activesupport/lib/active_support/callbacks.rb
# frozen_string_literal: true
require "active_support/concern"
require "active_support/descendants_tracker"
require "active_support/core_ext/array/extract_options"
require "active_support/core_ext/class/attribute"
require "active_support/core_ext/string/filters"
require "active_support/core_ext/object/blank"
require "thread"
module ActiveSupport
# = Active Support \Callbacks
#
# \Callbacks are code hooks that are run at key points in an object's life cycle.
# The typical use case is to have a base class define a set of callbacks
# relevant to the other functionality it supplies, so that subclasses can
# install callbacks that enhance or modify the base functionality without
# needing to override or redefine methods of the base class.
#
# Mixing in this module allows you to define the events in the object's
# life cycle that will support callbacks (via ClassMethods#define_callbacks),
# set the instance methods, procs, or callback objects to be called (via
# ClassMethods#set_callback), and run the installed callbacks at the
# appropriate times (via +run_callbacks+).
#
# By default callbacks are halted by throwing +:abort+.
# See ClassMethods#define_callbacks for details.
#
# Three kinds of callbacks are supported: before callbacks, run before a
# certain event; after callbacks, run after the event; and around callbacks,
# blocks that surround the event, triggering it when they yield. Callback code
# can be contained in instance methods, procs or lambdas, or callback objects
# that respond to certain predetermined methods. See ClassMethods#set_callback
# for details.
#
# class Record
# include ActiveSupport::Callbacks
# define_callbacks :save
#
# def save
# run_callbacks :save do
# puts "- save"
# end
# end
# end
#
# class PersonRecord < Record
# set_callback :save, :before, :saving_message
# def saving_message
# puts "saving..."
# end
#
# set_callback :save, :after do |object|
# puts "saved"
# end
# end
#
# person = PersonRecord.new
# person.save
#
# Output:
# saving...
# - save
# saved
module Callbacks
extend Concern
included do
extend ActiveSupport::DescendantsTracker
class_attribute :__callbacks, instance_writer: false, default: {}
end
CALLBACK_FILTER_TYPES = [:before, :after, :around].freeze
# Runs the callbacks for the given event.
#
# Calls the before and around callbacks in the order they were set, yields
# the block (if given one), and then runs the after callbacks in reverse
# order.
#
# If the callback chain was halted, returns +false+. Otherwise returns the
# result of the block, +nil+ if no callbacks have been set, or +true+
# if callbacks have been set but no block is given.
#
# run_callbacks :save do
# save
# end
#
#--
#
# As this method is used in many places, and often wraps large portions of
# user code, it has an additional design goal of minimizing its impact on
# the visible call stack. An exception from inside a :before or :after
# callback can be as noisy as it likes -- but when control has passed
# smoothly through and into the supplied block, we want as little evidence
# as possible that we were here.
def run_callbacks(kind, type = nil)
callbacks = __callbacks[kind.to_sym]
if callbacks.empty?
yield if block_given?
else
env = Filters::Environment.new(self, false, nil)
next_sequence = callbacks.compile(type)
# Common case: no 'around' callbacks defined
if next_sequence.final?
next_sequence.invoke_before(env)
env.value = !env.halted && (!block_given? || yield)
next_sequence.invoke_after(env)
env.value
else
invoke_sequence = Proc.new do
skipped = nil
while true
current = next_sequence
current.invoke_before(env)
if current.final?
env.value = !env.halted && (!block_given? || yield)
elsif current.skip?(env)
(skipped ||= []) << current
next_sequence = next_sequence.nested
next
else
next_sequence = next_sequence.nested
begin
target, block, method, *arguments = current.expand_call_template(env, invoke_sequence)
target.send(method, *arguments, &block)
ensure
next_sequence = current
end
end
current.invoke_after(env)
