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rails--rails/activesupport/lib/active_support/callbacks.rb
claudiob 9c65c539e2 Add config to halt callback chain on return false 
This stems from [a comment](rails#17227 (comment)) by @dhh.
In summary:

* New Rails 5.0 apps will not accept `return false` as a way to halt callback chains, and will not display a deprecation warning.
* Existing apps ported to Rails 5.0 will still accept `return false` as a way to halt callback chains, albeit with a deprecation warning.

For this purpose, this commit introduces a Rails configuration option:

```ruby
config.active_support.halt_callback_chains_on_return_false
```

For new Rails 5.0 apps, this option will be set to `false` by a new initializer
`config/initializers/callback_terminator.rb`:

```ruby
Rails.application.config.active_support.halt_callback_chains_on_return_false = false
```

For existing apps ported to Rails 5.0, the initializers above will not exist.
Even running `rake rails:update` will not create this initializer.

Since the default value of `halt_callback_chains_on_return_false` is set to
`true`, these apps will still accept `return true` as a way to halt callback
chains, displaying a deprecation warning.

Developers will be able to switch to the new behavior (and stop the warning)
by manually adding the line above to their `config/application.rb`.

A gist with the suggested release notes to add to Rails 5.0 after this
commit is available at https://gist.github.com/claudiob/614c59409fb7d11f2931
2015-01-02 15:31:56 -08:00

