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From Grzegorz Kossakowski <>
Subject Discussion about Maven
Date Sun, 03 Jun 2007 19:45:13 GMT

I talked with Maven developers on IRC today. I asked for the problem[1] we are currently facing.
They give me interesting advices and 
thoughts that may interest you. I paste cleaned up log file of the talk:

[15:32:18] <grek>	hi, I'm Grzegorz Kossakowski, a member of PMC of Apache Cocoon
[15:33:07] <grek>	I'm looking for help with Maven issues that seem to stop us from releasing
artifacts :(
[15:34:28] <grek>	being more precise, we are affected by this issue very badly:
[15:35:14] <grek>	Is there anyone eager to help?
[16:32:14] <wsmoak>	grek: it's marked for 2.0.4. can you confirm it also happens with
2.0.6 ?
[16:33:31] <wsmoak>	and... after a quick read, can you duplicate repository elements
where you need them, so you can proceed with the release ?
[16:34:01] <grek>	wsmoak: yes, it happens with 2.0.6
[16:35:22] <grek>	wsmoak: yes, we can do this (and done it before) but we have to ask
our *users* to put repository elements in *their* poms
[16:35:46] <grek>	I'll give you more links explaining the situation
[16:36:03] <wsmoak>	so it's not just a problem at release time?
[16:36:45] <wsmoak>	why can't the artifacts in that other repo be put in the central
[16:37:30] <grek>	they are waiting in your JIRA ready for upload AFAIR ;)
^^^^^^^^^^^^^^^^^^ here I confused commons-jci with xreporter artifacts that waited for upload
[16:38:56] <grek>	but the problem still persists, Cocoon has _lots_ of dependencies,
some of the stuff is just in between of conversion to 
the Maven
[16:39:05] <maxb>	Isn't central supposed to be selfcontained anyway?
[16:39:30] <grek>	what do you mean by self-contained?
[16:39:40] <wsmoak>	ok. assuming no problems with the upload bundle and carlos gets
them into central, is there still a problem?
[16:39:48] <jvanzyl>	if you mean a complete transitive closure, yes but we don't have
a way to check just yet
[16:40:50] <wsmoak>	poms in the central repo shouldn't define additional repositories
[16:41:14] <wsmoak>	it makes users in corporate environments nervous to see Maven trying
to download from random places
[16:41:28] <grek>	hmmm, good point
[16:41:47] <grek>	let me explain our situation and policy at Apache Cocoon
[16:42:46] <jvanzyl>	wsmoak: that would be a good rule to check for upload bundles actually
[16:42:58] <jvanzyl>	no external repository definitions
[16:43:03] 	 * jvanzyl makes a note
[16:43:24] <grek>	if we want release something as RC (or final) we have to make sure
that we do not depend on snapshot versions and all our 
dependencies are at central
[16:44:22] <grek>	however, we also release milestones which can depend on snapshots
and can define it's own repositories (for those 
unreleased artifacts)
[16:45:39] <grek>	and that's the case now, we want to release a milestone of our own
Maven plug-in so users can test it and report back if 
everything works
[16:45:50] <wsmoak>	grek:  "release" meaning you want these milestones in the central
[16:46:08] <grek>	wsmoak: yes
[16:46:28] <wsmoak>	then snapshots simply aren't allowed... you'll have to release milestones
of your dependencies.
[16:46:49] <wsmoak>	but these aren't really "users" you're asking to help test, are
they?  they're more involved than that.
[16:47:16] <wsmoak>	what's wrong with staging it on
and asking them to add a repository to their 
settings.xml to test ?
[16:47:49] <grek>	wsmoak: we have done exactly what you suggest