skipped.pop.invoke_after(env) while skipped&.first
break env.value
end
end
invoke_sequence.call
end
end
end
private
# A hook invoked every time a before callback is halted.
# This can be overridden in ActiveSupport::Callbacks implementors in order
# to provide better debugging/logging.
def halted_callback_hook(filter, name)
end
module Conditionals # :nodoc: all
class Value
def initialize(&block)
@block = block
end
def call(target, value); @block.call(value); end
end
end
module Filters # :nodoc: all
Environment = Struct.new(:target, :halted, :value)
class Before
def initialize(user_callback, user_conditions, chain_config, filter, name)
halted_lambda = chain_config[:terminator]
@user_callback, @user_conditions, @halted_lambda, @filter, @name = user_callback, user_conditions, halted_lambda, filter, name
freeze
end
attr_reader :user_callback, :user_conditions, :halted_lambda, :filter, :name
def call(env)
target = env.target
value = env.value
halted = env.halted
if !halted && user_conditions.all? { |c| c.call(target, value) }
result_lambda = -> { user_callback.call target, value }
env.halted = halted_lambda.call(target, result_lambda)
if env.halted
target.send :halted_callback_hook, filter, name
end
end
env
end
def apply(callback_sequence)
callback_sequence.before(self)
end
end
class After
attr_reader :user_callback, :user_conditions, :halting
def initialize(user_callback, user_conditions, chain_config)
halting = chain_config[:skip_after_callbacks_if_terminated]
@user_callback, @user_conditions, @halting = user_callback, user_conditions, halting
freeze
end
def call(env)
target = env.target
value = env.value
halted = env.halted
if (!halted || !@halting) && user_conditions.all? { |c| c.call(target, value) }
user_callback.call target, value
end
env
end
def apply(callback_sequence)
callback_sequence.after(self)
end
end
class Around
def initialize(user_callback, user_conditions)
@user_callback, @user_conditions = user_callback, user_conditions
freeze
end
def apply(callback_sequence)
callback_sequence.around(@user_callback, @user_conditions)
end
end
end
class Callback # :nodoc:
def self.build(chain, filter, kind, options)
if filter.is_a?(String)
raise ArgumentError, <<-MSG.squish
Passing string to define a callback is not supported. See the `.set_callback`
documentation to see supported values.
MSG
end
new chain.name, filter, kind, options, chain.config
end
attr_accessor :kind, :name
attr_reader :chain_config, :filter
def initialize(name, filter, kind, options, chain_config)
@chain_config = chain_config
@name = name
@kind = kind
@filter = filter
@if = check_conditionals(options[:if])
@unless = check_conditionals(options[:unless])
compiled
end
def merge_conditional_options(chain, if_option:, unless_option:)
options = {
if: @if.dup,
unless: @unless.dup
}
options[:if].concat Array(unless_option)
options[:unless].concat Array(if_option)
self.class.build chain, @filter, @kind, options
end
def matches?(_kind, _filter)
@kind == _kind && filter == _filter
end
def duplicates?(other)
case @filter
when Symbol
matches?(other.kind, other.filter)
else
false
end
end
def compiled
@compiled ||=
begin
user_conditions = conditions_lambdas
user_callback = CallTemplate.build(@filter, self)
case kind
when :before
Filters::Before.new(user_callback.make_lambda, user_conditions, chain_config, @filter, name)
when :after
Filters::After.new(user_callback.make_lambda, user_conditions, chain_config)
when :around
Filters::Around.new(user_callback, user_conditions)
end
end
end
# Wraps code with filter
def apply(callback_sequence)
compiled.apply(callback_sequence)
end
def current_scopes
Array(chain_config[:scope]).map { |s| public_send(s) }
end
private
EMPTY_ARRAY = [].freeze
private_constant :EMPTY_ARRAY
def check_conditionals(conditionals)
return EMPTY_ARRAY if conditionals.blank?
conditionals = Array(conditionals)
if conditionals.any?(String)
raise ArgumentError, <<-MSG.squish
Passing string to be evaluated in :if and :unless conditional
options is not supported. Pass a symbol for an instance method,
or a lambda, proc or block, instead.
MSG
end
conditionals.freeze
end
def conditions_lambdas
conditions =
@if.map { |c| CallTemplate.build(c, self).make_lambda } +
@unless.map { |c| CallTemplate.build(c, self).inverted_lambda }
conditions.empty? ? EMPTY_ARRAY : conditions
end
end
# A future invocation of user-supplied code (either as a callback,
# or a condition filter).
module CallTemplate # :nodoc: all
class MethodCall
def initialize(method)
