[REQ] Cleanup Jackson type info mess

General question: why some java generators use JsonTypeInfo.As.EXISTING_PROPERTY and some JsonTypeInfo.As.PROPERTY?

More specific question: why spring-java generator for following specification snippet:

    Service:
      type: object
      discriminator:
        propertyName: '@type'
      required:
        - '@type'
      properties:
        '@type':
          description: JSON type discriminator, must contain object type name
          type: string
    ConcreteService:
      allOf:
        - $ref: '#/components/schemas/Service'
        - type: object

creates sources as follows:

@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.EXISTING_PROPERTY, property = "@type", visible = true)
@JsonSubTypes({
  @JsonSubTypes.Type(value = ConcreteService.class, name = "ConcreteService"),
})

public class Service   {
  @JsonProperty("@type")
  private String atType;

?

Why is discriminator value exposed as object property? It should be invisibile from java developer point of view. What is even worse is that I have to manually set proper type in order to have @type filled in serialized json.

Considering yaml above I would expect that

@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.PROPERTY, property = "@type", visible = true)
@JsonSubTypes({
  @JsonSubTypes.Type(value = ConcreteService.class, name = "ConcreteService"),
})

public class Service   {
// no @type property!

is created.

Begin with the spring-java generator's handling of the supplied Service and ConcreteService discriminator schema, then compare how Java generators choose Jackson EXISTING_PROPERTY versus PROPERTY. No source file or test is named, so locate the generator logic and its relevant tests first; done means the generated model no longer exposes @type as a Java property while serialization still emits the discriminator correctly.