[16:48:08] <grek>	wait a minute, I'll provide links
[16:48:48] <wsmoak>	(btw, the Struts PMC has the same policy... snapshot dependencies
are allowed in alpha releases.)
[16:49:35] <grek> and my answers
in this thread
[16:50:11] <grek> <- here
is the user affected by the MNG-2743
[16:55:13] <wsmoak>	ok.  sounds like you're waiting on carlos to close a MAVENUPLOAD
[16:56:18] <BrianFox>	grek: you can use the enforcer plugin to make sure people are
using 2.0.6 to build cocoon 2.2
[16:56:30] <wsmoak>	Kenney's 2006-01-07 comment on COCOON-1975 sounds right on (and
that issue is closed).
[16:57:03] <grek>	BrianFox: we use it already, but will it work if someone just uses
the artifacts but does not build them?
[16:58:26] <BrianFox>	no. I just saw you comment in that thread asking Joakim which
version he used. With Enforcer you would know ;-)
[16:59:11] <BrianFox>	the prerequisites would affect "users" of plugins if that's what
you mean
[17:00:31] <grek>	we require Maven 2.0.6 not only for plug-ins/building but also when
people just depend on our artifacts, it's due to 
dependencyManagment fixed in 2.0.6
[17:00:56] <BrianFox>	i see
[17:01:27] <wsmoak>	I don't think you can force them to build their own projects with
[17:01:44] <wsmoak>	you can keep them from using your plugins *unless* they are on 2.0.6,
with the prerequisite element.
[17:01:52] <BrianFox>	right
[17:02:00] <grek>	I see
[17:02:17] <grek>	so we will have to put big, fat warnings everywhere to use 2.0.6
[17:02:33] <wsmoak>	so at this point it's just education-- encourage them to upgrade
to 2.0.6 and point them at the docs on how to prepare 
for upgrade.
[17:03:07] <grek>	yeah, but the original problem still persists I think
[17:03:37] <wsmoak>	true, but it's not even marked with a fix-for version, so I don't
think waiting is really an option
[17:04:06] <grek>	and I just realized that the dependency we are talking about here
(commons-jci-fam) does not wait for upload, I confused 
it with other artifacts waiting for upload
[17:05:40] <grek>	wsmoak: I'm aware of that you'll not fix it tomorrow but we really
have to find a solution, we have a lot of depdencencies 
for which we have to prepare poms and upload them
[17:06:36] <grek>	waiting for each upload is not an option for us when we talk about
milestone release, it happens to slowly I guess
[17:07:11] <wsmoak>	are these your own artifacts we're talking about ?
[17:08:25] <grek>	no, in this particular case it's a commons-jci-fam that is not a part
of Cocoon, obviously
[17:09:44] 	 * wsmoak will be back in ~30 min
[17:24:48] <grek>	after thinking about it for a while I'm starting to realize that you
are right and we should really push other folks to 
upload their artifacts to central
[17:29:02] <grek>	on the other hand, the issue I'm constantly referring to does not
allow us to make internal (not published on central) 
alpha/milestone releases
[17:29:44] <grek>	that could depend on unreleased stuff, of course
[17:32:14] <esm>	grek: totally unrelated to your issue - i like your solution using
an alternate testing-cocoon-settings.xml file
[17:33:21] <grek>	esm: thanks :)
[17:34:05] <esm>	having uses rm -rf ~/.m2/repository doesn't make sense and now I know
a better way :-)
[17:36:09] <grek>	esm: yeah, and if you work with mutliple projects you can test one
with empty, separate local repository and after testing 
continue the development of the another one without having to re-download the dependencies
[17:36:32] 	 * esm nods


