Building a p2 repository by resolving Tycho features from a Maven repository

Question

I\'m trying to build a p2 repository from Tycho feature artifacts which are deployed in a remote Maven repository, without having to install the artifacts into the local Mav

Answer 1

I am pretty impressed by your thorough analysis. You've almost got everything covered which is possible with the current Tycho version (0.22.0) - except for the solution which is so unintuitive that I wouldn't have expected anyone to be able to guess it (see below). Note however that there is a small fix required to also make the solution work for SNAPSHOT artifacts.

But first, I'd like to provide some technical (and historical) background for what you have observed:

pomDependencies=consider only works for plug-ins: The use case for this functionality was to allow referencing plug-ins (or more precisely OSGi bundles) from Maven repositories. So when the flag is set and the project has dependencies to JARs, Tycho will check if they are OSGi bundles, generate the p2 metadata for them on-the-fly, and add them to the target platform. There is no similar support for feature JARs because these usually don't exist in Maven repositories.

But what about Tycho-built projects? These may deploy into Maven repositories! Yes, this is true, and this is why I tried to extend the pomDependencies concept to allow for what you are trying to do. The idea was that every time Tycho considers a POM dependency for the target platform, it also checks if the p2 index files ...-p2metadata.xml and ...-p2artifacts.xml exist. However this turned out to infer a massive performance penalty because it generally takes very long for a Maven repository server to figure out that an artifact does not exist. So the remote download was disabled, and replaced with a look-up in the local Maven repository. In this way, two Tycho builds could set -Dtycho.localArtifacts=ignore and would still be able to exchange the artifacts specified in the POM via the local Maven repository.

Knowing these implementation details, we get to the following solution: Instead of only adding a POM dependency from the repository to the feature artifact, you also need to add dependencies to the p2metadata and p2artifacts files. Example:

<dependencies>
    <dependency>
        <groupId>myproject</groupId>
        <artifactId>myproject.feature</artifactId>
        <version>0.1.0-SNAPSHOT</version>
    </dependency>
    <dependency>
        <groupId>myproject</groupId>
        <artifactId>myproject.feature</artifactId>
        <version>0.1.0-SNAPSHOT</version>
        <classifier>p2metadata</classifier>
        <type>xml</type>
    </dependency>
    <dependency>
        <groupId>myproject</groupId>
        <artifactId>myproject.feature</artifactId>
        <version>0.1.0-SNAPSHOT</version>
        <classifier>p2artifacts</classifier>
        <type>xml</type>
    </dependency>
</dependencies>

This makes Maven also download these p2 index files, so Tycho recognizes the main artifact as Tycho artifact. In this way, you can also get an eclipse-feature into the target platform via POM dependencies - at least almost: With 0.22.0, the repository build passes, but the feature.jar artifact is missing. I already debugged this issue, and it is easy to fix.

Obviously the syntax with three <dependency> elements for every actual dependency is not nice. It should be possible to boil this down to a single p2artifacts element - but this is more work. In case you are interested in this feature, you could open an enhancement request in Tycho's issue tracker.