I am not sure I follow.
Do you want to allow multi-module projects where different modules
require different versions of maven?
If required version of maven is the same, why not require the same pom
format version for the entire build too? Are you concerned about changes
to pom.xml files when moving from one format version to the next or
something else?
--
Regards,
Igor
On 2014-06-19, 11:50, Stephen Connolly wrote:
If backwards compatible interoperability is not a requirement then:
If I upgrade one module in my multi-module build to Maven 5.1 then I am
forced right then and there to either:
* upgrade all of them to Maven 5.1; or
* remove the module from my multi-module build
Neither of these are a good user experience in my mind. Maven 5.1 should be
able to build a Maven [2.0,5.1] project without modifying the pom... it can
do that by loading shim layers on demand if necessary, but to my thinking
anything less is going to cause issues for users.
So to my thinking we just accept that Maven needs to evolve such that for
every version X.Y of Maven you know that you can build a Maven project from
the range [2.0,X.Y].
If you have a project that has a parent, then the parent must be in a pom
format that buildable by Maven [2.0,${project.prerequisites.maven}], so a
child pom requiring Maven 5.1 to build can have a parent pom that requires
Maven 5.0 to build but not a parent pom requiring Maven 5.2... there may
even be turtles all the way down to an ancestor pom that requires Maven
[2.0,3.0.3] to build (IIRC after 3.0.3 you get things like wildcards in
excludes due to aether injecting "bonus" functionality... that should have
been a modelVersion bump in the strictest sense... but well it wasn't)
I also think people overestimate how difficult it is to maintain backwards
compatibility.
I have a Jenkins plugin that was written against Hudson 1.96 and I can take
that .hpi file and drop it into Jenkins 1.568 and it still works
unmodified. Similarly I can upgrade a Jenkins installation jumping quite a
large number of versions without issue.
It is possible to evolve and maintain the ability to read older data... is
it easy? well it's not trivial, but it is a disservice to our users if we
don't try
On 19 June 2014 16:24, Paul Benedict <[email protected]> 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. 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 <
[email protected]> wrote:
On 19 June 2014 15:48, Igor Fedorenko <[email protected]> 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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