well ... the gwt plugin cannot actually work with the Luna release, since it has a package dependency for eclipse core.runtime [3.8.0.3.10.0], here ")" means that it does NOT include 3.10.0, which is used in the moon, but you can get rid of it by modifying the osgi package file, and then it will work fine with the moon, at least for me at the moment.
1 download the latest zip file of the update site from the google eclipse plugin site 2 unzip it 3, you will need to change 2 files first
osgi META INF / manifest file included in the jar with the name * gdt * e42 (sorry, forget the full name, you can find it when you try to install the plugin, luna will complain that some patch is missing) which is located in the directory plugins, just change the version of core.runtime from 3.10.0) to 3.10.0]
the other should be content.jar (possibly artifacts. jar), same thing above
you can now install the plugin if you have already installed RCP Eclipse
however, the installation will not be completed due to a change in the hash of md5,
finally copy the expected md5 from the error message dialog box to replace the old md5 value in the artifacts.jar file (possibly content.jar)
now reinstall the plugin, now it should work
UPDATED:
maybe you should remove the package version from MANIFEST.MF in com.google.gdt.eclipse.platform.e42 jar and change the version to "0.0.0" from content.xml in content.jar