private static ExtensionArtifact getSpecification(TreeLogger logger,
GeneratorContext context, JClassType userType)
throws UnableToCompleteException {
final ManifestInfo spec = userType.getAnnotation(Extension.ManifestInfo.class);
if (spec != null) {
return new ExtensionArtifact(spec.name(), spec.description(),
spec.version(), spec.permissions(), spec.updateUrl(),
createIconResources(logger, context, userType, spec.icons()),
spec.publicKey());
}