GH-4921 Turtle writer does not respect namespaces in IRIs

- Added tests to check to which degree parsing a Turtle file with unconventional prefixes and serializing it back again results preserves format

Author: reckart

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

@@ -460,14 +460,17 @@ public static String encodeURIString(String s) {
 	}
 
 	public static boolean isValidPrefixedName(String s) {
-		final int numberOfCodePoints = s.codePointCount(0, s.length());
-		for (int i = 1; i < numberOfCodePoints; i++) {
-			final int codePoint = s.codePointAt(i);
-			if (!isPN_CHARS(codePoint)) {
-				return false;
-			}
+		if (s == null || s.isEmpty()) {
+			return false;
 		}
-		return true;
+
+		if (!isPN_CHARS_BASE(s.codePointAt(0))) {
+			return false;
+		}
+
+		return s.codePoints() //
+				.skip(1) // Skip the first code point
+				.allMatch(TurtleUtil::isPN_CHARS);
 	}
 
 	/**

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

@@ -20,6 +20,7 @@
 import org.eclipse.rdf4j.model.Model;
 import org.eclipse.rdf4j.model.impl.DynamicModelFactory;
 import org.eclipse.rdf4j.model.util.Models;
+import org.eclipse.rdf4j.model.vocabulary.RDFS;
 import org.eclipse.rdf4j.rio.RDFFormat;
 import org.eclipse.rdf4j.rio.Rio;
 import org.eclipse.rdf4j.rio.WriterConfig;
@@ -97,7 +98,6 @@ public void testBlankNodeInlining1() throws Exception {
 		Model actual = Rio.parse(new StringReader(stringWriter.toString()), "", RDFFormat.TURTLE);
 
 		assertTrue(Models.isomorphic(expected, actual));
-
 	}
 
 	@Test
@@ -194,6 +194,54 @@ public void testNoBuffering() throws Exception {
 		assertTrue(Models.isomorphic(expected, actual));
 	}
 
+	@Test
+	public void testUnusualIrisAndPrefixesParseWriteCompare() throws Exception {
+		String data = "@prefix server-news: <news:comp.infosystems.www.servers.> .\n" +
+				"@prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .\n" +
+				"server-news:unix rdfs:label \"News on Unix\" .\n" +
+				"server-news:windows rdfs:label \"News on Windows\" .\n";
+
+		var expected = Rio.parse(new StringReader(data), "", RDFFormat.TURTLE);
+
+		var stringWriter = new StringWriter();
+		var config = new WriterConfig();
+		config.set(BasicWriterSettings.INLINE_BLANK_NODES, false);
+		config.set(BasicWriterSettings.PRETTY_PRINT, false);
+		Rio.write(expected, stringWriter, RDFFormat.TURTLE, config);
+
+		var actual = Rio.parse(new StringReader(stringWriter.toString()), "", RDFFormat.TURTLE);
+		assertThat(Models.isomorphic(expected, actual)).as("isomorphic").isTrue();
+
+		assertThat(stringWriter.toString()).isEqualTo(data);
+	}
+
+	@Test
+	public void testUnusualIrisAndPrefixesWriteParserWriteCompare() throws Exception {
+		var prefix = "server-news";
+		var ns = "news:comp.infosystems.www.servers.";
+
+		var config = new WriterConfig();
+		config.set(BasicWriterSettings.INLINE_BLANK_NODES, false);
+		config.set(BasicWriterSettings.PRETTY_PRINT, false);
+
+		var expectedModel = new DynamicModelFactory().createEmptyModel();
+		expectedModel.setNamespace(prefix, ns);
+		expectedModel.setNamespace(RDFS.PREFIX, RDFS.NAMESPACE);
+		expectedModel.add(vf.createIRI(ns, "unix"), RDFS.LABEL, vf.createLiteral("News on Unix"));
+		expectedModel.add(vf.createIRI(ns, "windows"), RDFS.LABEL, vf.createLiteral("News on Windows"));
+
+		var turtle1 = new StringWriter();
+		Rio.write(expectedModel, turtle1, RDFFormat.TURTLE, config);
+
+		var actualModel = Rio.parse(new StringReader(turtle1.toString()), "", RDFFormat.TURTLE);
+		assertThat(Models.isomorphic(expectedModel, actualModel)).as("isomorphic").isTrue();
+
+		var turtle2 = new StringWriter();
+		Rio.write(actualModel, turtle2, RDFFormat.TURTLE, config);
+
+		assertThat(turtle2.toString()).isEqualTo(turtle1.toString());
+	}
+
 	@Test
 	@Disabled
 	public void anotherBnodeTest() throws Exception {