/claim #519 /closes #519

Compile Time Validation

Both Scala 2 and Scala 3 have compile time validation. They extract the ShapeTree of SchemaA and SchemaB, and do a Tree.diff which returns added and removed, of the form List[List[Segement]]

Segement

private[migration] object Segment {
  case class Field(name: String) extends Segment
  case class Case(name: String)  extends Segment
  case object Element            extends Segment
  case object Key                extends Segment
  case object Value              extends Segment
  case object Wrapped            extends Segment
}

When .build is run, as we go through MigrationAction, each migration action collects Handled and Provided, which is also of the form List[List[Segement], which are then compared against added and removed. On success we compile.

Example of List[List[Segement]: List(Field("address"), Field("city")) -> It has one single path address.city

Note - This is a different List of Lists, rather than encoding level and field. I though having a clear path to the field which was added or removed was a better decision.

Deviations

Joint and Split for nested fields.

_.address.street + _.address.city → _.address.fullAddress -> this is done

_.address.street + _.origin.country → _.address.fullAddress -> This gets complex since now we have to extract values from multiple nested source paths, combine to targeted nested path, remove the nested source fields, and rebuilt the whole structure immutability.

So if the parent is not the same, it gracefully errors out at both runtime (if .buildpartial was used) and during compile validation (if .build was used)

No Serialization

DynamicMigration is Pure ADT and can be inspected structurally, but it cannot be fully serialize/deserialize it due to existential types in SchemaExpr. SchemaExpr[DynamicValue, ?], not sure how to deal with this.