Open and save projects as .qetz (zipped, opt-in)

Third stage of the zipped project file (#1440). A project is saved as a
.qetz when its file name ends in .qetz -- Save As offers it as a second
file type, and --resave, --set-titleblock, the script API's save() and
the live-mode snapshot follow the name too. Saving a .qet project still
writes a .qet; nothing changes unless the user picks .qetz.

Opening recognises a .qetz by its content (a zip), not its name, and
reads it as bytes: text mode would alter it on Windows. The project
document is joined back and read by the same code as a .qet. Crash
backups stay plain XML. Drag and drop, the open dialog and the
numbering import accept .qetz; the database export names its file from
the project's name without assuming ".qet".

Parts are now written without added indentation (one line each): the
symbol definitions are kept as read, whitespace included, and parts
that gained indentation made the next save differ (five forum projects).

Tests: tst_resaveunchanged::containerSavesTheSameProject (four examples
saved as .qetz, then as .qet, equal the straight .qet; pictures checked
to fail without the fix), tst_qetcontainer::noWhitespaceAdded. Outside
ctest: 341 of 341 projects QET can open (examples, bugtracker, GitHub,
forum) give the same .qet through a .qetz; 181.6 MB of .qet became
36.9 MB of .qetz.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019Wga9B92BNurDEtxxtCDxf

sources/container/qetcontainer.cpp

@@ -34,7 +34,10 @@ void setError(QString *error, const QString &text)
 	if (error) *error = text;
 }
 
-	//An element on its own, as a .qet is written (QET::writeXmlFile())
+	//An element on its own, written without adding indentation: the
+	//whitespace text already in the document (QETProject keeps the symbol
+	//definitions as they were read, spacing included) must come back as it
+	//was, or the next save writes it differently. Parts are one line.
 QByteArray serialize(const QDomNode &node)
 {
 	QDomDocument document;
@@ -42,7 +45,7 @@ QByteArray serialize(const QDomNode &node)
 							 QStringLiteral("xml"),
 							 QStringLiteral("version=\"1.0\" encoding=\"UTF-8\"")));
 	document.appendChild(document.importNode(node, true));
-	return document.toString(4).toUtf8();
+	return document.toString(-1).toUtf8();
 }
 
 	//A file name from a name chosen by the user: no folders, nothing a zip
@@ -136,6 +139,30 @@ bool QetContainer::parse(const QByteArray &xml, QDomDocument *document, QString
 #endif
 }
 
+/**
+	@brief QetContainer::isZip
+	A .qetz is recognised by what it holds, not its name: a crash backup
+	of a .qetz project is plain XML, and a renamed file is still a zip.
+*/
+bool QetContainer::isZip(const QByteArray &content)
+{
+	return content.startsWith("PK\x03\x04");
+}
+
+/**
+	@brief QetContainer::readDocument
+	The project document held in @p content: unzipped and joined for a
+	.qetz, parsed for a .qet.
+*/
+bool QetContainer::readDocument(const QByteArray &content, QDomDocument *document, QString *error)
+{
+	if (!isZip(content))
+		return parse(content, document, error);
+	QList<QetZip::Entry> entries;
+	return QetZip::fromBytes(content, &entries, error)
+			&& join(entries, document, error);
+}
+
 /**
 	@brief QetContainer::split
 	@param project : the project document, as QETProject::toXml() makes it

sources/container/qetcontainer.h

@@ -54,6 +54,10 @@ namespace QetContainer
 
 		/// Parse @p xml as a .qet is read (QETProject::openFile)
 	bool parse(const QByteArray &xml, QDomDocument *document, QString *error = nullptr);
+		/// true if @p content is a zip, so a .qetz rather than a .qet
+	bool isZip(const QByteArray &content);
+		/// The project document in @p content, a .qet or a .qetz
+	bool readDocument(const QByteArray &content, QDomDocument *document, QString *error = nullptr);
 }
 
 #endif // QETCONTAINER_H