DefaultModelXmlFactory: make location tracking opt-in—disabled by default, enabled when an InputLocationFormatter is provided.

Adapt formatter to Function<InputLocation,String> and write to the actually opened stream for path output.
Fixes #10939.

Author: arturobernalg

impl/maven-impl/src/main/java/org/apache/maven/impl/DefaultModelXmlFactory.java

@@ -30,6 +30,7 @@
 import org.apache.maven.api.annotations.Nonnull;
 import org.apache.maven.api.di.Named;
 import org.apache.maven.api.di.Singleton;
+import org.apache.maven.api.model.InputLocation;
 import org.apache.maven.api.model.InputSource;
 import org.apache.maven.api.model.Model;
 import org.apache.maven.api.services.xml.ModelXmlFactory;
@@ -121,22 +122,29 @@ public void write(XmlWriterRequest<Model> request) throws XmlWriterException {
         Path path = request.getPath();
         OutputStream outputStream = request.getOutputStream();
         Writer writer = request.getWriter();
-        Function<Object, String> inputLocationFormatter = request.getInputLocationFormatter();
+
         if (writer == null && outputStream == null && path == null) {
             throw new IllegalArgumentException("writer, outputStream or path must be non null");
         }
+
         try {
-            MavenStaxWriter w = new MavenStaxWriter();
-            if (inputLocationFormatter != null) {
-                w.setStringFormatter((Function) inputLocationFormatter);
+            final MavenStaxWriter xmlWriter = new MavenStaxWriter();
+            xmlWriter.setAddLocationInformation(false);
+
+            final Function<Object, String> fmtformatter = request.getInputLocationFormatter();
+            if (fmtformatter != null) {
+                xmlWriter.setAddLocationInformation(true);
+                final Function<InputLocation, String> adapter = fmtformatter::apply;
+                xmlWriter.setStringFormatter(adapter);
             }
+
             if (writer != null) {
-                w.write(writer, content);
+                xmlWriter.write(writer, content);
             } else if (outputStream != null) {
-                w.write(outputStream, content);
+                xmlWriter.write(outputStream, content);
             } else {
                 try (OutputStream os = Files.newOutputStream(path)) {
-                    w.write(os, content);
+                    xmlWriter.write(os, content);
                 }
             }
         } catch (Exception e) {

impl/maven-impl/src/test/java/org/apache/maven/impl/DefaultModelXmlFactoryTest.java

@@ -19,14 +19,18 @@
 package org.apache.maven.impl;
 
 import java.io.StringReader;
+import java.io.StringWriter;
+import java.util.function.Function;
 
 import org.apache.maven.api.model.Model;
 import org.apache.maven.api.services.xml.XmlReaderException;
 import org.apache.maven.api.services.xml.XmlReaderRequest;
+import org.apache.maven.api.services.xml.XmlWriterRequest;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
@@ -122,4 +126,62 @@ void testMalformedModelVersion() throws Exception {
         Model model = factory.read(request);
         assertEquals("invalid.version", model.getModelVersion());
     }
+
+    @Test
+    void testWriteWithoutFormatterDisablesLocationTracking() throws Exception {
+        // minimal valid model we can round-trip
+        String xml =
+                """
+                <project xmlns="http://maven.apache.org/POM/4.0.0">
+                  <modelVersion>4.0.0</modelVersion>
+                  <groupId>g</groupId>
+                  <artifactId>a</artifactId>
+                  <version>1</version>
+                </project>""";
+
+        Model model = factory.read(XmlReaderRequest.builder()
+                .reader(new StringReader(xml))
+                .strict(true)
+                .build());
+
+        StringWriter out = new StringWriter();
+        factory.write(XmlWriterRequest.<Model>builder()
+                .writer(out)
+                .content(model)
+                // no formatter -> tracking should be OFF
+                .build());
+
+        String result = out.toString();
+        assertFalse(result.contains("LOC_MARK"), "Unexpected marker found in output");
+    }
+
+    @Test
+    void testWriteWithFormatterEnablesLocationTracking() throws Exception {
+        String xml =
+                """
+                <project xmlns="http://maven.apache.org/POM/4.0.0">
+                  <modelVersion>4.0.0</modelVersion>
+                  <groupId>g</groupId>
+                  <artifactId>a</artifactId>
+                  <version>1</version>
+                </project>""";
+
+        Model model = factory.read(XmlReaderRequest.builder()
+                .reader(new StringReader(xml))
+                .strict(true)
+                .build());
+
+        StringWriter out = new StringWriter();
+        Function<Object, String> formatter = o -> "LOC_MARK";
+
+        factory.write(XmlWriterRequest.<Model>builder()
+                .writer(out)
+                .content(model)
+                .inputLocationFormatter(formatter)
+                .build());
+
+        String result = out.toString();
+        // Presence of our formatter's output proves tracking was enabled and formatter applied
+        assertTrue(result.contains("LOC_MARK"), "Expected formatter marker in output when tracking is enabled");
+    }
 }