[BUG][kotlin] `const: true` on boolean property generates uncompilable enum (Boolean vs String mismatch)

[denysgaievskyi]

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? (Reproduced on 7.14.0 and 7.21.0)
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?

Description

For an OpenAPI 3.1 spec with a property type: boolean + const: true, the Kotlin generator (kotlin client, jvm-ktor library) emits an inline enum class typed as kotlin.Boolean but populates the single enum entry with a String literal. The generated file does not compile.

Related but distinct: #10445 (request for const keyword), #22398 (missing validation for const). Neither covers the Kotlin-specific compile failure.

openapi-generator version

Reproduced on 7.14.0 and 7.21.0.

OpenAPI declaration file content or url

openapi: 3.1.0
info:
  title: Repro
  version: 1.0.0
paths: {}
components:
  schemas:
    ExceptionPeriod:
      type: object
      required: [startDate, endDate]
      properties:
        startDate: { type: string, format: date }
        endDate: { type: string, format: date }
        isClosed:
          type: boolean
          const: true
          description: Marker flag; when present always true.

Generation Details

kotlin client generator, jvm-ktor library (default options).

Steps to reproduce

1. Run codegen against the spec above.
2. Compile the generated Kotlin.

Actual output

enum class ExceptionPeriodIsClosed(@get:JsonValue val value: kotlin.Boolean) {
    @JsonProperty(value = "true")
    `true`("true");  // String passed where Boolean required
    ...
}

e: ExceptionPeriodIsClosed.kt:41:12 Argument type mismatch: actual type is 'String', but 'Boolean' was expected.

Expected output

Either:

• Emit the enum entry with true (Boolean) instead of "true" (String), or
• Do not promote const on a boolean to an enum at all — emit val isClosed: kotlin.Boolean? = null (a single-valued boolean is trivially true; validation can be tracked separately per [BUG] Missing validation for const keyword in generated code #22398).

Suggest a fix

In the Kotlin inline-enum promotion path, type-check the enum value and emit the literal matching the declared type, not always "$value" as a String.