build.xml

<project name="my-plugin" default="zip" basedir=".">
  <!-- properties -->
  <property name="plugin.name" value="Simple Time Tracker"/>
  <property name="plugin.version" value="1.4.0"/>
  <property name="build.dir" value="build"/>
  <property name="dist.dir" value="dist"/>
  <property name="zip.file" value="${dist.dir}/${plugin.name}-${plugin.version}.zip"/>

  <!-- remove old build and dist -->
  <target name="clean">
    <delete dir="${build.dir}"/>
    <delete dir="${dist.dir}"/>
  </target>

  <!-- prepare build directory -->
  <target name="init">
    <mkdir dir="${build.dir}"/>
    <mkdir dir="${dist.dir}"/>
    <copy todir="${build.dir}">
      <fileset dir="." excludes="lib/**,,dist/**,build.xml"/>
    </copy>
  </target>

  <!-- load last version -->
  <property file="version.properties"/>

  <!-- load last version from a file that only contains the version -->
  <loadfile property="version" srcFile="version.properties"/>

  <!-- define Python-based bump-version -->
  <scriptdef name="bump.version" language="python">
    <classpath>
      <pathelement location="lib/jython-standalone-2.7.4.jar"/>
    </classpath>
    <![CDATA[
current = project.getProperty("version")
parts   = current.split(".")
major, minor, patch = map(int, parts)
patch  += 1
if patch > 10:
    patch = 0
    minor += 1
new_version = "{}.{}.{}".format(major, minor, patch)
project.setProperty("new.version", new_version)
]]>
  </scriptdef>

  <!-- target to update version.properties and plugin.version -->
<target name="bump-version">
  <bump.version/>
  <!-- overwrite the file with just the new version string -->
  <echo file="version.properties" message="${new.version}"/>
  <property name="version"       value="${new.version}"/>
  <property name="plugin.version" value="${new.version}"/>
</target>

  <!-- zip depends on bump-version -->
  <target name="zip" depends="clean,init,bump-version">
    <zip destfile="${dist.dir}/${plugin.name}-${plugin.version}.zip" basedir="${build.dir}"/>
  </target>
</project>