Fixing bug applying VALUES outside of a GROUP BY

[robons]

Summary of changes

Altering order in which aggregate variable aliases are renamed to user-defined variable names to ensure that when defining a VALUES pattern outside of a GROUP BY, the variables in the query are correctly joined to those defined in the VALUES pattern.

The change fixes the following bug...

Example of bug

from pprint import pprint

from rdflib import Graph, URIRef, Literal, RDFS

graph = Graph()

graph.add((URIRef("http://example.com/something"), RDFS.label, Literal("Match on this.")))
graph.add((URIRef("http://example.com/something-else"), RDFS.label, Literal("Don't match on this.")))

results = graph.query("""
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>

SELECT ?obj ?label
WHERE {
    ?obj rdfs:label ?label
}
GROUP BY ?obj ?label
VALUES ( ?obj ) {
    ( <http://example.com/something> )
}
""")

pprint([row.asdict() for row in results])

results in the following erroneous output:

[{'label': rdflib.term.Literal('Match on this.'),
  'obj': rdflib.term.URIRef('http://example.com/something')},
 {'label': rdflib.term.Literal("Don't match on this."),
  'obj': rdflib.term.URIRef('http://example.com/something-else')}]

I would expect the the VALUES pattern to have filtered the results down to only include the result where ?obj is http://example.com/something, i.e.:

[{'label': rdflib.term.Literal('Match on this.'),
  'obj': rdflib.term.URIRef('http://example.com/something')}]

this is indeed the outcome when passing the data and query through the Apache JENA command line tools.

Checklist

• Checked that there aren't other open pull requests for
  the same change.
• Added tests for any changes that have a runtime impact.
• Checked that all tests and type checking passes.
• For changes that have a potential impact on users of this project:
  • (NA) Updated relevant documentation to avoid inaccuracies.
  • (NA) Considered adding additional documentation.
  • (NA) Considered adding an example in ./examples for new features.
  • (NA) Considered updating our changelog (CHANGELOG.md).
• Considered granting push permissions to the PR branch,
  so maintainers can fix minor issues and keep your PR up to date.

[coveralls]

Coverage: 90.658% (+0.001%) from 90.656% when pulling a44c2fc on robons:main into fbb8279 on RDFLib:main.

[aucampia]

Thanks for the PR @robons and apologies for the late review. The change and test looks good to me, so I'm going to merge it before Monday if there is no further feedback.