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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/kernel/reporting'
require 'active_support/core_ext/kernel/singleton_class'
require 'active_support/core_ext/string/filters'
require 'thread'
module ActiveSupport
# 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+).
#
# 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
end
CALLBACK_FILTER_TYPES = [:before, :after, :around]
# 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
def run_callbacks(kind, &block)
send "_run_#{kind}_callbacks", &block
end
private
def _run_callbacks(callbacks, &block)
if callbacks.empty?
block.call if block
else
runner = callbacks.compile
e = Filters::Environment.new(self, false, nil, block)
runner.call(e).value
end
end
# A hook invoked every time a before callback is halted.
# This can be overridden in AS::Callback implementors in order
# to provide better debugging/logging.
def halted_callback_hook(filter)
end
module Conditionals # :nodoc:
class Value
def initialize(&block)
@block = block
end
def call(target, value); @block.call(value); end
end
end
module Filters
Environment = Struct.new(:target, :halted, :value, :run_block)
class End
def call(env)
block = env.run_block
env.value = !env.halted && (!block || block.call)
env
end
end
ENDING = End.new
class Before
def self.build(callback_sequence, user_callback, user_conditions, chain_config, filter)
halted_lambda = chain_config[:terminator]
if chain_config.key?(:terminator) && user_conditions.any?
halting_and_conditional(callback_sequence, user_callback, user_conditions, halted_lambda, filter)
elsif chain_config.key? :terminator
halting(callback_sequence, user_callback, halted_lambda, filter)
elsif user_conditions.any?
conditional(callback_sequence, user_callback, user_conditions)
else
simple callback_sequence, user_callback
end
end
def self.halting_and_conditional(callback_sequence, user_callback, user_conditions, halted_lambda, filter)
callback_sequence.before do |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
end
end
env
end
end
private_class_method :halting_and_conditional
def self.halting(callback_sequence, user_callback, halted_lambda, filter)
callback_sequence.before do |env|
target = env.target
value = env.value
halted = env.halted
unless halted
result_lambda = -> { user_callback.call target, value }
env.halted = halted_lambda.call(target, result_lambda)
if env.halted
target.send :halted_callback_hook, filter
end
end
env
end
end
private_class_method :halting
def self.conditional(callback_sequence, user_callback, user_conditions)
callback_sequence.before do |env|
target = env.target
value = env.value
if user_conditions.all? { |c| c.call(target, value) }
user_callback.call target, value
end
env
end
end
private_class_method :conditional
def self.simple(callback_sequence, user_callback)
callback_sequence.before do |env|
user_callback.call env.target, env.value
env
end
end
private_class_method :simple
end
class After
def self.build(callback_sequence, user_callback, user_conditions, chain_config)
if chain_config[:skip_after_callbacks_if_terminated]
if chain_config.key?(:terminator) && user_conditions.any?
halting_and_conditional(callback_sequence, user_callback, user_conditions)
elsif chain_config.key?(:terminator)
halting(callback_sequence, user_callback)
elsif user_conditions.any?
conditional callback_sequence, user_callback, user_conditions
else
simple callback_sequence, user_callback
end
else
if user_conditions.any?
conditional callback_sequence, user_callback, user_conditions
else
simple callback_sequence, user_callback
end
end
end
def self.halting_and_conditional(callback_sequence, user_callback, user_conditions)
callback_sequence.after do |env|
target = env.target
value = env.value
halted = env.halted
if !halted && user_conditions.all? { |c| c.call(target, value) }
user_callback.call target, value
end
env
end
end
private_class_method :halting_and_conditional
def self.halting(callback_sequence, user_callback)
callback_sequence.after do |env|
unless env.halted
user_callback.call env.target, env.value
end
env
end
end
private_class_method :halting
def self.conditional(callback_sequence, user_callback, user_conditions)
callback_sequence.after do |env|
target = env.target
value = env.value
if user_conditions.all? { |c| c.call(target, value) }
user_callback.call target, value
end
env
end
end
private_class_method :conditional
def self.simple(callback_sequence, user_callback)
callback_sequence.after do |env|
user_callback.call env.target, env.value
env
end
end
private_class_method :simple
end
class Around
def self.build(callback_sequence, user_callback, user_conditions, chain_config)
if chain_config.key?(:terminator) && user_conditions.any?
halting_and_conditional(callback_sequence, user_callback, user_conditions)
elsif chain_config.key? :terminator
halting(callback_sequence, user_callback)
elsif user_conditions.any?
conditional(callback_sequence, user_callback, user_conditions)
else
simple(callback_sequence, user_callback)
end
end
def self.halting_and_conditional(callback_sequence, user_callback, user_conditions)
callback_sequence.around do |env, &run|
target = env.target
value = env.value
halted = env.halted
if !halted && user_conditions.all? { |c| c.call(target, value) }
user_callback.call(target, value) {
env = run.call env
env.value
}
env
else
run.call env
end
end
end
private_class_method :halting_and_conditional
def self.halting(callback_sequence, user_callback)
callback_sequence.around do |env, &run|
target = env.target
value = env.value
if env.halted
run.call env
else
user_callback.call(target, value) {
env = run.call env
env.value
}
env
end
end
end
private_class_method :halting
def self.conditional(callback_sequence, user_callback, user_conditions)
callback_sequence.around do |env, &run|
target = env.target
value = env.value
if user_conditions.all? { |c| c.call(target, value) }
user_callback.call(target, value) {
env = run.call env
env.value
}
env
else
run.call env
end
end
end
private_class_method :conditional
def self.simple(callback_sequence, user_callback)
callback_sequence.around do |env, &run|
user_callback.call(env.target, env.value) {
env = run.call env
env.value
}
env
end
end
private_class_method :simple
end
end
class Callback #:nodoc:#
def self.build(chain, filter, kind, options)
new chain.name, filter, kind, options, chain.config
end
attr_accessor :kind, :name
attr_reader :chain_config
def initialize(name, filter, kind, options, chain_config)
@chain_config = chain_config
@name = name
@kind = kind
@filter = filter
@key = compute_identifier filter
@if = Array(options[:if])
@unless = Array(options[:unless])
end
def filter; @key; end
def raw_filter; @filter; end
def merge(chain, new_options)
options = {
:if => @if.dup,
:unless => @unless.dup
}
options[:if].concat Array(new_options.fetch(:unless, []))
options[:unless].concat Array(new_options.fetch(:if, []))
self.class.build chain, @filter, @kind, options
end
def matches?(_kind, _filter)
@kind == _kind && filter == _filter
end
def duplicates?(other)
case @filter
when Symbol, String
matches?(other.kind, other.filter)
else
false
end
end
# Wraps code with filter
def apply(callback_sequence)
user_conditions = conditions_lambdas
user_callback = make_lambda @filter
