Handle recursive types #284
Description
Currently, our generic CaseClassTypeInfo and CaseClassSerializer don't handle recursive case classes. This issue is created from PR discussions in #280.
I was able to hack something in LowPrioImplicits thanks to the cache of TI: the idea is to store an incomplete temporary TI without field serializers initialized to break the recursivity, and do the field serializers initialization only once, after: it finds temporary TI in the cache so it doesn't try to initialize it another time, effectively breaking the recursivity.
If we want to handle recursivity in CaseClassSerializer we have to do something similar with a global cache for all recursively processed fields (at least getLength, isImmutableType, isImmutableSerializer, createInstance, equals, hashCode and maybe the most tricky one snapshotConfiguration) and find a coherent short-circuit for each (what is the length of a recursive serializer? In theory, its length is infinite, in practice it can be -1).
Similar problems occur also on CaseClassTypeInfo and its parent TupleTypeInfoBase: getFlatFields, getTypeAt, getTotalFields, equals, hashCode and toString.
Maybe memoization or dynamic programming can help to solve these problems: https://stackoverflow.com/a/6185005/6176274