Add support for automatic module name

src/it/automatic-name/pom.xml

@@ -0,0 +1,45 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+  Licensed to the Apache Software Foundation (ASF) under one
+  or more contributor license agreements.  See the NOTICE file
+  distributed with this work for additional information
+  regarding copyright ownership.  The ASF licenses this file
+  to you under the Apache License, Version 2.0 (the
+  "License"); you may not use this file except in compliance
+  with the License.  You may obtain a copy of the License at
+
+  http://www.apache.org/licenses/LICENSE-2.0
+
+  Unless required by applicable law or agreed to in writing,
+  software distributed under the License is distributed on an
+  "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+  KIND, either express or implied.  See the License for the
+  specific language governing permissions and limitations
+  under the License.
+-->
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
+  <modelVersion>4.0.0</modelVersion>
+  <groupId>org.apache.maven.plugins</groupId>
+  <artifactId>automatic-name</artifactId>
+  <version>1.0-SNAPSHOT</version>
+  <packaging>jar</packaging>
+  <name>automatic-name-it</name>
+  <organization>
+    <name>jar plugin it</name>
+  </organization>
+  <properties>
+    <maven.compiler.release>11</maven.compiler.release>
+  </properties>
+  <build>
+    <plugins>
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-jar-plugin</artifactId>
+        <version>@project.version@</version>
+        <configuration>
+          <automaticModuleName>org.apache.maven.its.it.issue520</automaticModuleName>
+        </configuration>
+      </plugin>
+    </plugins>
+  </build>
+</project>

src/it/automatic-name/src/main/java/org/apache/maven/its/it/issue520/Main.java

@@ -0,0 +1,25 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.maven.its.it.issue520;
+
+public final class Main {
+    public static void main(String[] args) {
+        System.out.println("Hello World!");
+    }
+}

src/it/automatic-name/verify.groovy

@@ -0,0 +1,74 @@
+
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+import java.io.*;
+import java.util.*;
+import java.util.jar.*;
+import org.apache.commons.io.*;
+
+boolean result = true;
+
+try
+{
+    File target = new File( basedir, "target" );
+    if ( !target.exists() || !target.isDirectory() )
+    {
+        System.err.println( "target file is missing or not a directory." );
+        return false;
+    }
+
+    File artifact = new File( target, "automatic-name-1.0-SNAPSHOT.jar" );
+    if ( !artifact.exists() || artifact.isDirectory() )
+    {
+        System.err.println( "artifact file " + file + " is missing or a directory." );
+        return false;
+    }
+
+    JarFile jar = new JarFile( artifact );
+    Enumeration jarEntries = jar.entries();
+    while ( jarEntries.hasMoreElements() )
+    {
+        JarEntry entry = (JarEntry) jarEntries.nextElement();
+        if ( !entry.isDirectory() )
+        {
+            // Only compare files
+            if ( entry.getName().equals( "META-INF/MANIFEST.MF" ) )
+            {
+                String manifest = IOUtils.toString( jar.getInputStream ( entry ) );
+                int index = manifest.indexOf( "Automatic-Module-Name: org.apache.maven.its.it.issue520" );
+                if ( index <= 0 )
+                {
+                    System.err.println( "MANIFEST doesn't contain: 'Automatic-Module-Name: org.apache.maven.its.it.issue520'" );
+                    return false;
+                }
+                return true;
+            }
+        }
+    }
+    System.err.println( "MANIFEST.MF not found" );
+    return false;
+}
+catch( Throwable e )
+{
+    e.printStackTrace();
+    result = false;
+}
+
+return result;

src/main/java/org/apache/maven/plugins/jar/AbstractJarMojo.java

@@ -139,6 +139,15 @@ public abstract class AbstractJarMojo extends AbstractMojo {
     @Parameter(property = "maven.jar.detectMultiReleaseJar", defaultValue = "true")
     private boolean detectMultiReleaseJar;
 
+    /**
+     * Establish the automatic module name of the module in the JAR.
+     * Ignored if the JAR contains a {@code module-info.class} file.
+     *
+     * @since 3.6.0
+     */
+    @Parameter(property = "maven.jar.automaticModuleName")
+    private String automaticModuleName;
+
     /**
      * If set to {@code false}, the files and directories that by default are excluded from the resulting archive,
      * like {@code .gitignore}, {@code .cvsignore} etc. will be included.
@@ -297,6 +306,15 @@ public File createArchive() throws MojoExecutionException {
         boolean containsModuleDescriptor =
                 Arrays.stream(includedFiles).anyMatch(p -> p.endsWith(MODULE_DESCRIPTOR_FILE_NAME));
 
+        if (automaticModuleName != null && !automaticModuleName.isEmpty()) {
+            if (containsModuleDescriptor) {
+                getLog().warn("Not setting automatic module name, because a module descriptor was found.");
+            } else {
+                getLog().debug("Adding 'Automatic-Module-Name: " + automaticModuleName + "' manifest entry.");
+                archive.addManifestEntry("Automatic-Module-Name", automaticModuleName);
+            }
+        }
+
         String archiverName = containsModuleDescriptor ? "mjar" : "jar";
 
         MavenArchiver archiver = new MavenArchiver();