[jboss-dev-forums] [Design of JBoss Build System] - Re: Shared Parent POM for dependencyManagement

[ALRubinger]

Sat in on Freenode #maven for a bit tonight to see if I could sort some of this out.  Brian Fox of the Maven PMC was very helpful; I'll attach some relevant snippets below and a link to the full (edited for brevity) transcript at the end.

"dimitris at jboss.org" wrote : I'm surprised maven doesn't understand versioning (1.0.1 > 1.0.0)

"#maven" wrote : Brian: Will Maven know that 1.0.0 is less than 1.0.1?  -> yes.
  | Brian: the next thing: The fundamental problem is that maven has no idea that 1.0.1 is after 1.0.0  ... isn't true

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"adrian at jboss.org" wrote : Now which version of common-core gets used?
  | The answer is common-core:1.0.1 because jbossmc is first in the list

"#maven" wrote : Brian: "The answer is common-core:1.0.1 because jbossmc is first in the list" ... is also not true
  | ALR: "Closest wins", you mean.
  | Brian: it will use 1.0.1 because it's comparing at the same level
  | Brian: right. closest wins applies first

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Some additional insight that might help us:

"#maven" wrote : Brian: ok, so a few things that might not be known..
  | ALR: All ears.
  | Brian: dependencyManagement will apply to transitive dependencies since 2.0.6
  | Brian: so your common-core thing... if you put that in depMgt, all that first discussion goes away. it will be what you set (provided it's not defined anywhere else)

This is the main suggestion; use "dependencyManagement" more frequently than simple "dependency".

"#maven" wrote : Brian: the other thing to know, specifying a version like "1.0" is just a suggestion
  | Brian: technically the range is [,] with a recommendation on 1.0
  | Brian: so that means that [1.0] is very different.
  | Brian: so that's another way to influence the resolution. It's probably not the best way to do it though
  | ALR: Meaning, "[1.0]" is concrete.
  | ALR: And "1.0" is suggested?
  | Brian: correct
  | Brian: 1.0 means you want 1.0 but it lets maven have the flexibility to choose
  | Brian: [1.0]  means that's the only thing you can get. It _should_ either give you 1.0 or fail the build because there's a conflict
  | ALR: And what if we specify [1.0] somewhere, and [1.1] is somewhere else transitively?
  | Brian: it should fail
  | ALR: :)
  | Brian: i think this is a heavy handed approach that may make things worse
  | ALR: Brian: But it gives us fail-fast.
  | Brian: yes. You could also use the enforcer for that

So we can also look at locking down versions by placing them in brackets, forcing a version conflict failure if there's a problem.  Brian alludes to some problems here; I'm not sure in which way these might manifest themselves.

Also worth a look is the Enforcer Plugin http://maven.apache.org/plugins/maven-enforcer-plugin/.

Edited transcript: http://www.alrubinger.com/jboss/pound-maven.txt

S,
ALR

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