How to get source bundles when using tycho-p2-extras to mirror an eclipse p2 repository - eclipse-rcp

Question

I want to create a mirror of an eclipse p2 repository containing the needed ius for building an rcp application. The mirroring did work and the needed bundles are locally stored. I can reference them from my tycho build and from my eclipse ide. It works but the targetdefinition file, containing the folder of the eclipse p2 mirror, complains about the missing source bundles.
I read and tried the switches tycho-p2-extras offers but no switch seems to solve that problem.
<build>
<plugins>
<plugin>
<groupId>org.eclipse.tycho.extras</groupId>
<artifactId>tycho-p2-extras-plugin</artifactId>
<version>${tycho.version}</version>
<executions>
<execution>
<phase>prepare-package</phase>
<goals>
<goal>mirror</goal>
</goals>
</execution>
</executions>
<configuration>
<source>
<!-- source repositories to mirror from -->
<!-- supported layouts are "p2-metadata", "p2-artifacts", and "p2"
(for joint repositories; default) -->
<repository>
<id>eclipse-2018-09</id>
<url>http://download.eclipse.org/releases/2018-09</url>
<layout>p2</layout>
</repository>
<repository>
<id>eclipse-2018-09-tech</id>
<url>https://download.eclipse.org/technology/epp/packages/2018-09/</url>
<layout>p2</layout>
</repository>
</source>
<!-- List of IUs to mirror. If omitted, allIUs will be mirrored. -->
<!-- Omitted IU version element means latest version of the IU -->
<ius>
<iu>
<id>org.eclipse.e4.rcp.feature.group</id>
</iu>
<iu>
<id>org.eclipse.emf.common.feature.group</id>
</iu>
<iu>
<id>org.eclipse.emf.ecore.feature.group</id>
</iu>
<iu>
<id>org.eclipse.equinox.executable.feature.group</id>
</iu>
<iu>
<id>org.eclipse.ui.themes</id>
</iu>
<iu>
<id>org.objectweb.asm</id>
</iu>
<iu>
<id>org.eclipse.swt</id>
</iu>
</ius>
<!-- The destination directory to mirror to. -->
<destination>${project.build.directory}/repository</destination>
<!-- Whether only strict dependencies should be followed. -->
<!-- "strict" means perfect version match -->
<followStrictOnly>false</followStrictOnly>
<!-- Whether or not to follow optional requirements. -->
<includeOptional>true</includeOptional>
<!-- Whether or not to follow non-greedy requirements. -->
<includeNonGreedy>true</includeNonGreedy>
<!-- Filter properties. E.g. filter only one platform -->
<!--
<filter>
<osgi.os>win32</osgi.os>
<osgi.ws>win32</osgi.ws>
<osgi.arch>x86_64</osgi.arch>
</filter>
-->
<!-- Whether to filter the resulting set of IUs to only -->
<!-- include the latest version of each IU -->
<latestVersionOnly>false</latestVersionOnly>
<!-- don't mirror artifacts, only metadata -->
<mirrorMetadataOnly>false</mirrorMetadataOnly>
<!-- whether to compress the content.xml/artifacts.xml -->
<compress>false</compress>
<!-- whether to append to the target repository content -->
<append>true</append>
<!-- whether to mirror pack200 artifacts also. Available since tycho-extras
0.17.0 -->
<includePacked>true</includePacked>
</configuration>
</plugin>
</plugins>
</build>

Answer 1

As far as I know, there's no such option in the tycho-p2-extras-plugin:mirror goal, because there's no such option in the Eclipse mirror application on which the plugin relies.
You have to mirror the corresponding source features yourself (which will automatically mirror the related sources of the included bundles).
However, some projects provide features that automatically include all the sources, for example, org.eclipse.emf.sdk.feature.group. You will also mirror all the sources if you mirror such a feature.