@method_name = method
end
# Return the parts needed to make this call, with the given
# input values.
#
# Returns an array of the form:
#
# [target, block, method, *arguments]
#
# This array can be used as such:
#
# target.send(method, *arguments, &block)
#
# The actual invocation is left up to the caller to minimize
# call stack pollution.
def expand(target, value, block)
[target, block, @method_name]
end
def make_lambda
lambda do |target, value, &block|
target.send(@method_name, &block)
end
end
def inverted_lambda
lambda do |target, value, &block|
!target.send(@method_name, &block)
end
end
end
class ObjectCall
def initialize(target, method)
@override_target = target
@method_name = method
end
def expand(target, value, block)
[@override_target || target, block, @method_name, target]
end
def make_lambda
lambda do |target, value, &block|
(@override_target || target).send(@method_name, target, &block)
end
end
def inverted_lambda
lambda do |target, value, &block|
!(@override_target || target).send(@method_name, target, &block)
end
end
end
class InstanceExec0
def initialize(block)
@override_block = block
end
def expand(target, value, block)
[target, @override_block, :instance_exec]
end
def make_lambda
lambda do |target, value, &block|
target.instance_exec(&@override_block)
end
end
def inverted_lambda
lambda do |target, value, &block|
!target.instance_exec(&@override_block)
end
end
end
class InstanceExec1
def initialize(block)
@override_block = block
end
def expand(target, value, block)
[target, @override_block, :instance_exec, target]
end
def make_lambda
lambda do |target, value, &block|
target.instance_exec(target, &@override_block)
end
end
def inverted_lambda
lambda do |target, value, &block|
!target.instance_exec(target, &@override_block)
end
end
end
class InstanceExec2
def initialize(block)
@override_block = block
end
def expand(target, value, block)
raise ArgumentError unless block
[target, @override_block || block, :instance_exec, target, block]
end
def make_lambda
lambda do |target, value, &block|
raise ArgumentError unless block
target.instance_exec(target, block, &@override_block)
end
end
def inverted_lambda
lambda do |target, value, &block|
raise ArgumentError unless block
!target.instance_exec(target, block, &@override_block)
end
end
end
class ProcCall
def initialize(target)
@override_target = target
end
def expand(target, value, block)
[@override_target || target, block, :call, target, value]
end
def make_lambda
lambda do |target, value, &block|
(@override_target || target).call(target, value, &block)
end
end
def inverted_lambda
lambda do |target, value, &block|
!(@override_target || target).call(target, value, &block)
end
end
end
# Filters support:
#
# Symbols:: A method to call.
# Procs:: A proc to call with the object.
# Objects:: An object with a <tt>before_foo</tt> method on it to call.
#
# All of these objects are converted into a CallTemplate and handled
# the same after this point.
def self.build(filter, callback)
case filter
when Symbol
MethodCall.new(filter)
when Conditionals::Value
ProcCall.new(filter)
when ::Proc
if filter.arity > 1
InstanceExec2.new(filter)
elsif filter.arity > 0
InstanceExec1.new(filter)
else
InstanceExec0.new(filter)
end
else
ObjectCall.new(filter, callback.current_scopes.join("_").to_sym)
end
end
end
# Execute before and after filters in a sequence instead of
# chaining them with nested lambda calls, see:
# https://github.com/rails/rails/issues/18011
class CallbackSequence # :nodoc:
def initialize(nested = nil, call_template = nil, user_conditions = nil)
@nested = nested
@call_template = call_template
@user_conditions = user_conditions
@before = nil
@after = nil
end
def before(before)
@before ||= []
@before.unshift(before)
self
end
def after(after)
@after ||= []
@after.push(after)
self
end
def around(call_template, user_conditions)
CallbackSequence.new(self, call_template, user_conditions)
end
def skip?(arg)
arg.halted || !@user_conditions.all? { |c| c.call(arg.target, arg.value) }
end
attr_reader :nested
def final?
!@call_template
end
def expand_call_template(arg, block)
@call_template.expand(arg.target, arg.value, block)
end
def invoke_before(arg)
@before&.each { |b| b.call(arg) }
end
def invoke_after(arg)
@after&.each { |a| a.call(arg) }
end
end
class CallbackChain # :nodoc:
include Enumerable
attr_reader :name, :config
def initialize(name, config)
@name = name
@config = {
scope: [:kind],
terminator: default_terminator
}.merge!(config)
@chain = []
@all_callbacks = nil
@single_callbacks = {}
@mutex = Mutex.new
end
def each(&block); @chain.each(&block); end
def index(o); @chain.index(o); end
def empty?; @chain.empty?; end
def insert(index, o)
@all_callbacks = nil
@single_callbacks.clear
@chain.insert(index, o)
end
def delete(o)
@all_callbacks = nil
@single_callbacks.clear
@chain.delete(o)
end
def clear
@all_callbacks = nil
@single_callbacks.clear
@chain.clear
self
end
def initialize_copy(other)
@all_callbacks = nil
@single_callbacks = {}
@chain = other.chain.dup
@mutex = Mutex.new
end
def compile(type)
if type.nil?
