Refactor AS::Callbacks halt config and fix the documentation

Move from `AS::Callbacks::CallbackChain.halt_and_display_warning_on_return_false`
to `AS::Callbacks.halt_and_display_warning_on_return_false` base on
[this
discussion](https://github.com/rails/rails/pull/21218#discussion_r39354580)

Fix the documentation broken by 0a120a818d413c64ff9867125f0b03788fc306f8

1 files changed, 14 insertions, 11 deletions

diff --git a/guides/source/upgrading_ruby_on_rails.md b/guides/source/upgrading_ruby_on_rails.md
index 52464a1c51..490bda3571 100644
--- a/guides/source/upgrading_ruby_on_rails.md
+++ b/guides/source/upgrading_ruby_on_rails.md
@@ -55,23 +55,26 @@ Upgrading from Rails 4.2 to Rails 5.0
 
 ### Halting callback chains by returning `false`
 
-In Rails 4.2, when a 'before' callback returns `false` in ActiveRecord,
-ActiveModel and ActiveModel::Validations, then the entire callback chain
-is halted. In other words, successive 'before' callbacks are not executed,
-and neither is the action wrapped in callbacks.
+In Rails 4.2, when a 'before' callback returns `false` in Active Record
+and Active Model, then the entire callback chain is halted. In other words,
+successive 'before' callbacks are not executed, and neither is the action wrapped
+in callbacks.
 
-In Rails 5.0, returning `false` in a callback will not have this side effect
-of halting the callback chain. Instead, callback chains must be explicitly
-halted by calling `throw(:abort)`.
+In Rails 5.0, returning `false` in an Active Record or Active Model callback
+will not have this side effect of halting the callback chain. Instead, callback
+chains must be explicitly halted by calling `throw(:abort)`.
 
-When you upgrade from Rails 4.2 to Rails 5.0, returning `false` in a callback
-will still halt the callback chain, but you will receive a deprecation warning
-about this upcoming change.
+When you upgrade from Rails 4.2 to Rails 5.0, returning `false` in those kind of
+callbacks will still halt the callback chain, but you will receive a deprecation
+warning about this upcoming change.
 
 When you are ready, you can opt into the new behavior and remove the deprecation
 warning by adding the following configuration to your `config/application.rb`:
 
-    config.active_support.halt_callback_chains_on_return_false = false
+    ActiveSupport.halt_callback_chains_on_return_false = false
+
+Note that this option will not affect Active Support callbacks since they never
+halted the chain when any value was returned.
 
 See [#17227](https://github.com/rails/rails/pull/17227) for more details.