OpenAPITools/openapi-generator · error · RuntimeException

{enumSerializationLibrary} is an invalid enum property namin

Error message

{enumSerializationLibrary} is an invalid enum property naming option. Please choose from:
  {availableValues}

What it means

KotlinClientCodegen.setSerializationLibrary maps the 'serializationLibrary' additional property onto the enum {moshi, gson, jackson, kotlinx_serialization} via valueOf(). Unknown or case-mismatched values raise IllegalArgumentException, rethrown as a RuntimeException listing the four valid names. Default is moshi. The message wording ('invalid enum property naming option') is copy-pasted from modelPropertyNaming code and misleading — this is about the serialization library.

Source

Thrown at modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/KotlinClientCodegen.java:384

        }
        this.useCoroutines = useCoroutines;
    }

    /**
     * Sets the serialization engine for Kotlin
     *
     * @param enumSerializationLibrary The string representation of the serialization library as defined by
     *                                 {@link org.openapitools.codegen.languages.KotlinClientCodegen.SERIALIZATION_LIBRARY_TYPE}
     */
    public void setSerializationLibrary(final String enumSerializationLibrary) {
        try {
            this.serializationLibrary = SERIALIZATION_LIBRARY_TYPE.valueOf(enumSerializationLibrary);
        } catch (IllegalArgumentException ex) {
            StringBuilder sb = new StringBuilder(enumSerializationLibrary + " is an invalid enum property naming option. Please choose from:");
            for (SERIALIZATION_LIBRARY_TYPE t : SERIALIZATION_LIBRARY_TYPE.values()) {
                sb.append("\n  ").append(t.name());
            }
            throw new RuntimeException(sb.toString());
        }
    }

    @Override
    public String modelFilename(String templateName, String modelName) {
        String suffix = modelTemplateFiles().get(templateName);
        // If this was a proper template method, i wouldn't have to make myself throw up by doing this....
        if (getGenerateRoomModels() && suffix.startsWith("RoomModel")) {
            return roomModelFileFolder() + File.separator + toModelFilename(modelName) + suffix;
        } else {
            return modelFileFolder() + File.separator + toModelFilename(modelName) + suffix;
        }
    }

    public String roomModelFileFolder() {
        return outputFolder + File.separator + sourceFolder + File.separator + roomModelPackage.replace('.', File.separatorChar);
    }

View on GitHub (pinned to fcec517be3)

Solutions

Use exactly `moshi`, `gson`, `jackson`, or `kotlinx_serialization`.
Remember the default is moshi, so omitting the option is always safe.
Note library couplings enforced elsewhere: jvm-volley requires gson (line 749), the spring libraries require jackson (line 875) — set the value the library demands, not just any enum member.

Example fix

# before
openapi-generator-cli generate -g kotlin -i api.yaml -p serializationLibrary=kotlinx-serialization
# after
openapi-generator-cli generate -g kotlin -i api.yaml -p serializationLibrary=kotlinx_serialization

Defensive patterns

Strategy: validation

Validate before calling

# shell: kotlin serialization allowlist (default moshi)
sl="${SERIALIZATION_LIBRARY:-moshi}"
case "$sl" in
  moshi|gson|jackson|kotlinx_serialization) ;;
  *) echo "serializationLibrary must be moshi|gson|jackson|kotlinx_serialization, got: $sl" >&2; exit 2 ;;
esac

Type guard

// Kotlin
enum class KotlinSerialization(val option: String) { MOSHI("moshi"), GSON("gson"), JACKSON("jackson"), KOTLINX("kotlinx_serialization") }

fun serializationLibraryOf(v: String): KotlinSerialization? =
    KotlinSerialization.entries.firstOrNull { it.option == v }

Try / catch

try {
    DefaultGenerator().opts(clientOptInput).generate()
} catch (e: RuntimeException) {
    // message lists valid names despite the misleading 'property naming' wording
    throw IllegalStateException("Invalid kotlin serializationLibrary: ${e.message}", e)
}

Prevention

Remember the underscore: kotlinx_serialization, never kotlinx-serialization.
Pair the value with the library: spring ⇒ jackson, volley ⇒ gson, default ⇒ moshi.
Validate via the enum in build scripts instead of trusting free-text input.

When it happens

Trigger: `-g kotlin -p serializationLibrary=kotlinx-serialization` (hyphen instead of underscore), `KotlinxSerialization`, `Jackson` (capitalized), `gson-wasm`, `serde`; also `SerializationLibrary` (wrong key) leading to defaults elsewhere.

Common situations: Hyphen/underscore confusion for kotlinx_serialization; capitalized values from hand-written YAML; copying values from the Micronaut (micronaut_serde_jackson) or Java generators whose vocabularies differ.

Related errors

AI-assisted analysis of OpenAPITools/openapi-generator@fcec517be3 (2026-08-22). Data as JSON: /api/errors/2d5320d2b55a4966. Report an issue: GitHub.