DIRECTIVE_DEFINITION

The directive is applied to a directive.

Directives on directives is an experimental feature. Because GQLDirectiveExtension implements a sealed interface, you might have to handle the when case even though you did not opt into the feature. If that is the case, and if you do not want to support the experimental feature, you can safely ignore the case:

@OptIn(ApolloExperimental::class)
when (location) {
  // ...
  DIRECTIVE_DEFINITION -> error("irectives on directives is an experimental feature and is currently not supported. See https://github.com/graphql/graphql-spec/pull/567 for more details.")
}