SPARQL Scoping issue for filters inside EXISTS

[hmottestad]

Current Behavior

See: #4169

PREFIX : <http://example/>
SELECT * WHERE {
	?a :p ?n
	FILTER NOT EXISTS {
		?a :q ?m .
		FILTER(?n = ?m)
	}
}

?n inside the FILTER clause is considered a new scope.

Expected Behavior

?n inside the FILTER clause should be in scope with the ?n in ?a :p ?n.

Steps To Reproduce

No response

Version

4.x

Are you interested in contributing a solution yourself?

Yes

Anything else?

No response

[hmottestad]

We use the following code to decide if a variable is in scope for a FILTER operation:

	public static boolean isPartOfSubQuery(QueryModelNode node) {
		if (node instanceof SubQueryValueOperator) {
			return true;
		}

		QueryModelNode parent = node.getParentNode();
		if (parent == null) {
			return false;
		} else {
			return isPartOfSubQuery(parent);
		}
	}

And EXISTS is among the effective sub classes of SubQueryValueOperator: