Fix renamed and duplicated namespaces in QXmlStreamWriter

The XML stream writer previously added namespace declarations with the
same URL as existing ones, but new names, and renamed the XML elements
to use the new namespaces instead of the existing ones.

[ChangeLog] Fix renamed and duplicated namespaces in QXmlStreamWriter.

Pick-to: 6.5
Fixes: QTBUG-75456
Change-Id: I90706e067ac9991e9e6cd79ccb2373e4c6210b7b
Done-With: Philip Allgaier <philip.allgaier@bpcompass.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>
(cherry picked from commit 13f673939d9dadbcc398aefa4c1449a8a21d2308)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/corelib/serialization/qxmlstream.cpp

@@ -2879,6 +2879,11 @@ class QXmlStreamWriterPrivate : public QXmlStreamPrivateTagStack
     QXmlStreamWriter *q_ptr;
     Q_DECLARE_PUBLIC(QXmlStreamWriter)
 public:
+    enum class StartElementOption {
+        KeepEverything = 0, // write out every attribute, namespace, &c.
+        OmitNamespaceDeclarations = 1,
+    };
+
     QXmlStreamWriterPrivate(QXmlStreamWriter *q);
     ~QXmlStreamWriterPrivate() {
         if (deleteDevice)
@@ -2888,7 +2893,8 @@ public:
     void write(QAnyStringView s);
     void writeEscaped(QAnyStringView, bool escapeWhitespace = false);
     bool finishStartElement(bool contents = true);
-    void writeStartElement(QAnyStringView namespaceUri, QAnyStringView name);
+    void writeStartElement(QAnyStringView namespaceUri, QAnyStringView name,
+                           StartElementOption option = StartElementOption::KeepEverything);
     QIODevice *device;
     QString *stringDevice;
     uint deleteDevice :1;
@@ -2903,6 +2909,7 @@ public:
     NamespaceDeclaration emptyNamespace;
     qsizetype lastNamespaceDeclaration;
 
+    NamespaceDeclaration &addExtraNamespace(QAnyStringView namespaceUri, QAnyStringView prefix);
     NamespaceDeclaration &findNamespace(QAnyStringView namespaceUri, bool writeDeclaration = false, bool noDefault = false);
     void writeNamespaceDeclaration(const NamespaceDeclaration &namespaceDeclaration);
 
@@ -3043,6 +3050,32 @@ bool QXmlStreamWriterPrivate::finishStartElement(bool contents)
     return hadSomethingWritten;
 }
 
+QXmlStreamPrivateTagStack::NamespaceDeclaration &
+QXmlStreamWriterPrivate::addExtraNamespace(QAnyStringView namespaceUri, QAnyStringView prefix)
+{
+    const bool prefixIsXml = prefix == "xml"_L1;
+    const bool namespaceUriIsXml = namespaceUri == "http://www.w3.org/XML/1998/namespace"_L1;
+    if (prefixIsXml && !namespaceUriIsXml) {
+        qWarning("Reserved prefix 'xml' must not be bound to a different namespace name "
+                 "than 'http://www.w3.org/XML/1998/namespace'");
+    } else if (!prefixIsXml && namespaceUriIsXml) {
+        const QString prefixString = prefix.toString();
+        qWarning("The prefix '%ls' must not be bound to namespace name "
+                 "'http://www.w3.org/XML/1998/namespace' which 'xml' is already bound to",
+                 qUtf16Printable(prefixString));
+    }
+    if (namespaceUri == "http://www.w3.org/2000/xmlns/"_L1) {
+        const QString prefixString = prefix.toString();
+        qWarning("The prefix '%ls' must not be bound to namespace name "
+                 "'http://www.w3.org/2000/xmlns/'",
+                 qUtf16Printable(prefixString));
+    }
+    auto &namespaceDeclaration = namespaceDeclarations.push();
+    namespaceDeclaration.prefix = addToStringStorage(prefix);
+    namespaceDeclaration.namespaceUri = addToStringStorage(namespaceUri);
+    return namespaceDeclaration;
+}
+
 QXmlStreamPrivateTagStack::NamespaceDeclaration &QXmlStreamWriterPrivate::findNamespace(QAnyStringView namespaceUri, bool writeDeclaration, bool noDefault)
 {
     for (NamespaceDeclaration &namespaceDeclaration : reversed(namespaceDeclarations)) {
@@ -3621,11 +3654,7 @@ void QXmlStreamWriter::writeNamespace(QAnyStringView namespaceUri, QAnyStringVie
     if (prefix.isEmpty()) {
         d->findNamespace(namespaceUri, d->inStartElement);
     } else {
-        Q_ASSERT(!((prefix == "xml"_L1) ^ (namespaceUri == "http://www.w3.org/XML/1998/namespace"_L1)));
+        auto &namespaceDeclaration = d->addExtraNamespace(namespaceUri, prefix);
-        Q_ASSERT(namespaceUri != "http://www.w3.org/2000/xmlns/"_L1);
-        QXmlStreamWriterPrivate::NamespaceDeclaration &namespaceDeclaration = d->namespaceDeclarations.push();
-        namespaceDeclaration.prefix = d->addToStringStorage(prefix);
-        namespaceDeclaration.namespaceUri = d->addToStringStorage(namespaceUri);
         if (d->inStartElement)
             d->writeNamespaceDeclaration(namespaceDeclaration);
     }
@@ -3774,7 +3803,8 @@ void QXmlStreamWriter::writeStartElement(QAnyStringView namespaceUri, QAnyString
     d->writeStartElement(namespaceUri, name);
 }
 
