Le ven. 9 juin 2023 à 08:59, Hervé Boutemy <herve.bout...@free.fr> a écrit :
> adding a new POM element in build POM was supposed to be something for > Maven 5 > and to trigger a POM 5 version, to make clear that we are leaving the > Maven 3 > space (that uses POM version 4, hence the need for version clarification > between Maven and it POM model version) > > if we enter that space before having released Maven 4, we're adding more > complexity: do you really want to work on Maven 5 now? > > > another aspect: > do we want to have this new improvement only for Maven 4/5 or also have it > for > Maven 3.9? > in Maven 3.9, such little enhancement were implemented as XML attributes > Fwiw, if I reduce the diff between the XSD generated with 3.0 and with 3.9.x, I end up with the following diff https://gist.github.com/gnodet/f8dfd3206ebf55d6e4610a25e683120b So, you're right, no new elements have been introduced. A few attributes added, one element removed. However I really don't understand how adding an attribute vs an element makes the POM more compatible. Our own generated parser will reject any unknown new attribute the same way as an unknown element (that's for any maven 3.x version). Here's what happen if I use a maven 3.2.5 to read a POM with an element that has been introduced later: https://gist.github.com/gnodet/35a3ad4d449e586dc282c08eacc82ed0 So I'm not really buying the argument about attribute / element at this point. If that could be clarified, it would be nice ! So I think the question comes down to: do we prefer modifying/overwriting the schema as we did in the past or do we prefer cleanly versioning it. In both cases, I think we need to keep it compatible, i.e. only add elements/attributes. The first option is much easier to implement: just do nothing as we did in the past, but this has the drawback of not giving people/tools much warning or information about possible changes. We simply overwrite the schema from the web site with the latest one at each release, hoping that tools will not see the change and that they don't really cache the schema (in case you really need the latest). The other option is to more properly version the schema. This would need additional code if we want to correctly detect which version is the lower version needed to correctly write a given POM. But even for doc changes, I think it may be preferable to micro version the schemas. The scm.child.xxx attributes that were added are not meaningful for the consumer afaik: they are used for build time and for doc, when you use an artifact as a dependency (i.e. on the consumer side), those attributes won't be used. So from a consumer POV, they don't carry any semantics and can safely be silently discarded. This is also the case for this new priority attribute, as it only affects the current project or child projects. In that sense this new feature could just be silently added to the schema as previous things, so I'm fine with not versioning the schema now if that's the consensus. The problem (and that's really something we need to fix), is that we don't any real difference between the build POM and the consumer POM schemas. We also don't make a real difference between consuming as a bom / dependency / plugin, and consuming as a parent. Both cases are really different, as the first one could strip out most of the <build> section. One possibility would be to more formerly identify those 3 use cases (build on file system, consuming as a dependency and consuming as a child). Note that we're currently lacking a build schema, so that when using the build/consumer POM, your build schema cannot be validated, as it's missing some elements. One possibility would be to simply make some elements non mandatory in the schema. The model validation would check those anyway. For the consumer POM for non "pom" packaging, would it make sense to streamline the uploaded POM even more: i.e. remove all build stuff from it (pluginRepositories, pluginManagent, plugins, reporting, etc...) or is there any use case for keeping those ? We could attach the build pom (i.e. we're currently switching the POM when installing/deploying it, but it's attached with a "consumer" classifier during the build). Guillaume > > and of course, independently from this XML mapping and version details, > there > is the question to be seriously discussed about the feature itself: is > this > opportunity of introducing the "priority" field something we want (that > reuses > an implementation that is de-facto already existing internally for a long > time, it just exposes it) > > Regards, > > Hervé > > > Le jeudi 8 juin 2023, 22:56:27 CEST Guillaume Nodet a écrit : > > While working on an issue [1], I've raised a PR [2] which is adding an > xml > > element to the POM. So I raised the model version to 4.2.0. My > > understanding is that the build/consumer POM feature [3] was created so > > that we could keep compatibility. This is clearly indicated in the wiki > > page: "Maven is stuck on POM v4 for a long time now, because changing > the > > POM version and publishing artifacts on Maven Central with this new model > > would break consumers using either older Maven versions or other build > > tools (that use POM v4 as a compatibility format)." > > > > However, I think this axiom is false. What happens, is that all maven > > versions are perfectly capable of consuming any model when used as a BOM > / > > dependency / plugin, as the parser simply ignores any unknown attribute > or > > element. I can install a jar with the 4.2.0 model and consume it with > any > > 3.x version without any problem. The only issue is when using that > project > > as a parent, in which case, the validation is strict and fails with the > > 4.2.0 model. > > > > So, saying that "new model would break consumers using [...] older Maven > > versions" is just wrong, as they work perfectly when consuming the POM as > > dependencies. I can create a small git repo if you want to experiment, > but > > that has been first checked by @cstamas, then double checked by myself. > > > > Now, the discussion is whether we want to allow modifications to the POM > > model and support new versions of it. I think this would be quite safe, > > provided that there's no incompatible changes, i.e. it's only adding new > > elements/attributes. > > I don't think this goes against the build/consumer feature, as I think > the > > main benefit of this feature is to allow default values using sane > > conventions (mainly the project layout on the file system, which is not > > available anymore in the remote repository, so this data has to be > present > > for consumers). > > > > So, the question: should we go ahead and allow introducing newer POM > models > > to bring in a few features that have been delayed for a long time because > > the assumption was that the model could never change ? One possibility > to > > minimize the disruption would be to have a smart POM writer : i.e. it > could > > transform the POM to a 4.0.0 model if no new features are actually used, > so > > that only projects actually using the newly introduced features would > > actually use the 4.x pom version. > > > > Guillaume > > > > [1] https://issues.apache.org/jira/browse/MNG-7804 > > [2] https://github.com/apache/maven/pull/1147 > > [3] > https://cwiki.apache.org/confluence/display/MAVEN/Build+vs+Consumer+POM > > > > > > --------------------------------------------------------------------- > To unsubscribe, e-mail: dev-unsubscr...@maven.apache.org > For additional commands, e-mail: dev-h...@maven.apache.org > > -- ------------------------ Guillaume Nodet
