[BUG][Kotlin] Integer enums outputs as a string

[CHervaudBetclic]

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• 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

When using the generator for kotlin with the kotlinx serialization method, integer enums will be correctly serialized from integer to kotlin integer, but will be incorrectly deserialized from kotlin integer to string
This:

@Serializable
enum class SomeCode(val value: kotlin.Int) {
    @SerialName(value = "0")
    _0(0)
}

Should be this:

@Serializable
enum class SomeCode(val value: kotlin.Int) {
    @SerialName(value = 0)
    _0(0),
}

openapi-generator version

Latest (7.12.0)

OpenAPI declaration file content or url

openapi: 3.0.3
info:
  title: Demo
  version: v1

components:
  schemas:
    Code:
      type: integer
      enum:
        - 0

paths:
  /do:
    get:
      summary: Do something
      responses:
        200:
          description: Successful response
          content:
            application/json:
              schema:
                type: object
                required:
                  - code
                properties:
                  code:
                    $ref: '#/components/schemas/Code'

Generation Details

Generate with Docker command:

docker run --rm -v $(pwd):/local openapitools/openapi-generator-cli generate -i /local/Test.yml -g kotlin -o /local/out/kotlin

Steps to reproduce

Generate with Docker command:

docker run --rm -v $(pwd):/local openapitools/openapi-generator-cli generate -i /local/Test.yml -g kotlin -o /local/out/kotlin

Related issues/PRs

Suggest a fix

The bug seems to be caused by the following line:

    @SerialName(value = {{#lambda.doublequote}}{{{value}}}{{/lambda.doublequote}})

Where double quotes are hard-coded
They should be conditionally added, whether it's a dataType string or integer.
I'm not sure if we can do conditional checks like that is the mustaches syntax, let me know if we can, it would be a pleasure to create a PR

[CHervaudBetclic]

After intensive test with our real use case, kotlinx seems to have a hard time dealing with integer enums native serialization
We may need to implement a custom serializer in order for it to work

[rlnt]

The linked PR included in 7.14.0 breaks compilation as the @SerialName annotation requires a string, so your current output was correct. I see that a release is scheduled for 7.15.0, which hasn't been released yet. I just wanted to leave this here in case someone gets a compilation error and finds this issue like I did.

[rlnt]

@wing328 I saw your PR #21765

This has been marked as the 7.15.0 milestone, which has already been released. I updated to that release, and it still generates like this:

@Serializable
enum class Option(val value: kotlin.Int) {

    @SerialName(value = "0")
    Option1(0),

    @SerialName(value = "1")
    Option2(1),

    @SerialName(value = "2")
    Option3(2),

	//...
}

It results in sending these values as strings in the HTTP body.

[wing328]

cc @CHervaudBetclic - the original author of the PR

[CHervaudBetclic]

@rlnt
Using the following openapi spec

openapi: 3.0.3
info:
  title: Test API
  description: API to test
  version: 0.0.1

paths:
  /test:
    get:
      responses:
        '200':
          description: OK
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/Test'

components:
  schemas:
    Test:
      type: integer
      enum:
        - 1
        - 2

With the following config:

{
  "modelPackage": "com.test",
  "serializationLibrary": "kotlinx_serialization",
  "dateLibrary": "kotlinx-datetime",
  "library": "jvm-ktor",
  "enumPropertyNaming": "UPPERCASE",
  "globalProperties": {
    "apis": false,
    "models": "",
    "apiDocs": false,
    "modelDocs": false,
    "apiTests": false,
    "modelTests": false
  }
}

Using the docker run --rm -v ${PWD}:/local openapitools/openapi-generator-cli generate -i /local/openapi.yml -g kotlin -o /local/out -c /local/config.json command generates:

/**
 *
 * Please note:
 * This class is auto generated by OpenAPI Generator (https://openapi-generator.tech).
 * Do not edit this file manually.
 *
 */

@file:Suppress(
    "ArrayInDataClass",
    "EnumEntryName",
    "RemoveRedundantQualifierName",
    "UnusedImport"
)

package com.test


import kotlinx.serialization.SerialName
import kotlinx.serialization.Serializable

/**
 * 
 *
 * Values: _1,_2
 */
@Serializable
enum class Test(val value: kotlin.Int) {

    @SerialName(value = 1)
    _1(1),

    @SerialName(value = 2)
    _2(2);

    /**
     * Override [toString()] to avoid using the enum variable name as the value, and instead use
     * the actual value defined in the API spec file.
     *
     * This solves a problem when the variable name and its value are different, and ensures that
     * the client sends the correct enum values to the server always.
     */
    override fun toString(): kotlin.String = value.toString()

    companion object {
        /**
         * Converts the provided [data] to a [String] on success, null otherwise.
         */
        fun encode(data: kotlin.Any?): kotlin.String? = if (data is Test) "$data" else null

        /**
         * Returns a valid [Test] for [data], null otherwise.
         */
        fun decode(data: kotlin.Any?): Test? = data?.let {
          val normalizedData = "$it".lowercase()
          values().firstOrNull { value ->
            it == value || normalizedData == "$value".lowercase()
          }
        }
    }
}

So LGTM, can you provide a reproduction?

[rlnt]

@CHervaudBetclic Your setup has a few questionable things. We are talking about Kotlin. Why do you use jvm-ktor? That would use the @Json annotation. My personal config looks like this:

openApiGenerate {
    generatorName = "kotlin"
    remoteInputSpec = openApiSpecUrl
    outputDir = layout.buildDirectory.dir("generated/openapi").get().asFile.path
    packageName = "${appId}.openapi"
    generateModelTests = false
    generateApiTests = false
    cleanupOutput = true
    configOptions = mapOf(
        "dateLibrary" to "kotlinx-datetime",
        "enumPropertyNaming" to "UPPERCASE",
        "library" to "jvm-ktor",
        "omitGradlePluginVersions" to "true",
        "omitGradleWrapper" to "true",
        "sourceFolder" to "commonMain/kotlin"
    )
}

Additionally, if it were really generated like @SerialName(value = 1), that would be invalid, since the SerialName annotation only takes a string argument. Passing an integer value to it would result in a compiler error.
This problem was also mentioned on the initial attempt to fix that problem: #21248 (comment)

[rlnt]

I assume this commit is supposed to remove the SerialName annotation if the type is not a string. Not too sure on the syntax. It's just a guess. However, it doesn't seem to work for me.
17bf1ad

[rlnt]

Okay, after a bit more investigation, it turns out this is a deeper lying issue. You are using jvm-ktor. This indeed fixes the issue on 7.15.0, but only in combination with "serializationLibrary": "kotlinx_serialization". I didn't have this option set previously because it clashes with "library": "multiplatform" as described here: #18904 (comment)

I guess that your fix only works if the serialization library is explicitly set to kotlinx_serialization, and because that isn't the case when using multiplatform as the library, it doesn't do anything. So the other issue would have to be resolved first.

It will generate without the SerialName annotation afterwards, which is correct.

I sadly can't use jvm-ktor because it doesn't support a custom HTTP client.

[rlnt]

The problem is here https://github.com/OpenAPITools/openapi-generator/blob/master/modules/openapi-generator/src/main/resources/kotlin-client/enum_class.mustache#L68-L70

You only check if it's a string when kotlinx serialization is enabled. But the multiplatform library is a separate section and doesn't include the isString check.