Hi,
One of my long standing wishes has made it to the master branch of Maven: the
support for build/consumer pom.
With this we can finally start improving the pom without breaking the Maven eco
system.
Up until now the pom.xml has been distributed (installed/deployed) as is to
both local and remote repositories.
The good thing is that is it fast and there is no magic.
However, it sometimes implies adding redundant information and it also blocks
any chance of improvement for Maven
The challenge is to make it possible to have an locally an improved "build" pom
while distributing a model 4.0.0 compatible "consumer" pom.
The whole architecture of Maven was built upon an immutable pom.xml, so it took
a while to split this, but I managed to solve this.
And to confirm that it works, some transformations have been added for the next
Maven release
The local pom it still model 4.0.0 compatible, but some redundant elements are
not required anymore.
- in case the <parent/> is located at its relativePath (default: ../pom.xml),
the version can be removed. groupId and artifactId are still required to ensure
it is being matched with the right parent.
- dependencies that are part of the reactor don't need a version anymore
These are implemented steps to get from the file model to the raw model, where
the required versions are added.
When distributing the pom, the previous transformations are done, but also:
- cifriendly placeholders in versions (${sha1}, ${revision}, ${changelist})
will be resolved.
- <modules> from <project> will be removed
- <relativePath> from <parent> will be removed
These cleanups are context aware, if they appear in some configuration, they
won't be touched.
One of our integration-tests[1] demonstrates how new poms in a multimodule
project might look like.
Even though the latter steps look quite small (removing elements with relative
paths), it should give us enough feedback about the whole process.
The status is that it is ready to be embedded in supporting tools like IDEs.
We should give them time to work on this and share feedback.
It might require some adjustments in Maven to improve user experience.
In the meantime we need to work on plugins that will have impact by these
changes.
Most significant is are signing maven plugins such as the maven-gpg-plugin,
which needs to work with the distributed pom instead of the local pom.
Also all packaging plugin that can include the pom.xml and pom.properties in
their archive should switch to the distributed pom.
The maven-shade-plugin was marked as well, but at first glance this looks fine.
In the end all our plugins must be verified, just to be sure.
So there's enough to work on.
In general I avoid giving timelines about how fast a new release will be
available.
Due to the overhead, the small amount of available time of the few volunteers
working on Maven, I prefer to have a worth set of changes.
In this case the impact of the changes can be huge, and I want to have enough
faith that we won't introduce irreversible mistakes.
Don't expect a new official release in the 3 next months, however we might have
alpha or beta releases.
There is a wiki page that explains this topic in more detail[2]
It is still a draft, as there are still parts where we need to reach consensus.
This page is intended as a base for discussions by Maven developers, users and
related projects, such as IDEs, Repository Managers, CI Servers, etc.
Looking forward for any feedback,
Robert Scholte
Apache Maven project
[1]
https://github.com/apache/maven-integration-testing/tree/master/core-it-suite/src/test/resources/mng-6656-buildconsumer
[2] https://cwiki.apache.org/confluence/display/MAVEN/Build+vs+Consumer+POM
