instructure/canvas-lms · error · CedarAi::Errors::GraderError

An unexpected error occurred while grading.

Error message

An unexpected error occurred while grading.

What it means

The final rescue in GradeService#call catches every non-Cedar exception (bugs, DB errors, nil rubric data, etc.), logs '[GradeService] Unexpected error: ...', and re-raises CedarAi::Errors::GraderError with the fixed user-safe message 'An unexpected error occurred while grading.' It deliberately hides internal details from end users.

Solutions

1. Search server logs for '[GradeService] Unexpected error: <Class>' to find the real root cause.
2. Validate rubric_data shape before calling the service (each criterion has :description and criteria ratings).
3. Fix the underlying bug (nil guards, data normalization) rather than treating the generic message.
4. Retry the grading job after correcting the input data.

Example fix

# before
service.call(rubric_data: nil)
# after
raise ArgumentError, 'rubric_data is required' if rubric_data.blank?
service.call(rubric_data: rubric_data)

raise ArgumentError, 'rubric_data must be an array of criteria' unless rubric_data.is_a?(Array) && rubric_data.all? { |c| c[:description].present? }

begin
  GradeService.call(...)
rescue CedarAi::Errors::GraderError => e
  if e.message == 'An unexpected error occurred while grading.'
    check_server_logs_for_root_cause
  end
end

When it happens

Trigger: Any unexpected exception inside the grading flow: nil/malformed rubric_data passed to normalize_rubric_for_prompt, DB errors saving grades, NoMethodError from unexpected submission shape, I18n/translation issues — anything not a CedarClientError.

Common situations: Rubric data with unexpected structure (missing :description keys), nil rubric passed in, database constraint failures while persisting grades, code regressions after a Cedar integration change.

Understand the failure class

Background: "This is a bug, please report it": internal invariant violations, unreachable panics, and SNH errors explained — this error's family across 47 libraries.

Related errors

• friendly_cedar_error_for(e)
• A new_id, '# ', referenced an existing # and the # with #…
• A new_integration_id, '#
• A student referenced a non-existent user #
• A user did not pass validation

AI-assisted analysis of instructure/canvas-lms@1c9f0bb801 (2026-09-15). Data as JSON: /api/errors/f049e1c00e817b0e. Report an issue: GitHub.

Appendix: source

Thrown at app/services/grade_service.rb:64

        feature_slug: "grading-assistance",
        root_account_uuid: @root_account_uuid,
        current_user: @current_user
      )

      map_grade_essay_results_to_canvas(grading_results, @rubric)
    # These subclasses have static, user-safe messages and can be shown directly.
    # If new CedarClientError subclasses are added with user-safe messages, add them here.
    rescue InstructureMiscPlugin::Extensions::CedarClient::ValidationError,
           InstructureMiscPlugin::Extensions::CedarClient::CedarLimitReachedError,
           InstructureMiscPlugin::Extensions::CedarClient::UnsupportedLanguageError,
           InstructureMiscPlugin::Extensions::CedarClient::ContentTooLongError => e
      raise CedarAi::Errors::GraderError, friendly_cedar_error_for(e)
    rescue InstructureMiscPlugin::Extensions::CedarClient::CedarClientError => e
      Rails.logger.error("[GradeService] Cedar API error: #{e.message}")
      raise CedarAi::Errors::GraderError, friendly_cedar_error_for(e)
    rescue => e
      Rails.logger.error("[GradeService] Unexpected error: #{e.class}: #{e.message}")
      raise CedarAi::Errors::GraderError, I18n.t("An unexpected error occurred while grading.")
    end
  end

  def self.normalize_rubric_for_prompt(rubric_data)
    rubric_data.each_with_object({}) do |criterion, acc|
      key = criterion[:description]
      acc[key] = {
        "Criteria" => (criterion[:ratings] || []).map do |rating|
          {
            "Description" => rating_description_for(criterion, rating),
            "Points" => rating[:points]
          }
        end,
        "MaximumPoints" => criterion[:points]
      }
    end
  end

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