The latest version of Apache Ant aims to solve several of the scalability limitations that made it difficult to use earlier Ant versions on complex projects.

According to a presentation [PDF] by Steve Loughran, a member of the Ant development team and author of Manning's Java Development with Ant, one interesting new Ant feature is improved support for scripting. While Ant 1.6 introduced the scriptdef and scriptfilter tags, 1.7 adds more scripting support with the scriptcondition (implement a condition), scriptselector> (select files), and scriptmapper (map file names) tags. According to Loughran, BeanShell, Jython, Groovy, JavaScript, JRuby, Rexx, and other scripting languages can be used with Ant.

In the presentation, Loughran shows how simple defining scripts inside an Ant file is:

<scriptdef name="repeat" language="ruby">
  <attribute name="from"/>
  <attribute name="to"/>
  <attribute name="message"/>

  attr = $bsf.lookupBean("attributes")
  from = attr.get("from")
  to = attr.get("to")
  message = attr.get("message")
  from.upto(to) {|i| print "#{1}:", message, "\n"}
</scriptdef>

<target name="1to5">
  <repeat from="1" to="5" message="hello, world"/>
</target>

Another feature that had support in Ant 1.6 and is now present in 1.7 in a more robust way, is the concept of Antlibs. The Ant documentation notes that Ant uses antlibs to outsource optional tasks to, supplanting the existing optional Ant task framework. In a response to Artima's coverage of Ant 1.7's beta release, Loughran pointed out that:

Antlib support has been in ant1.6.5; we have just been refining things for Ant1.7.

By declaring an xmlns for a library, xmns:ac=antlib://net/sf/antcontrib;, Ant will autoload the library and make its tasks, types and macros available in the new namespace. This does mean that you have to deal with xmlns, but it stops problems with every app server stack providing a task called <deploy>. Now you can have <tomcat:deploy> next to <glassfish:deploy>.

If you are writing third party libraries for Ant, write and ship an antlib today just by adding a new descriptor, antlib.xml. And what is the format of that? It's a subset of Ant's own language, with <taskdef>, <typesef>, <presetdef> and <macrodef> being the current set of allowed tasks.

There's one problem with antlibs right now, is that all this automatic stuff works if the new lib dirs are on the classpath. For ant on the command line, you can use the -lib option, or stick stuff in ~/.ant/lib. For IDEs you need to force it on. Otherwise you need to use a typedef command, something like:

<typdef uri="antlib://net/sf/antcontrib" classpath="../lib/**/*.jar" />

Ant 1.7 introduces a resource framework as well. According to the Ant project documentation,

Some of the core Ant tasks such as <copy/> are now able to process not only file system resources but also zip entries, tar entries, paths, ... Resource collections group resources, and can be further combined with operators such as union and intersection. This can be extended by custom resources and custom tasks using resources.

What have you found to be the biggest previous Ant limitations in your projects?