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From Nicolas Lalevée <nicolas.lale...@hibnet.org>
Subject Re: Easyant - Plugin conflict management
Date Tue, 20 Aug 2013 16:50:16 GMT

Le 20 août 2013 à 14:22, Jean-Louis Boudart <jeanlouis.boudart@gmail.com> a écrit
:

> I've commited changes on trunk with some unit tests if you want to have a
> look.
> 
> Known limitation :
> * system plugins doesn't participate *yet* to global plugin resolution
> * plugins classpath created dinamically will all contains the whole
> resolution graph (not really a problem)
> 
> Point 1 : this can even affect performance. Invoking resolve process one
> time seems much more speed that invoking plugins individually.

This seems strange to me. Do you have an idea why ?

> Point 2 : Even if there is no much activity, i suggest to keep backward
> compatibility

fine for me.

> Point 3 : By two steps i meant running a global resolve (for all plugins
> and buildtypes including transitive ones). And then have a second class
> invoked to perform individual import of ant build file by picking them from
> the ResolveReport.

ok I see. This make totally sense.

> You can check  ResolvePlugins and ImportDeferred class in trunk if you want
> to see concrete stuff.

I usually do a very quick review of the code to keep me informed of what is going on and see
if nothing bug me, and as always, it seems great. But I need to get into this more deeply
to see how it really works.

Nicolas

> 
> 
> 
> 
> 2013/8/17 Nicolas Lalevée <nicolas.lalevee@hibnet.org>
> 
>> Long overdue response.
>> 
>> Le 3 août 2013 à 13:33, Jean-Louis Boudart <jeanlouis.boudart@gmail.com>
>> a écrit :
>> 
>>> Hi there,
>>> 
>>> It becomes necesssary to manage conflicts between plugins.
>>> This issues has been raised many time and is referenced on jira[1].
>>> 
>>> Currently easyant offers import task taking some specific attributes to
>>> resolve a plugin (mainly organisation, module name and revision).
>>> <ea:import org="mycompany" module="myplugin" revision="x.x"/>
>>> 
>>> This task will :
>>> * resolve the given plugin or buildtypr
>>> * create a dynamic classpath for this plugin
>>> * expose location of others extra files through properties (ex
>>> checkstyle.xml containing checkstyle rules, this files is shipped in the
>>> plugin). Thoses properties will then be reused by the plugin itself
>>> * import the real ant file (invoke the importTask from ant core under the
>>> hood)
>>> 
>>> This task is currently used :
>>> * dynamically by easyant to load system plugins (skeletons for example)
>>> * dynamically by easyant when you specify <ea:build> or <ea:plugin>
tags
>>> in module.ivy files
>>> * invoked in plugin ant file itselfs
>>> * invoked in module.ant if users has complex needs
>>> 
>>> Additionnal there is two "alliases" for this task to import plugins and
>>> buildtype.
>>> <ea:plugin module="compile-java" revision="0.9"/>
>>> <ea:plugin module="build-std-java" revision="0.9"/>
>>> If organisation attribute is not specified on aliases  default one will
>> be
>>> used.
>>> 
>>> It does the job but it doesn't handle conflict between plugins.
>>> 
>>> Some plugins relies on abstract ones.
>>> Exemple:
>>> package-jar depends on abstract-package, abstract-package depends on
>>> abstract-compile, but compile-java plugin also depends on
>> abstract-compile.
>>> Which versi of abstract-compile will be taken in case both plugins load
>>> different version ? The answer is the first one !
>>> This becomes more problematic on buildtypes, as buildtypes loads a set of
>>> plugins (including themself others abstract-plugins).
>>> 
>>> Ok so now you should have a quick picture of the problem.
>>> 
>>> What could be done  ?
>>> 
>>> We can rely on ivy to describe dependency on plugins. But then how could
>> we
>>> know in which order plugins should be loaded ?
>>> 
>>> I suggest to introduce a deferred import mechanism.
>>> 
>>> We should split responsibility in two distinct steps.
>>> 1 - resolve (based on ivy) the whole graph of plugins and store the
>> resolve
>>> report somewhere as a reusable reference in ant project
>>> 2 - invoke a new import task should import already resolved plugins (the
>>> task could rely on the report stored as a reference in ant project)
>>> 
>>> Exemple :
>>> compile java will have an ivy dependency on abstract-compile
>>> <dependency org="org.apache.easyant.plugins" module="abstract-compile"
>>> revision="1.0"/>
>>> 
>>> The compile java ant script will import the resolved plugin
>>> <ea:import-deferred org="org.apache.easyant.plugins"
>>> module="abstract-compile"/>
>>> 
>>> Note that i'm not fixed yet with the task name. Any suggestion (even for
>>> alliases are welcome).
>>> 
>>> To maintain backward compatibility i'm in favor of creating new aliases
>>> "import-plugin" and "import-buildtype" instead of reusing existing ones.
>>> 
>>> People would be able to continue using existing task with known the
>>> limitation (no conflict management on plugins).
>>> This can help if someone wants to load plugins in module.ant after
>> setting
>>> a few properties.
>>> 
>>> I also recommend adding a warning on existing task to recommend people
>>> using the new import mechanism.
>>> 
>>> What do you think ?
>> 
>> I see 3 points here.
>> 
>> First, managing plugin dependencies: with Ivy, of course, we couldn't
>> agree more :)
>> 
>> Then about creating new tasks to keep backward compatibility. I think we
>> can break backward compatibility. Easyant is not yet 1.0 and I do not see
>> much activity on the user list. I would prefer bugging the current users
>> than having an error-prone and deprecated task around.
>> 
>> Third there is the resolve in two steps. I really like the idea. I am not
>> sure though if we need this in order to bring conflict management in plugin
>> dependencies. And I am not sure how far you are willing to go.
>> Actually this is a larger topic which has bugging me recently. The way we
>> use the ivy.xml is generally either to tight or insecure. For instance when
>> using version ranges in an ivy.xml, since the content of the repository is
>> expected to change over time, then the resolve may change over time since
>> new versions might fit the range. Range makes things unreliable over time,
>> so often I restrict myself to not use any range. But it's kind of a shame
>> to not use ranges in a dependency manager.
>> I continued experimenting with the OSGi mapping in Ivy. And the OSGi
>> version semantics are very loose. It is because it represents what versions
>> of software it is compatible with, not the versions we will be using in
>> your specific unit test or application. So relying on OSGi manifest to
>> resolve dependencies is not safe at all. That's why I implemented the
>> fixdeps [1] task. From a very loose specification of the dependencies, it
>> will produce an ivy.xml which is very tight and secure.
>> Then, when adding dependencies to a project, we edit the
>> ivy-specification.xml and run fixdeps. The build then relies on the
>> produced ivy.xml. A nice side effect is that since there is only non
>> transitive fixed dependencies to resolve, resolve is fast: either the
>> module is here either it's not. And with proper caching, everything works
>> with the filesystem.
>> But, as wrote above, I'm not sure if that's why you suggested the two
>> steps resolve.
>> 
>> Nicolas
>> 
>> [1] http://ant.apache.org/ivy/history/trunk/use/fixdeps.html
>> 
>> 
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>> 
> 
> 
> -- 
> Jean Louis Boudart
> Independent consultant
> Apache EasyAnt commiter http://ant.apache.org/easyant/


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