quarkusio/quarkus · error · IllegalArgumentException

Couldn't fetch '' class from index

Error message

Couldn't fetch '' class from index

What it means

JandexUtil.resolveTypeParameters walks the class/interface hierarchy in a Jandex index to find the captured generic arguments of a target type. If the input class itself cannot be found in the supplied IndexView, fetchFromIndex throws ClassNotIndexedException which is rethrown as IllegalArgumentException("Couldn't fetch '<name>' class from index"). The index must contain every class on the path to the target.

Source

Thrown at core/deployment/src/main/java/io/quarkus/deployment/util/JandexUtil.java:76

     *
     * If we call
     *
     * <pre>
     *
     * JandexUtil.resolveTypeParameters(DotName.createSimple(MyList.class.getName()),
     *         DotName.createSimple(List.class.getName()), index)
     *
     * </pre>
     *
     * then the result will contain a single element of class ClassType whose name() would return a DotName for String
     */
    public static List<Type> resolveTypeParameters(DotName input, DotName target, IndexView index) {
        final ClassInfo inputClassInfo;
        try {
            inputClassInfo = fetchFromIndex(input, index);
        } catch (Exception e) {
            // keep compatibility with what clients already expect
            throw new IllegalArgumentException("Couldn't fetch '" + input.toString() + "' class from index", e);
        }

        Type startingType = getType(inputClassInfo, index);
        Set<DotName> unindexedClasses = new LinkedHashSet<>();
        final List<Type> result = findParametersRecursively(startingType, target,
                new HashSet<>(), index, unindexedClasses);
        // null means not found
        if (result == null) {
            if (unindexedClasses.isEmpty()) {
                // no un-indexed classes means that there were no problems traversing the class and interface hierarchies
                return Collections.emptyList();
            }
            throw new IllegalArgumentException(
                    "The following classes were not part of the index and could be the reason that the captured generic type of '"
                            + target + "' could not be determined: " + unindexedClasses);
        }

        return result;

View on GitHub (pinned to e1c734241f)

Solutions

1. Ensure the class is added to the index: for build steps, augment the index via AdditionalClassesIndexBuildItem or register-for-index patterns
2. Verify the exact binary name (FQCN, not Class.getName() of array/inner with $ mismatches) used for the DotName
3. Check that the index you pass is the full application index (CuratedApplication/index) not a partial one
4. If the class may legitimately be absent, guard with index.getClassByName(input) == null before calling

Example fix

// before
List<Type> params = JandexUtil.resolveTypeParameters(input, target, partialIndex);
// after
if (partialIndex.getClassByName(input) == null) {
    input = additionalIndex.getClassByName(input); // or throw a clear build error
}
List<Type> params = JandexUtil.resolveTypeParameters(input, target, index);

if (index.getClassByName(input) == null) {
    throw new IllegalStateException(input + " is not indexed; add it via AdditionalClassesIndexBuildItem");
}
List<Type> params = JandexUtil.resolveTypeParameters(input, target, index);

try {
    return JandexUtil.resolveTypeParameters(input, target, index);
} catch (IllegalArgumentException e) {
    if (e.getMessage().contains("Couldn't fetch")) {
        log.warn("Class not in index: " + input);
        return Collections.emptyList(); // or re-index
    }
    throw e;
}

When it happens

Trigger: Calling JandexUtil.resolveTypeParameters(input, target, index) where input's DotName is not in the IndexView — e.g. using a limited application index that excludes the class, a generated class not indexed yet, or a fully qualified name that doesn't match the indexed binary name.

Common situations: Build steps computing generic bindings (e.g. resolving Entity/repository type parameters) for classes from external jars not included in the Jandex index; typos in class names built with DotName.createSimple; indexes built with too-narrow package filters.

Related errors

• The following classes were not part of the index and could b
• Our supertype instance does not match supertype declared ar
• Unsupported type: " + type
• Missing type argument mapping for
• Illegal type in hierarchy:

AI-assisted analysis of quarkusio/quarkus@e1c734241f (2026-09-05). Data as JSON: /api/errors/2e40532767d4406d. Report an issue: GitHub.