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]

4 files changed, 135 insertions, 19 deletions

diff --git a/actionmailer/CHANGELOG.md b/actionmailer/CHANGELOG.md
index 6d91d4fbd6..88e8a36eaa 100644
--- a/actionmailer/CHANGELOG.md
+++ b/actionmailer/CHANGELOG.md
@@ -6,6 +6,14 @@
 
     *Gannon McGibbon*
 
+*   Add `Base.unregister_observer`, `Base.unregister_observers`,
+    `Base.unregister_interceptor`, `Base.unregister_interceptors`,
+    `Base.unregister_preview_interceptor` and `Base.unregister_preview_interceptors`.
+    This makes it possible to dynamically add and remove email observers and
+    interceptors at runtime in the same way they're registered.
+
+    *Claudio Ortolina*, *Kota Miyake*
+
 *   Rails 6 requires Ruby 2.4.1 or newer.
 
     *Jeremy Daer*
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
 
diff --git a/actionmailer/test/base_test.rb b/actionmailer/test/base_test.rb
index 4124aa00bd..7898996c30 100644
--- a/actionmailer/test/base_test.rb
+++ b/actionmailer/test/base_test.rb
@@ -618,37 +618,52 @@ class BaseTest < ActiveSupport::TestCase
     end
   end
 
-  test "you can register an observer to the mail object that gets informed on email delivery" do
+  test "you can register and unregister an observer to the mail object that gets informed on email delivery" do
     mail_side_effects do
       ActionMailer::Base.register_observer(MyObserver)
       mail = BaseMailer.welcome
       assert_called_with(MyObserver, :delivered_email, [mail]) do
         mail.deliver_now
       end
+
+      ActionMailer::Base.unregister_observer(MyObserver)
+      assert_not_called(MyObserver, :delivered_email, returns: mail) do
+        mail.deliver_now
+      end
     end
   end
 
-  test "you can register an observer using its stringified name to the mail object that gets informed on email delivery" do
+  test "you can register and unregister an observer using its stringified name to the mail object that gets informed on email delivery" do
     mail_side_effects do
       ActionMailer::Base.register_observer("BaseTest::MyObserver")
       mail = BaseMailer.welcome
       assert_called_with(MyObserver, :delivered_email, [mail]) do
         mail.deliver_now
       end
+
+      ActionMailer::Base.unregister_observer("BaseTest::MyObserver")
+      assert_not_called(MyObserver, :delivered_email, returns: mail) do
+        mail.deliver_now
+      end
     end
   end
 
-  test "you can register an observer using its symbolized underscored name to the mail object that gets informed on email delivery" do
+  test "you can register and unregister an observer using its symbolized underscored name to the mail object that gets informed on email delivery" do
     mail_side_effects do
       ActionMailer::Base.register_observer(:"base_test/my_observer")
       mail = BaseMailer.welcome
       assert_called_with(MyObserver, :delivered_email, [mail]) do
         mail.deliver_now
       end
+
+      ActionMailer::Base.unregister_observer(:"base_test/my_observer")
+      assert_not_called(MyObserver, :delivered_email, returns: mail) do
+        mail.deliver_now
+      end
     end
   end
 
-  test "you can register multiple observers to the mail object that both get informed on email delivery" do
+  test "you can register and unregister multiple observers to the mail object that both get informed on email delivery" do
     mail_side_effects do
       ActionMailer::Base.register_observers("BaseTest::MyObserver", MySecondObserver)
       mail = BaseMailer.welcome
@@ -657,6 +672,14 @@ class BaseTest < ActiveSupport::TestCase
           mail.deliver_now
         end
       end
+
+      ActionMailer::Base.unregister_observers("BaseTest::MyObserver", MySecondObserver)
+      assert_not_called(MyObserver, :delivered_email, returns: mail) do
+        mail.deliver_now
+      end
+      assert_not_called(MySecondObserver, :delivered_email, returns: mail) do
+        mail.deliver_now
+      end
     end
   end
 
@@ -670,37 +693,52 @@ class BaseTest < ActiveSupport::TestCase
     def self.previewing_email(mail); end
   end
 
-  test "you can register an interceptor to the mail object that gets passed the mail object before delivery" do
+  test "you can register and unregister an interceptor to the mail object that gets passed the mail object before delivery" do
     mail_side_effects do
       ActionMailer::Base.register_interceptor(MyInterceptor)
       mail = BaseMailer.welcome
       assert_called_with(MyInterceptor, :delivering_email, [mail]) do
         mail.deliver_now
       end
+
+      ActionMailer::Base.unregister_interceptor(MyInterceptor)
+      assert_not_called(MyInterceptor, :delivering_email, returns: mail) do
+        mail.deliver_now
+      end
     end
   end
 
-  test "you can register an interceptor using its stringified name to the mail object that gets passed the mail object before delivery" do
+  test "you can register and unregister an interceptor using its stringified name to the mail object that gets passed the mail object before delivery" do
     mail_side_effects do
       ActionMailer::Base.register_interceptor("BaseTest::MyInterceptor")
       mail = BaseMailer.welcome
       assert_called_with(MyInterceptor, :delivering_email, [mail]) do
         mail.deliver_now
       end
+
+      ActionMailer::Base.unregister_interceptor("BaseTest::MyInterceptor")
+      assert_not_called(MyInterceptor, :delivering_email, returns: mail) do
+        mail.deliver_now
+      end
     end
   end
 
