- base class method wins against a (default) interface method,
so an abstract base class method should always be implemented
in a derived class;
- interface methods clash regardless of abstract/default
with possibly undefined behavior at run-time,
so a class or interface should always define its own method
for methods inherited from multiple interfaces and not from base class;
- meaningful diagnostics for class inheriting conflicting JVM signatures.
Since no override will happen under Java 8 rules,
ACCIDENTAL_OVERRIDE is misleading for this case;
- update testData.
1. Must be initialized in-place
2. Can not be open/abstract
3. Can not be an override
4. Can not be delegated
5. Initializer must be a compile-time constant
6. No getters
7. `const` is not applicable to vars or locals
8. `const val` should be whether top-level property or object member
Ilya Gorbunov