Minor Rails 6.1 fix, plus autoload Delayed::Job constant (#2)

This fixes an issue I was seeing on a very slim Rails 6.1 app -- essentially, `ActiveSupport.on_load(:active_record)` was not triggering at all during `rake delayed:work`, resulting in a missing constant error. Previous versions of rails seem to load `ActiveRecord::Base` during boot, but 6.1 seems to have found a way to optimize that step away.

This PR moves the `delayed/job.rb` class to `app/models` and converts the gem's `Railtie` to an `Engine`, allowing it to autoload files in `app/models` by convention. In cases where we are not in a Rails app (and `Rails::Engine` is not defined), we fall back on loading active_record manually and then running a `require_relative` of the specific `job.rb` file. I based this on other "rails-engine-optional" gems I've encountered, and confirmed that it works in an `irb` console.

I also removed `require 'delayed/serialization/active_record'` because it would already be loaded inside of `require 'delayed/yaml_ext'`. It also only applies to `syck` which dates back to Ruby 1.9, and we should consider removing support for it entirely. (It can still be installed via the `syck` gem, but `psych` has been the default for many, many years.)

.rubocop_todo.yml

@@ -1,12 +1,12 @@
 # This configuration was generated by
 # `rubocop --auto-gen-config --auto-gen-only-exclude --exclude-limit 99999`
-# on 2021-04-16 17:24:59 UTC using RuboCop version 1.12.1.
+# on 2021-08-28 18:08:22 UTC using RuboCop version 1.20.0.
 # The point is for the user to remove these configuration records
 # one by one as the offenses are removed from the code base.
 # Note that changes in the inspected code, or installation of new
 # versions of RuboCop, may require this file to be generated again.
 
-# Offense count: 12
+# Offense count: 13
 Betterment/ActiveJobPerformable:
   Exclude:
     - 'lib/delayed/performable_mailer.rb'
@@ -17,30 +17,13 @@ Betterment/ActiveJobPerformable:
     - 'spec/autoloaded/struct.rb'
     - 'spec/sample_jobs.rb'
 
-# Offense count: 1
-Betterment/Timeout:
-  Exclude:
-    - 'spec/worker_spec.rb'
-
 # Offense count: 4
 # Configuration parameters: AllowedMethods.
 # AllowedMethods: enums
 Lint/ConstantDefinitionInBlock:
   Exclude:
     - 'spec/message_sending_spec.rb'
 
-# Offense count: 1
-# Configuration parameters: AllowComments.
-Lint/EmptyFile:
-  Exclude:
-    - 'spec/delayed/serialization/test.rb'
-
-# Offense count: 1
-# Configuration parameters: MaximumRangeSize.
-Lint/MissingCopEnableDirective:
-  Exclude:
-    - 'lib/delayed/worker.rb'
-
 # Offense count: 2
 Lint/MissingSuper:
   Exclude:
@@ -52,35 +35,31 @@ Lint/ShadowingOuterLocalVariable:
   Exclude:
     - 'spec/helper.rb'
 
-# Offense count: 2
+# Offense count: 1
 # Configuration parameters: AllowComments, AllowNil.
 Lint/SuppressedException:
   Exclude:
     - 'lib/delayed/backend/base.rb'
-    - 'lib/delayed/worker.rb'
 
-# Offense count: 8
+# Offense count: 4
 # Configuration parameters: IgnoredMethods, CountRepeatedAttributes, Max.
 Metrics/AbcSize:
   Exclude:
-    - 'lib/delayed/backend/job_preparer.rb'
-    - 'lib/delayed/command.rb'
     - 'lib/delayed/message_sending.rb'
     - 'lib/delayed/psych_ext.rb'
     - 'lib/delayed/worker.rb'
 
-# Offense count: 2
+# Offense count: 1
 RSpec/AnyInstance:
   Exclude:
     - 'spec/delayed/job_spec.rb'
-    - 'spec/delayed/command_spec.rb'
 
 # Offense count: 2
 RSpec/ExpectInHook:
   Exclude:
     - 'spec/delayed/job_spec.rb'
 
-# Offense count: 104
+# Offense count: 91
 # Configuration parameters: AssignmentOnly.
 RSpec/InstanceVariable:
   Exclude:
@@ -100,16 +79,10 @@ RSpec/StubbedMock:
     - 'spec/performable_method_spec.rb'
     - 'spec/worker_spec.rb'
 
-# Offense count: 2
-RSpec/SubjectStub:
-  Exclude:
-    - 'spec/delayed/command_spec.rb'
-
-# Offense count: 12
+# Offense count: 6
 # Configuration parameters: IgnoreNameless, IgnoreSymbolicNames.
 RSpec/VerifiedDoubles:
   Exclude:
-    - 'spec/delayed/command_spec.rb'
     - 'spec/lifecycle_spec.rb'
     - 'spec/performable_mailer_spec.rb'
     - 'spec/performable_method_spec.rb'
@@ -121,20 +94,6 @@ Rails/ApplicationMailer:
   Exclude:
     - 'spec/performable_mailer_spec.rb'
 
