GH-3681 Fix TurtleWriter list handling for rdf:type rdf:List

Author: hmottestad

core/rio/turtle/src/main/java/org/eclipse/rdf4j/rio/turtle/TurtleWriter.java

@@ -305,6 +305,11 @@ protected void handleStatementInternal(Statement st, boolean endRDFCalled, boole
 
 		try {
 			if (inlineBNodes) {
+				if (pred.equals(RDF.TYPE) && obj.equals(RDF.LIST) && subj instanceof BNode
+						&& isWellFormedCollection(subj)) {
+					// skip explicit rdf:type rdf:List for collections we will inline as Turtle lists
+					return;
+				}
 				if ((pred.equals(RDF.FIRST) || pred.equals(RDF.REST)) && isWellFormedCollection(subj)) {
 					// we only use list shorthand syntax if the collection is considered well-formed
 					handleList(st, canShortenObjectBNode);
@@ -357,6 +362,9 @@ private boolean isWellFormedCollection(Resource subj) {
 							// second rdf:rest statement on same subject is invalid.
 							return false;
 						}
+					} else if (pred.equals(RDF.TYPE) && RDF.LIST.equals(st.getObject())) {
+						// allow explicit rdf:type rdf:List
+						continue;
 					} else {
 						// non-list-structure statement connected to collection subject blank node
 						return false;

core/rio/turtle/src/test/java/org/eclipse/rdf4j/rio/turtle/TurtleWriterTest.java

@@ -15,11 +15,17 @@
 
 import java.io.StringReader;
 import java.io.StringWriter;
+import java.util.List;
 
+import org.eclipse.rdf4j.model.BNode;
 import org.eclipse.rdf4j.model.IRI;
 import org.eclipse.rdf4j.model.Model;
 import org.eclipse.rdf4j.model.impl.DynamicModelFactory;
+import org.eclipse.rdf4j.model.impl.TreeModel;
 import org.eclipse.rdf4j.model.util.Models;
+import org.eclipse.rdf4j.model.util.RDFCollections;
+import org.eclipse.rdf4j.model.util.Values;
+import org.eclipse.rdf4j.model.vocabulary.RDF;
 import org.eclipse.rdf4j.model.vocabulary.RDFS;
 import org.eclipse.rdf4j.rio.RDFFormat;
 import org.eclipse.rdf4j.rio.Rio;
@@ -390,6 +396,37 @@ public void testBNodeValuesInList() throws Exception {
 		assertTrue(Models.isomorphic(expected, actual));
 	}
 
+	@Test
+	public void testRdfCollectionsListNotFullyInlined() throws Exception {
+		String namespace = "http://example.com/ns#";
+		IRI cities = Values.iri(namespace, "Cities");
+		IRI listPredicate = Values.iri(namespace, "list");
+		BNode listHead = vf.createBNode("n1");
+
+		Model model = new TreeModel();
+		model.setNamespace("ex", namespace);
+		model.setNamespace("rdf", RDF.NAMESPACE);
+
+		RDFCollections.asRDF(List.of(
+				Values.iri(namespace, "NewYork"),
+				Values.iri(namespace, "Rio"),
+				Values.iri(namespace, "Tokyo")), listHead, model);
+		model.add(cities, listPredicate, listHead);
+
+		WriterConfig config = new WriterConfig();
+		config.set(BasicWriterSettings.INLINE_BLANK_NODES, true);
+		config.set(BasicWriterSettings.PRETTY_PRINT, true);
+
+		StringWriter stringWriter = new StringWriter();
+		Rio.write(model, stringWriter, RDFFormat.TURTLE, config);
+
+		String expected = String.join("\n", "@prefix ex: <http://example.com/ns#> .",
+				"@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .",
+				"", "ex:Cities ex:list (ex:NewYork ex:Rio ex:Tokyo) .", "");
+
+		assertThat(stringWriter.toString()).isEqualTo(expected);
+	}
+
 	@Test
 	public void testBNodeValuesInList2() throws Exception {
 		String data = "" +