differ, writes nothing and returns
"someone else changed the file on disk at <time> since it was opened".

- Interactive save (Ctrl+S, and the save on closing a project) asks:
  "Someone else changed <file> on disk at <time> since you opened it" with
  Save as a copy (opens Save As), Overwrite, or Cancel.
- Scripts (--run), the command line, MCP and the autosave timer have no one
  to ask, so they keep the refusal (autosave logs it). Setting
  QET_OVERWRITE_CHANGED=1 makes a script overwrite on purpose.
- A file that does not exist yet, and a Save As to another name, are not a
  conflict; after Save As the remembered state is the new file's.

No change to what is written, so .qet and .qetz stay as they were.

Evidence: new tst_changedondisk (unchanged file saves twice; a file written
behind the open project is refused; the override overwrites; a Save As
target is no conflict) fails on the changed-file case without the source
change and passes with it. Full ctest 107/107. Physical check with
qet-gui-dialog.sh: file modified behind the open project, Ctrl+S shows the
three-button dialog.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MgPFANhWgD66V3v9KVKV58
---
 sources/projectview.cpp            |  52 +++++++++++++-
 sources/projectview.h              |   1 +
 sources/qetproject.cpp             |  79 ++++++++++++++++++++-
 sources/qetproject.h               |  11 ++-
 tests/qttest/CMakeLists.txt        |  12 ++++
 tests/qttest/tst_changedondisk.cpp | 107 +++++++++++++++++++++++++++++
 6 files changed, 257 insertions(+), 5 deletions(-)
 create mode 100644 tests/qttest/tst_changedondisk.cpp

diff --git a/sources/projectview.cpp b/sources/projectview.cpp
index 158cc2ae5..b6e85aef2 100644
--- a/sources/projectview.cpp
+++ b/sources/projectview.cpp
@@ -268,7 +268,9 @@ bool ProjectView::tryClosing()
 		QString filepath = askUserForFilePath();
 		if (filepath.isEmpty()) return(false); // users may cancel the closing
 	}
-	QETResult result = m_project -> write();
+	bool cancelled = false;
+	QETResult result = writeProject(&cancelled);
+	if (cancelled) return(false);
 	updateWindowTitle();
 	if (!result.isOk()) emit(errorEncountered(result.errorMessage()));
 	return(result.isOk());
@@ -753,6 +755,50 @@ QETResult ProjectView::saveCopyForOlderVersions()
 	return(m_project->writeCopyForOlderVersions(path));
 }
 
+/**
+	@brief ProjectView::writeProject
+	Write the project file. If the file was changed on disk since this QET
+	read or wrote it, ask what to do first: a plain save would replace
+	the other change.
+	@param cancelled set to true if the user gave up, or chose to save a
+	copy and did not complete it: nothing was saved to the project's file
+	@return the result of the write
+*/
+QETResult ProjectView::writeProject(bool *cancelled)
+{
+	*cancelled = false;
+	QDateTime when;
+	if (!m_project -> changedOnDisk(&when)) {
+		return(m_project -> write());
+	}
+
+	const QString name = QFileInfo(m_project -> writeTarget()).fileName();
+	QMessageBox box(QMessageBox::Warning,
+					tr("File changed on disk", "message box title"),
+					tr("Someone else changed %1 on disk at %2 since you opened it.\n\n"
+					   "Saving over it would lose their changes.")
+						.arg(name, QLocale::system().toString(when, QLocale::ShortFormat)),
+					QMessageBox::NoButton, this);
+	QPushButton *copy_button = box.addButton(tr("Save as a copy"), QMessageBox::AcceptRole);
+	QPushButton *overwrite_button = box.addButton(tr("Overwrite"), QMessageBox::DestructiveRole);
+	box.addButton(QMessageBox::Cancel);
+	box.setDefaultButton(copy_button);
+	box.setEscapeButton(QMessageBox::Cancel);
+	box.exec();
+
+	if (box.clickedButton() == overwrite_button) {
+		return(m_project -> write(true));
+	}
+	if (box.clickedButton() == copy_button) {
+		QETResult result = saveAs();
+			//The Save As dialog was cancelled: the project is still modified
+		if (m_project -> projectWasModified()) *cancelled = true;
+		return(result);
+	}
+	*cancelled = true;
+	return(QETResult());
+}
+
 /**
 	Save project content, then write the project file. May
 	call saveAs if no filepath was provided before.
@@ -795,7 +841,9 @@ QETResult ProjectView::doSave()
 	}
 
