I don't know if this has been discussed before, so please forgive me if
this is the case.
Many applications of Maven require the use of artifact variants (i.e.
the same version of an artifact built in different ways). Examples are
the native Mojo discussion from [1], which require different variants
for architecture/operating system/system (AOS), etc. Another example is
a debug, release or obfuscated build of a jar. I don't think these
variants can be defined in advance, because Maven cannot anticipate the
possible variants people will want to produce. Also, in native land, a
mere AOS will not suffice, since a library can be built with or without
zlib/png/jpeg/whatever support. In addition, it should be possible to
define alternatives if a variant is missing: If there's no debug build
in the repo, Maven should be able to automatically use the normal one,
or if there's no library optimized for the core2 processor, Maven
should automatically use the i686 version.
Therefor this proposal is for Maven to support a generic and flexible
variant system, inspired by Gentoo's USE variables [2]. A project would
declare a variant section in its pom, specifying what variants are
available, e.g.
<variant>
<atom>
<name>arch</name>
<description>System architecture</description>
<default>i386</default>
<options>
<option>
<value>i386</value>
<description>Generic i386
processor</description>
</option>
<option>
<value>i686</value>
<description>Generic i686
processor</description>
<alternatives>i386</alternatives>
</option>
</options>
</atom>
<atom>
<name>build</name>
<description>Build type</description>
<optional>true</optional>
<options>
<option>
<value>debug</value>
<description>Include debug
information</description>
</option>
<option>
<value>obfuscated</value>
<description>Obfuscate the code</description>
</option>
</options>
</atom>
</variant>
Option names and values should be unique within a project (no option
value "debug" can be used in other options than "build" in the
example). A project would also specify (e.g. via profiles) which
variant is active, on a global and on a per-dependency scale:
<use>
<option>
<name>arch</name>
<value>i686</value>
</option>
<option>
<name>build</name>
<value>debug</value>
</option>
</use>
When resolving artifacts, Maven checks if all required ooptions are
specified, and their values are valid. It then builds a variant
specifier ("i686-debug") and uses this to resolve the artifact. I'm not
sure if the classifier should be used for this, or if an additional
field should be introduced, though. If an optional option :) is
missing, it is ommited from the specifier (i.e. if "build" were
unspecified in the example, the variant specifier would be "i686").
Also, if the artifact cannot be found with the variant specifier, maven
tries omitting optional options. In the example, if the "i686-debug"
variant is not present, we try the "i686" variant. It also tries to use
alternatives, so in the example, we would also try "i386-debug" and
"i386". There should be a well defined order, of course, in which the
variants are tried.
Regards,
Jochen
[1] http://docs.codehaus.org/display/MAVEN/Support+for+other+languages
[2] http://www.gentoo.org/doc/en/handbook/handbook-x86.xml?part=2&chap=2
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