class GraphQL::StaticValidation::DirectivesAreDefined

def validate(context)
  directive_names = context.schema.directives.keys
  context.visitor[GraphQL::Language::Nodes::Directive] << -> (node, parent) {
    validate_directive(node, directive_names, context)
  }
end

def validate_directive(ast_directive, directive_names, context)
  if !directive_names.include?(ast_directive.name)
    context.errors << message("Directive @#{ast_directive.name} is not defined", ast_directive, context: context)
    GraphQL::Language::Visitor::SKIP
  else
    nil
  end
end