 	// write to file
-	QETResult result = m_project -> write();
+	bool cancelled = false;
+	QETResult result = writeProject(&cancelled);
+	if (cancelled) return(QETResult());
 	updateWindowTitle();
 	// This marks the stack's current index as the new "saved" point (so isClean()/cleanChanged() correctly
 	// resume tracking unsaved changes from here) without discarding the undo history. Edits made before this save 
diff --git a/sources/projectview.h b/sources/projectview.h
index eec92dcc7..ec0c0feeb 100644
--- a/sources/projectview.h
+++ b/sources/projectview.h
@@ -131,6 +131,7 @@ class ProjectView : public QWidget
 		QETResult save();
 		QETResult saveAs();
 		QETResult doSave();
+		QETResult writeProject(bool *cancelled);
 		QETResult saveCopyForOlderVersions();
 		int cleanProject();
 		void updateWindowTitle();
diff --git a/sources/qetproject.cpp b/sources/qetproject.cpp
index 45ef03635..56971cf4b 100644
--- a/sources/qetproject.cpp
+++ b/sources/qetproject.cpp
@@ -386,7 +386,13 @@ void QETProject::init()
 		connect(&m_autosave_timer, &QTimer::timeout, this, [this]()
 		{
 			if(!this->m_file_path.isEmpty())
-				this->write();
+			{
+					//No one is there to ask: a file changed behind this
+					//QET is left alone
+				const QETResult result = this->write();
+				if (!result.isOk())
+					qWarning() << "autosave:" << result.errorMessage();
+			}
 		});
 		m_autosave_timer.start();
 	}
@@ -471,6 +477,7 @@ QETProject::ProjectState QETProject::openFile(QFile *file)
 		//Extract the content of the xml. The raw bytes are kept : a project
 		//file without a persisted uuid derives its uuid from them.
 	const QByteArray content = file->readAll();
+	rememberDiskState();
 		//Each folio's text is kept while it is not built (readDiagramsXml()):
 		//from a .qet only, a .qetz is a zip of parts
 	if (!content.startsWith("PK\x03\x04"))
@@ -2723,7 +2730,64 @@ QETResult QETProject::writeCopyForOlderVersions(const QString &path)
 	return(QETResult());
 }
 
-QETResult QETProject::write()
+/**
+	@brief QETProject::rememberDiskState
+	Remember the size and modification time of the project file, as this QET
+	has just read or written it. changedOnDisk() compares against them.
+*/
+void QETProject::rememberDiskState()
+{
+	const QFileInfo info(m_file_path);
+	m_disk_path = m_file_path;
+	m_disk_size = info.exists() ? info.size() : -1;
+	m_disk_mtime = info.exists() ? info.lastModified() : QDateTime();
+}
+
+/**
+	@brief QETProject::writeTarget
+	@return the file write() writes to: the .qetz beside a project read
+	from a .qet, else the project's own file
+*/
+QString QETProject::writeTarget() const
+{
+	return m_opened_from_qet ? besideContainerPath() : m_file_path;
+}
+
+/**
+	@brief QETProject::changedOnDisk
+	@param when set to the modification time of the file now on disk
+	@return true if the file write() would replace is not the one this QET
+	last read or wrote: another user, another program or another QET saved
+	it since. A file that does not exist yet, or one this QET never read
+	or wrote (Save As to another name), is not a change.
+*/
+bool QETProject::changedOnDisk(QDateTime *when) const
+{
+	const QString target = writeTarget();
+	if (target.isEmpty() || target != m_disk_path || m_disk_size < 0)
+		return false;
+	const QFileInfo info(target);
+	if (!info.exists())
+		return false;
+	if (info.size() == m_disk_size && info.lastModified() == m_disk_mtime)
+		return false;
+	if (when)
+		*when = info.lastModified();
+	return true;
+}
+
+/**
+	@brief QETProject::write
+	Save the project in a file.
+	If the file was changed on disk since this QET read or wrote it, nothing
+	is written and the result says so: the interactive save asks the user
+	first (ProjectView) and calls again with @p overwrite_changed; scripts,
+	the command line, autosave and MCP have no one to ask and keep the
+	refusal. Setting QET_OVERWRITE_CHANGED=1 in the environment overwrites
+	without asking, for a script that means to.
+	@param overwrite_changed write even if the file changed on disk
+*/
+QETResult QETProject::write(bool overwrite_changed)
 {
 		// this operation requires a filepath
 	if (m_file_path.isEmpty())
@@ -2759,6 +2823,15 @@ QETResult QETProject::write()
 			return(QString("the file %1 was opened read-only and thus will not be written").arg(m_file_path));
 	}
 
