Description

Kotlin client enums generated with the Jackson serialization library are deserialized by ordinal instead of by the numeric value defined in the OpenAPI schema. When a server legitimately returns -1 for an enum whose values
are [-1, 0, 1], Jackson throws InvalidFormatException: index value outside legal index range [0..2].

openapi-generator version

7.17.0 (regression vs Java templates, which already emit the proper annotations)

OpenAPI declaration file content or url

  openapi: 3.0.0
  info:
    title: Numeric enum repro
    version: latest
  paths:
    /example:
      get:
        operationId: getExample
        responses:
          '200':
            description: ok
            content:
              application/json:
                schema:
                  $ref: '#/components/schemas/ExampleModel'
  components:
    schemas:
      ExampleModel:
        type: object
        required:
          - source
        properties:
          source:
            $ref: '#/components/schemas/ExampleNumericEnum'
      ExampleNumericEnum:
        type: integer
        format: int32
        enum:
          - -1
          - 0
          - 1

Generation Details

CLI (but same via Gradle/Maven plugin):

openapi-generator-cli generate -g kotlin -i numeric-enum.yaml -o out --library jvm-retrofit2 --additional-properties=serializationLibrary=jackson

Steps to reproduce

1. Generate the Kotlin client as above.
2. Call the generated API when the server responds with {"source":-1}.
3. Observe Jackson throwing InvalidFormatException: index value outside legal index range [0..2] because ExampleNumericEnum lacks @JsonCreator/@jsonvalue.

Related issues/PRs

• Similar to, but distinct from, [Bug][Java] jaxrs-cxf-client missing annotation when generating Enum #5077 (which was fixed for Java clients only).

Suggest a fix

Annotate Kotlin enums the same way the Java templates already do: add @get:JsonValue to the backing value and @JsonCreator @JvmStatic to the factory method so Jackson binds numeric values by value instead of by ordinal.