Ivy Informed Requirements & Design

[Mark R Maxey]

Hello,

Like many, I've been following Jigsaw from afar - mainly through the last 2
year's worth of JavaOne sessions.  Thank you for tackling this immense
problem.  While I'm just a nobody, I'd like to offer up some concepts for
your consideration.

Maven has a large footprint & you've rightly been letting it inform your
direction.  However, I would suggest a better alternative is Ivy.  Ivy is a
pure dependency analysis tool independent of Java.  It gives you the
dependency information and repository management while letting you do with
it what you want.

Here are a couple of Ivy features I think are relevant for Jigsaw:



CI & Build Promotion
Here is a common use case: multiple teams are working on multiple modules
concurrently.   Some teams want stability and rely on milestone releases.
Some teams want to rely on integration / snapshot releases.  This could
happen, for example, in the JDK where a few related modules are undergoing
changes by different teams for different reasons simultaneously.

My concern is that the manual update of the version number in the
module-info.java file is too cumbersome.  Maven snapshots aren't so bad
since it is just a static suffix, i.e., "-SNAPSHOT", that would be
infrequently updated.  However, I prefer Ivy's unique one-up numbers /
timestamps because of the flexibility to rollback to previous builds.

Build promotion also needs to be considered.  Hudson/Jenkins is often used
to promote an integration / snapshot build to a milestone release and a
milestone to a GA release. Ivy & Maven can also do this.  All of these
involve changing the version numbers on lots of modules.

It seems to me that Jigsaw needs some way of easily modifying a module's
version without rebuilding it.  I'd like to hear your thoughts on how this
lifecycle would play out under Jigsaw.



Repositories & Local Caches
It is great that you are looking to integrate with Maven repositories.
Here are a few related tidbits from Ivy applicable to Jigsaw:

   Ivy supports a variety of resolvers for different types of artifact
   repositories, e.g., URL based, file based, SSH, etc.  It can also chain
   these together in ways that allow you to specify search order.
   You should check out the work Gradle is doing on dependency caches.  I'm
   betting you're going to run into the same problems with Java modules.
   Ivy also supports a sophisticated set of conflict resolution policies.
   You can tell Ivy how to extract the GAVC out of the file path.  This
   allows for a more customizable repository directory structure.



I understand these are advanced concepts that probably aren't targeted for
your initial release.  Many may be tasks to leave to 3rd party tool
vendors.   I simply suggest that you let them inform your roadmap forward.


Thanks!
Mark Maxey