+	if (!overwrite_changed && qEnvironmentVariableIntValue("QET_OVERWRITE_CHANGED") == 0) {
+		QDateTime when;
+		if (changedOnDisk(&when))
+			return(failed(tr("someone else changed the file on disk at %1 since it was opened, "
+							 "and saving would overwrite that. Save to another name, or "
+							 "set QET_OVERWRITE_CHANGED=1 to overwrite it.")
+						  .arg(QLocale::system().toString(when, QLocale::ShortFormat))));
+	}
+
 	QString error_message;
 	if (isContainerPath(m_file_path))
 	{
@@ -2778,6 +2851,8 @@ QETResult QETProject::write()
 			return(failed(error_message));
 	}
 
+	rememberDiskState();
+
 		// The project has just been written to a writable file (e.g. saved to
 		// a new location with "Save As"), so it is no longer read-only.
 	if (isReadOnly())
diff --git a/sources/qetproject.h b/sources/qetproject.h
index e2c7f0f9d..f2c021b86 100644
--- a/sources/qetproject.h
+++ b/sources/qetproject.h
@@ -39,6 +39,7 @@
 #	include <KAutoSaveFile>
 #endif
 
+#include <QDateTime>
 #include <QHash>
 #include <QSet>
 #include <QUuid>
@@ -332,7 +333,10 @@ class QETProject : public QObject
 						   QStringList *kept_parts = nullptr);
 		static QString spliceKeptFolios(QString text, const QHash<int, QByteArray> &kept_folios);
 		bool close();
-		QETResult write();
+		QETResult write(bool overwrite_changed = false);
+		QString writeTarget() const;
+		void rememberDiskState();
+		bool changedOnDisk(QDateTime *when = nullptr) const;
 		bool isReadOnly() const;
 			/// Opened from a .qetz of a later format (opened read-only)
 		bool isFromLaterVersion() const {return m_from_later_version;}
@@ -554,6 +558,11 @@ class QETProject : public QObject
 		bool m_kept_folios_trusted = false;
 			/// Read from a .qet whose path nobody chose since: saved beside it
 		bool m_opened_from_qet = false;
+			/// The project file as this QET last read or wrote it, to see
+			/// whether something else changed it since (changedOnDisk())
+		QString m_disk_path;
+		qint64 m_disk_size = -1;
+		QDateTime m_disk_mtime;
 			/// Saving a .qetz may copy the part of a folio not built
 			/// (toXml(), stage D4)
 		bool m_kept_parts_trusted = false;
diff --git a/tests/qttest/CMakeLists.txt b/tests/qttest/CMakeLists.txt
index 32f68efc8..535842a96 100644
--- a/tests/qttest/CMakeLists.txt
+++ b/tests/qttest/CMakeLists.txt
@@ -931,6 +931,18 @@ if(QET_HAS_SCRIPTING)
     "QET_TEST_BINARY_PATH=\"$<TARGET_FILE:qelectrotech>\""
     "QET_EXAMPLES_DIR=\"${QET_DIR}/examples\"")
 
