Add support for schema evolution

Does avro4k support reading the default value and putting it into the Avro schema? Found an issue doing an experiment with schema evolution where newer version couldn’t read older version Version “0.1.0”

@Serializable
data class WebhookData(val firstName: String, val lastName: String, val age: Int? = null)

{
  "type" : "record",
  "name" : "WebhookData",
  "namespace" : "com.shoprunner.data.webhook.model",
  "fields" : [ {
    "name" : "firstName",
    "type" : "string"
  }, {
    "name" : "lastName",
    "type" : "string"
  }, {
    "name" : "age",
    "type" : [ "null", "int" ]
  } ]
}

Version “0.2.0”

@Serializable
data class WebhookData(val firstName: String, val lastName: String, val age: Int? = null, val favoriteColor: String? = null)

{
  "type" : "record",
  "name" : "WebhookData",
  "namespace" : "com.shoprunner.data.webhook.model",
  "fields" : [ {
    "name" : "firstName",
    "type" : "string"
  }, {
    "name" : "lastName",
    "type" : "string"
  }, {
    "name" : "age",
    "type" : [ "null", "int" ]
  }, {
    "name" : "favoriteColor",
    "type" : [ "null", "string" ]
  } ]
}

But since default values aren’t set, it can’t read the older data.

[alexhwoods]

Here’s one I’m messing around with:

      test("Is nullable a sufficient default value?") {
         @AvroName("Task")
         @Serializable
         data class Writer(val name: String?)

         @AvroName("Task")
         @Serializable
         data class Reader(@AvroDefault(Avro.NULL) val id: String?, val name: String?)

         val writerSchema = Avro.default.schema(Writer.serializer())
         val readerSchema = Avro.default.schema(Reader.serializer())

         val pairCompatibility = SchemaCompatibility.checkReaderWriterCompatibility(
            readerSchema,
            writerSchema
         )

         pairCompatibility.result shouldBe compatible()
      }
   }

It passes. If you take away the null default value, you get READER_FIELD_MISSING_DEFAULT_VALUE

[thake]

Closing this issue as it seems to be fixed