Use QSaveFile (if available) to write designs to disk.

Always check the status of the QTextStream to catch problems like disk
full.
In addition QSaveFile can ensure the old file is not destroyed as it's
using a temporary file which is committed at the end by just renaming it
to the output file name.

src/MainWindow.h

@@ -15,6 +15,7 @@
 #include <QMutex>
 #include <QSet>
 #include <QTime>
+#include <QIODevice>
 
 enum export_type_e {
 	EXPORT_TYPE_UNKNOWN,
@@ -113,6 +114,7 @@ private:
 	void compile(bool reload, bool forcedone = false);
 	void compileCSG(bool procevents);
 	bool maybeSave();
+        void saveError(const QIODevice &file, const std::string &msg);
 	bool checkEditorModified();
 	QString dumpCSGTree(AbstractNode *root);
 	static void consoleOutput(const std::string &msg, void *userdata);

src/mainwin.cc

@@ -93,6 +93,16 @@
 #include <QClipboard>
 #include <QDesktopWidget>
 
+#if (QT_VERSION < QT_VERSION_CHECK(5, 1, 0))
+// Set dummy for Qt versions that do not have QSaveFile
+#define QT_FILE_SAVE_CLASS QFile
+#define QT_FILE_SAVE_COMMIT true
+#else
+#include <QSaveFile>
+#define QT_FILE_SAVE_CLASS QSaveFile
+#define QT_FILE_SAVE_COMMIT if (saveOk) { saveOk = file.commit(); } else { file.cancelWriting(); }
+#endif
+
 #include <fstream>
 
 #include <algorithm>
@@ -1322,6 +1332,16 @@ void MainWindow::saveBackup()
 	return writeBackup(this->tempFile);
 }
 
+void MainWindow::saveError(const QIODevice &file, const std::string &msg) {
+	const std::string messageFormat = msg + " %s (%s)";
+	const char *fileName = this->fileName.toLocal8Bit().constData();
+	PRINTB(messageFormat.c_str(), fileName % file.errorString().toLocal8Bit().constData());
+
+	const std::string dialogFormatStr = msg + "\n\"%1\"\n(%2)";
+	const QString dialogFormat(dialogFormatStr.c_str());
+	QMessageBox::warning(this, windowTitle(), dialogFormat.arg(this->fileName).arg(file.errorString()));
+}
+
 /*!
 	Save current document.
 	Should _always_ write to disk, since this is called by SaveAs - i.e. don't try to be
@@ -1331,26 +1351,37 @@ void MainWindow::actionSave()
 {
 	if (this->fileName.isEmpty()) {
 		actionSaveAs();
+		return;
+	}
+
+	setCurrentOutput();
+
+	// If available (>= Qt 5.1), use QSaveFile to ensure the file is not
+	// destroyed if the device is full. Unfortunately this is not working
+	// as advertised (at least in Qt 5.3) as it does not detect the device
+	// full properly and happily commits a 0 byte file.
+	// Checking the QTextStream status flag after flush() seems to catch
+	// this condition.
+	QT_FILE_SAVE_CLASS file(this->fileName);
+	if (!file.open(QIODevice::WriteOnly | QIODevice::Truncate | QIODevice::Text)) {
+		saveError(file, _("Failed to open file for writing"));
 	}
 	else {
-		setCurrentOutput();
-		QFile file(this->fileName);
-		if (!file.open(QIODevice::WriteOnly | QIODevice::Truncate | QIODevice::Text)) {
-			PRINTB("Failed to open file for writing: %s (%s)", 
-			this->fileName.toLocal8Bit().constData() % file.errorString().toLocal8Bit().constData());
-			QMessageBox::warning(this, windowTitle(), tr("Failed to open file for writing:\n %1 (%2)")
-					.arg(this->fileName).arg(file.errorString()));
-		}
-		else {
-			QTextStream writer(&file);
-			writer.setCodec("UTF-8");
-			writer << this->editor->toPlainText();
-			PRINTB("Saved design '%s'.", this->fileName.toLocal8Bit().constData());
+		QTextStream writer(&file);
+		writer.setCodec("UTF-8");
+		writer << this->editor->toPlainText();
+		writer.flush();
+		bool saveOk = writer.status() == QTextStream::Ok;
+		QT_FILE_SAVE_COMMIT;
+		if (saveOk) {
+			PRINTB(_("Saved design '%s'."), this->fileName.toLocal8Bit().constData());
 			this->editor->setContentModified(false);
+		} else {
+			saveError(file, _("Error saving design"));
 		}
-		clearCurrentOutput();
-		updateRecentFiles();
 	}
+	clearCurrentOutput();
+	updateRecentFiles();
 }
 
 void MainWindow::actionSaveAs()