Classpath validator and sbt builder fight about classpath validity when using m2eclipse
The new classpath validator requires that only one Scala library is in the build path, it can have any name. The sbt builder is looking for a 'scala-library.jar' and only for that. The scala libraries provided by m2eclipse in the 'maven dependencies' are named 'scala-libray-<version>.jar'.
All this contributes to make m2eclipse unusable: - if the eclipse variable is in the build path, the classpath validator complains that there are too many scala libraries in the build path - if the eclipse variable is not in the build path, the sbt builder complains that it cannot find the scala library.
In addition, it is also possible that the 'maven dependencies' provides multiple, compatible but different scala libraries.