-# Offense count: 2
-# Configuration parameters: Include.
-# Include: app/**/*.rb, config/**/*.rb, lib/**/*.rb
-Rails/Exit:
-  Exclude:
-    - 'lib/delayed/command.rb'
-
-# Offense count: 1
-# Configuration parameters: Include.
-# Include: app/**/*.rb, config/**/*.rb, db/**/*.rb, lib/**/*.rb
-Rails/Output:
-  Exclude:
-    - 'lib/delayed/command.rb'
-
 # Offense count: 2
 # Cop supports --auto-correct.
 # Configuration parameters: Include.
@@ -148,20 +107,19 @@ Rails/RakeEnvironment:
 # ForbiddenMethods: decrement!, decrement_counter, increment!, increment_counter, insert, insert!, insert_all, insert_all!, toggle!, touch, touch_all, update_all, update_attribute, update_column, update_columns, update_counters, upsert, upsert_all
 Rails/SkipsModelValidations:
   Exclude:
-    - 'lib/delayed/job.rb'
+    - 'app/models/delayed/job.rb'
 
-# Offense count: 4
+# Offense count: 2
 # Cop supports --auto-correct.
 # Configuration parameters: EnforcedStyle.
 # SupportedStyles: strict, flexible
 Rails/TimeZone:
   Exclude:
-    - 'lib/delayed/tasks.rb'
     - 'lib/delayed/worker.rb'
-    - 'spec/message_sending_spec.rb'
     - 'spec/worker_spec.rb'
 
 # Offense count: 2
+# Cop supports --auto-correct.
 Rake/Desc:
   Exclude:
     - 'Rakefile'
@@ -179,13 +137,6 @@ Security/YAMLLoad:
     - 'spec/helper.rb'
     - 'spec/yaml_ext_spec.rb'
 
-# Offense count: 1
-# Configuration parameters: EnforcedStyle.
-# SupportedStyles: if, case, both
-Style/MissingElse:
-  Exclude:
-    - 'lib/delayed/job.rb'
-
 # Offense count: 2
 Style/MissingRespondToMissing:
   Exclude:
@@ -198,9 +149,3 @@ Style/MissingRespondToMissing:
 Style/OptionalBooleanParameter:
   Exclude:
     - 'lib/delayed/performable_method.rb'
-
-# Offense count: 2
-# Cop supports --auto-correct.
-Style/StderrPuts:
-  Exclude:
-    - 'lib/delayed/command.rb'

CHANGELOG.md

@@ -11,19 +11,28 @@ and this project aims to adhere to [Semantic Versioning](http://semver.org/spec/
 ### Removed <!-- for now removed features. -->
 ### Fixed <!-- for any bug fixes. -->
 
+## [0.2.0] - 2021-08-30
+### Fixed
+- Fix the loading of `Delayed::Job` constant on newly-generated Rails 6.1 apps. (previously, the
+  constant would not be available until `ActiveRecord::Base` was referenced for the first time)
+### Changed
+- The `Delayed::Railtie` is now a `Delayed::Engine`, allowing it to autoload constants via Rails'
+  built-in autoloader. In a non-Rails context, `require 'delayed'` will eager-load its models.
+
 ## [0.1.1] - 2021-08-19
 ### Added
 - This CHANGELOG file!
 ### Fixed
 - Fix the gemspec description, which had previously been written in rdoc format (causing it to
   appear garbled on rubygems.org).
 
-## [0.1.0] - 2021-08-18
+## [0.1.0] - 2021-08-17
 ### Added
 - Initial release! This repo is the result of some merging, squashing, and commit massaging, in
   preparation for a public release! The goal was to maintain historical commit authorship of the
   ancestor repos (`delayed_job` and `delayed_job_active_record`), plus the changes from Betterment's
   internal forks.
 
+[0.2.0]: https://github.com/betterment/delayed/compare/v0.1.1...v0.2.0
 [0.1.1]: https://github.com/betterment/delayed/compare/v0.1.0...v0.1.1
 [0.1.0]: https://github.com/betterment/delayed/releases/tag/v0.1.0

delayed.gemspec

@@ -18,7 +18,7 @@ Gem::Specification.new do |spec|
   spec.require_paths  = ['lib']
   spec.summary        = 'a multi-threaded, SQL-driven ActiveJob backend used at Betterment to process millions of background jobs per day'
 
-  spec.version        = '0.1.1'
+  spec.version        = '0.2.0'
   spec.metadata       = {
     'changelog_uri' => 'https://github.com/betterment/delayed/blob/main/CHANGELOG.md',
     'bug_tracker_uri' => 'https://github.com/betterment/delayed/issues',

lib/delayed.rb

@@ -14,11 +14,12 @@
 require 'delayed/backend/base'
 require 'delayed/backend/job_preparer'
 require 'delayed/worker'
-require 'delayed/railtie' if defined?(Rails::Railtie)
 
-ActiveSupport.on_load(:active_record) do
-  require 'delayed/serialization/active_record'
-  require 'delayed/job'
+if defined?(Rails::Engine)
+  require 'delayed/engine'
+else
+  require 'active_record'
+  require_relative '../app/models/delayed/job'
 end
 
 ActiveSupport.on_load(:active_job) do

lib/delayed/railtie.rb → lib/delayed/engine.rb

@@ -1,5 +1,5 @@
 module Delayed
-  class Railtie < Rails::Railtie
+  class Engine < Rails::Engine
     rake_tasks do
       load 'delayed/tasks.rb'
     end