[BUG][KOTLIN] Naming conflict among enum entries in case of integer values

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

Enums that have their values as an integer number can have unresolved naming conflicts, which cause compilation errors. The problem is that when the generator chooses a name for the enum entry, it doesn't take into account the sign of the integer value. Meaning that values, for example, 12 and -12 will get the same name - _12.

Please note that such an issue exists in the latest versions. For example, in 6.5.0, there is no such problem.

openapi-generator version

7.16.0

OpenAPI declaration file content or url

{
  "openapi": "3.0.1",
  "info": {
    "title": "Test.Api",
    "version": "1.0.0"
  },
  "components": {
    "schemas": {
      "IntegerEnum": {
        "enum": [
          0,
          1,
          12,
          122,
          -122,
          -12,
          -1
        ],
        "type": "integer",
        "format": "int32"
      }
    }
  }
}

results into:

// ...

import com.squareup.moshi.Json
import com.squareup.moshi.JsonClass

/**
 * 
 *
 * Values: _0,_1,_12,_122,_12222,_1222,_1222
 */

@JsonClass(generateAdapter = false)
enum class IntegerEnum(val value: kotlin.Int) {

    @Json(name = "0")
    _0(0),

    @Json(name = "1")
    _1(1),

    @Json(name = "12")
    _12(12),

    @Json(name = "122")
    _122(122),

    @Json(name = "-122")
    _12222(-122),

    @Json(name = "-12")
    _1222(-12),

    @Json(name = "-1")
    _1222(-1);
}

Suggestion

Suggestion is to follow such naming - _12 for 12 (positive number), _m12 for -12 (negative number).

Start by reproducing the issue with the OpenAPI declaration in the report and inspect the Kotlin enum generation path. Compare generated names for positive and negative integer values, including the listed collisions. Done means the generated enum entries have distinct valid Kotlin names while preserving their original serialized values.