Redmine

I wrote a plugin which shall in the controller_issues_edit_before_save hook apply some modifications to the issue depending upon its properties, and perform sanity checks on the user's input which may raise an exception. The exception shall be displayed like other errors (e.g. XXX cannot be blank etc.) in the red box in the UI, blocking the issue changes from being saved.

The following stripped down code works fine, but I didn't find a documentation how in the case of an error the message can be displayed in the UI:

module MyExtension
  class MyHooks < Redmine::Hook::ViewListener
    def controller_issues_edit_before_save(context = {})
      issue = context[:issue]
      begin
        # the following function is rather complex, and may raise MyExtension::Errors::MyError...
        issue.my_modifications_an_checks
      rescue MyExtension::Errors::MyError => e
        # ...which is caught properly here...
        Rails.logger.info "# my issue sanity check failed with #{e.message}" 
        # ...but how can I display the error in the UI and cancel saving the issue at this point?
      end
    end
  end
end

Thanks in advance, Albrecht.