error: newSource1.scala:3: Symbol 'type stuberrors.A' is missing from the classpath.
This symbol is required by 'class stuberrors.B'.
Make sure that type A is in your classpath and check for conflicting dependencies with `-Ylog-classpath`.
A full rebuild may help if 'B.class' was compiled against an incompatible version of stuberrors.
    class C extends B
                    ^