Module: ActiveSupport::Deprecation::DeprecatedConstantAccessor

# File 'activesupport/lib/active_support/deprecation/constant_accessor.rb', line 6

def self.included(base)
  require "active_support/inflector/methods"

  extension = Module.new do
    def const_missing(missing_const_name)
      if class_variable_defined?(:@@_deprecated_constants)
        if (replacement = class_variable_get(:@@_deprecated_constants)[missing_const_name.to_s])
          replacement[:deprecator].warn(replacement[:message] || "#{name}::#{missing_const_name} is deprecated! Use #{replacement[:new]} instead.", caller_locations)
          return ActiveSupport::Inflector.constantize(replacement[:new].to_s)
        end
      end
      super
    end

    # Provides a way to rename constants with a deprecation cycle in which
    # both the old and new names work, but using the old one prints a
    # deprecation message.
    #
    # In order to rename <tt>A::B</tt> to <tt>C::D</tt>, you need to delete the
    # definition of <tt>A::B</tt> and declare the deprecation in A:
    #
    #   require "active_support/deprecation"
    #
    #   module A
    #     include ActiveSupport::Deprecation::DeprecatedConstantAccessor
    #
    #     deprecate_constant "B", "C::D", deprecator: ActiveSupport::Deprecation.new
    #   end
    #
    # The first argument is a constant name (no colons). It is the name of
    # the constant you want to deprecate in the enclosing class or module.
    #
    # The second argument is the constant path of the replacement. That
    # has to be a full path even if the replacement is defined in the same
    # namespace as the deprecated one was.
    #
    # In both cases, strings and symbols are supported.
    #
    # The deprecator keyword argument is the object that will print the
    # deprecation message, an instance of ActiveSupport::Deprecation.
    #
    # With that in place, references to <tt>A::B</tt> still work, they
    # evaluate to <tt>C::D</tt> now, and trigger a deprecation warning:
    #
    #   DEPRECATION WARNING: A::B is deprecated! Use C::D instead.
    #   (called from ...)
    #
    # The message can be customized with the optional message keyword
    # argument.
    #
    # For this to work, a const_missing hook is installed. When client
    # code references the deprecated constant, the callback prints the
    # message and constantizes the replacement.
    #
    # Caveat: If the deprecated constant name is reachable in a different
    # namespace and Ruby constant lookup finds it, the hook won't be
    # called and the deprecation won't work as intended. This may happen,
    # for example, if an ancestor of the enclosing namespace has a
    # constant with the same name. This is an unsupported edge case.
    def deprecate_constant(old_constant_name, new_constant_path, deprecator:, message: nil)
      class_variable_set(:@@_deprecated_constants, {}) unless class_variable_defined?(:@@_deprecated_constants)
      class_variable_get(:@@_deprecated_constants)[old_constant_name.to_s] = { new: new_constant_path, message: message, deprecator: deprecator }
    end
  end
  base.singleton_class.prepend extension
end