Stefan Bodewig's Weblog

Wed, 06. Jan 2010

Antoine Levy-Lambert has recently built the first release candidate for Ant 1.8.0 and called for a vote, so we should be close to the first Ant release since eighteen months. This release mostly brings enhancements and bug fixes to many tasks and types (this is the real strength of Ant IMHO) but there also are a few core changes, the full list is here.

My personal top five changes (I know there are six items, but the first one doesn't count ;-):

More than 275 fixed Bugzilla issues.
Lexically scoped local properties, i.e. properties that are only defined inside a target, sequential block or similar environment. This is very useful inside of <macrodef>s where a macro can now define a temporary property that will disappear once the task has finished.
<import> can now import from any file- or URL-providing resource - this includes <javaresource>. This means <import> can read build file snippets from JARs or fixed server URLs. There are several other improvements in the area of import.
Various improvements to the directory scanning code that help with symbolic link cycles (as can be found on MacOS X Java installations for example) and improve scanning performance. For big directory trees the improvement is dramatic.
The way developers can extend Ant's property expansion algorithm has been rewritten (breaking the older API) to be easier to use a be more powerful. The whole local properties mechanism is implemented using that API and could be implemented in a separate library without changes in Ant's core. Things like the yet-to-be-released props Antlib can now provide often required "scripty" fuctions without touching Ant itself.
At the same time the if and unless attributes have been rewritten to do the expected thing if applied to a property expansion (i.e. if="${foo}" will mean "yes, do it" if ${foo} expands to true, in Ant 1.7.1 it would mean "no" unless a property named "true" existed). This adds "testing conditions" as a new use-case to property expansion.

A new top-level element <extension-point> assists in writing re-usable build files that are meant to be imported. <extension-point> has a name and a dependency-list like <target> and can be used like a <target> from the command line or a dependy-list but the importing build file can add targets to the <extension-point>'s depends list.
In Ant 1.7.1 one would use something like

imported.xml:
<project name="imported"...>
  ...
  <target name="setup">
    ...
  </target>
  <target name="compile" depends="setup">
    ...
  </target>
</project>

importing.xml
<project ...>
  ...
  <import file="imported.xml">
  <target name="setup" depends="imported.setup">
    ... stuff that should happen before compile ...
  </target>
</project>

to define a pre-compilation stage by target overriding. With some planning it can be improved to

imported.xml:
<project name="imported"...>
  ...
  <target name="setup">
    ...
  </target>
  <target name="ready-to-compile" depends="setup"/>
  <target name="compile" depends="ready-to-compile">
    ...
  </target>
</project>

importing.xml
<project ...>
  ...
  <import file="imported.xml">
  <target name="ready-to-compile" depends="imported.ready-to-compile">
    ... stuff that should happen before compile ...
  </target>
</project>

In Ant 1.8.0 one would write this as

imported.xml:
<project name="imported"...>
  ...
  <target name="setup">
    ...
  </target>
  <extension-point name="ready-to-compile" depends="setup"/>
  <target name="compile" depends="ready-to-compile">
    ...
  </target>
</project>

importing.xml
<project ...>
  ...
  <import file="imported.xml">
  <target name="pre-compile" extensionOf="ready-to-compile">
    ... stuff that should happen before compile ...
  </target>
</project>

and the pre-compile target was added to ready-to-compile dependeny-list.

extension-point and some changes in import and its new cousin include have been inspired by Easyant which can now use an un-patched version of Ant together with a custom ProjectHelper to create a build system quite different from Ant's original ideas. ProjectHelper is the mechanism that allowed me to sketch JavaFront or Nicolas Lalevée to write GroovyFront which lets you write build files in Groovy.

path: /en/Apache/Ant | #