Friday, 22 August 2008

XML is not the build system you're looking for

Last night I attended a Skills Matter "In the Brain" session on Gant given by Russel Winder at their offices in London:

"I will be doing an "In the Brain" session on Gant (The Groovy way of scripting Ant tasks) on Thursday 2008-08-21 18:30. This will happen at Skills Matter, 1 Seckford Street, London EC1R 0BE, UK. The Skills Matter announcement is here.

"As part of this session I am going to undertake "The Gant Challenge". The idea is for people to bring small examples of Ant (or other) builds that really irritate them so we can create the Gant version live and show that Gant can do the business where Ant often cannot.

"If you are in the area then, feel free to drop by -- though you need to register beforehand so some forethought is needed. This is planned as a 90min session after which things move to a local hostelry. "

90 minutes soon became 120, but it was very informative and very interesting. The basic gist is that, although Ant is a powerful build system, XML is not the best way of specifying the steps in a build process. Chiefly because it is verbose, not human readable as a programming language can be and it's difficult to do common programming tasks such as if, for, foreach, switch, etc.

Gant is written in Groovy and sits on top of Ant giving an extra layer of indirection to existing Ant tasks. I had only heard of Groovy before and never used it, so Russel spent a little time showing me, and the others, simple Groovy programs and how to run them. I was also introduced to a new concept known as closures.

Gant build scripts are also Groovy programs and bring with them all the power of the Groovy programming language, so it is possible to do just about anything and have a more readable, less verbose methos of describing buils steps:

includeTargets << gant.targets.Clean
cleanPattern << [ '**/*~' , '**/*.bak' ]
cleanDirectory << 'build'

target ( stuff : 'A target to do some stuff.' ) {
println ( 'Stuff' )
depends ( clean )
echo ( message : 'A default message from Ant.' )
otherStuff ( )

target ( otherStuff : 'A target to do some other stuff' ) {
println ( 'OtherStuff' )
echo ( message : 'Another message from Ant.' )
clean ( )

setDefaultTarget ( stuff )

This was all very attractive to me, despite needing to add yet another tool to our build environment installation. The only real snag is that currently, it appears, Gant does not support custom Ant tasks. So there is no way we could use it with Axis or Emma for example. Russel has asked me to make a Jira entry to this effect and I will later today.

Overall it was a very interesting, informative and enjoyable session. I always enjoy anything that Russel is involved in, he has a lot of Charisma. It was certainly worth the five hour round trip from Norwich for the evening.