commit 7c6c749c952153170e82b791d97086e99fe2a3cb
Author: Stefan Bodewig <bodewig@apache.org>
Date:   Mon May 8 18:44:07 2017 +0200

    add magic property that override's tstamp's idea of "now"
    
    https://bz.apache.org/bugzilla/show_bug.cgi?id=61079

diff --git a/manual/Tasks/tstamp.html b/manual/Tasks/tstamp.html
index 82812a579..6baa0c882 100644
--- a/manual/Tasks/tstamp.html
+++ b/manual/Tasks/tstamp.html
@@ -40,6 +40,12 @@
 to indicate, for example, the release date. The best place for this task is
 probably in an initialization target.</p>
 
+<p><em>Since Ant 1.9.10</em> the magic
+  property <code>ant.tstamp.now</code> can be used to specify a fixed
+  date value in order to create reproducible builds. Its value must be
+  a number and is interpreted as seconds since the epoch (midnight
+  1970-01-01).</p>
+
 <h3>Parameters</h3>
 <table border="1" cellpadding="2" cellspacing="0">
   <tr>
diff --git a/manual/running.html b/manual/running.html
index 529afc7dc..3bfb500c8 100644
--- a/manual/running.html
+++ b/manual/running.html
@@ -485,6 +485,11 @@
   <a href="argumentprocessor.html#repository">ArgumentProcessor internal repository</a>.
   </td>
 </tr>
+<tr>
+  <td><code>ant.tstamp.now</code></td>
+  <td>number, seconds since the epoch (midnight 1970-01-01)</td>
+  <td>The value to use as current time and date for &lt;tstamp&gt;</td>
+</tr>
 </table>
 
 <p>
diff --git a/src/main/org/apache/tools/ant/MagicNames.java b/src/main/org/apache/tools/ant/MagicNames.java
index bc39a2578..67ab8a810 100644
--- a/src/main/org/apache/tools/ant/MagicNames.java
+++ b/src/main/org/apache/tools/ant/MagicNames.java
@@ -289,5 +289,18 @@ public final class MagicNames {
      * Value {@value}
      */
     public static final String HTTP_AGENT_PROPERTY = "ant.http.agent";
+
+    /**
+     * Magic property that can be set to contain a value for tstamp's
+     * "now" in order to make builds that use the task create
+     * reproducible results.
+     *
+     * <p>The value is expected to be a number representing the date
+     * as seconds since the epoch.</p>
+     *
+     * Value: {@value}
+     * @since Ant 1.9.10
+     */
+    public static final String TSTAMP_NOW = "ant.tstamp.now";
 }
 
diff --git a/src/main/org/apache/tools/ant/taskdefs/Tstamp.java b/src/main/org/apache/tools/ant/taskdefs/Tstamp.java
index 805427aba..a6a35d7b4 100644
--- a/src/main/org/apache/tools/ant/taskdefs/Tstamp.java
+++ b/src/main/org/apache/tools/ant/taskdefs/Tstamp.java
@@ -32,6 +32,7 @@ import java.util.Vector;
 
 import org.apache.tools.ant.BuildException;
 import org.apache.tools.ant.Location;
+import org.apache.tools.ant.MagicNames;
 import org.apache.tools.ant.Project;
 import org.apache.tools.ant.Task;
 import org.apache.tools.ant.types.EnumeratedAttribute;
@@ -68,7 +69,7 @@ public class Tstamp extends Task {
      */
     public void execute() throws BuildException {
         try {
-            Date d = new Date();
+            Date d = getNow();
 
             Enumeration i = customFormats.elements();
             while (i.hasMoreElements()) {
@@ -110,6 +111,22 @@ public class Tstamp extends Task {
     }
 
     /**
+     * Return the {@link Date} instance to use as base for DSTAMP, TSTAMP and TODAY.
+     */
+    protected Date getNow() {
+        String magicNow = getProject().getProperty(MagicNames.TSTAMP_NOW);
+        if (magicNow != null && magicNow.length() > 0) {
+            try {
+                return new Date(1000 * Long.parseLong(magicNow));
+            } catch (NumberFormatException ex) {
+                log("magic property " + MagicNames.TSTAMP_NOW + " ignored as "
+                    + magicNow + " is not a valid number");
+            }
+        }
+        return new Date();
+    }
+
+    /**
      * This nested element that allows a property to be set
      * to the current date and time in a given format.
      * The date/time patterns are as defined in the
diff --git a/src/tests/antunit/taskdefs/tstamp-test.xml b/src/tests/antunit/taskdefs/tstamp-test.xml
new file mode 100644
index 000000000..c9bebf866
--- /dev/null
+++ b/src/tests/antunit/taskdefs/tstamp-test.xml
@@ -0,0 +1,27 @@
+<?xml version="1.0"?>
+<!--
+  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 default="antunit" xmlns:au="antlib:org.apache.ant.antunit">
+  <import file="../antunit-base.xml" />
+
+  <target name="testMagicProperty">
+    <local name="ant.tstamp.now"/>
+    <property name="ant.tstamp.now" value="100000"/>
+    <tstamp/>
+    <au:assertPropertyEquals name="DSTAMP" value="19700102"/>
+  </target>
+</project>