Create flexport-rubocop extension with NewGlobalModel cop

.gitignore

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+/.bundle/
+/.yardoc
+/_yardoc/
+/coverage/
+/doc/
+/pkg/
+/spec/reports/
+/tmp/
+
+# rspec failure tracking
+.rspec_status
+
+Gemfile.lock

.rspec

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+--format documentation
+--color
+--require spec_helper

.rubocop.yml

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+Layout/ExtraSpacing:
+  Enabled: true
+  AllowForAlignment: false
+
+Metrics/BlockLength:
+  Enabled: true
+  Exclude:
+    - spec/**/*.rb
+
+Naming/FileName:
+  Exclude:
+    - lib/rubocop-flexport.rb

.travis.yml

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+language: ruby
+sudo: false
+rvm:
+  - 2.3
+  - 2.4
+  - 2.5
+  - 2.6
+install:
+  - gem install bundler
+  - bundle install
+script:
+  - bundle exec rspec
+  - bundle exec rubocop

Gemfile

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+# frozen_string_literal: true
+
+source 'https://rubygems.org'
+
+git_source(:github) { |repo_name| "https://github.com/#{repo_name}" }
+
+# Specify your gem's dependencies in rubocop-flexport.gemspec
+gemspec
+gem 'rake'
+gem 'rspec'
+gem 'rubocop', github: 'rubocop-hq/rubocop'

LICENSE.txt

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+The MIT License (MIT)
+
+Copyright (c) 2019 Flexport Inc.
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.

README.md

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-# rubocop-flexport
-Flexport Rubocop Config and Custom Cops
+# Rubocop::Flexport
+
+This repo is for cops developed at Flexport that don't make sense to upstream
+into any of the existing RuboCop repos. When possible, we prefer upstreaming.
+
+## Installation
+
+Add this line to your application's Gemfile:
+
+```ruby
+gem 'rubocop-flexport'
+```
+
+And then execute:
+
+    $ bundle
+
+Or install it yourself as:
+
+    $ gem install rubocop-flexport
+
+## Usage
+
+Put this into your .rubocop.yml:
+
+```
+require:
+  - rubocop-flexport
+```
+
+## Development
+
+After checking out the repo, run `bin/setup` to install dependencies. Then, run
+`rake spec` to run the tests. You can also run `bin/console` for an interactive
+prompt that will allow you to experiment.
+
+To install this gem onto your local machine, run `bundle exec rake install`.
+
+To test it locally against your main codebase, update your Gemfile to something
+like below and then run `bundle install`:
+
+```
+gem "rubocop-flexport", path: "/Users/<user>/rubocop-flexport"
+```
+
+To release a new version, update the version number in `version.rb`, and then
+run `bundle exec rake release`, which will create a git tag for the version,
+push git commits and tags, and push the `.gem` file to [rubygems.org](https://rubygems.org).
+
+## Contributing
+
+Bug reports and pull requests are welcome on GitHub at https://github.com/flexport/rubocop-flexport.
+This project is intended to be a safe, welcoming space for collaboration, and
+contributors are expected to adhere to the
+[Contributor Covenant](http://contributor-covenant.org) code of conduct.
+
+## License
+
+The gem is available as open source under the terms of the [MIT License](https://opensource.org/licenses/MIT).

Rakefile

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+# frozen_string_literal: true
+
+require 'bundler/gem_tasks'
+require 'rspec/core/rake_task'
+
+RSpec::Core::RakeTask.new(:spec)
+
+task default: :spec
+
+require 'rspec/core/rake_task'
+
+RSpec::Core::RakeTask.new(:spec) do |spec|
+  spec.pattern = FileList['spec/**/*_spec.rb']
+end
+
+desc 'Generate a new cop with a template'
+task :new_cop, [:cop] do |_task, args|
+  require 'rubocop'
+
+  cop_name = args.fetch(:cop) do
+    warn 'usage: bundle exec rake new_cop[Department/Name]'
+    exit!
+  end
+
+  github_user = `git config github.user`.chop
+  github_user = 'your_id' if github_user.empty?
+
+  generator = RuboCop::Cop::Generator.new(cop_name, github_user)
+
+  generator.write_source
+  generator.write_spec
+  generator.inject_require(root_file_path: 'lib/rubocop/cop/flexport_cops.rb')
+  generator.inject_config(config_file_path: 'config/default.yml')
+
+  puts generator.todo
+end