-  test "you can register an interceptor using its symbolized underscored name to the mail object that gets passed the mail object before delivery" do
+  test "you can register and unregister an interceptor using its symbolized underscored name to the mail object that gets passed the mail object before delivery" do
     mail_side_effects do
       ActionMailer::Base.register_interceptor(:"base_test/my_interceptor")
       mail = BaseMailer.welcome
       assert_called_with(MyInterceptor, :delivering_email, [mail]) do
         mail.deliver_now
       end
+
+      ActionMailer::Base.unregister_interceptor(:"base_test/my_interceptor")
+      assert_not_called(MyInterceptor, :delivering_email, returns: mail) do
+        mail.deliver_now
+      end
     end
   end
 
-  test "you can register multiple interceptors to the mail object that both get passed the mail object before delivery" do
+  test "you can register and unregister multiple interceptors to the mail object that both get passed the mail object before delivery" do
     mail_side_effects do
       ActionMailer::Base.register_interceptors("BaseTest::MyInterceptor", MySecondInterceptor)
       mail = BaseMailer.welcome
@@ -709,6 +747,14 @@ class BaseTest < ActiveSupport::TestCase
           mail.deliver_now
         end
       end
+
+      ActionMailer::Base.unregister_interceptors("BaseTest::MyInterceptor", MySecondInterceptor)
+      assert_not_called(MyInterceptor, :delivering_email, returns: mail) do
+        mail.deliver_now
+      end
+      assert_not_called(MySecondInterceptor, :delivering_email, returns: mail) do
+        mail.deliver_now
+      end
     end
   end
 
@@ -888,8 +934,6 @@ class BaseTest < ActiveSupport::TestCase
       klass.default_params = old
     end
 
-    # A simple hack to restore the observers and interceptors for Mail, as it
-    # does not have an unregister API yet.
     def mail_side_effects
       old_observers = Mail.class_variable_get(:@@delivery_notification_observers)
       old_delivery_interceptors = Mail.class_variable_get(:@@delivery_interceptors)
@@ -928,7 +972,7 @@ class BasePreviewInterceptorsTest < ActiveSupport::TestCase
     def self.previewing_email(mail); end
   end
 
-  test "you can register a preview interceptor to the mail object that gets passed the mail object before previewing" do
+  test "you can register and unregister a preview interceptor to the mail object that gets passed the mail object before previewing" do
     ActionMailer::Base.register_preview_interceptor(MyInterceptor)
     mail = BaseMailer.welcome
     stub_any_instance(BaseMailerPreview) do |instance|
@@ -938,9 +982,14 @@ class BasePreviewInterceptorsTest < ActiveSupport::TestCase
         end
       end
     end
+
+    ActionMailer::Base.unregister_preview_interceptor(MyInterceptor)
+    assert_not_called(MyInterceptor, :previewing_email, returns: mail) do
+      BaseMailerPreview.call(:welcome)
+    end
   end
 
-  test "you can register a preview interceptor using its stringified name to the mail object that gets passed the mail object before previewing" do
+  test "you can register and unregister a preview interceptor using its stringified name to the mail object that gets passed the mail object before previewing" do
     ActionMailer::Base.register_preview_interceptor("BasePreviewInterceptorsTest::MyInterceptor")
     mail = BaseMailer.welcome
     stub_any_instance(BaseMailerPreview) do |instance|
@@ -950,9 +999,14 @@ class BasePreviewInterceptorsTest < ActiveSupport::TestCase
         end
       end
     end
+
+    ActionMailer::Base.unregister_preview_interceptor("BasePreviewInterceptorsTest::MyInterceptor")
+    assert_not_called(MyInterceptor, :previewing_email, returns: mail) do
+      BaseMailerPreview.call(:welcome)
+    end
   end
 
-  test "you can register an interceptor using its symbolized underscored name to the mail object that gets passed the mail object before previewing" do
+  test "you can register and unregister a preview interceptor using its symbolized underscored name to the mail object that gets passed the mail object before previewing" do
     ActionMailer::Base.register_preview_interceptor(:"base_preview_interceptors_test/my_interceptor")
     mail = BaseMailer.welcome
     stub_any_instance(BaseMailerPreview) do |instance|
@@ -962,9 +1016,14 @@ class BasePreviewInterceptorsTest < ActiveSupport::TestCase
         end
       end
     end
+
+    ActionMailer::Base.unregister_preview_interceptor(:"base_preview_interceptors_test/my_interceptor")
+    assert_not_called(MyInterceptor, :previewing_email, returns: mail) do
+      BaseMailerPreview.call(:welcome)
+    end
   end
 
-  test "you can register multiple preview interceptors to the mail object that both get passed the mail object before previewing" do
+  test "you can register and unregister multiple preview interceptors to the mail object that both get passed the mail object before previewing" do
     ActionMailer::Base.register_preview_interceptors("BasePreviewInterceptorsTest::MyInterceptor", MySecondInterceptor)
     mail = BaseMailer.welcome
     stub_any_instance(BaseMailerPreview) do |instance|
@@ -976,6 +1035,14 @@ class BasePreviewInterceptorsTest < ActiveSupport::TestCase
         end
       end
     end
+
+    ActionMailer::Base.unregister_preview_interceptors("BasePreviewInterceptorsTest::MyInterceptor", MySecondInterceptor)
+    assert_not_called(MyInterceptor, :previewing_email, returns: mail) do
+      BaseMailerPreview.call(:welcome)
+    end
+    assert_not_called(MySecondInterceptor, :previewing_email, returns: mail) do
+      BaseMailerPreview.call(:welcome)
+    end
   end
 end