Hi Jason, Jason van Zyl wrote on Thursday, April 26, 2007 1:52 PM:
> On 26 Apr 07, at 6:05 AM 26 Apr 07, Arik Kfir wrote: > >> IMO, if the project claims to be backwards-compatible, then it should >> include the older classes. If they can exist side-by-side, there >> should be no issue. >> > > I don't think you can force every project to do this, and I think > that users would intuitively users expect that two versions of, say, > junit that are declared should show up. So what Jorg is > asking for is > not unreasonable and I'm really just trying to think of the > repercussions of allowing multiple versions i.e. do we have any > plugins keying off special versions of classes: the surefire plugin > for example. I think the JMock example is perfectly valid and is > something that could be addressed in 2.1 but here is my concern and > generally why we took the strategy of not allowing this to begin with: > > The classpath order is now derived from the order of the listing of > the dependencies. So in a particular project what if one case > requires class C1 from version 1.0 of JMock, and another case that > requires class C1 from version 2.0 of JMock? How are you going to > satisfy those two conditions and in general how are you going to > protect against classes that have the same name in different > versions > of the JAR where both are needed?. When this case arises you are > going to need a form of paritioning, yes? Well, Nat *is* a bright guy :) Although both versions share the same root package, they have no overlap in claases itself. It is the perfect case for a "slotted" artifact - both development branches can be used at same time. And they continue development in both. > Because you're > going to end > up requiring features from the new version which means using the > newer classes. If you are going to need some way to say "for this > group of tests use this version of JMock" and "for this other set of > tests use that version of JMock" then you've gotten yourself into a > case that cannot be satisfied easy. > > If projects could guaranteed that version N and the next major > upgrade guaranteed compatibility of the intersection of classes in > the different versions and additions were a superset of that then > adding both versions would be fine. But this is often not the case > and you get into real problems because the general rule for major > version number changes is that the API can break which means that a > class in 2.0 could be significantly different in API and structure > then its equivalent in 1.0. If the project does not play nice, Maven cannot help you. Look at the ASM nightmare. Plain CGLIB 2.x depends on ASM 1.x while popular packages like Hibernate-3 or Groovy use ASM 2.x. Unfortunately both ASM versions are not compatible and either you break the artifacts depending on CGLIB or the other ones. CGLIB solved this by the -nodep artifact that contains the necessary ASM 1.x classes with a different package name, but, alas, this is also quite a hack. However, this mess was caused by the ASM project team itself. > In Ant you might create a separate classpath with different JARs and > apply that to a different set of classes. We avoid this by simply > saying, this is just too complicated and take your tests, create > another module that uses the new version of JMock and be done with it. > > What is easier: creating a separate module which has this > simple rule > of allowing only one version of a dependency and using all the same > patterns of every other type of Maven module. Or allow multiple > versions and then start trying to rig up ways to defend against > incompatibilities and partitioning sets of classes for use with a > particular dependency? I think just making another module is easier. Therefore the slots. The project itself can introduce them, if two major versions can be used at same time. Think about a hypothetical commons-logging 2.0 (it is discussed) that might have a different API. I am quite sure Jakarta folks will ensure that 2.x and 1.x series can be used at the same time - simply because even in the Maven repo itself ~ 2000 artifacts depend on it. Without something like the slots, you will never be able to create a new Maven-based project using JCL 2.x ... > Are you sure you can defend against and cope with the two > versions of > JMock without any problem? Nat is a bright guy, and is probably very > careful about changes between versions but lots of project are not > and we decided not to allow multiple versions to protect people from > less then stringent practices that generally happen in real life. Yep. > We tried to make the rules for a single module simple, and make it > simple to create new one. It's just so much easier for the rest of > the tool chain to understand then trying to deal with the > innumerable > variations that occurs when multiple anything is allowed: multiple > versions, multiple source trees, and multiple artifacts per unit of > work which is a POM/module in Maven. > > That's the not so short answer, but the reason why we do what we do. > I know what users expect to happen, but try to think of the counter > examples where things might go wrong by using multiple versions in > the same module. If your project cannot define the deps directly, the module approach does not work. See the JCL example. - Jörg --------------------------------------------------------------------- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