-void QXmlStreamWriterPrivate::writeStartElement(QAnyStringView namespaceUri, QAnyStringView name)
+void QXmlStreamWriterPrivate::writeStartElement(QAnyStringView namespaceUri, QAnyStringView name,
+                                                StartElementOption option)
 {
     if (!finishStartElement(false) && autoFormatting)
         indent(tagStack.size());
@@ -3790,8 +3820,10 @@ void QXmlStreamWriterPrivate::writeStartElement(QAnyStringView namespaceUri, QAn
     write(tag.name);
     inStartElement = lastWasStartElement = true;
 
-    for (qsizetype i = lastNamespaceDeclaration; i < namespaceDeclarations.size(); ++i)
+    if (option != StartElementOption::OmitNamespaceDeclarations) {
-        writeNamespaceDeclaration(namespaceDeclarations[i]);
+        for (qsizetype i = lastNamespaceDeclaration; i < namespaceDeclarations.size(); ++i)
+            writeNamespaceDeclaration(namespaceDeclarations[i]);
+    }
     tag.namespaceDeclarationsSize = lastNamespaceDeclaration;
 }
 
@@ -3805,6 +3837,7 @@ void QXmlStreamWriterPrivate::writeStartElement(QAnyStringView namespaceUri, QAn
  */
 void QXmlStreamWriter::writeCurrentToken(const QXmlStreamReader &reader)
 {
+    Q_D(QXmlStreamWriter);
     switch (reader.tokenType()) {
     case QXmlStreamReader::NoToken:
         break;
@@ -3815,12 +3848,19 @@ void QXmlStreamWriter::writeCurrentToken(const QXmlStreamReader &reader)
         writeEndDocument();
         break;
     case QXmlStreamReader::StartElement: {
-        writeStartElement(reader.namespaceUri(), reader.name());
+        // Namespaces must be added before writeStartElement is called so new prefixes are found
-        const QXmlStreamNamespaceDeclarations decls = reader.namespaceDeclarations();
+        QList<QXmlStreamPrivateTagStack::NamespaceDeclaration> extraNamespaces;
-        for (const auto &namespaceDeclaration : decls) {
+        for (const auto &namespaceDeclaration : reader.namespaceDeclarations()) {
-            writeNamespace(namespaceDeclaration.namespaceUri(),
+            auto &extraNamespace = d->addExtraNamespace(namespaceDeclaration.namespaceUri(),
-                           namespaceDeclaration.prefix());
+                                                        namespaceDeclaration.prefix());
+            extraNamespaces.append(extraNamespace);
         }
+        d->writeStartElement(
+                reader.namespaceUri(), reader.name(),
+                QXmlStreamWriterPrivate::StartElementOption::OmitNamespaceDeclarations);
+        // Namespace declarations are written afterwards
+        for (const auto &extraNamespace : std::as_const(extraNamespaces))
+            d->writeNamespaceDeclaration(extraNamespace);
         writeAttributes(reader.attributes());
              } break;
     case QXmlStreamReader::EndElement:

tests/auto/corelib/serialization/qxmlstream/tst_qxmlstream.cpp

@@ -1778,6 +1778,22 @@ void tst_QXmlStream::roundTrip_data() const
                 "<child xmlns:unknown=\"http://mydomain\">Text</child>"
             "</father>"
         "</root>\n";
+
+    // When a namespace is introduced by an attribute of an element,
+    // that element can exercise the namespace in its tag.
+    // This used (QTBUG-75456) to lead to the namespace definition
+    // being wrongly duplicated, with a new name.
+    QTest::newRow("QTBUG-75456") <<
+        "<?xml version=\"1.0\"?>"
+        "<abc:root xmlns:xsd=\"http://www.w3.org/2001/XMLSchema\" xmlns:abc=\"ns1\">"
+            "<abc:parent>"
+                "<abc:child xmlns:unknown=\"http://mydomain\">Text</abc:child>"
+            "</abc:parent>"
+            "<def:parent xmlns:def=\"ns2\" id=\"test\">"
+                "<def:child id=\"Timmy\">More text</def:child>"
+                "<def:child id=\"Jimmy\">Even more text</def:child>"
+            "</def:parent>"
+        "</abc:root>\n";
 }
 
 void tst_QXmlStream::entityExpansionLimit() const