[kotlin-client] Fix enum @JsonCreator to throw for unknown values instead of null, fixes #22662

modules/openapi-generator/src/main/resources/kotlin-client/enum_class.mustache

@@ -106,14 +106,34 @@ import kotlinx.serialization.*
         /**
          * Returns a valid [{{classname}}] for [data], null otherwise.
          */
-        {{#jackson}}@JvmStatic
-        @JsonCreator
-        {{/jackson}}{{^nonPublicApi}}{{#explicitApi}}public {{/explicitApi}}{{/nonPublicApi}}fun decode(data: kotlin.Any?): {{classname}}? = data?.let {
+{{^jackson}}
+        {{^nonPublicApi}}{{#explicitApi}}public {{/explicitApi}}{{/nonPublicApi}}fun decode(data: kotlin.Any?): {{classname}}? = data?.let {
           val normalizedData = "$it".lowercase()
           values().firstOrNull { value ->
             it == value || normalizedData == "$value".lowercase()
           }
         }
+{{/jackson}}
+{{#jackson}}
+        @JvmStatic
+        @JsonCreator
+        {{^nonPublicApi}}{{#explicitApi}}public {{/explicitApi}}{{/nonPublicApi}}fun decode(data: kotlin.Any?): {{classname}}{{#isNullable}}?{{/isNullable}} {
+          if (data == null) {
+{{#isNullable}}
+            return null
+{{/isNullable}}
+{{^isNullable}}
+            throw IllegalArgumentException("Value for {{classname}} cannot be null")
+{{/isNullable}}
+          }
+          val normalizedData = "$data".lowercase()
+          return values().firstOrNull { value ->
+            data == value || normalizedData == "$value".lowercase()
+          }{{#isNullable}}{{/isNullable}}{{^isNullable}}{{#enumUnknownDefaultCase}}
+            ?: {{#allowableValues}}{{#enumVars}}{{#-last}}{{&name}}{{/-last}}{{/enumVars}}{{/allowableValues}}{{/enumUnknownDefaultCase}}{{^enumUnknownDefaultCase}}
+            ?: throw IllegalArgumentException("Unknown {{classname}} value: $data"){{/enumUnknownDefaultCase}}{{/isNullable}}
+        }
+{{/jackson}}
     }
 }
 {{#kotlinx_serialization}}{{#enumUnknownDefaultCase}}

modules/openapi-generator/src/test/java/org/openapitools/codegen/kotlin/KotlinClientCodegenModelTest.java

@@ -714,6 +714,61 @@ public void testJacksonEnumsUseJsonCreator() throws IOException {
       TestUtils.assertFileContains(enumKt, "@JsonCreator");
   }
 
+  @Test
+  public void testJacksonEnumsThrowForUnknownValue() throws IOException {
+      File output = Files.createTempDirectory("test").toFile();
+      output.deleteOnExit();
+
+      final CodegenConfigurator configurator = new CodegenConfigurator()
+              .setGeneratorName("kotlin")
+              .setLibrary("jvm-retrofit2")
+              .setAdditionalProperties(new HashMap<>() {{
+                put(CodegenConstants.SERIALIZATION_LIBRARY, "jackson");
+                put(CodegenConstants.MODEL_PACKAGE, "model");
+              }})
+              .setInputSpec("src/test/resources/3_0/kotlin/issue22534-kotlin-numeric-enum.yaml")
+              .setOutputDir(output.getAbsolutePath().replace("\\", "/"));
+
+      final ClientOptInput clientOptInput = configurator.toClientOptInput();
+      DefaultGenerator generator = new DefaultGenerator();
+
+      generator.opts(clientOptInput).generate();
+
+      final Path enumKt = Paths.get(output + "/src/main/kotlin/model/ExampleNumericEnum.kt");
+
+      // Verify that the decode function throws IllegalArgumentException for unknown values
+      TestUtils.assertFileContains(enumKt, "throw IllegalArgumentException(\"Unknown ExampleNumericEnum value: $data\")");
+  }
+
+  @Test
+  public void testJacksonEnumsWithUnknownDefaultCase() throws IOException {
+      File output = Files.createTempDirectory("test").toFile();
+      output.deleteOnExit();
+
+      final CodegenConfigurator configurator = new CodegenConfigurator()
+              .setGeneratorName("kotlin")
+              .setLibrary("jvm-retrofit2")
+              .setAdditionalProperties(new HashMap<>() {{
+                put(CodegenConstants.SERIALIZATION_LIBRARY, "jackson");
+                put(CodegenConstants.MODEL_PACKAGE, "model");
+                put(CodegenConstants.ENUM_UNKNOWN_DEFAULT_CASE, "true");
+              }})
+              .setInputSpec("src/test/resources/3_0/kotlin/issue22534-kotlin-numeric-enum.yaml")
+              .setOutputDir(output.getAbsolutePath().replace("\\", "/"));
+
+      final ClientOptInput clientOptInput = configurator.toClientOptInput();
+      DefaultGenerator generator = new DefaultGenerator();
+
+      generator.opts(clientOptInput).generate();
+
+      final Path enumKt = Paths.get(output + "/src/main/kotlin/model/ExampleNumericEnum.kt");
+
+      // With enumUnknownDefaultCase=true, should return the default value instead of throwing
+      TestUtils.assertFileContains(enumKt, "@JsonEnumDefaultValue");
+      // Should NOT contain throw for unknown values when enumUnknownDefaultCase is enabled
+      TestUtils.assertFileNotContains(enumKt, "throw IllegalArgumentException(\"Unknown ExampleNumericEnum value");
+  }
+
     @Test(description = "convert an empty model to object")
     public void emptyModelKotlinxSerializationTest() throws IOException {
         final Schema<?> schema = new ObjectSchema()

samples/client/echo_api/kotlin-jvm-spring-3-restclient/src/main/kotlin/org/openapitools/client/models/StringEnumRef.kt

@@ -62,11 +62,15 @@ enum class StringEnumRef(@get:JsonValue val value: kotlin.String) {
          */
         @JvmStatic
         @JsonCreator
-        fun decode(data: kotlin.Any?): StringEnumRef? = data?.let {
-          val normalizedData = "$it".lowercase()
-          values().firstOrNull { value ->
-            it == value || normalizedData == "$value".lowercase()
+        fun decode(data: kotlin.Any?): StringEnumRef {
+          if (data == null) {
+            throw IllegalArgumentException("Value for StringEnumRef cannot be null")
           }
+          val normalizedData = "$data".lowercase()
+          return values().firstOrNull { value ->
+            data == value || normalizedData == "$value".lowercase()
+          }
+            ?: unknown_default_open_api
         }
     }
 }

samples/client/echo_api/kotlin-jvm-spring-3-webclient/src/main/kotlin/org/openapitools/client/models/StringEnumRef.kt

@@ -62,11 +62,15 @@ enum class StringEnumRef(@get:JsonValue val value: kotlin.String) {
          */
         @JvmStatic
         @JsonCreator
-        fun decode(data: kotlin.Any?): StringEnumRef? = data?.let {
-          val normalizedData = "$it".lowercase()
-          values().firstOrNull { value ->
-            it == value || normalizedData == "$value".lowercase()
+        fun decode(data: kotlin.Any?): StringEnumRef {
+          if (data == null) {
+            throw IllegalArgumentException("Value for StringEnumRef cannot be null")
           }
+          val normalizedData = "$data".lowercase()
+          return values().firstOrNull { value ->
+            data == value || normalizedData == "$value".lowercase()
+          }
+            ?: unknown_default_open_api
         }
     }
 }