Logs an error in the Rails logs when installment processing fails

At the moment, by default, all installment prceissing errors are
swallowed and there's no way for a developer to understand what's
happening. Of course they can create a custom handler with the
processing_error_handler configuration provided but usually, when
the first errors happen, it's too late and those errors are lost.

We are not raising errors of this job because if there's a retry
mechanism in place for Active Job, the installment will be
reprocessed twice. Once by Active Job and once by the installment
retry mechanism already provided by the extension.

Logging to Rails.error is a middle-ground that allows to intercept
the message of the exception. Still, creating a custom handler
based on the bug tracker/exception handler used is the suggested
option here.

lib/generators/solidus_subscriptions/install/templates/initializer.rb

@@ -31,7 +31,9 @@
   # on an error tracking system.
   # Though not recommended due to the retry mechanisms built into this gem, the error can be
   # re-raised if the default retry behaviour is required in ActiveJob.
-  # config.processing_error_handler = nil
+  #
+  # By default, it only logs the error message using Rails.logger.error.
+  # config.processing_error_handler = SolidusSubscriptions::ProcessingErrorHandlers::RailsLogger
 
   # ========================================= Dispatchers ==========================================
   #

lib/solidus_subscriptions/configuration.rb

@@ -4,14 +4,14 @@ module SolidusSubscriptions
   class Configuration
     attr_accessor(
       :maximum_total_skips, :maximum_reprocessing_time, :churn_buster_account_id,
-      :churn_buster_api_key, :clear_past_installments, :processing_error_handler
+      :churn_buster_api_key, :clear_past_installments
     )
 
     attr_writer(
       :success_dispatcher_class, :failure_dispatcher_class, :payment_failed_dispatcher_class,
       :out_of_stock_dispatcher, :maximum_successive_skips, :reprocessing_interval,
       :minimum_cancellation_notice, :processing_queue, :subscription_line_item_attributes,
-      :subscription_attributes, :subscribable_class, :order_creator_class
+      :subscription_attributes, :subscribable_class, :order_creator_class, :processing_error_handler
     )
 
     def success_dispatcher_class
@@ -34,6 +34,11 @@ def out_of_stock_dispatcher_class
       @out_of_stock_dispatcher_class.constantize
     end
 
+    def processing_error_handler
+      @processing_error_handler ||= 'SolidusSubscriptions::ProcessingErrorHandlers::RailsLogger'
+      @processing_error_handler.constantize
+    end
+
     def maximum_successive_skips
       @maximum_successive_skips ||= 1
     end

lib/solidus_subscriptions/engine.rb

@@ -6,6 +6,7 @@
 require 'solidus_subscriptions/permitted_attributes'
 require 'solidus_subscriptions/configuration'
 require 'solidus_subscriptions/processor'
+require 'solidus_subscriptions/processing_error_handlers/rails_logger'
 
 module SolidusSubscriptions
   class Engine < Rails::Engine

lib/solidus_subscriptions/processing_error_handlers/rails_logger.rb

@@ -0,0 +1,23 @@
+# frozen_string_literal: true
+
+module SolidusSubscriptions
+  module ProcessingErrorHandlers
+    class RailsLogger
+      def self.call(exception)
+        new(exception).call
+      end
+
+      def initialize(exception)
+        @exception = exception
+      end
+
+      def call
+        Rails.logger.error exception.message
+      end
+
+      private
+
+      attr_reader :exception
+    end
+  end
+end

spec/jobs/solidus_subscriptions/process_installment_job_spec.rb

@@ -12,7 +12,22 @@
   end
 
   context 'when handling #perform errors' do
+    it 'by default logs exception data without raising exceptions' do
+      checkout = instance_double(SolidusSubscriptions::Checkout).tap do |c|
+        allow(c).to receive(:process).and_raise('test error')
+      end
+      allow(SolidusSubscriptions::Checkout).to receive(:new).and_return(checkout)
+      allow(Rails.logger).to receive(:error)
+
+      expect {
+        described_class.perform_now(build_stubbed(:installment))
+      }.not_to raise_error
+
+      expect(Rails.logger).to have_received(:error).with("test error").ordered
+    end
+
     it 'swallows error when a proc is not configured' do
+      stub_config(processing_error_handler: nil )
       checkout = instance_double(SolidusSubscriptions::Checkout).tap do |c|
         allow(c).to receive(:process).and_raise('test error')
       end