+  # Saving refuses a project file another user or program changed since it was
+  # opened (QETProject::changedOnDisk()); QET_OVERWRITE_CHANGED=1 overrides.
+  add_executable(
+    tst_changedondisk
+    tst_changedondisk.cpp)
+  add_test(NAME tst_changedondisk COMMAND tst_changedondisk)
+  add_dependencies(tst_changedondisk qelectrotech)
+  target_link_libraries(tst_changedondisk PRIVATE Qt::Test)
+  target_compile_definitions(tst_changedondisk PRIVATE
+    "QET_TEST_BINARY_PATH=\"$<TARGET_FILE:qelectrotech>\""
+    "QET_EXAMPLES_DIR=\"${QET_DIR}/examples\"")
+
   # qet.elementTerminals() lists each terminal's uuid and qet.terminalIndex()
   # turns element uuid + terminal uuid back into the index the conductor
   # calls take, on examples/perceuse.qet (two terminals at one point).
diff --git a/tests/qttest/tst_changedondisk.cpp b/tests/qttest/tst_changedondisk.cpp
new file mode 100644
index 000000000..7b18aac68
--- /dev/null
+++ b/tests/qttest/tst_changedondisk.cpp
@@ -0,0 +1,107 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+#include <QtTest>
+
+#include <QFile>
+#include <QProcess>
+#include <QProcessEnvironment>
+#include <QTemporaryDir>
+
+// Saving a project replaced the file whatever had happened to it since it was
+// opened: another user's save, or another program's, was lost without a word.
+// QETProject now remembers the file as it read or wrote it and write() refuses
+// when the file on disk is no longer that one. Driven through the real
+// binary's --run: qet.save(<the project's own path>) writes the file behind
+// the open project without updating what it remembers, which is exactly "someone
+// else saved"; qet.save('') is the project's own save.
+class tst_changedondisk : public QObject
+{
+	Q_OBJECT
+
+	QTemporaryDir m_dir;
+	QString m_project; // a .qetz made from examples/741.qet
+
+	QString run(const QString &script, const QString &project, bool overwrite = false)
+	{
+		const QString path = m_dir.filePath(QStringLiteral("probe.js"));
+		const QString home = m_dir.filePath(QStringLiteral("home"));
+		QDir().mkpath(home);
+		QFile f(path);
+		if (!f.open(QIODevice::WriteOnly)) return QString();
+		f.write(script.toUtf8());
+		f.close();
+
+		QProcessEnvironment env = QProcessEnvironment::systemEnvironment();
+		env.insert(QStringLiteral("QT_QPA_PLATFORM"), QStringLiteral("offscreen"));
+		env.insert(QStringLiteral("QET_ENABLE_SCRIPTING"), QStringLiteral("1"));
+		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.remove(QStringLiteral("QET_OVERWRITE_CHANGED"));
+		if (overwrite)
+			env.insert(QStringLiteral("QET_OVERWRITE_CHANGED"), QStringLiteral("1"));
+		QProcess proc;
+		proc.setProcessEnvironment(env);
+		proc.start(QStringLiteral(QET_TEST_BINARY_PATH),
+				   {QStringLiteral("--run"), path, project});
+		if (!proc.waitForFinished(120000)) return QString();
+		return QString::fromUtf8(proc.readAllStandardOutput() + proc.readAllStandardError());
+	}
+
+private slots:
+	void initTestCase()
+	{
+		QVERIFY(m_dir.isValid());
+		QVERIFY(QFile::exists(QStringLiteral(QET_TEST_BINARY_PATH)));
+		const QString qet = m_dir.filePath(QStringLiteral("p.qet"));
+		QVERIFY(QFile::copy(QStringLiteral(QET_EXAMPLES_DIR "/741.qet"), qet));
+		// a .qet is saved as a .qetz beside it; that .qetz is the project below
+		const QString out = run(QStringLiteral("qet.log('R ' + qet.save(''));\n"), qet);
+		QVERIFY2(out.contains(QStringLiteral("R true")), qPrintable(out));
+		m_project = m_dir.filePath(QStringLiteral("p.qetz"));
+		QVERIFY(QFile::exists(m_project));
+	}
+
+	void unchangedFileSaves()
+	{
+		const QString out = run(QStringLiteral(
+			"qet.log('R1 ' + qet.save(''));\nqet.log('R2 ' + qet.save(''));\n"), m_project);
+		QVERIFY2(out.contains(QStringLiteral("R1 true")), qPrintable(out));
+		// the project's own save updates what it remembers: a second one is no change
+		QVERIFY2(out.contains(QStringLiteral("R2 true")), qPrintable(out));
+	}
+
+	void changedFileIsNotOverwritten()
+	{
+		const QString script = QStringLiteral(
+			"qet.save(%1);\nqet.log('R ' + qet.save(''));\n")
+			.arg(QStringLiteral("'") + m_project + QStringLiteral("'"));
+		const QString out = run(script, m_project);
+		QVERIFY2(out.contains(QStringLiteral("R false")), qPrintable(out));
+		QVERIFY2(out.contains(QStringLiteral("changed the file on disk")), qPrintable(out));
+	}
+
+	void overrideOverwrites()
+	{
+		const QString script = QStringLiteral(
+			"qet.save(%1);\nqet.log('R ' + qet.save(''));\n")
+			.arg(QStringLiteral("'") + m_project + QStringLiteral("'"));
+		const QString out = run(script, m_project, true);
+		QVERIFY2(out.contains(QStringLiteral("R true")), qPrintable(out));
+	}
+
+	void saveAsTargetIsNotAConflict()
+	{
+		const QString other = m_dir.filePath(QStringLiteral("other.qetz"));
+		const QString script = QStringLiteral(
+			"qet.log('R1 ' + qet.save(%1));\nqet.log('R2 ' + qet.save(%1));\n")
+			.arg(QStringLiteral("'") + other + QStringLiteral("'"));
+		const QString out = run(script, m_project);
+		QVERIFY2(out.contains(QStringLiteral("R1 true")), qPrintable(out));
+		QVERIFY2(out.contains(QStringLiteral("R2 true")), qPrintable(out));
+	}
+};
+
+QTEST_APPLESS_MAIN(tst_changedondisk)
+
+#include "tst_changedondisk.moc"