@all_callbacks || @mutex.synchronize do
final_sequence = CallbackSequence.new
@all_callbacks ||= @chain.reverse.inject(final_sequence) do |callback_sequence, callback|
callback.apply(callback_sequence)
end
end
else
@single_callbacks[type] || @mutex.synchronize do
final_sequence = CallbackSequence.new
@single_callbacks[type] ||= @chain.reverse.inject(final_sequence) do |callback_sequence, callback|
type == callback.kind ? callback.apply(callback_sequence) : callback_sequence
end
end
end
end
def append(*callbacks)
callbacks.each { |c| append_one(c) }
end
def prepend(*callbacks)
callbacks.each { |c| prepend_one(c) }
end
protected
attr_reader :chain
private
def append_one(callback)
@all_callbacks = nil
@single_callbacks.clear
remove_duplicates(callback)
@chain.push(callback)
end
def prepend_one(callback)
@all_callbacks = nil
@single_callbacks.clear
remove_duplicates(callback)
@chain.unshift(callback)
end
def remove_duplicates(callback)
@all_callbacks = nil
@single_callbacks.clear
@chain.delete_if { |c| callback.duplicates?(c) }
end
def default_terminator
Proc.new do |target, result_lambda|
terminate = true
catch(:abort) do
result_lambda.call
terminate = false
end
terminate
end
end
end
module ClassMethods
def normalize_callback_params(filters, block) # :nodoc:
type = CALLBACK_FILTER_TYPES.include?(filters.first) ? filters.shift : :before
options = filters.extract_options!
filters.unshift(block) if block
[type, filters, options.dup]
end
# This is used internally to append, prepend and skip callbacks to the
# CallbackChain.
def __update_callbacks(name) # :nodoc:
self.descendants.prepend(self).reverse_each do |target|
chain = target.get_callbacks name
yield target, chain.dup
end
end
# Install a callback for the given event.
#
# set_callback :save, :before, :before_method
# set_callback :save, :after, :after_method, if: :condition
# set_callback :save, :around, ->(r, block) { stuff; result = block.call; stuff }
#
# The second argument indicates whether the callback is to be run +:before+,
# +:after+, or +:around+ the event. If omitted, +:before+ is assumed. This
# means the first example above can also be written as:
#
# set_callback :save, :before_method
#
# The callback can be specified as a symbol naming an instance method; as a
# proc, lambda, or block; or as an object that responds to a certain method
# determined by the <tt>:scope</tt> argument to #define_callbacks.
#
# If a proc, lambda, or block is given, its body is evaluated in the context
# of the current object. It can also optionally accept the current object as
# an argument.
#
# Before and around callbacks are called in the order that they are set;
# after callbacks are called in the reverse order.
#
# Around callbacks can access the return value from the event, if it
# wasn't halted, from the +yield+ call.
#
# ===== Options
#
# * <tt>:if</tt> - A symbol or an array of symbols, each naming an instance
# method or a proc; the callback will be called only when they all return
# a true value.
#
# If a proc is given, its body is evaluated in the context of the
# current object. It can also optionally accept the current object as
# an argument.
# * <tt>:unless</tt> - A symbol or an array of symbols, each naming an
# instance method or a proc; the callback will be called only when they
# all return a false value.
#
# If a proc is given, its body is evaluated in the context of the
# current object. It can also optionally accept the current object as
# an argument.
# * <tt>:prepend</tt> - If +true+, the callback will be prepended to the
# existing chain rather than appended.
def set_callback(name, *filter_list, &block)
type, filters, options = normalize_callback_params(filter_list, block)
self_chain = get_callbacks name
mapped = filters.map do |filter|
Callback.build(self_chain, filter, type, options)
end
__update_callbacks(name) do |target, chain|
options[:prepend] ? chain.prepend(*mapped) : chain.append(*mapped)
