[kotlin-client] Support for integer enums for multiplatform with custom serializer

[wing328]

based on #21983 and added a test to cover integer enums

cc @karismann (2019/03) @Zomzog (2019/04) @andrewemery (2019/10) @4brunu (2019/11) @yutaka0m (2020/03) @stefankoppier (2022/06) @e5l (2024/10) @dennisameling (2026/02)

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---

Summary by cubic

Adds a custom kotlinx.serialization serializer for non-string enums in the Kotlin Multiplatform client so integer/number enums encode and decode correctly. This fixes incorrect handling of numeric enums in multiplatform builds.

• New Features
  • Generate {{classname}}Serializer for non-string enums that uses the underlying {{dataType}}.serializer() and maps by value.
  • Annotate multiplatform non-string enums with @Serializable(with = ...); apply @SerialName only for string enums.
  • Add missing kotlinx.serialization imports (Decoder, Encoder, builtins.serializer).

^{Written for commit 96c5385. Summary will update on new commits.}

[cubic-dev-ai]

4 issues found across 36 files

Prompt for AI agents (unresolved issues)

Check if these issues are valid — if so, understand the root cause of each and fix them. If appropriate, use sub-agents to investigate and fix each issue separately.


<file name="modules/openapi-generator/src/main/resources/kotlin-client/enum_class.mustache">

<violation number="1" location="modules/openapi-generator/src/main/resources/kotlin-client/enum_class.mustache:187">
P3: Use `entries` instead of `values()` in enum deserialization to avoid per-call array allocation.</violation>
</file>

<file name="samples/client/petstore/kotlin-enum-integers-multiplatform/src/test/kotlin/org/openapitools/client/models/CodeTest.kt">

<violation number="1" location="samples/client/petstore/kotlin-enum-integers-multiplatform/src/test/kotlin/org/openapitools/client/models/CodeTest.kt:24">
P2: This test file currently has no actual test case, so it does not validate integer enum behavior.</violation>
</file>

<file name="samples/client/petstore/kotlin-enum-integers-multiplatform/src/commonMain/kotlin/org/openapitools/client/infrastructure/ApiClient.kt">

<violation number="1" location="samples/client/petstore/kotlin-enum-integers-multiplatform/src/commonMain/kotlin/org/openapitools/client/infrastructure/ApiClient.kt:23">
P1: The public primary constructor allows creating `ApiClient` without initializing `client`, which can crash at runtime with `UninitializedPropertyAccessException`.</violation>
</file>

<file name="samples/client/petstore/kotlin-enum-integers-multiplatform/src/test/kotlin/org/openapitools/client/apis/DefaultApiTest.kt">

<violation number="1" location="samples/client/petstore/kotlin-enum-integers-multiplatform/src/test/kotlin/org/openapitools/client/apis/DefaultApiTest.kt:30">
P2: This test case is empty, so it always passes and provides no coverage for the behavior it is named to validate.</violation>
</file>

_{Reply with feedback, questions, or to request a fix. Tag @cubic-dev-ai to re-run a review.}

[cubic-dev-ai]

P1: The public primary constructor allows creating ApiClient without initializing client, which can crash at runtime with UninitializedPropertyAccessException.

Prompt for AI agents

Check if this issue is valid — if so, understand the root cause and fix it. At samples/client/petstore/kotlin-enum-integers-multiplatform/src/commonMain/kotlin/org/openapitools/client/infrastructure/ApiClient.kt, line 23:

<comment>The public primary constructor allows creating `ApiClient` without initializing `client`, which can crash at runtime with `UninitializedPropertyAccessException`.</comment>

<file context>
@@ -0,0 +1,188 @@
+
+import org.openapitools.client.auth.*
+
+open class ApiClient(
+        private val baseUrl: String
+) {
</file context>

[cubic-dev-ai]

P2: This test file currently has no actual test case, so it does not validate integer enum behavior.

Prompt for AI agents

Check if this issue is valid — if so, understand the root cause and fix it. At samples/client/petstore/kotlin-enum-integers-multiplatform/src/test/kotlin/org/openapitools/client/models/CodeTest.kt, line 24:

<comment>This test file currently has no actual test case, so it does not validate integer enum behavior.</comment>

<file context>
@@ -0,0 +1,29 @@
+import org.openapitools.client.models.Code
+
+class CodeTest : ShouldSpec() {
+    init {
+        // uncomment below to create an instance of Code
+        //val modelInstance = Code()
</file context>

[cubic-dev-ai]

P2: This test case is empty, so it always passes and provides no coverage for the behavior it is named to validate.

Prompt for AI agents

Check if this issue is valid — if so, understand the root cause and fix it. At samples/client/petstore/kotlin-enum-integers-multiplatform/src/test/kotlin/org/openapitools/client/apis/DefaultApiTest.kt, line 30:

<comment>This test case is empty, so it always passes and provides no coverage for the behavior it is named to validate.</comment>

<file context>
@@ -0,0 +1,37 @@
+        //val apiInstance = DefaultApi()
+
+        // to test doGet
+        should("test doGet") {
+            // uncomment below to test doGet
+            //val result : DoGet200Response = apiInstance.doGet()
</file context>

[cubic-dev-ai]

P3: Use entries instead of values() in enum deserialization to avoid per-call array allocation.

Prompt for AI agents

Check if this issue is valid — if so, understand the root cause and fix it. At modules/openapi-generator/src/main/resources/kotlin-client/enum_class.mustache, line 187:

<comment>Use `entries` instead of `values()` in enum deserialization to avoid per-call array allocation.</comment>

<file context>
@@ -172,3 +177,20 @@ internal object {{classname}}Serializer : KSerializer<{{classname}}> {
+
+    override fun deserialize(decoder: Decoder): {{classname}} {
+        val value = decoder.decodeSerializableValue({{{dataType}}}.serializer())
+        return {{classname}}.values().firstOrNull { it.value == value }
+            ?: throw IllegalArgumentException("Unknown enum value: $value")
+    }
</file context>

Suggested change

	return {{classname}}.values().firstOrNull { it.value == value }
	return {{classname}}.entries.firstOrNull { it.value == value }