gitlab-org--gitlab-foss/app/models/system_note_metadata.rb

class SystemNoteMetadata < ActiveRecord::Base
  # These notes's action text might contain a reference that is external.
  # We should always force a deep validation upon references that are found
  # in this note type.
  # Other notes can always be safely shown as all its references are
  # in the same project (i.e. with the same permissions)
  TYPES_WITH_CROSS_REFERENCES = %w[
    commit cross_reference
    close duplicate
  ].freeze

  ICON_TYPES = %w[
    commit description merge confidential visible label assignee cross_reference
    title time_tracking branch milestone discussion task moved
    opened closed merged duplicate locked unlocked
    outdated
  ].freeze

  validates :note, presence: true
  validates :action, inclusion: ICON_TYPES, allow_nil: true

  belongs_to :note
end