Generating of syntactically incorrect queries when evaluating a service pattern

[galgonek]

Version

5.3.0

What happened?

I have noticed that during the evaluation of a federated query, Jena performs substitution of a variable for a RDF term even in cases where the given RDF term cannot be valid.

This can be demonstrated by the following federated query:

SELECT * WHERE {
  VALUES ?P { "literal" }

  SERVICE <https://idsm.elixir-czech.cz/sparql/endpoint/idsm> {
      ?S ?P ?O.
  }
}

Jena sends the following query to the endpoint:

SELECT  *
WHERE
  { ?S  "literal"  ?O }

However, such a query is not syntactically correct.

Relevant output and stacktrace

Are you interested in making a pull request?

None