feat(fallbacks): do not allow fallbacks for method steps

BACKLOG.md

@@ -234,3 +234,17 @@ Although it is very flexible and easy to reuse from the maintenance point of vie
 In case it starts to cause any visible performance penalty, it can be refactored using regular `||=` or `if defined?`.
 
 ---
+
+### Consider to create parent result while copying results
+
+| Priority | Complexity | Status | Tags |
+| - | - | - | - |
+| Medium | Moderate | TODO | parent-result |
+
+Fallbacks have no access to their original results.
+
+When fallback result is used, original result is NOT in the parents chain.
+
+It is OK?
+
+---

lib/convenient_service/service/configs/standard.rb

@@ -212,11 +212,13 @@ class self::Step
             end
 
             middlewares :result do
-              use ConvenientService::Plugins::Step::CanHaveFallbacks::Middleware.with(fallback_true_status: :failure)
-
               insert_after \
                 ConvenientService::Plugins::Step::HasResult::Middleware,
                 ConvenientService::Plugins::Step::CanHaveParentResult::Middleware
+
+              insert_after \
+                ConvenientService::Plugins::Step::HasResult::Middleware,
+                ConvenientService::Plugins::Step::CanHaveFallbacks::Middleware.with(fallback_true_status: :failure)
             end
           end
 

lib/convenient_service/service/plugins/can_have_rollbacks/middleware.rb

@@ -4,9 +4,6 @@ module ConvenientService
   module Service
     module Plugins
       module CanHaveRollbacks
-        ##
-        # @api private
-        #
         class Middleware < MethodChainMiddleware
           intended_for :result, entity: :service
 
@@ -27,6 +24,9 @@ def next(...)
           # @param result [ConvenientService::Service::Plugins::HasJSendResult::Entities::Result]
           # @return [void]
           #
+          # @internal
+          #   IMPORTANT: Uses recursion inside `rollback_organizer`. Recursion has two exit conditions. When service has no steps. When service has only method steps.
+          #
           def rollback_result(result)
             result.from_step? ? rollback_organizer(result.service) : rollback_service(result.service)
           end

lib/convenient_service/service/plugins/can_have_steps/entities/step/plugins/can_have_fallbacks/exceptions.rb

@@ -10,6 +10,12 @@ module Plugins
               module CanHaveFallbacks
                 module Exceptions
                   class FallbackResultIsNotOverridden < ::ConvenientService::Exception
+                    ##
+                    # @param step [ConvenientService::Service::Plugins::CanHaveSteps::Entities::Step]
+                    # @param service [ConvenientService::Service]
+                    # @param status [Symbol]
+                    # @return [void]
+                    #
                     def initialize_with_kwargs(step:, service:, status:)
                       message = <<~TEXT
                         Neither `fallback_#{status}_result` nor `fallback_result` methods of `#{service.class}` are overridden, but the step is marked to be fallbacked.
@@ -20,6 +26,22 @@ def initialize_with_kwargs(step:, service:, status:)
                       initialize(message)
                     end
                   end
+
+                  class MethodStepCanNotHaveFallback < ::ConvenientService::Exception
+                    ##
+                    # @param step [ConvenientService::Service::Plugins::CanHaveSteps::Entities::Step]
+                    # @return [void]
+                    #
+                    def initialize_with_kwargs(step:)
+                      message = <<~TEXT
+                        Method step can NOT have fallback.
+
+                        Either remove `fallback` option from step `:#{step.method}` in `#{step.container.klass}` or consider to refactor it into a service step.
+                      TEXT
+
+                      initialize(message)
+                    end
+                  end
                 end
               end
             end

lib/convenient_service/service/plugins/can_have_steps/entities/step/plugins/can_have_fallbacks/middleware.rb

@@ -71,17 +71,21 @@ def fallback_true_status
 
                   ##
                   # @return [ConvenientService::Service::Plugins::HasJSendResult::Entities::Result]
-                  # @raise [ConvenientService::Service::Plugins::CanHaveSteps::Entities::Step::Plugins::CanHaveFallbacks::Exceptions::FallbackResultIsNotOverridden]
+                  # @raise [ConvenientService::Service::Plugins::CanHaveSteps::Entities::Step::Plugins::CanHaveFallbacks::Exceptions::FallbackResultIsNotOverridden, ConvenientService::Service::Plugins::CanHaveSteps::Entities::Step::Plugins::CanHaveFallbacks::Exceptions::MethodStepCanNotHaveFallback]
                   #
                   def fallback_failure_result
+                    refute_method_step!
+
                     fallback_failure_result_own_method&.call || fallback_result_own_method&.call || ::ConvenientService.raise(Exceptions::FallbackResultIsNotOverridden.new(step: step, service: service, status: :failure))
                   end
 
                   ##
                   # @return [ConvenientService::Service::Plugins::HasJSendResult::Entities::Result]
-                  # @raise [ConvenientService::Service::Plugins::CanHaveSteps::Entities::Step::Plugins::CanHaveFallbacks::Exceptions::FallbackResultIsNotOverridden]
+                  # @raise [ConvenientService::Service::Plugins::CanHaveSteps::Entities::Step::Plugins::CanHaveFallbacks::Exceptions::FallbackResultIsNotOverridden, ConvenientService::Service::Plugins::CanHaveSteps::Entities::Step::Plugins::CanHaveFallbacks::Exceptions::MethodStepCanNotHaveFallback]
                   #
                   def fallback_error_result
+                    refute_method_step!
+
                     fallback_error_result_own_method&.call || fallback_result_own_method&.call || ::ConvenientService.raise(Exceptions::FallbackResultIsNotOverridden.new(step: step, service: service, status: :error))
                   end
 
