Rails 5.2 changes in callbacks

In version 5.1 you may see deprecation warnings in after_save callbacks (related to changes in ActiveRecord::Dirty module).
But since 5.2 these changes were applied.

For examples, I will use Rails 4.2.11 and Rails 5.2.3 and model User with email attribute. Let's do:

u = User.new(email: '[e-mail]')
u.save
u.email = '[e-mail]'
u.save

and look at after_save callback in time of last save.

1. attribute_changed?

Rails 4

> email_changed?
=> true

Rails 5.2

> email_changed?
=> false

but you can use saved_changes?

> saved_change_to_email?
=> true

2. changed?

Rails 4

> changed?
=> true

Rails 5.2

> changed?
=> false

but you can use saved_changes?

> saved_changes?
=> true

3. changes

Rails 4

> changes
=> {"email"=>["[e-mail]", "[e-mail]"]}

Rails 5.2

> changes
=> {}

but you can use saved_changes

> saved_changes
=> {"email"=>["[e-mail]", "[e-mail]"]}

4. previous_changes

Rails 4

> previous_changes
=> {"email"=>[nil, "[e-mail]"]}

Rails 5.2
Now, this method returns the changes that were just saved (like saved_changes).

> previous_changes
=> {"email"=>["[e-mail]", "[e-mail]"]}

this method has no replacement.