Add recovering what can be read of a damaged .qetz (--recover)

A .qetz that does not open as it is -- a picture's file missing (as
the title-change fault wrote them), a folio file missing, a row deleted
from project.sqlite by hand (issue #1458), a damaged database -- was
refused whole, and nothing in QElectroTech could get anything back.

QetContainer::recover() reads what it can and says what it left out:
an entry that cannot be unpacked, a missing folio file or picture, a
symbol or wire that does not match the database, and, when the
database cannot be read at all, the information it held (the wires go
too, as it holds their ends). join(), restore() and QetZip::fromBytes()
take an optional list for this; given none they refuse as before.
`qelectrotech --recover damaged.qetz out.qet` writes what was read to a
.qet and lists what was left out.

Measured on industrial (50 folios, 618 symbols, 671 wires): a wire row
deleted -> 670 wires, the rest whole; a folio file missing -> 49
folios; a database page overwritten -> every folio and symbol drawn, no
wires and no symbol information. A zip cut short (no central directory)
still cannot be read.

Tests: recoverLeavesOutOnlyTheDamage (nothing, folio file, wire row,
database page), recoverMissingPicture, recoverNotAZipRefused; they fail
with the database side kept strict. The strict cases pass unchanged.
ctest 106/106.

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

sources/container/qetcontainer.cpp

@@ -184,6 +184,25 @@ bool QetContainer::readDocument(const QByteArray &content, QDomDocument *documen
 			&& join(entries, document, error, nullptr, pictures, format);
 }
 
+/**
+	@brief QetContainer::recover
+	What can be read of the .qetz @p content, a damaged one, into @p project:
+	a folio file, a picture or an entry that cannot be read is left out,
+	symbols and wires that do not match the database lose what it held, and
+	a database that cannot be read loses it all (wires, whose ends it holds,
+	go too). Each thing left out is said in @p lost.
+	@return false, with @p error, when nothing can be read: not a zip, no
+	project.xml, or a later format
+*/
+bool QetContainer::recover(const QByteArray &content, QDomDocument *project, QStringList *lost, QString *error)
+{
+	QStringList none;
+	if (!lost) lost = &none;
+	QList<QetZip::Entry> entries;
+	return QetZip::fromBytes(content, &entries, error, lost)
+			&& join(entries, project, error, nullptr, nullptr, nullptr, lost);
+}
+
 QString QetContainer::pictureFile(const QDomElement &image)
 {
 	return image.attribute(ImageFileAttribute);
@@ -421,23 +440,35 @@ QList<QetZip::Entry> QetContainer::split(const QDomDocument &project, const QStr
 	for a later one this may read (its min-reader allows it).
 */
 bool QetContainer::join(const QList<QetZip::Entry> &entries, QDomDocument *project, QString *error,
-						QStringList *folio_files, Pictures *pictures, int *format)
+						QStringList *folio_files, Pictures *pictures, int *format, QStringList *lost)
 {
+		//Recovering a damaged project (recover()): what is missing or
+		//damaged is noted in lost and left out, instead of refusing it all
+	const auto noted = [error, lost](const QString &problem) {
+		if (lost) {
+			lost->append(problem);
+			return true;
+		}
+		setError(error, problem);
+		return false;
+	};
 	QHash<QString, QByteArray> files;
 	for (const QetZip::Entry &entry : entries)
 		files.insert(entry.name, entry.data);
 
 	const QByteArray mimetype = files.value(QStringLiteral("mimetype"));
-	if (mimetype != QByteArray(MimeType) && mimetype != QByteArray(OldMimeType)) {
-		setError(error, QStringLiteral("not a QElectroTech project (.qetz)"));
+	if (mimetype != QByteArray(MimeType) && mimetype != QByteArray(OldMimeType)
+			&& !noted(QStringLiteral("not a QElectroTech project (.qetz)")))
 		return false;
-	}
 	QDomDocument manifest;
-	if (!parse(files.value(QStringLiteral("manifest.xml")), &manifest, error))
+	QString manifest_error;
+	const bool has_manifest = parse(files.value(QStringLiteral("manifest.xml")), &manifest, &manifest_error);
+	if (!has_manifest && !noted(manifest_error))
 		return false;
 	bool ok = false;
 	const int min_reader = manifest.documentElement().attribute(QStringLiteral("min-reader")).toInt(&ok);
-	if (!ok || min_reader > Format) {
+		//A later format is not damage: refused all the same
+	if (has_manifest && (!ok || min_reader > Format)) {
 		setError(error, QStringLiteral("made by a later QElectroTech (format %1, this one reads up to %2)")
 				 .arg(manifest.documentElement().attribute(QStringLiteral("format")))
 				 .arg(Format));
@@ -460,29 +491,33 @@ bool QetContainer::join(const QList<QetZip::Entry> &entries, QDomDocument *proje
 				&& file.startsWith(QLatin1String("folios/")))
 			folio_files->append(file);
 		if (!files.contains(file)) {
-			setError(error, QStringLiteral("part \"%1\" is missing").arg(file));
-			return false;
+			if (!noted(QStringLiteral("part \"%1\" is missing").arg(file))) return false;
+			part.parentNode().removeChild(part);
+			continue;
 		}
 		QDomDocument document;
 		QString part_error;
 		if (!parse(files.value(file), &document, &part_error)) {
-			setError(error, QStringLiteral("%1: %2").arg(file, part_error));
-			return false;
+			if (!noted(QStringLiteral("%1: %2").arg(file, part_error))) return false;
+			part.parentNode().removeChild(part);
+			continue;
 		}
 		part.parentNode().replaceChild(project->importNode(document.documentElement(), true), part);
 	}
 
 		//Pictures back to base64, as the image's first child, or into
 		//pictures
-	const QDomNodeList images = project->elementsByTagName(QStringLiteral("image"));
-	for (int i = 0 ; i < images.size() ; ++i)
+	const QDomNodeList image_list = project->elementsByTagName(QStringLiteral("image"));
+	QList<QDomElement> images;
+	for (int i = 0 ; i < image_list.size() ; ++i) images << image_list.at(i).toElement();
+	for (QDomElement image : images)
 	{
-		QDomElement image = images.at(i).toElement();
 		if (!image.hasAttribute(ImageFileAttribute)) continue;
 		const QString file = image.attribute(ImageFileAttribute);
 		if (!files.contains(file)) {
-			setError(error, QStringLiteral("picture \"%1\" is missing").arg(file));
-			return false;
+			if (!noted(QStringLiteral("picture \"%1\" is missing").arg(file))) return false;
+			image.parentNode().removeChild(image);
+			continue;
 		}
 		if (pictures) {
 			pictures->insert(file, files.value(file));
@@ -496,7 +531,12 @@ bool QetContainer::join(const QList<QetZip::Entry> &entries, QDomDocument *proje
 		//The engineering data back from project.sqlite (format 2 on)
 	if (files.contains(QStringLiteral("project.sqlite"))
 		&& !QetContainerDb::restore(project->documentElement(),
-									files.value(QStringLiteral("project.sqlite")), error))
+									files.value(QStringLiteral("project.sqlite")), error, lost))
 		return false;
+	if (lost) {
+		if (!files.contains(QStringLiteral("project.sqlite")))
+			lost->append(QStringLiteral("project.sqlite is missing"));
+		QetContainerDb::dropLeftovers(project->documentElement(), lost);
+	}
 	return true;
 }