QXmlStreamWriter ignores default namespace for attributes?

David Lichti

Consider the following code:

const QString nsA( "namespaceA" );
const QString nsB( "namespaceB" );

QString out;
QXmlStreamWriter writer( &out );
writer.setAutoFormatting( true );

writer.writeDefaultNamespace( nsA );
writer.writeNamespace( nsB, "nsb" );

writer.writeStartDocument();

writer.writeStartElement( nsA, "root" );

writer.writeEmptyElement( nsA, "element" );
writer.writeAttribute( nsA, "attribute", "value" );
writer.writeAttribute( nsB, "attribute", "value" );

writer.writeEndElement();

writer.writeEndDocument();

producing the following XML:

<?xml version="1.0"?>
<root xmlns="namespaceA" xmlns:nsb="namespaceB">
    <element xmlns:n1="namespaceA" n1:attribute="value" nsb:attribute="value"/>
</root>

Obviously, the writer recognizes the namespace of <element> to be the previously declared default namespace. But this fails for attribute1, which has the same namespace. Instead, the writer declares a new namespace prefix. In contrast, for attribute2, the writer remembers that its namespace was declared earlier and uses the specified prefix nsb.

It seems that QXmlStreamWriter::writeAttribute is only considering prefixed namespaces, but not the default namespace. Is this a bug in Qt (5.15), or am I doing it wrong?