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To: dev@ant.apache.org
From: Hans Dockter <mail@dockter.biz>
Subject: Generating a Maven pom from Ivy
Date: Mon, 13 Oct 2008 13:56:47 +0200

Hi,

I have submitted code into the Gradle trunk for auto generating a  
Maven pom descriptor file from an Ivy ModuleDescriptor.  This code is  
all on the Ivy API level. Not everything we want to implement is  
implemented yet. We are happy to offer this code eventually to the  
Apache Ivy project (there is some code in Ivy for generating a pom  
out of ivy objects but this code is pretty limited and was not usable  
for our purpose).

What our code does:

One challenge is how to map between configurations and scopes, as  
dependencies can belong to more than one configuration. In our code  
we allow to map a configuration to one and only one scope. Different  
configurations can be mapped to more than one scope. One can assign  
also a priority to a particular mapping. Let's look at a couple of  
cases:

- A dependency belongs to only one configuration: The first thing we  
check is whether there is a mapping for this configuration. If there  
is none, the dependency is by default not added to the pom. By  
setting the global property 'includeUnmappedConfigurations' to true  
such a dependency would be added. If the configuration is mapped, the  
scope mapping is clear and the dependency is added.
- A dependency belongs to more than one mapped configuration: If the  
mapped configurations map to the same scope the situation is clear.  
If the mapped configurations map to different scopes the  
configuration mapping with the highest priority is chosen. If there  
is more than one configuration with a highest priority and they map  
to different scopes an exception is thrown.

Exclude Rules: Our code has an exclude rule converter. This converter  
gets an Ivy exclude rule and returns a Maven exclude rule or null. If  
null is returned the exclude rule is not reflected in the pom. The  
current simple logic of the converter is, that it returns a non null  
value if the Ivy exclude rule uses an exact matcher and the name as  
well as the organization of the module is specified.

Functionality that is still missing:
- Integrating the new Ivy 'override' rules the same way as the  
exclude rules.
- Artifact dependencies are not mapped yet.
- Fine grained customization

The last point I think is very important. Due to the more powerful  
elements Ivy has and many , often subtle, differences between Ivy and  
Maven, auto generation can't always produce the result that is  
needed. What we want to enable is that the user can modify any  
property of an auto generated Maven dependency element. Customization  
should also allow to remove auto generated elements as well as add  
new elements.  One thing we want to provide is a conversion listener.  
A hook would getdev all the created MavenDependency object and can  
analyze and modify them. Alternatively such a hook can provide a  
'query by example' filter to get only a subset of the generated  
MavenDependency elements.

Feedback is welcome

- Hans


--
Hans Dockter
Gradle Project lead
http://www.gradle.org


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