mavenplugins/tycho/PREBUILT

This folder mirrors a small subset of artifacts from Maven Central [1].

In order to create this mirror, we do the following steps:
 
 1. Create a settings.xml [2] file that specifies the location for the
    repository.
 2. Run maven to build the IDE. This process will use Tycho and download
    and cache all the dependencies in the specified repository.
 3. Remove the folder p2 inside the repository, which contains artifacts
    generated during the build in step 2. We only need cached artifacts.
 4. Update settings.xml to specify that it should run in offline mode,
    and make sure that the repository has all the necessary contents.

Step 1: Create a settings.xml

<?xml version="1.0" encoding="UTF-8"?>
<settings xmlns="http://maven.apache.org/SETTINGS/1.0.0" 
          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
          xsi:schemaLocation="http://maven.apache.org/SETTINGS/1.0.0
          http://maven.apache.org/xsd/settings-1.0.0.xsd">
  <localRepository>/path/to/tycho/tycho-dependencies-m2repo</localRepository>
  <offline>false</offline>
</settings>

Step 2: Run maven using the above settings.xml

 $ cd /path/to/folder/with/pom.xml
 $ mvn -s /path/to/above/settings.xml package

This should download and cache all the necessary dependencies in the repository
specified in the settings.xml.

Step 3: Remove unnecessary files from the repository. It turns out that Tycho
also populates a whole bunch of eclipse plugins into the p2 folder inside the
repository. These don't need to be checked in, so they can be removed.

Step 4: Validate that the repository contains everything necessary by changing
the offline attribute to true, and then rebuild.

If everything goes well, then the repository can be checked in.

TODO

This method could possibly be automated using the Maven Dependency plugin [3].
The "copy-dependencies" task from that plugin allows you to recursively copy
all the dependencies of a particular POM. Here is an example command to download
all the dependencies for com.android.tools:sdklib:22.7.2

 $ mvn org.apache.maven.plugins:maven-dependency-plugin:2.8:copy-dependencies \
    -f ~/.m2/repository/com/android/tools/sdklib/22.7.2/sdklib-22.7.2.pom \
    -DoutputDirectory=`pwd`/target \
    -Dmdep.copyPom=true \
    -Dmdep.useRepositoryLayout=true

Unfortunately, this doesn't seem to work for the Tycho plugin since it seems
like a more complicated multi module setup. The POM for the Tycho plugin specifies
sub modules which the dependency plugin doesn't seem to be able to cope with.

[1] http://search.maven.org/
[2] https://maven.apache.org/settings.html
[3] http://maven.apache.org/plugins/maven-dependency-plugin/