bin/console

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+#!/usr/bin/env ruby
+# frozen_string_literal: true
+
+require 'bundler/setup'
+require 'rubocop/flexport'
+
+# You can add fixtures and/or initialization code here to make experimenting
+# with your gem easier. You can also use a different console, if you like.
+
+# (If you use this, don't forget to add pry to your Gemfile!)
+# require "pry"
+# Pry.start
+
+require 'irb'
+IRB.start(__FILE__)

bin/setup

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+#!/usr/bin/env bash
+set -euo pipefail
+IFS=$'\n\t'
+set -vx
+
+bundle install
+
+# Do any other automated setup that you need to do here

config/default.yml

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+Flexport/NewGlobalModel:
+  Description: 'Disallows addition of new global models to `app/models`. Prefer Rails Engines or namespaces.'
+  Enabled: true
+  VersionAdded: '0.1.0'
+  GlobalModelsPath: 'app/models/'
+  AllowNamespacedGlobalModels: true

lib/rubocop-flexport.rb

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+# frozen_string_literal: true
+
+require 'rubocop'
+
+require_relative 'rubocop/flexport'
+require_relative 'rubocop/flexport/version'
+require_relative 'rubocop/flexport/inject'
+
+RuboCop::Flexport::Inject.defaults!
+
+require_relative 'rubocop/cop/flexport_cops'

