[BUG][KOTLIN-CLIENT] OAS 3.x: Default enum value rendered without stating the enum name as query param

[mscheerschmidt-mhp]

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

Goal: I want to $ref(erence) to defined parameters when defining query parameters for REST endpoints.
For that I use components/parameters. The param might be an optional enum with a default value.

Expected: When referencing to either components/parameters or at endpoint to its components/schema, the default enum value should be set.

Actual: the enum value is rendered without the enum class name, yielding a compile error.

Both OAS 3.0.3 and 3.1.0 are affected.

openapi-generator version

id("org.openapi.generator") version "7.12.0"

OpenAPI declaration file content or url

openapi: 3.0.3
info:
  title: My service
  description: My service
  version: 1.0.0
servers:
  - url: 'https://app.com/api/v1'
components:
  parameters:
    DocumentFormatParameter:
      in: query
      name: format
      schema:
        $ref: '#/components/schemas/DocumentFormat'
  schemas:
    DocumentFormat:
      title: Document Format
      type: string
      enum: [ PDF, JSON ]
      default: PDF
paths:
  /hello:
    get:
      operationId: getHello
      parameters:
        - $ref: '#/components/parameters/DocumentFormatParameter' # renders to 'format: DocumentFormat? = PDF'
        - in: query
          name: format2
          schema:
            $ref: '#/components/schemas/DocumentFormat' # renders to 'format2: DocumentFormat? = PDF'
        - name: format3
          in: query
          schema:
            title: Title # this title is ignored, instead: 'Format3GetHello'
            type: string
            enum:
              - PDF
              - JSON
            default: PDF # renders to 'Format3GetHello.PDF'
      responses:
        200:
          description: OK

Generation Details

openApiGenerate {
    generatorName.set("kotlin")
    inputSpec.set("$projectDir/src/main/resources/openapi.yaml")
    outputDir.set("$buildDir/generated")
    apiPackage.set("com.example.api")
    modelPackage.set("com.example.model")
    library.set("jvm-retrofit2")
    configOptions.set(
        mapOf(
            "dateLibrary" to "java8",
            "enumPropertyNaming" to "original",
            "serializationLibrary" to "jackson",
            "useCoroutines" to "true",
        ),
    )
}

Steps to reproduce

Take the openapi.yaml and generate code. See resulting DefaultApi.kt file.
See the comments in example OAS on where it goes all wrong.

@GET("hello")
    suspend fun getHello(@Query("format") format: DocumentFormat? = PDF, @Query("format2") format2: DocumentFormat? = PDF, @Query("format3") format3: Format3GetHello? = Format3GetHello.PDF): Response<Unit>

Related issues/PRs

Suggest a fix

I think the culprit is within the mustache file modules/openapi-generator/src/main/resources/kotlin-client/param_default_value.mustache where we always include the OperationId as a prefix for the default enum value.
Instead the name of referenced schema enum should be taken into account.