ActionMailer::Base can unregister observer(s) and interceptor(s). (#32207)

* ActionMailer::Base can unregister observer(s) and interceptor(s).

One or multiple mail observers can be unregistered using
`ActionMailer::Base.unregister_observers` or
`ActionMailer::Base.unregister_observer`.

One or multiple mail interceptors can be unregistered using
`ActionMailer::Base.unregister_interceptors` or
`ActionMailer::Base.unregister_interceptor`.

For preview interceptors, it's possible to use
`ActionMailer::Base.unregister_preview_interceptors` or
`ActionMailer::Base.unregister_preview_interceptor`.

* Ensure to be reset registered observer(s) and interceptor(s)

* Add explanation to CHANGELOG

* Add original author's name

[Kota Miyake + Rafael Mendonça França + Claudio Ortolina]

2 files changed, 46 insertions, 5 deletions

diff --git a/actionmailer/lib/action_mailer/base.rb b/actionmailer/lib/action_mailer/base.rb
index 3af95081ee..7f22af83b0 100644
--- a/actionmailer/lib/action_mailer/base.rb
+++ b/actionmailer/lib/action_mailer/base.rb
@@ -475,11 +475,21 @@ module ActionMailer
         observers.flatten.compact.each { |observer| register_observer(observer) }
       end
 
+      # Unregister one or more previously registered Observers.
+      def unregister_observers(*observers)
+        observers.flatten.compact.each { |observer| unregister_observer(observer) }
+      end
+
       # Register one or more Interceptors which will be called before mail is sent.
       def register_interceptors(*interceptors)
         interceptors.flatten.compact.each { |interceptor| register_interceptor(interceptor) }
       end
 
+      # Unregister one or more previously registered Interceptors.
+      def unregister_interceptors(*interceptors)
+        interceptors.flatten.compact.each { |interceptor| unregister_interceptor(interceptor) }
+      end
+
       # Register an Observer which will be notified when mail is delivered.
       # Either a class, string or symbol can be passed in as the Observer.
       # If a string or symbol is passed in it will be camelized and constantized.
@@ -487,6 +497,13 @@ module ActionMailer
         Mail.register_observer(observer_class_for(observer))
       end
 
+      # Unregister a previously registered Observer.
+      # Either a class, string or symbol can be passed in as the Observer.
+      # If a string or symbol is passed in it will be camelized and constantized.
+      def unregister_observer(observer)
+        Mail.unregister_observer(observer_class_for(observer))
+      end
+
       # Register an Interceptor which will be called before mail is sent.
       # Either a class, string or symbol can be passed in as the Interceptor.
       # If a string or symbol is passed in it will be camelized and constantized.
@@ -494,6 +511,13 @@ module ActionMailer
         Mail.register_interceptor(observer_class_for(interceptor))
       end
 
+      # Unregister a previously registered Interceptor.
+      # Either a class, string or symbol can be passed in as the Interceptor.
+      # If a string or symbol is passed in it will be camelized and constantized.
+      def unregister_interceptor(interceptor)
+        Mail.unregister_interceptor(observer_class_for(interceptor))
+      end
+
       def observer_class_for(value) # :nodoc:
         case value
         when String, Symbol
diff --git a/actionmailer/lib/action_mailer/preview.rb b/actionmailer/lib/action_mailer/preview.rb
index 0aea84fd2b..500b3bede0 100644
--- a/actionmailer/lib/action_mailer/preview.rb
+++ b/actionmailer/lib/action_mailer/preview.rb
@@ -31,22 +31,39 @@ module ActionMailer
         interceptors.flatten.compact.each { |interceptor| register_preview_interceptor(interceptor) }
       end
 
+      # Unregister one or more previously registered Interceptors.
+      def unregister_preview_interceptors(*interceptors)
+        interceptors.flatten.compact.each { |interceptor| unregister_preview_interceptor(interceptor) }
+      end
+
       # Register an Interceptor which will be called before mail is previewed.
       # Either a class or a string can be passed in as the Interceptor. If a
       # string is passed in it will be constantized.
       def register_preview_interceptor(interceptor)
-        preview_interceptor = \
+        preview_interceptor = interceptor_class_for(interceptor)
+
+        unless preview_interceptors.include?(preview_interceptor)
+          preview_interceptors << preview_interceptor
+        end
+      end
+
+      # Unregister a previously registered Interceptor.
+      # Either a class or a string can be passed in as the Interceptor. If a
+      # string is passed in it will be constantized.
+      def unregister_preview_interceptor(interceptor)
+        preview_interceptors.delete(interceptor_class_for(interceptor))
+      end
+
+      private
+
+        def interceptor_class_for(interceptor)
           case interceptor
           when String, Symbol
             interceptor.to_s.camelize.constantize
           else
             interceptor
           end
-
-        unless preview_interceptors.include?(preview_interceptor)
-          preview_interceptors << preview_interceptor
         end
-      end
     end
   end