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From Jason van Zyl <>
Subject Re: Evolving the POM format
Date Thu, 19 Jun 2014 15:32:44 GMT

On Jun 19, 2014, at 11:24 AM, Paul Benedict <> wrote:

> I am curious why you interoperability as a requirement? Perhaps questioning
> that may seem outrageous, but I see no problem with saying that you need to
> upgrade to Maven X.Y to read newer POM formats.

To build a project that is certainly fine. If a project starts using a Ruby-based POM you
will need a newer version of Maven to build the project. The issue of interoperability arises
when projects that want to use what was built by the project using the Ruby-based POM. Say
the Guice project starts using a Ruby-based POM: you do not want to force everyone who uses
Guice to use a version of Maven that has the capability to read a Ruby-based POM. I think
it would be an enormously limiting move to require that. Build with whatever you want but
let's make it easy to consume for everyone which means making those dependencies usable by
all the existing versions of Maven. The build-time information is mostly, if not completely,
irrelevant at consumption time.

> If a vendor wants to
> backport their project into older POM formats, that should be the vendor's
> shoulders and not be a concern of Maven core. If Maven does publish older
> formats of POMs, you then have to decide how many older formats do you want
> to publish? One day there will be a 4.1 or 5.0, and it's going to
> complicate the world if Maven takes on the burden of interoperability.
> Cheers,
> Paul
> On Thu, Jun 19, 2014 at 9:57 AM, Stephen Connolly <
>> wrote:
>> On 19 June 2014 15:48, Igor Fedorenko <> wrote:
>>> On 2014-06-19, 10:30, Stephen Connolly wrote:
>>>> - Igor is*mostly*  right in that we should not deploy the pom that is
>> used
>>>> to build to the repository...
>>>> - Where Igor is wrong is that for <packaging>pom</packaging>
we should
>>>> actually deploy the build time pom to the repository... probably with
>> the
>>>> classifier `build`... this is safe as `pom` does cannot have a
>> classifier
>>>> in model version 4.0.0.
>>>> - You couple that with a simple and obvious restriction... your parent
>>>> must
>>>> be the same or earlier version of Maven. You cannot have as a parent a
>>>> newer version of Maven than the child is built with.
>>> I think there is more to this.
>>> At very least we need to decide what to do with <parent> in 4.0.0
>>> compatible poms. Maybe we should always deploy effective pom with
>>> build-related elements removed.
>> Well I think the simple thing is that the 4.0.0 pom is fully resolved when
>> you have a builder pom
>>> I am also not sure if it is enough to deploy "build" parent poms as is.
>>> Your suggested "parent must be the same or earlier version of Maven"
>>> implies new versions of Maven can read older pom formats, which I think
>>> will significantly limit our flexibility to evolve pom format.
>> They need to be able to parse it into the model. Perhaps they do the
>> parsing by downloading a parser. But I think it is reasonable to expect
>> that we can convert older build pom formats into newer ones and just let
>> Maven take care of it... if we cannot do that then we are really creating a
>> brand new build tool rather than evolving Maven
>>> I wonder
>>> if we can have different solution for force parent poms, like
>>> org.apache:apache, which are used by multiple projects and different
>>> versions of maven and project-specific parent poms, where it is much
>>> easier to require specific version of maven.
>> Well the simple way is we have deployed the 4.0.0 parent pom as
>> org.apache:apache:14:pom if you want to upgrade your parent to
>> org.apache:apache:15 then you will need to require Maven 4.0+ to build. If
>> you don't want to upgrade your build time requirements, then don't upgrade
>> the parent... and if we need to "fix" things in the parent for 4.0.0
>> consumers, we can always deploy org.apache:apache:14.1 as a newer 4.0.0
>> model pom
>>> --
>>> Regards,
>>> Igor
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Jason van Zyl
Founder,  Apache Maven

Selfish deeds are the shortest path to self destruction.

 -- The Seven Samuari, Akira Kurosawa

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