class RBS::NoMixinFoundError

def self.check!(type_name, env:, member:)
  dic = case
        when type_name.class?
          env.class_decls
        when type_name.interface?
          env.interface_decls
        else
          raise
        end
  dic.key?(type_name) or raise new(type_name: type_name, member: member)
end

def initialize(type_name:, member:)
  @type_name = type_name
  @member = member
  super "#{Location.to_string location}: Could not find mixin: #{type_name}"
end

def location
  member.location
end