Hi Christian,
so I finally looked into the issue.
The error occurs, as we use package imports where ever we need classes from the org.eclipse.emf.edit.ui bundle.
The problem with this bundle is, that it relies on the org.eclipse.ui bundle. The org.eclipse.ui bundle then relies on the org.eclipse.ui.workbench and its Activator starts up the 3.x workbench.
What we did to support RAP in the j2ee mode (no workbench) and plain e4 applications, was to create a "org.eclipse.emf.rap.edit.ui.minimal" bundle.
This is basically a copy of the org.eclipse.emf.edit.ui bundle but without dependencies to org.eclipse.ui .
My understanding is that most of the time the eclipse compiler as well as tycho are satisfied if this bundle is opened. But from time to time eclipse shows compile errors.
We wanted to contribute this bundle to emf but Ed was never fond of it, as it is not possible to get it in without any breakages.
So our concrete suggestion was to create a "org.eclipse.emf.edit.ui.core" bundle without org.eclipse.ui dependencies and keep the current org.eclipse.emf.edit.ui bundle but let it extend the new bundle by providing classes with the org.eclipse.ui interfaces.
This would be basically transparent for the users, except for users with a bundle based run config, which would need to add the new bundle.
We're open for better suggestions.
Cheers,
Eugen
_______________________________________________