[17:44:22] <grek>	wsmoak: can you give us an advice on making this internal releases
I talked above?
[17:46:12] <grek>	in order to gather some early feedback from users we really need to
make those releases that depend on snapshots or 
released artifacts not available at central yet and I guess that we would be fine if Maven
just been doing what we expect from him to do
[17:46:45] <wsmoak>	grek: seems like you're mostly there.  "release" your milestone,
but deploy it to a staging area and have users add that 
repo to their settings.xml
[17:47:29] <wsmoak>	since you can't release with snapshot dependencies, push the other
projects to release to central.
[17:48:09] <grek>	starts to make sense
[17:49:18] <grek>	if so, why Maven allows to define repositories at pom level if they
do not work and are discouraged in a fact?
[17:58:55] <jvanzyl>	a mistake that will be corrected in 2.1
[17:59:14] <jvanzyl>	and you just won't be able to put them in a POM
[17:59:25] <jvanzyl>	but that's a big change so we can't do it in 2.0.x
[17:59:30] <grek>	ah I see
[17:59:37] <jvanzyl>	but you can still abide by the practice of doing what is in 2.1
[17:59:48] <jvanzyl>	define all your repos up front in a shared settings.xml
[18:00:08] <jvanzyl>	so that your POMs don't change when you use different repos underneath
for whatever reason
[18:00:21] <jvanzyl>	your infrastructure requirements should not be passed on to your
[18:00:32] <grek>	yes, I totally agree
[18:01:48] <grek>	I'm only disappointed that you don't document this good practices
and don't refer to them whenever someone has the problem 
similar to our
[18:04:03] <grek>	jvanzyl: one more thing if we have this shared settings file how we
can tell Maven that it will should use that file while 
building Cocoon?
[18:04:37] <grek>	I guess that people will not be happy with -s option or replacing
their default settings file
[18:06:27] <jvanzyl>	we could do something like map repository settings to a groupId
[18:06:40] <jvanzyl>	so you would have them in your settings for work on cocoon, haven't
quite figured it out
[18:06:46] <wsmoak>	grek:  I use different sets of repos by putting them all in one
settings.xml, inside profiles.
[18:07:00] <jvanzyl>	so we'll try to make it convenient
[18:07:10] <jvanzyl>	but defining repos in POMs was a definite mistake
[18:07:20] <kenney>	maybe it's an idea to export a part of the settings, like the profile,
as a 'project settings' artifact
[18:07:59] <kenney>	it would contain properties needed by the projects to build (like
j2ee app locations or database info), and the 
repositories required to build/use that project
[18:08:14] <grek>	wsmoak: but then you still have to define which profile to use with
-P option, right?
[18:08:36] <kenney>	grek: not necesarily, you can active a profile in any pom
[18:08:36] <wsmoak>	yes... these are your project developers we're talking about, right
[18:08:39] <jvanzyl>	yes, we'll make it easier
[18:08:57] <jvanzyl>	no reason we can't generally map some settings for a groupId
[18:09:01] <wsmoak>	there are many ways to activate a profile, as long as all of you
agree on some conventions.
[18:09:11] <jvanzyl>	so all your junk for org.apache.cocoon gets picked up
[18:10:09] <esm>	grek: we use this at Pluto:
[18:10:21] <esm>	alluding to what wsmoak said
[18:10:31] <esm>	just a profile devs activate to test builds, etc
[18:10:43] <grek>	activating profiles that contain infrastructure info in poms does
not seem to be a neat idea, still you have your poms 
bloated with infrastructure stuff
[18:11:20] <esm>	we ask the devs to modify ~/.m2/settings.xml instead of putting stuff
[18:11:21] <grek>	jvanzyl: what about simplest solution possible: searching for settings.xml
file along pom.xml ?
[18:11:52] <kenney>	grek: there's already profiles.xml that serves that purpose
[18:11:52] <jvanzyl>	esm: right that's what generally happens
[18:12:30] <grek>	kenney: any documentation?
[18:12:38] <jvanzyl>	grek: i've really just started trying to collect everything i've
found working at big places with 500+ devs
[18:12:48] <kenney>	grek: euh, ? :)
[18:12:59] <jvanzyl>	and i'm about to start another one and they've agreed to let me
publish the information
[18:13:25] <grek>	kenney: I was asking if profiles.xml is somewhere documented, but
I hope it really is :)
[18:13:31] <kenney>
[18:14:42] <grek>	jvanzyl: does it mean that we'll see your conclusions on dev list
[18:15:13] <grek>	kenney: thanks, starting to read this
[18:15:32] <jvanzyl>	no, i'm just starting a project that will probably last a year
[18:15:37] <jvanzyl>	but as i go i will
[18:15:46] <jvanzyl>	first deliverable is in 8 weeks so probably around then
[18:16:06] <jvanzyl>	but 2.1 will move along quickly after next week
[18:16:41] <grek>	I'm getting lost here, do you want to say that you are going to propose
replacement for Maven?
[18:16:47] <jvanzyl>	no
[18:17:13] <jvanzyl>	this is a client project where i'm using maven
[18:17:18] <grek>	ah, I see
[18:17:37] <grek>	and why do you mean that 2.1 will move along quickly?
[18:18:43] <grek>	from lurking at dev I had an impression that 2.1 is not going to be
released soon (I mean, a year period)
[18:19:16] <wsmoak>	it can look that way, then jvanzyl stays up for three days straight
and suddenly all the bugs are closed ;)
[18:19:42] <grek>	wsmoak: heheh ;)
[18:19:57] <jvanzyl>	yah, it's not moved in a while as we try to bridge 2.0.x with 2.1.x
so there's no shock
[18:20:03] <jvanzyl>	all 2.0.x stuff will run in 2.1.x
[18:20:26] <jvanzyl>	it's actually quite stable
[18:20:29] <wsmoak>	... except stuff that defines repositories in the pom ?  if it's
no longer allowed, how's that going to work?
[18:20:58] <jvanzyl>	pom readers used keyed of the version of the POM
[18:21:09] <wsmoak>	ah, the model version
[18:21:16] <jvanzyl>	that will be harder
[18:21:19] <jvanzyl>	the plugins are easier
[18:22:08] <grek>	if I can have a huble request... could you write really good docs
explaining what and why was changed and how to migrate?
[18:23:07] <grek>	Cocoon has suffered for long time because of lack of migration guides
and I think Maven should not repeat others' mistakes
[18:23:19] <jvanzyl>
[18:23:52] <jvanzyl>	all here:
[18:23:58] <jvanzyl>
[18:24:06] <jvanzyl>	those top three is where you'll see everything
[18:25:06] <esm>	btw the docs for upgrading to 2.0.6 were nice - the dependencyManagment
[18:25:16] <grek>	great, I'm happy to hear these all good news
[18:25:20] <grek>	yes, I agree with esm


