Ant: how to write optional nested elements - ant

Question

Say that I need to do something like:
<copy todir="${DEPLOYMENT_DIR}" overwrite="true">
<fileset dir="dir1" />
<fileset dir="dir2" />
<fileset dir="dir3" />
...
<if>
<equals arg1="${SPECIAL_BUILD}" arg2="true"/>
<then>
<fileset dir="dir7" />
<fileset dir="dir8" />
...
</then>
</if>
</copy>
(The real task is not copy, I'm just using it to illustrate the point.)
Ant will complain that my task doesn't support nested <if> which is fair enough. I've been thinking along these lines:
I could add a macrodef with an "element" attribute like this:
<macrodef name="myCopy">
<element name="additional-path" />
<sequential>
<copy todir="${DEPLOYMENT_DIR}" overwrite="true">
<fileset dir="dir1" />
<fileset dir="dir2" />
<fileset dir="dir3" />
...
<additional-path/>
</copy>
</sequential>
</macrodef>
But that would mean that the caller (target) must specify the additional path which I want to avoid (if many targets call this task, they would have to repeat the fileset definitions in the additional-path element).
How to code the additional filesets inside the macrodef so that Ant doesn't complain?

Answer 1

AntContrib has an Ant FileSet object augmented with if and unless conditions.
http://ant-contrib.sourceforge.net/fileset.html
if Sets the property name for the 'if' condition. The fileset will be
ignored unless the property is
defined. The value of the property is
insignificant, but values that would
imply misinterpretation ("false",
"no") will throw an exception when
evaluated.
unless Set the property name for the 'unless' condition. If named
property is set, the fileset will be
ignored. The value of the property is
insignificant, but values that would
imply misinterpretation ("false",
"no") of the behavior will throw an
exception when evaluated.
You could use it like this:
<copy todir="${DEPLOYMENT_DIR}" overwrite="true">
<fileset dir="dir1" />
<fileset dir="dir2" />
<fileset dir="dir3" />
...
<fileset dir="dir7" if="SPECIAL_BUILD" />
<fileset dir="dir8" if="SPECIAL_BUILD" />
</copy>

Answer 2

One way (not sure if a good one) to achieve that is to create two macrodefs - one "public" for general use and one "internal" that does the real work and is intended to be called only from the "public" macro. Like this:
<macrodef name="task-for-public-use">
<sequential>
<if>
<equal arg1="${SPECIAL_BUILD}" arg2="true" />
<then>
<internal-task>
<additional-path>
...
</additional-path>
</internal-task>
</then>
<else>
<internal-task ... />
</else>
</if>
</sequential>
</macrodef>
<macrodef name="internal-task">
<element name="additional-path" />
<sequential>
<copy ...>
...
<additional-path/>
</copy>
</sequential>
</macrodef>
I don't like it much though and hope there's a better way.