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Subject: Maybe we should open up "depends" for all targets [again]
Date: Wed, 9 Dec 2009 22:35:06 +0100
Message-Id: <9AE74498-8186-4ACD-B981-074E0343CD46@hibnet.org>
To: Ant Developers List <dev@ant.apache.org>
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Well, the title of this mail is referencing [1], as announced I was =
thinking that we should, but after gathering my ideas and writing this =
email, I am not so sure.

So was introduced lately the concept of target group in Ant. I found it =
quite interesting as it would help writing sharable ant script, just as =
it is used in EasyAnt. I have a "build system" to maintain, shared =
between several different kind of project, simple java ones, webapp =
ones, flex app ones, flex lib ones, webservice ones, etc... All of these =
projects share the same release process and dependency management (Ivy =
of course ;) ). So I have a common-build.xml, a common-build-java.xml, a =
common-build-webapp.xml, a common-build-flex, etc...

There is some sort of inheritance between those build scripts: =
common-build-java.xml depends on common-build.xml, =
common-build-webapp.xml depends on common-build.java, etc... I have a =
"dist" target in common-build which expect things to be build before =
being published with Ivy. Then in common-build-java I have targets to =
build jars, and "dist" is overridden so "dist" depends on the targets =
that build jars:
<target name=3D"dist" depends=3D"jar,sources,common-build.dist" />
In common-build-webapp "dist" is overridden so it depends on the target =
that build a war. In common-build-flex "dist" is overridden so it =
depends on the target that build a swf.

And here comes the trouble: multi "inheritance" doesn't work well. If I =
have a webapp project that require some flex to be build, here comes the =
mess. Depending of the order of import of common-build-webapp.xml and =
common-build-flex.xml, either the flex will be published, either the =
war. I have to override "dist" in the project's build.xml so it =
explicitly call the build of the java, the swc and the war.

Here would help target group. If I define "dist" a target group, =
everything will then work fine. And I think that attaching a target to a =
target group is a way more proper than overriding targets, as it doesn't =
change any dependency declared between targets in common-build, it just =
adds new ones. If I focus on seeing an Ant build script as a DAG (direct =
acyclic graph), properly overriding a DAG seems to me just adding new =
edges and targets, not changing them. And many overriding (which we can =
see as multi inheritance) can apply without interacting. Adding targets =
to the dependency of another target (as target groups do) seems to be =
the way to go.

But using target groups expect me to know which part of the common-build =
can be extended. And I got every day some new need on some project that =
require a specific move in the common-build workflow.=20

On the other hand, if I today look closely to the 2200 lines of the =
common build files I maintain, I have very few targets that I need to be =
changed as a target group. And for most of them, they are already empty =
of tasks. The actual heavy customization required by some project, are =
done in the project itself. In the project itself I don't need to care =
about reusability or extension, so target overriding is fine.

To conclude, I don't know if opening up targets dependency can be that =
useful, I don't know if there is real use case where you want a =
spaghetti of target dependencies to be opened to a third party. Maybe it =
is better to explicit where target dependencies can be injected by using =
a special element, the target groups. Now thinking loud, maybe a simple =
attribute on target like dependencies=3D"public" would also fit ?

Nicolas

[1] =
http://old.nabble.com/Maybe-we-should-open-up-%22depends%22-for-all-target=
s-p20603861.html


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