GH-3220 Fix property path object list handling

Author: hmottestad

core/queryparser/sparql/src/main/java/org/eclipse/rdf4j/query/parser/sparql/TupleExprBuilder.java

@@ -1449,6 +1449,36 @@ public TupleExpr visit(ASTPathSequence pathSeqNode, Object data) throws VisitorE
 			subjVar = mapValueExprToVar(data);
 		}
 
+		List<ValueExpr> objectList = null;
+		if (!(data instanceof PathSequenceContext)) {
+			ASTObjectList objectListNode = getObjectList(pathSeqNode);
+			if (objectListNode != null) {
+				@SuppressWarnings("unchecked")
+				List<ValueExpr> evaluatedObjectList = (List<ValueExpr>) objectListNode.jjtAccept(this, null);
+				objectList = evaluatedObjectList;
+
+				if (objectList.size() > 1) {
+					TupleExpr result = null;
+					for (ValueExpr objectItem : objectList) {
+						PathSequenceContext objectContext = new PathSequenceContext();
+						objectContext.scope = graphPattern.getStatementPatternScope();
+						objectContext.contextVar = graphPattern.getContextVar();
+						objectContext.startVar = subjVar;
+						objectContext.endVar = mapValueExprToVar(objectItem);
+
+						TupleExpr pathExpr = (TupleExpr) pathSeqNode.jjtAccept(this, objectContext);
+
+						if (result == null) {
+							result = pathExpr;
+						} else {
+							result = new Join(result, pathExpr);
+						}
+					}
+					return result;
+				}
+			}
+		}
+
 		List<ASTPathElt> pathElements = pathSeqNode.getPathElements();
 		int pathLength = pathElements.size();
 
@@ -1470,10 +1500,15 @@ public TupleExpr visit(ASTPathSequence pathSeqNode, Object data) throws VisitorE
 
 					// We handle this here instead of higher up in the tree visitor because here we have
 					// a reference to the "temporary" endVar that needs to be replaced.
-					@SuppressWarnings("unchecked")
-					List<ValueExpr> objectList = (List<ValueExpr>) getObjectList(pathSeqNode).jjtAccept(this, null);
+					List<ValueExpr> finalObjectList = objectList;
+					if (finalObjectList == null) {
+						@SuppressWarnings("unchecked")
+						List<ValueExpr> evaluatedObjectList = (List<ValueExpr>) getObjectList(pathSeqNode)
+								.jjtAccept(this, null);
+						finalObjectList = evaluatedObjectList;
+					}
 
-					for (ValueExpr objectItem : objectList) {
+					for (ValueExpr objectItem : finalObjectList) {
 						Var objectVar = mapValueExprToVar(objectItem);
 						Var replacement = objectVar;
 						if (objectVar.equals(subjVar)) { // corner case for cyclic expressions, see SES-1685

core/queryparser/sparql/src/test/java/org/eclipse/rdf4j/query/parser/sparql/TestPropPathMisbehaviour.java

@@ -10,9 +10,14 @@
  *******************************************************************************/
 package org.eclipse.rdf4j.query.parser.sparql;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertNotNull;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
+import java.util.List;
+import java.util.Set;
+import java.util.stream.Collectors;
+
 import org.eclipse.rdf4j.query.algebra.ArbitraryLengthPath;
 import org.eclipse.rdf4j.query.algebra.Distinct;
 import org.eclipse.rdf4j.query.algebra.Join;
@@ -22,6 +27,7 @@
 import org.eclipse.rdf4j.query.algebra.TupleExpr;
 import org.eclipse.rdf4j.query.algebra.Union;
 import org.eclipse.rdf4j.query.algebra.ZeroLengthPath;
+import org.eclipse.rdf4j.query.algebra.helpers.collectors.StatementPatternCollector;
 import org.eclipse.rdf4j.query.parser.ParsedQuery;
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.BeforeEach;
@@ -109,4 +115,30 @@ public void testGH3053() {
 				"expect Union Right arg to be StatementPattern");
 		assertTrue(!proj2.isSubquery(), "expect projection to do NOT be a subQuery");
 	}
+
+	@Test
+	public void testGH3220() {
+		String query = "select * where { ?i <urn:prop1> / <urn:prop2> ?v1, ?v2 . }";
+		ParsedQuery parsedQuery = parser.parseQuery(query, "http://example.org/");
+
+		assertNotNull(parsedQuery);
+
+		List<StatementPattern> statementPatterns = StatementPatternCollector
+				.process(parsedQuery.getTupleExpr());
+
+		List<StatementPattern> prop1Patterns = statementPatterns.stream()
+				.filter(sp -> sp.getPredicateVar().hasValue()
+						&& "urn:prop1".equals(sp.getPredicateVar().getValue().stringValue()))
+				.collect(Collectors.toList());
+
+		assertEquals(2, prop1Patterns.size(),
+				"expected each object list entry to yield its own statement pattern for the first path element");
+
+		Set<String> intermediateVarNames = prop1Patterns.stream()
+				.map(sp -> sp.getObjectVar().getName())
+				.collect(Collectors.toSet());
+
+		assertEquals(2, intermediateVarNames.size(),
+				"expected unique intermediate variable per object list entry for the first path element");
+	}
 }