[18:49:08] <grek>	argh, I'm having some problems with internet connection
[18:49:29] <kenney>	is there a plugin out there that can check wheter something is done
with the exception in a catch clause?
[18:49:42] <kenney>	esp. stuff like this: catch ( Exception e ) { throw new FooException("bar!");
[18:50:06] <grek>	it's sign to go offline, so I would like to thank all of you for the
information and tips you have given to me
[18:50:19] <grek>	thanks! :)
[18:50:36] <esm>	kenney: can you configure a PMD rule to find those?
[18:50:43] <esm>	grek: ttyl
[18:50:46] <kenney>	hm, maybe
[18:54:10] <grek>	ok, it's time leave, thanks again for your help, have a nice evening,

Ok, it's time for conclusions:
1. Defining repositories is considered harmful and we should get rid of all of them
2. I think that we should move repository information to profiles.xml, but it's a subject
of discussion
3. We cannot put milestones that depend on snapshot versions on central. It means that we
can't upload following artifacts:

But we still can have it in our staging repository and ask our early testers to customize
their settings.xml for or create new one. I don't 
see it as a big deal really, but I'm thinking about other implications. Especially, not all
milestones will be available on the central, 
there will be "gap" in version number. On the other hand, milestones are just our internal
releases and I think we can live with these gaps.

What do you think?

Grzegorz Kossakowski

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