lib/rubocop/cop/flexport/new_global_model.rb

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+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module Flexport
+      # This cop disallows adding new models to the `app/models` directory.
+      #
+      # The goal is to encourage developers to put new models inside Rails
+      # Engines (or at least namespaces), where they can be more modularly
+      # isolated and ownership is clear.
+      #
+      # Use RuboCop's standard `Exclude` file list parameter to exclude
+      # existing global model files from counting as violations for this cop.
+      #
+      # @example AllowNamespacedGlobalModels: true (default)
+      #   # When `AllowNamespacedGlobalModels` is true, the cop only forbids
+      #   # additions at the top-level directory.
+      #
+      #   # bad
+      #   # path: app/models/my_new_global_model.rb
+      #   class MyNewGlobalModel < ApplicationRecord
+      #     # ...
+      #   end
+      #
+      #   # good
+      #   # path: app/models/my_namespace/my_new_global_model.rb
+      #   class MyNamespace::MyNewGlobalModel < ApplicationRecord
+      #     # ...
+      #   end
+      #
+      #   # good
+      #   # path: engines/my_engine/app/models/my_engine/my_new_engine_model.rb
+      #   class MyEngine::MyNewEngineModel < ApplicationRecord
+      #     # ...
+      #   end
+      #
+      # @example AllowNamespacedGlobalModels: false
+      #   # When `AllowNamespacedGlobalModels` is false, the cop forbids all
+      #   # new models in this directory and its descendants.
+      #
+      #   # bad
+      #   # path: app/models/my_new_global_model.rb
+      #   class MyNewGlobalModel < ApplicationRecord
+      #     # ...
+      #   end
+      #
+      #   # bad
+      #   # path: app/models/my_namespace/my_new_global_model.rb
+      #   class MyNamespace::MyNewGlobalModel < ApplicationRecord
+      #     # ...
+      #   end
+      #
+      #   # good
+      #   # path: engines/my_engine/app/models/my_engine/my_new_engine_model.rb
+      #   class MyEngine::MyNewEngineModel < ApplicationRecord
+      #     # ...
+      #   end
+      class NewGlobalModel < Cop
+        ALLOW_NAMESPACES_MSG =
+          'Do not add new top-level global models in `app/models`. ' \
+          'Prefer namespaced models like `app/models/foo/bar.rb` or ' \
+          'or models inside Rails Engines.'
+
+        DISALLOW_NAMESPACES_MSG =
+          'Do not add new global models in `app/models`. ' \
+          'Instead add new models to Rails Engines.'
+
+        def investigate(processed_source)
+          return if processed_source.blank?
+
+          path = processed_source.file_path
+          return unless global_rails_model?(path)
+
+          add_offense(processed_source.ast)
+        end
+
+        private
+
+        def message(_node)
+          return ALLOW_NAMESPACES_MSG if allow_namespaced_global_models
+
+          DISALLOW_NAMESPACES_MSG
+        end
+
+        def global_rails_model?(path)
+          return false unless path.include?(global_models_path)
+          return false if path.include?('/concerns/')
+          return false if in_engine?(path)
+          return false if allowed_namespace?(path)
+
+          true
+        end
+
+        def allowed_namespace?(path)
+          return false unless allow_namespaced_global_models
+
+          parts = path.split(global_models_path)
+          parts.last.split('/').length > 1
+        end
+
+        def in_engine?(path)
+          return true if path.include?('/engines/')
+
+          # Engines model dirs are structured like:
+          #   my_engine/app/models/my_engine/my_model.rb.
+          # We detect models whose directory structure matches
+          # this pattern even if they aren't children of an
+          # "/engines/" directory.
+          parts = path.split(global_models_path)
+          potential_engine_name = parts.last.split('/').first
+          engine_models_path = File.join(
+            potential_engine_name,
+            global_models_path,
+            potential_engine_name
+          )
+          path.include?(engine_models_path)
+        end
+
+        def global_models_path
+          path = cop_config['GlobalModelsPath']
+          path += '/' unless path.end_with?('/')
+          path
+        end
+
+        def allow_namespaced_global_models
+          cop_config['AllowNamespacedGlobalModels']
+        end
+      end
+    end
+  end
+end

lib/rubocop/cop/flexport_cops.rb

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+# frozen_string_literal: true
+
+require_relative 'flexport/new_global_model'

lib/rubocop/flexport.rb

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+# frozen_string_literal: true
+
+require 'rubocop/flexport/version'
+
+module RuboCop
+  # Namespace for Flexport-specific RuboCop cops.
+  module Flexport
+    class Error < StandardError; end
+    PROJECT_ROOT = Pathname.new(__dir__).parent.parent.expand_path.freeze
+    CONFIG_DEFAULT = PROJECT_ROOT.join('config', 'default.yml').freeze
+    CONFIG = YAML.safe_load(CONFIG_DEFAULT.read).freeze
+
+    private_constant(:CONFIG_DEFAULT, :PROJECT_ROOT)
+  end
+end

lib/rubocop/flexport/inject.rb

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+# frozen_string_literal: true
+
+# The original code is from https://github.com/rubocop-hq/rubocop-rspec/blob/master/lib/rubocop/rspec/inject.rb
+# See https://github.com/rubocop-hq/rubocop-rspec/blob/master/MIT-LICENSE.md
+module RuboCop
+  module Flexport
+    # Because RuboCop doesn't yet support plugins, we have to monkey patch in a
+    # bit of our configuration.
+    module Inject
+      def self.defaults!
+        path = CONFIG_DEFAULT.to_s
+        hash = ConfigLoader.send(:load_yaml_configuration, path)
+        config = Config.new(hash, path)
+        puts "configuration from #{path}" if ConfigLoader.debug?
+        config = ConfigLoader.merge_with_default(config, path)
+        ConfigLoader.instance_variable_set(:@default_configuration, config)
+      end
+    end
+  end
+end