case kind
when :before
Filters::Before.build(callback_sequence, user_callback, user_conditions, chain_config, @filter)
when :after
Filters::After.build(callback_sequence, user_callback, user_conditions, chain_config)
when :around
Filters::Around.build(callback_sequence, user_callback, user_conditions, chain_config)
end
end
private
def invert_lambda(l)
lambda { |*args, &blk| !l.call(*args, &blk) }
end
# Filters support:
#
# Symbols:: A method to call.
# Strings:: Some content to evaluate.
# 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 lambda and handled
# the same after this point.
def make_lambda(filter)
case filter
when Symbol
lambda { |target, _, &blk| target.send filter, &blk }
when String
l = eval "lambda { |value| #{filter} }"
lambda { |target, value| target.instance_exec(value, &l) }
when Conditionals::Value then filter
when ::Proc
if filter.arity > 1
return lambda { |target, _, &block|
raise ArgumentError unless block
target.instance_exec(target, block, &filter)
}
end
if filter.arity <= 0
lambda { |target, _| target.instance_exec(&filter) }
else
lambda { |target, _| target.instance_exec(target, &filter) }
end
else
scopes = Array(chain_config[:scope])
method_to_call = scopes.map{ |s| public_send(s) }.join("_")
lambda { |target, _, &blk|
filter.public_send method_to_call, target, &blk
}
end
end
def compute_identifier(filter)
case filter
when String, ::Proc
filter.object_id
else
filter
end
end
def conditions_lambdas
@if.map { |c| make_lambda c } +
@unless.map { |c| invert_lambda make_lambda c }
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
def initialize(&call)
@call = call
@before = []
@after = []
end
def before(&before)
@before.unshift(before)
self
end
def after(&after)
@after.push(after)
self
end
def around(&around)
CallbackSequence.new do |*args|
around.call(*args) {
self.call(*args)
}
end
end
def call(*args)
@before.each { |b| b.call(*args) }
value = @call.call(*args)
@after.each { |a| a.call(*args) }
value
end
end
# An Array with a compile method.
class CallbackChain #:nodoc:#
include Enumerable
attr_reader :name, :config
# If true, any callback returning +false+ will halt the entire callback
# chain and display a deprecation message. If false, callback chains will
# only be halted by calling +throw :abort+. Defaults to +true+.
class_attribute :halt_and_display_warning_on_return_false
self.halt_and_display_warning_on_return_false = true
def initialize(name, config)
@name = name
@config = {
scope: [:kind],
terminator: default_terminator
}.merge!(config)
@chain = []
@callbacks = nil
@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)
@callbacks = nil
@chain.insert(index, o)
end
def delete(o)
@callbacks = nil
@chain.delete(o)
end
def clear
@callbacks = nil
@chain.clear
self
end
def initialize_copy(other)
@callbacks = nil
@chain = other.chain.dup
@mutex = Mutex.new
end
def compile
@callbacks || @mutex.synchronize do
final_sequence = CallbackSequence.new { |env| Filters::ENDING.call(env) }
@callbacks ||= @chain.reverse.inject(final_sequence) do |callback_sequence, callback|
callback.apply callback_sequence
end
end
end
def append(*callbacks)
callbacks.each { |c| append_one(c) }
end
def prepend(*callbacks)
callbacks.each { |c| prepend_one(c) }
end
protected
def chain; @chain; end
private
def append_one(callback)
@callbacks = nil
remove_duplicates(callback)
@chain.push(callback)
end
def prepend_one(callback)
@callbacks = nil
remove_duplicates(callback)
@chain.unshift(callback)
end
def remove_duplicates(callback)
@callbacks = nil
@chain.delete_if { |c| callback.duplicates?(c) }
end
def default_terminator
Proc.new do |target, result_lambda|
terminate = true
catch(:abort) do
result = result_lambda.call if result_lambda.is_a?(Proc)
if halt_and_display_warning_on_return_false && result == false
display_deprecation_warning_for_false_terminator
else
terminate = false
end
end
terminate
end
end
def display_deprecation_warning_for_false_terminator
ActiveSupport::Deprecation.warn(<<-MSG.squish)
Returning `false` in a callback will not implicitly halt a callback chain in the next release of Rails.
To explicitly halt a callback chain, please use `throw :abort` instead.
MSG
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] + ActiveSupport::DescendantsTracker.descendants(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_meth
# set_callback :save, :after, :after_meth, if: :condition
# set_callback :save, :around, ->(r, block) { stuff; result = block.call; stuff }
#
# The second arguments 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_meth
#
# The callback can be specified as a symbol naming an instance method; as a
# proc, lambda, or block; as a string to be instance evaluated; 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 naming an instance method or a proc; the
# callback will be called only when it returns a +true+ value.
# * <tt>:unless</tt> - A symbol naming an instance method or a proc; the
# callback will be called only when it returns a +false+ value.
# * <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.
#
# class Writer < Person
# skip_callback :validate, :before, :check_membership, if: -> { self.age > 18 }
# end
def skip_callback(name, *filter_list, &block)
type, filters, options = normalize_callback_params(filter_list, block)
__update_callbacks(name) do |target, chain|
filters.each do |filter|
filter = chain.find {|c| c.matches?(type, filter) }
if filter && options.any?
new_filter = filter.merge(chain, options)
chain.insert(chain.index(filter), new_filter)
end
chain.delete(filter)
end
target.set_callbacks name, chain
end
end
# Remove all set callbacks for the given event.
def reset_callbacks(name)
callbacks = get_callbacks name
ActiveSupport::DescendantsTracker.descendants(self).each do |target|
chain = target.get_callbacks(name).dup
callbacks.each { |c| chain.delete(c) }
target.set_callbacks name, chain
end
self.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 return result of the callback will be called
# with the lambda.
#
# define_callbacks :validate, terminator: ->(target, result) { result == false }
#
# In this example, if any before validate callbacks returns +false+,
# any successive before and around callback is not executed.
# Defaults to +false+, meaning no value halts the chain.
#
# * <tt>:skip_after_callbacks_if_terminated</tt> - Determines if after
# callbacks should be terminated by the <tt>:terminator</tt> option. By
# default after callbacks executed no matter if callback chain was
# terminated or not. Option makes sense only when <tt>:terminator</tt>
# option is specified.
#
# * <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>.
#
# NOTE: +method_name+ passed to `define_model_callbacks` must not end with
# `!`, `?` or `=`.
def define_callbacks(*names)
options = names.extract_options!
names.each do |name|
class_attribute "_#{name}_callbacks"
set_callbacks name, CallbackChain.new(name, options)
module_eval <<-RUBY, __FILE__, __LINE__ + 1
def _run_#{name}_callbacks(&block)
_run_callbacks(_#{name}_callbacks, &block)
end
RUBY
end
end
protected
def get_callbacks(name)
send "_#{name}_callbacks"
end
def set_callbacks(name, callbacks)
send "_#{name}_callbacks=", callbacks
end
end
end
end
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