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From org.apache.maven.u...@io7m.com
Subject Re: Defining a property designed to be overridden?
Date Thu, 02 Mar 2017 17:02:19 GMT
On 2017-03-02T10:29:30 -0600
Curtis Rueden <ctrueden@wisc.edu> wrote:

> > it seems that I can only require that the XML elements be overridden
> > in *all* descendant POMs, and this introduces too much redundancy.  
> 
> I see.
> 
> Would it be sufficient if the requireElements rule had a multiModule flag
> which, if set, green-lighted the build when the stated elements are defined
> in the local parent POM? This feature would assume you are using the
> aggregator==parent scheme, and follow the <relativePath> declared in the
> <parent> of each POM. If it finds a POM there, it would parse it and then
> check for the required elements in _that_ POM instead of the initial one.
> And do this recursively, in case you have a multi-layered multi-module
> build.
> 
> The downside of this approach: modules of a project would only build if the
> parent is available locally. E.g.: if you try to build one module of a
> multi-module build which has been physically disconnected from its parent
> (e.g., a partial SVN checkout), the enforcer would fail because it would
> not find the local parent POM to validate against. One can also imagine
> various "aggegator != parent" organizations where the parent is not
> available locally, which would also all fail to support this scheme.
> 

I'd need to think a bit more about it, but I personally dislike
relativePath and have never used it (across hundreds of projects),
pretty much for the sorts of reasons you've described. Hard-coding
paths that represent links to other modules seems like a horrendously
bad idea.

I've written a few plugins, but I'm not intimately familiar with the
Maven API: Shouldn't it be possible to recursively retrieve the parent
POMs from the reactor (and failing that, the local and remote
repositories) within the plugin? That would remove the need for
<relativePath>.

If that is possible, then I think the pseudocode is:

  let root(p) be the root POM of project p
  let parent(p) be the parent of p
  let definesElements(p) return true if p defines the required elements

  Project q = p
  while (!done) {
    if (q == root(p)) {
      throw RequiredElementsMissing()
    }

    if (definesElements(q)) {
      done = true
    }

    q = parent(p)
  }

This feels like it would achieve what I need with only minimal
assumptions about the hierarchy of projects.

M

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