target.set_callbacks name, chain
end
end
# Skip a previously set callback. Like #set_callback, <tt>:if</tt> or
# <tt>:unless</tt> options may be passed in order to control when the
# callback is skipped.
#
# Note: this example uses +PersonRecord+ and +#saving_message+, which you
# can see defined here[rdoc-ref:ActiveSupport::Callbacks]
#
# class Writer < PersonRecord
# attr_accessor :age
# skip_callback :save, :before, :saving_message, if: -> { age > 18 }
# end
#
# When if option returns true, callback is skipped.
#
# writer = Writer.new
# writer.age = 20
# writer.save
#
# Output:
# - save
# saved
#
# When if option returns false, callback is NOT skipped.
#
# young_writer = Writer.new
# young_writer.age = 17
# young_writer.save
#
# Output:
# saving...
# - save
# saved
#
# An <tt>ArgumentError</tt> will be raised if the callback has not
# already been set (unless the <tt>:raise</tt> option is set to <tt>false</tt>).
def skip_callback(name, *filter_list, &block)
type, filters, options = normalize_callback_params(filter_list, block)
options[:raise] = true unless options.key?(:raise)
__update_callbacks(name) do |target, chain|
filters.each do |filter|
callback = chain.find { |c| c.matches?(type, filter) }
if !callback && options[:raise]
raise ArgumentError, "#{type.to_s.capitalize} #{name} callback #{filter.inspect} has not been defined"
end
if callback && (options.key?(:if) || options.key?(:unless))
new_callback = callback.merge_conditional_options(chain, if_option: options[:if], unless_option: options[:unless])
chain.insert(chain.index(callback), new_callback)
end
chain.delete(callback)
end
target.set_callbacks name, chain
end
end
# Remove all set callbacks for the given event.
def reset_callbacks(name)
callbacks = get_callbacks name
self.descendants.each do |target|
chain = target.get_callbacks(name).dup
callbacks.each { |c| chain.delete(c) }
target.set_callbacks name, chain
end
set_callbacks(name, callbacks.dup.clear)
end
# Define sets of events in the object life cycle that support callbacks.
#
# define_callbacks :validate
# define_callbacks :initialize, :save, :destroy
#
# ===== Options
#
# * <tt>:terminator</tt> - Determines when a before filter will halt the
# callback chain, preventing following before and around callbacks from
# being called and the event from being triggered.
# This should be a lambda to be executed.
# The current object and the result lambda of the callback will be provided
# to the terminator lambda.
#
# define_callbacks :validate, terminator: ->(target, result_lambda) { result_lambda.call == false }
#
# In this example, if any before validate callbacks returns +false+,
# any successive before and around callback is not executed.
#
# The default terminator halts the chain when a callback throws +:abort+.
#
# * <tt>:skip_after_callbacks_if_terminated</tt> - Determines if after
# callbacks should be terminated by the <tt>:terminator</tt> option. By
# default after callbacks are executed no matter if callback chain was
# terminated or not. This option has no effect if <tt>:terminator</tt>
# option is set to +nil+.
#
# * <tt>:scope</tt> - Indicates which methods should be executed when an
# object is used as a callback.
#
# class Audit
# def before(caller)
# puts 'Audit: before is called'
# end
#
# def before_save(caller)
# puts 'Audit: before_save is called'
# end
# end
#
# class Account
# include ActiveSupport::Callbacks
#
# define_callbacks :save
# set_callback :save, :before, Audit.new
#
# def save
# run_callbacks :save do
# puts 'save in main'
# end
# end
# end
#
# In the above case whenever you save an account the method
# <tt>Audit#before</tt> will be called. On the other hand
#
# define_callbacks :save, scope: [:kind, :name]
#
# would trigger <tt>Audit#before_save</tt> instead. That's constructed
# by calling <tt>#{kind}_#{name}</tt> on the given instance. In this
# case "kind" is "before" and "name" is "save". In this context +:kind+
# and +:name+ have special meanings: +:kind+ refers to the kind of
# callback (before/after/around) and +:name+ refers to the method on
# which callbacks are being defined.
#
# A declaration like
#
# define_callbacks :save, scope: [:name]
#
# would call <tt>Audit#save</tt>.
#
# ===== Notes
#
# +names+ passed to +define_callbacks+ must not end with
# <tt>!</tt>, <tt>?</tt> or <tt>=</tt>.
#
# Calling +define_callbacks+ multiple times with the same +names+ will
# overwrite previous callbacks registered with #set_callback.
def define_callbacks(*names)
options = names.extract_options!
names.each do |name|
name = name.to_sym
([self] + self.descendants).each do |target|
target.set_callbacks name, CallbackChain.new(name, options)
end
module_eval <<-RUBY, __FILE__, __LINE__ + 1
def _run_#{name}_callbacks(&block)
run_callbacks #{name.inspect}, &block
end
def self._#{name}_callbacks
get_callbacks(#{name.inspect})
end
def self._#{name}_callbacks=(value)
set_callbacks(#{name.inspect}, value)
end
def _#{name}_callbacks
__callbacks[#{name.inspect}]
end
RUBY
end
end
protected
def get_callbacks(name) # :nodoc:
__callbacks[name.to_sym]
end
def set_callbacks(name, callbacks) # :nodoc:
unless singleton_class.method_defined?(:__callbacks, false)
self.__callbacks = __callbacks.dup
end
self.__callbacks[name.to_sym] = callbacks
self.__callbacks
end
end
end
end