Updated the Jar task to have an whenmanifestonly attribute,

creating the possibility to skip jar files that would 
otherwise only contain a jar file. Also started to use this
for the optional tasks in the build.xml

git-svn-id: https://svn.apache.org/repos/asf/ant/core/trunk@293157 13f79535-47bb-0310-9956-ffa450edef68

build.xml

@@ -777,7 +777,8 @@
     </manifest>
 
     <jar destfile="${build.lib}/${name}-launcher.jar"
-      basedir="${build.classes}">
+      basedir="${build.classes}"
+      whenmanifestonly="fail">
       <selector refid="ant.launcher"/>
       <manifest>
         <attribute name="Main-Class" value="org.apache.tools.ant.launch.Launcher"/>
@@ -786,7 +787,8 @@
 
     <jar destfile="${build.lib}/${name}.jar"
       basedir="${build.classes}"
-      manifest="${manifest}">
+      manifest="${manifest}"
+      whenmanifestonly="fail">
       <not>
         <selector id="non-core">
           <or>
@@ -835,7 +837,8 @@
 
     <jar destfile="${build.lib}/${bootstrap.jar}"
       basedir="${build.classes}"
-      manifest="${manifest}">
+      manifest="${manifest}"
+      whenmanifestonly="fail">
       <include name="${ant.package}/Main.class"/>
       <metainf dir="${build.dir}">
         <include name="LICENSE.txt"/>
@@ -849,7 +852,8 @@
 
     <jar destfile="${build.lib}/ant-nodeps.jar"
       basedir="${build.classes}"
-      manifest="${manifest.tmp}">
+      manifest="${manifest.tmp}"
+      whenmanifestonly="skip">
       <and>
         <selector refid="non-core"/>
         <not>
@@ -895,7 +899,8 @@
       <sequential>
         <jar destfile="${build.lib}/${optional.jars.prefix}-@{dep}.jar"
           basedir="${build.classes}"
-          manifest="${manifest.tmp}">
+	  manifest="${manifest.tmp}"
+	  whenmanifestonly="skip">
           <selector refid="needs.@{dep}"/>
         </jar>
       </sequential>
@@ -928,7 +933,8 @@
 
     <jar destfile="${build.lib}/${optional.jars.prefix}-weblogic.jar"
       basedir="${build.classes}"
-      manifest="${manifest.tmp}">
+      manifest="${manifest.tmp}"
+      whenmanifestonly="skip">
       <or>
         <selector refid="needs.weblogic.ejbc"/>
         <selector refid="needs.weblogic.ddcreator"/>

docs/manual/CoreTasks/jar.html

@@ -43,6 +43,13 @@ note that ZIP files store file modification times with a granularity
 of two seconds.  If a file is less than two seconds newer than the
 entry in the archive, Ant will not consider it newer.</p>
 
+<p>The <code>whenmanifestonly</code> parameter controls what happens when no 
+files, apart from the manifest file, match.
+If <code>skip</code>, the JAR is not created and a warning is issued.
+If <code>fail</code>, the JAR is not created and the build is halted with an error.
+If <code>create</code>, (default) an empty JAR file (only containing a manifest) 
+is created.</p>
+
 <p>(The Jar task is a shortcut for specifying the manifest file of a JAR file.
 The same thing can be accomplished by using the <i>fullpath</i>
 attribute of a zipfileset in a Zip task. The one difference is that if the
@@ -155,6 +162,11 @@ to a value other than its default, <code>&quot;add&quot;</code>.</b></p>
       the destination file if it already exists.  Default is &quot;false&quot;.</td>
     <td valign="top" align="center">No</td>
   </tr>
+  <tr>
+    <td valign="top">whenmanifestonly</td>
+    <td valign="top">behavior when no files match.  Valid values are &quot;fail&quot;, &quot;skip&quot;, and &quot;create&quot;.  Default is &quot;create&quot;.</td>
+    <td valign="top" align="center">No</td>
+  </tr>
   <tr>
     <td valign="top">duplicate</td>
     <td valign="top">behavior when a duplicate file is found.  Valid values are &quot;add&quot;, &quot;preserve&quot;, and &quot;fail&quot;.  The default value is &quot;add&quot;.  </td>

src/main/org/apache/tools/ant/taskdefs/Jar.java

@@ -140,6 +140,8 @@ public class Jar extends Zip {
     private ZipExtraField[] JAR_MARKER = new ZipExtraField[] {
         JarMarker.getInstance()
     };
+    
+    protected String emptyBehavior = "create";
 
     /** constructor */
     public Jar() {
@@ -160,6 +162,16 @@ public class Jar extends Zip {
             Project.MSG_WARN);
     }
 
+    /**
+     * Not used for jar files.
+     * @param we not used
+     * @ant.attribute ignore="true"
+     */
+    public void setWhenmanifestonly(WhenEmpty we) {
+        emptyBehavior = we.getValue();
+    }
+
+    
     /**
      * Set the destination file.
      * @param jarFile the destination file
@@ -677,6 +689,18 @@ public class Jar extends Zip {
             return true;
         }
 
+        if (emptyBehavior.equals("skip")) {
+                log("Warning: skipping " + archiveType + " archive "
+                    + zipFile + " because no files were included.",
+                    Project.MSG_WARN);
+                return true;
+        } else if (emptyBehavior.equals("fail")) {
+            throw new BuildException("Cannot create " + archiveType
+                                     + " archive " + zipFile
+                                     + ": no files were included.",
+                                     getLocation());
+        }
+        
         ZipOutputStream zOut = null;
         try {
             log("Building MANIFEST-only jar: "
@@ -737,6 +761,7 @@ public class Jar extends Zip {
      */
     public void reset() {
         super.reset();
+        emptyBehavior = "create";
         configuredManifest = null;
         filesetManifestConfig = null;
         mergeManifestsMain = false;