JsonWorldでrootがarrayなjson schemaを作る

as_json_schemaをoverrideして無理矢理作れる。

module Api
  module Resources
    class User
      include JsonWorld::DSL

      property(
        :id,
        type: Integer,
      )
      property(
        :screen_name,
        type: String,
      )
    end
    class Users
      include JsonWorld::DSL

      property(
        :users,
        type: Array,
        items: {
          type: Api::Resources::User
        }
      )

      attr_reader :users

      # @param [Api::Resources::User] users
      def initialize(users)
        @users = users
      end

      def self.as_json_schema
        super[:properties][:users]
      end

      def as_json(options = {})
        super(options)["users"]
      end
    end
  end
end

puts Api::Resources::User.to_json_schema
# =>
#{
#  "properties": {
#    "id": {
#      "type": "integer"
#    },
#    "screen_name": {
#      "type": "string"
#    }
#  },
#  "required": [
#    "id",
#    "screen_name"
#  ]
#}

puts Api::Resources::Users.to_json_schema
# =>
#{
#  "items": {
#    "properties": {
#      "id": {
#        "type": "integer"
#      },
#      "screen_name": {
#        "type": "string"
#      }
#    },
#    "required": [
#      "id",
#      "screen_name"
#    ]
#  },
#  "type": "array"
#}

参考

JsonWorldでモデルからJSON Schemaを生成する - Qiita

json_worldの全体的な使い方はこれを見る