Investigate ability to improve error messages

[EvgeniyEsaulkov]

The goal is to make error messages more readable and clear for FE applications. It would be nice if the structure of error message will be displayed in the docs

[EvgeniyEsaulkov]

Dealing with errors in mutations

They occur due wrong user input and should provide useful feedback to the user. Solution was suggested by Dmitry Tsepelev in his article GraphQL on Rails: On the way to perfection.
We can define ValidationErrorType:

module Types
  class ValidationErrorsType < Types::BaseObject
    field :details, String, null: false
    field :full_messages, [String], null: false

    def details
      object.details.to_json
    end
  end
end

and customize type of returned object in mutation:

module Mutations
  class SignUp < BaseMutation
    argument :input, Types::SignUpInput, required: true

    field :authentication, Types::AuthenticationType, null: true
    field :errors, Types::ValidationErrorsType, null: true

    def resolve(input:)
      signup_user = SignupUser.call(input.to_h)

      if signup_user.success?
        { authentication: signup_user }
      else
        { errors: signup_user.user.errors }
      end
    end
  end
end

But in this case we can miss other types of errors such as authentication errors or 'wrong file type' (when we try to upload avatar image). So maybe it would be better to define common ErrorType:

module Types
  class ErrorType < Types::BaseObject
    field :message, String, null: false
  end
end

and use it like this:

module Mutations
  class SignUp < BaseMutation
    argument :input, Types::SignUpInput, required: true

    field :authentication, Types::AuthenticationType, null: true
    field :errors, [Types::ErrorType], null: true

    def resolve(input:)
      signup_user = SignupUser.call(input.to_h)

      if signup_user.success?
        { authentication: signup_user }
      else
        { errors: signup_user.error_data }
      end
    end
  end
end

[EvgeniyEsaulkov]

After discussing with FE developers I think we don't need to implement this feature for now