[BUG][KOTLIN] Kotlin generator emits @get:JsonProperty causing Jackson deserialization to fail in some cases

Description

When generating Kotlin models with serializationLibrary=jackson, the generator uses @get:JsonProperty.
This causes Jackson to fail deserialization for Kotlin data classes in some cases, because the annotation is placed on the getter instead of the constructor parameter or backing field.

Jackson’s Kotlin module binds via constructor parameters, so @get: is effectively ignored. Jackson does have some magic of it's own, so usually it will work out these things itself. In my specific case it is sadly not so.

openapi-generator version

7.16.0, probably earlier versions too

OpenAPI declaration file content

components:
  schemas:
    MyRestModel:
      type: object
      properties:
        t_start:
          type: string
          format: date-time

Generation Details

openapi-generator generate \
  -i openapi.yaml \
  -g kotlin \
  -o generated \
  --library jvm-spring-restclient \
  --additional-properties=serializationLibrary=jackson,useSpringBoot3=true

Steps to reproduce

1. Run CLI command
2. Inspect generated model:

Generated model snippet:

data class MyRestModel(
    @get:JsonProperty("t_start")
    val tStart: java.time.OffsetDateTime? = null,
)

Suggest a fix

Generator should use either @param: or @field: for Jackson in Kotlin, or provide a config option to choose the annotation target. I can see that the kotlin-wiremock combo already uses @param.

Perhaps some of the other Kotlin serialization libraries would benefit from this as well.

Start by running the provided OpenAPI Generator command and inspecting the generated MyRestModel annotation. Compare the Kotlin templates with modules/openapi-generator/src/main/resources/kotlin-wiremock/model.mustache, which already uses @param:. Done means the Jackson Kotlin model uses a constructor-parameter or field target rather than @get:JsonProperty and the reported deserialization case is addressed.