The removal of the scala* libs from the maven classpath container seem to cause WTP war file creations to not put those libs into the WEB-INF/lib folder.
As a workaround, you can add the Scala classpath container manually to the deployment assembly list (project preferences), but it would be much nicer to have those libs being added to the war automatically.
I'm not a WTP's user. you create war with a native WTP action or via "mvn package" (from eclipse) ?
Just by dragging and dropping the project onto the server in the Servers view.
Unless Scala IDE requires the Scala Classpath Container, m2e-scala should simply remove it from the project classpath, as all the classpath management should be driven by Maven. Doing so, the WTP integration would just work OOTB (provided m2e-wtp is installed).
If that's not an option, then, what you should do is mark the Scala Classpath Container as deployable in m2e-scala. No need to add a dependency on WTP, m2e-wtp or any other 3rd party features : Check if the Maven Classpath Library has the "org.eclipse.jst.component.dependency" classpath attribute. If it does, then copy it and add it to the Scala Classpath Library too.
You'll end up with :
<classpathentry kind="con" path="org.scala-ide.sdt.launching.SCALA_CONTAINER">
<attribute name="org.eclipse.jst.component.dependency" value="/WEB-INF/lib"/>
Only problem is it will make all dependencies from that library deployed on WTP servers (*-library, *-dbc, *-swing). If they're not all required at runtime by scala web apps, you should then loop on all individual classpath entries of the Scala Classpath Container. For each jar that must not be deployed (I dunno how you decide that), you add a "org.eclipse.jst.component.nondependency" attribute. See how it's done in m2e-wtp : http://git.eclipse.org/c/m2e-wtp/org.eclipse.m2e.wtp.git/tree/org.eclipse.m2e.wtp/src/org/eclipse/m2e/wtp/WebProjectConfiguratorDelegate.java#n372
I created PR #22 to address the problem.
Currently all the jars from the Scala lib will be deployed, I didn't have time to write all the boilerplate code for specific jar handling.
If you want to test it, a zipped update site is attached to https://issues.jboss.org/browse/JBDS-2259