Deprecate `false` as the way to halt AR callbacks

Before this commit, returning `false` in an ActiveRecord `before_` callback
such as `before_create` would halt the callback chain.

After this commit, the behavior is deprecated: will still work until
the next release of Rails but will also display a deprecation warning.

The preferred way to halt a callback chain is to explicitly `throw(:abort)`.

1 files changed, 3 insertions, 3 deletions

diff --git a/activerecord/lib/active_record/callbacks.rb b/activerecord/lib/active_record/callbacks.rb
index 497ce8c15c..f44e5af5de 100644
--- a/activerecord/lib/active_record/callbacks.rb
+++ b/activerecord/lib/active_record/callbacks.rb
@@ -192,14 +192,14 @@ module ActiveRecord
   #
   # == <tt>before_validation*</tt> returning statements
   #
-  # If the returning value of a +before_validation+ callback can be evaluated to +false+, the process will be
+  # If the +before_validation+ callback throws +:abort+, the process will be
   # aborted and <tt>Base#save</tt> will return +false+. If Base#save! is called it will raise a
   # ActiveRecord::RecordInvalid exception. Nothing will be appended to the errors object.
   #
   # == Canceling callbacks
   #
-  # If a <tt>before_*</tt> callback returns +false+, all the later callbacks and the associated action are
-  # cancelled. If an <tt>after_*</tt> callback returns +false+, all the later callbacks are cancelled.
+  # If a <tt>before_*</tt> callback throws +:abort+, all the later callbacks and
+  # the associated action are cancelled.
   # Callbacks are generally run in the order they are defined, with the exception of callbacks defined as
   # methods on the model, which are called last.
   #