Index: src/etc/testcases/taskdefs/optional/propertyfile.xml
===================================================================
RCS file: /home/cvspublic/ant/src/etc/testcases/taskdefs/optional/propertyfile.xml,v
retrieving revision 1.4
diff -u -r1.4 propertyfile.xml
--- src/etc/testcases/taskdefs/optional/propertyfile.xml	11 Jul 2003 21:25:35 -0000	1.4
+++ src/etc/testcases/taskdefs/optional/propertyfile.xml	23 Oct 2003 16:45:20 -0000
@@ -84,6 +84,12 @@
        </propertyfile>
     </target>
 
+    <target name="testNoOp">
+        <propertyfile file="${test.propertyfile}">
+            <entry key="existing.prop" value="37"/>
+        </propertyfile>
+    </target>
+
 </project>
 
 
Index: src/main/org/apache/tools/ant/taskdefs/optional/PropertyFile.java
===================================================================
RCS file: /home/cvspublic/ant/src/main/org/apache/tools/ant/taskdefs/optional/PropertyFile.java,v
retrieving revision 1.32
diff -u -r1.32 PropertyFile.java
--- src/main/org/apache/tools/ant/taskdefs/optional/PropertyFile.java	17 Sep 2003 20:11:43 -0000	1.32
+++ src/main/org/apache/tools/ant/taskdefs/optional/PropertyFile.java	23 Oct 2003 16:45:20 -0000
@@ -71,6 +71,7 @@
 import java.util.Properties;
 import java.util.Vector;
 import org.apache.tools.ant.BuildException;
+import org.apache.tools.ant.Project;
 import org.apache.tools.ant.Task;
 import org.apache.tools.ant.types.EnumeratedAttribute;
 
@@ -171,8 +172,17 @@
     public void execute() throws BuildException {
         checkParameters();
         readFile();
-        executeOperation();
-        writeFile();
+        boolean modified = executeOperation();
+        String path = propertyfile.getAbsolutePath();
+        if (!propertyfile.exists()) {
+            log("Creating new property file: " + path);
+            writeFile();
+        } else if (modified) {
+            log("Updating property file: " + path);
+            writeFile();
+        } else {
+            log("No change made to " + path, Project.MSG_VERBOSE);
+        }
     }
 
     public Entry createEntry() {
@@ -181,11 +191,13 @@
         return e;
     }
 
-    private void executeOperation() throws BuildException {
+    private boolean executeOperation() throws BuildException {
+        boolean didSomething = false;
         for (Enumeration e = entries.elements(); e.hasMoreElements();) {
             Entry entry = (Entry) e.nextElement();
-            entry.executeOn(properties);
+            didSomething |= entry.executeOn(properties);
         }
+        return didSomething;
     }
 
     private void readFile() throws BuildException {
@@ -193,8 +205,6 @@
         properties = new Properties();
         try {
             if (propertyfile.exists()) {
-                log("Updating property file: "
-                    + propertyfile.getAbsolutePath());
                 FileInputStream fis = null;
                 try {
                     fis = new FileInputStream(propertyfile);
@@ -205,18 +215,6 @@
                         fis.close();
                     }
                 }
-            } else {
-                log("Creating new property file: "
-                    + propertyfile.getAbsolutePath());
-                FileOutputStream out = null;
-                try {
-                    out = new FileOutputStream(propertyfile.getAbsolutePath());
-                    out.flush();
-                } finally {
-                    if (out != null) {
-                        out.close();
-                    }
-                }
             }
         } catch (IOException ioe) {
             throw new BuildException(ioe.toString());
@@ -351,7 +349,12 @@
             field = unit.getCalendarField();
         }
 
-        protected void executeOn(Properties props) throws BuildException {
+        /**
+         * Process this entry.
+         * @param props the list of properties to work on
+         * @return true if a change was made
+         */
+        protected boolean executeOn(Properties props) throws BuildException {
             checkParameters();
 
             // type may be null because it wasn't set
@@ -379,6 +382,8 @@
 
             // Insert as a string by default
             props.put(key, newValue);
+            
+            return !newValue.equals(oldValue);
         }
 
         /**
Index: src/testcases/org/apache/tools/ant/taskdefs/optional/PropertyFileTest.java
===================================================================
RCS file: /home/cvspublic/ant/src/testcases/org/apache/tools/ant/taskdefs/optional/PropertyFileTest.java,v
retrieving revision 1.9
diff -u -r1.9 PropertyFileTest.java
--- src/testcases/org/apache/tools/ant/taskdefs/optional/PropertyFileTest.java	7 Sep 2003 09:40:40 -0000	1.9
+++ src/testcases/org/apache/tools/ant/taskdefs/optional/PropertyFileTest.java	23 Oct 2003 16:45:20 -0000
@@ -175,6 +175,29 @@
     }
 */
 
+    /**
+     * Confirm that if the task would not actually change any properties,
+     * the file is not touched.
+     */
+    public void testNoOp() {
+        File tpf = new File(testPropsFilePath);
+        assertTrue(tpf.exists());
+        long mtime1 = tpf.lastModified();
+        long size1 = tpf.length();
+        assertTrue(mtime1 != 0L);
+        assertTrue(size1 != 0L);
+        try {
+            // Make sure some measurable time has elapsed.
+            Thread.sleep(100);
+        } catch (InterruptedException e) {}
+        executeTarget("testNoOp");
+        assertTrue(tpf.exists());
+        long mtime2 = tpf.lastModified();
+        long size2 = tpf.length();
+        assertEquals("Timestamp of " + testPropsFilePath + " was not changed", mtime1, mtime2);
+        assertEquals("Size of " + testPropsFilePath + " was not changed", size1, size2);
+    }
+
     private Properties getTestProperties() throws Exception {
         Properties testProps = new Properties();
         FileInputStream propsFile = new FileInputStream(testPropsFilePath);