Action Mailer: Declarative exception handling with `rescue_from`.

Follows the same pattern as controllers and jobs. Exceptions raised in
delivery jobs (enqueued by `#deliver_later`) are also delegated to the
mailer's rescue_from handlers, so you can handle the DeserializationError
raised by delivery jobs:

```ruby
class MyMailer < ApplicationMailer
  rescue_from ActiveJob::DeserializationError do
    …
  end
```

ActiveSupport::Rescuable polish:
* Add the `rescue_with_handler` class method so exceptions may be
  handled at the class level without requiring an instance.
* Rationalize `exception.cause` handling. If no handler matches the
  exception, fall back to the handler that matches its cause.
* Handle exceptions raised elsewhere. Pass `object: …` to execute
  the `rescue_from` handler (e.g. a method call or a block to
  instance_exec) against a different object. Defaults to `self`.

2 files changed, 2 insertions, 42 deletions

diff --git a/actionpack/lib/action_controller/metal/rescue.rb b/actionpack/lib/action_controller/metal/rescue.rb
index f1c967b982..17f4030f25 100644
--- a/actionpack/lib/action_controller/metal/rescue.rb
+++ b/actionpack/lib/action_controller/metal/rescue.rb
@@ -6,17 +6,6 @@ module ActionController #:nodoc:
     extend ActiveSupport::Concern
     include ActiveSupport::Rescuable
 
-    def rescue_with_handler(exception)
-      if exception.cause
-        handler_index = index_of_handler_for_rescue(exception) || Float::INFINITY
-        cause_handler_index = index_of_handler_for_rescue(exception.cause)
-        if cause_handler_index && cause_handler_index <= handler_index
-          exception = exception.cause
-        end
-      end
-      super(exception)
-    end
-
     # Override this method if you want to customize when detailed
     # exceptions must be shown. This method is only called when
     # consider_all_requests_local is false. By default, it returns
@@ -31,7 +20,7 @@ module ActionController #:nodoc:
         super
       rescue Exception => exception
         request.env['action_dispatch.show_detailed_exceptions'] ||= show_detailed_exceptions?
-        rescue_with_handler(exception) || raise(exception)
+        rescue_with_handler(exception) || raise
       end
   end
 end
diff --git a/actionpack/test/controller/rescue_test.rb b/actionpack/test/controller/rescue_test.rb
index ed78f859ce..c088e5a043 100644
--- a/actionpack/test/controller/rescue_test.rb
+++ b/actionpack/test/controller/rescue_test.rb
@@ -131,22 +131,6 @@ class RescueController < ActionController::Base
   def missing_template
   end
 
-  def io_error_in_view
-    begin
-      raise IOError.new('this is io error')
-    rescue
-      raise ActionView::TemplateError.new(nil)
-    end
-  end
-
-  def zero_division_error_in_view
-    begin
-      raise ZeroDivisionError.new('this is zero division error')
-    rescue
-      raise ActionView::TemplateError.new(nil)
-    end
-  end
-
   def exception_with_more_specific_handler_for_wrapper
     raise RecordInvalid
   rescue
@@ -251,17 +235,6 @@ class ControllerInheritanceRescueControllerTest < ActionController::TestCase
 end
 
 class RescueControllerTest < ActionController::TestCase
-
-  def test_io_error_in_view
-    get :io_error_in_view
-    assert_equal 'io error', @response.body
-  end
-
-  def test_zero_division_error_in_view
-    get :zero_division_error_in_view
-    assert_equal 'action_view templater error', @response.body
-  end
-
   def test_rescue_handler
     get :not_authorized
     assert_response :forbidden
@@ -276,7 +249,6 @@ class RescueControllerTest < ActionController::TestCase
       get :record_invalid
     end
   end
-
   def test_rescue_handler_with_argument_as_string
     assert_called_with @controller, :show_errors, [Exception] do
       get :record_invalid_raise_as_string
@@ -314,7 +286,6 @@ class RescueControllerTest < ActionController::TestCase
     get :resource_unavailable
     assert_equal "RescueController::ResourceUnavailable", @response.body
   end
-
   def test_block_rescue_handler_with_argument_as_string
     get :resource_unavailable_raise_as_string
     assert_equal "RescueController::ResourceUnavailableToRescueAsString", @response.body
@@ -322,7 +293,7 @@ class RescueControllerTest < ActionController::TestCase
 
   test 'rescue when wrapper has more specific handler than cause' do
     get :exception_with_more_specific_handler_for_wrapper
-    assert_response :unprocessable_entity
+    assert_response :forbidden
   end
 
   test 'rescue when cause has more specific handler than wrapper' do