generate META-INF/MANIFEST.MF if useDefaultManifestFile is set

The MANIFEST.MF might be provided as a resource or generated by a
previous step, e.g. the bnd-maven-plugin and must neither be writtern or
overwritten if <useDefaultManifestFile> is configured to true

Author: Erwin Tratar

org.sonatype.m2e.mavenarchiver.tests/projects/mavenarchiver/mavenarchiver-p006/pom.xml

@@ -0,0 +1,30 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project>
+	<modelVersion>4.0.0</modelVersion>
+	<groupId>org.sonatype.m2e.mavenarchiver.tests</groupId>
+	<artifactId>mavenarchiver-p006</artifactId>
+	<version>1.0.0-SNAPSHOT</version>
+	<build>
+      <plugins>
+	      <plugin>
+	        <artifactId>maven-compiler-plugin</artifactId>
+	        <version>2.0.2</version>
+	      </plugin>
+	      <plugin>
+	        <artifactId>maven-jar-plugin</artifactId>
+	        <version>2.2</version>
+	        <configuration>
+		        <useDefaultManifestFile>true</useDefaultManifestFile>
+	        </configuration>
+	      </plugin>
+	      <plugin>
+	        <artifactId>maven-resources-plugin</artifactId>
+	        <version>2.4.1</version>
+	      </plugin>
+	      <plugin>
+	        <artifactId>maven-surefire-plugin</artifactId>
+	        <version>2.4.3</version>
+	      </plugin>
+    </plugins>
+  </build>
+</project>

org.sonatype.m2e.mavenarchiver.tests/projects/mavenarchiver/mavenarchiver-p006/src/main/resources/META-INF/MANIFEST.MF

@@ -0,0 +1,2 @@
+Built-By: You know who
+Class-Path: custom.jar

org.sonatype.m2e.mavenarchiver.tests/src/org/sonatype/m2e/mavenarchiver/MavenArchiverTest.java

@@ -11,7 +11,6 @@
 import org.eclipse.core.resources.IncrementalProjectBuilder;
 import org.eclipse.core.runtime.CoreException;
 import org.eclipse.core.runtime.IPath;
-import org.eclipse.core.runtime.NullProgressMonitor;
 import org.eclipse.m2e.core.MavenPlugin;
 import org.eclipse.m2e.core.embedder.ArtifactKey;
 import org.eclipse.m2e.core.internal.IMavenConstants;
@@ -243,6 +242,27 @@ private void _testProvidedManifest(String pomLocation) throws Exception
         assertTrue("Invalid Classpath in manifest : " + manifest, manifest.contains("Class-Path: custom.jar"));
     }
 
+    @Test
+    public void test006_UseDefaultManifestFile() throws Exception 
+    {
+    	IProject project = importProject("projects/mavenarchiver/mavenarchiver-p006/pom.xml");
+    	waitForJobsToComplete();
+    	
+    	IFile manifestFile = project.getFile("src/main/resources/META-INF/MANIFEST.MF");
+    	assertTrue("The manifest was deleted", manifestFile.exists());
+
+    	// trigger a full build
+        project.build( IncrementalProjectBuilder.FULL_BUILD, monitor );
+        waitForJobsToComplete();
+        assertNoErrors(project);
+
+    	IFile generatedManifestFile = project.getFile("target/classes/META-INF/MANIFEST.MF");
+    	assertTrue("A manifest is missing", generatedManifestFile.exists());
+    	
+    	String manifest =getAsString(generatedManifestFile);
+    	assertTrue("Built-By is invalid:"+manifest, manifest.contains("Built-By: You know who"));
+    }
+    
     public void testMECLIPSEWTP163_ParentMustBeResolved()
             throws Exception
     {

org.sonatype.m2e.mavenarchiver/src/org/sonatype/m2e/mavenarchiver/internal/AbstractMavenArchiverConfigurator.java

@@ -430,6 +430,12 @@ private void reflectManifestGeneration(MavenProject mavenProject, MojoExecution
     Xpp3Dom originalConfig = mojoExecution.getConfiguration();
     Xpp3Dom customConfig = Xpp3DomUtils.mergeXpp3Dom(new Xpp3Dom("configuration"), originalConfig);
 
+    Xpp3Dom useDefaultManifestFile = customConfig.getChild("useDefaultManifestFile");
+    if (useDefaultManifestFile != null && Boolean.parseBoolean(useDefaultManifestFile.getValue())) {
+        //<useDefaultManifestFile>true</useDefaultManifestFile> -> assume manifest is provided or generated by other mojo
+        return;
+    }
+    
     //Add custom manifest entries
     customizeManifest(customConfig, mavenProject);