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From "Assaf Arkin" <ar...@intalio.com>
Subject OSGi support round two
Date Thu, 08 May 2008 02:10:53 GMT
I circulated a proposal on buildr-dev to make transitive dependencies and
version matching the focal point for Buildr 1.4.  Briefly it will allow you
to do something like this:

  compile.with foo

Which will download, install and compile with foo, but also all of foo's
dependencies.  Or if foo is another project, bring all of that project's
dependencies with it.  It will help keep buildfiles smaller by only
specifying the top packages it's using, and let Buildr figure out the rest.

Version matching means that foo can specify the package name but no version
number, and Buildr will attempt to match the most recent version for that
package.  Or you can specify some constraints, like >= 1.2 or != 1.3.


Right now we provide support for using and publishing packages, and it's
loosely based on the Maven 2 repository model.  We got the basics working,
just no support for transitive dependencies (other than an experimental
transitive method) and version matching.  To that we can also add OSGi
support, which means putting OSGi meta-data inside the packages (in
MANIFEST.MF) and reading it from them, in addition or instead of POM
(depending on source and target).

The problem is, doing both Maven and OSGi, and transitive dependencies and
version matching.  They don't like to co-exist, because OSGi and Maven
handle dependencies and version numbers differently.  Without going into too
much details, I'll illustrate with a simple example.

Let's say you have three versions of the same JAR: 1.2.0-RC2, 1.2.0-2 and
1.2.0-10.  The way Maven works, if the dependency just specifies "1.2", then
the most recent version is 1.2.0-10 because 10 is higher than 2 and numbers
are higher than alphanumeric.

The way OSGi (and most other packaging mechanisms) work, the last part of
the version number (qualifier) is just a string.  Being a string, the most
recent version is RC2, next is 2, and 10 is the oldest.  Developers who use
OSGi never run into this problem because they package everything using
versions like 1.2.0, 1.2.0-B45 or 1.2.0-R20080506.


If we pick one model and support it natively, it will get all the cool
features and we'll do best effort on the other model.  Say we pick OSGi,
then we'll have a local repository that looks like an OSGi repository, we'll
use OSGi version numbers, and make Maven artifacts look like OSGi bundles.
 In reverse, if we go with Maven, we keep the same local repository model,
etc

Some things I'm not sure we can even do, e.g. Maven snapshots mess with
OSGi, not sure we can support them if we do both, but OSGi has timestamped
version numbers that achieve the same thing.

So part two is which one of these two models we do natively for transitive
dependencies and version matching, and which one we fake to work like the
other?

Assaf

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