crash in Turtle-related serializers due to malformed `rdf:XMLLiteral` datatype

[doriantaylor]

I got a crash when trying to serialize a graph containing rdf:XMLLiteral terms. I went and pulled them out of the store, and the few terms in the repository that are XML literals, the datatype is a String:

[11] pry(#<Intertwingler::CLI>)> lol.dump :turtle
NoMethodError: undefined method `invalid?' for "http://www.w3.org/1999/02/22-rdf-syntax-ns#XMLLiteral":String (NoMethodError)

      return false if datatype? && datatype.invalid?
                                           ^^^^^^^^^
from /var/lib/gems/3.2.0/gems/rdf-3.3.2/lib/rdf/model/literal.rb:447:in `valid?'

I have tracked down the culprit; looks like and it's ostensibly specific to XML literals:

require 'rdf'
require 'rdf/ntriples'
require 'rdf/xsd'

test = RDF::NTriples::Reader.parse_object('"<strong xmlns=\"http://www.w3.org/1999/xhtml\">hi</strong>"^^<http://www.w3.org/1999/02/22-rdf-syntax-ns#XMLLiteral>')

test.datatype
# "http://www.w3.org/1999/02/22-rdf-syntax-ns#XMLLiteral"

Now: run this code again, commenting out require 'rdf/xsd'.

It looks like the RDF::XSD constructor does not coerce the datatype:

rdf-xsd/lib/rdf/xsd/xml.rb

Line 40 in e55b14b

@datatype = datatype || DATATYPE

…probably just putting RDF::URI(datatype) would fix this bug.