custom_rules.xml

<?xml version="1.0" encoding="UTF-8"?>
<project>

  <target name="-getgitdetails" >
    <exec executable="git" outputproperty="git.describe">
      <arg value="describe"/>
    </exec>
    <exec executable="git" outputproperty="git.revision">
      <arg value="rev-parse"/>
      <arg value="HEAD"/>
    </exec>
  </target>

  <target name="rename-release-with-version-number" depends="-getgitdetails">
    <xmlproperty file="AndroidManifest.xml"
                 prefix="themanifest"
                 collapseAttributes="true"/>
    <!--  see ${sdk.dir}/tools/ant/build.xml -set-release-mode -->
    <property name="out.packaged.file"
              location="${out.absolute.dir}/${ant.project.name}-v${git.describe}-unsigned.apk" />
    <property name="out.final.file"
              location="${out.absolute.dir}/${ant.project.name}-v${git.describe}.apk" />
  </target>

  <target name="-set-release-mode"
          depends="rename-release-with-version-number,android_rules.-set-release-mode">
    <echo message="target: ${build.target}"></echo>
  </target>

  <target name="-post-package" depends="-getgitdetails">
    <property file="${sdk.dir}/tools/source.properties"/>
    <property name="meta.inf.dir" value="${out.dir}/META-INF"/>
    <property name="build.manifest.file" value="${meta.inf.dir}/BUILD.MF"/>
    <mkdir dir="${meta.inf.dir}"/>
    <manifest file="${build.manifest.file}">
      <attribute name="Implementation-Package-Name" value="${themanifest.manifest.package}"/>
      <attribute name="Implementation-Version-Name" value="${themanifest.manifest.android:versionName}"/>
      <attribute name="Implementation-Version-Code" value="${themanifest.manifest.android:versionCode}"/>
      <attribute name="Git-Revision" value="${git.revision}"/>
      <attribute name="Android-SDK-Release" value="${Pkg.Revision}"/>
      <attribute name="Android-SDK-Host-OS" value="${Archive.HostOs}"/>
      <attribute name="Android-SDK-aapt" value="${aapt}"/>
      <attribute name="Android-SDK-zipalign" value="${zipalign}"/>
    </manifest>
    <condition property="build.is.debug" value="true" else="false">
      <equals arg1="${build.target}" arg2="debug" />
    </condition>
    <!-- adding BUILD.MF breaks debug builds, but not releases -->
    <if condition="${build.is.debug}">
      <else>
        <jar update="true" destfile="${out.packaged.file}">
          <fileset dir="${out.dir}" includes="META-INF/BUILD.MF"/>
        </jar>
      </else>
    </if>
  </target>
</project>