@@ -115,6 +119,19 @@ def fallback_result_own_method
                   def service
                     @service ||= step.service.klass.new(**step.input_values)
                   end
+
+                  ##
+                  # @return [void]
+                  # @raise [ConvenientService::Service::Plugins::CanHaveSteps::Entities::Step::Plugins::CanHaveFallbacks::Exceptions::MethodStepCanNotHaveFallback]
+                  #
+                  # @internal
+                  #   TODO: Consider to move this assertion to the build time.
+                  #
+                  def refute_method_step!
+                    return unless step.method_step?
+
+                    raise Exceptions::MethodStepCanNotHaveFallback.new(step: step)
+                  end
                 end
               end
             end

spec/lib/convenient_service/examples/dry/gemfile/dry_service/config_spec.rb

@@ -532,10 +532,10 @@
                 ConvenientService::Common::Plugins::CachesReturnValue::Middleware,
                 ConvenientService::Service::Plugins::CanHaveSteps::Entities::Step::Plugins::HasResult::Middleware,
 
+                ConvenientService::Service::Plugins::CanHaveSteps::Entities::Step::Plugins::CanHaveFallbacks::Middleware.with(fallback_true_status: :failure),
                 ConvenientService::Service::Plugins::CanHaveSteps::Entities::Step::Plugins::CanHaveParentResult::Middleware,
                 ConvenientService::Service::Plugins::CanHaveSteps::Entities::Step::Plugins::RaisesOnNotResultReturnValue::Middleware,
-                ConvenientService::Service::Plugins::CanHaveSteps::Entities::Step::Plugins::CanBeMethodStep::CanBeExecuted::Middleware,
-                ConvenientService::Service::Plugins::CanHaveSteps::Entities::Step::Plugins::CanHaveFallbacks::Middleware.with(fallback_true_status: :failure)
+                ConvenientService::Service::Plugins::CanHaveSteps::Entities::Step::Plugins::CanBeMethodStep::CanBeExecuted::Middleware
               ]
             end
 

spec/lib/convenient_service/examples/rails/gemfile/rails_service/config_spec.rb

@@ -534,10 +534,10 @@
                 ConvenientService::Common::Plugins::CachesReturnValue::Middleware,
                 ConvenientService::Service::Plugins::CanHaveSteps::Entities::Step::Plugins::HasResult::Middleware,
 
+                ConvenientService::Service::Plugins::CanHaveSteps::Entities::Step::Plugins::CanHaveFallbacks::Middleware.with(fallback_true_status: :failure),
                 ConvenientService::Service::Plugins::CanHaveSteps::Entities::Step::Plugins::CanHaveParentResult::Middleware,
                 ConvenientService::Service::Plugins::CanHaveSteps::Entities::Step::Plugins::RaisesOnNotResultReturnValue::Middleware,
-                ConvenientService::Service::Plugins::CanHaveSteps::Entities::Step::Plugins::CanBeMethodStep::CanBeExecuted::Middleware,
-                ConvenientService::Service::Plugins::CanHaveSteps::Entities::Step::Plugins::CanHaveFallbacks::Middleware.with(fallback_true_status: :failure)
+                ConvenientService::Service::Plugins::CanHaveSteps::Entities::Step::Plugins::CanBeMethodStep::CanBeExecuted::Middleware
               ]
             end
 

spec/lib/convenient_service/service/configs/standard_spec.rb

@@ -526,10 +526,10 @@
                 ConvenientService::Common::Plugins::CachesReturnValue::Middleware,
                 ConvenientService::Service::Plugins::CanHaveSteps::Entities::Step::Plugins::HasResult::Middleware,
 
+                ConvenientService::Service::Plugins::CanHaveSteps::Entities::Step::Plugins::CanHaveFallbacks::Middleware.with(fallback_true_status: :failure),
                 ConvenientService::Service::Plugins::CanHaveSteps::Entities::Step::Plugins::CanHaveParentResult::Middleware,
                 ConvenientService::Service::Plugins::CanHaveSteps::Entities::Step::Plugins::RaisesOnNotResultReturnValue::Middleware,
-                ConvenientService::Service::Plugins::CanHaveSteps::Entities::Step::Plugins::CanBeMethodStep::CanBeExecuted::Middleware,
-                ConvenientService::Service::Plugins::CanHaveSteps::Entities::Step::Plugins::CanHaveFallbacks::Middleware.with(fallback_true_status: :failure)
+                ConvenientService::Service::Plugins::CanHaveSteps::Entities::Step::Plugins::CanBeMethodStep::CanBeExecuted::Middleware
               ]
             end
 

spec/lib/convenient_service/service/plugins/can_have_steps/entities/step/plugins/can_have_fallbacks/exceptions_spec.rb

@@ -0,0 +1,12 @@
+# frozen_string_literal: true
+
+require "spec_helper"
+
+require "convenient_service"
+
+RSpec.describe ConvenientService::Service::Plugins::CanHaveSteps::Entities::Step::Plugins::CanHaveFallbacks::Exceptions, type: :standard do
+  include ConvenientService::RSpec::PrimitiveMatchers::BeDescendantOf
+
+  specify { expect(described_class::FallbackResultIsNotOverridden).to be_descendant_of(ConvenientService::Exception) }
+  specify { expect(described_class::MethodStepCanNotHaveFallback).to be_descendant_of(ConvenientService::Exception) }
+end