MONGOID-5304: Add Rubocop static code analyzer (#5243)

Co-authored-by: Dmitry Rybakov <dmitry.rybakov@mongodb.com>

Author: johnnyshields

.github/workflows/rubocop.yml

@@ -0,0 +1,20 @@
+---
+name: Rubocop
+
+on: [push, pull_request]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    env:
+      CI: true
+      TESTOPTS: "-v"
+    steps:
+      - uses: actions/checkout@v3
+      - name: Set up Ruby 3.0
+        uses: ruby/setup-ruby@v1
+        with:
+          ruby-version: 3.0
+          bundler-cache: true
+      - name: Run RuboCop
+        run: bundle exec rubocop --parallel

.rubocop.yml

@@ -0,0 +1,70 @@
+inherit_from: .rubocop_todo.yml
+
+require:
+  - rubocop-performance
+  - rubocop-rails
+  - rubocop-rake
+  - rubocop-rspec
+
+AllCops:
+  TargetRubyVersion: 2.6
+  NewCops: enable
+  Exclude:
+    - 'spec/shared/lib/mrss/**/*'
+    - 'vendor/**/*'
+
+# -----------------------------------
+# TODO: Enable and fix the cops below
+# -----------------------------------
+
+Gemspec:
+  Enabled: false
+
+Layout:
+  Enabled: false
+
+Lint:
+  Enabled: false
+
+Metrics:
+  Enabled: false
+
+Naming:
+  Enabled: false
+
+Performance:
+  Enabled: false
+
+Rake:
+  Enabled: false
+
+Rails:
+  Enabled: false
+
+RSpec:
+  Enabled: false
+
+Security:
+  Exclude:
+    - 'spec/**/*'
+
+Style:
+  Enabled: false
+
+# --------------------------------------
+# Cops below this line set intentionally
+# --------------------------------------
+
+Bundler/OrderedGems:
+  Enabled: false
+
+Gemspec/OrderedDependencies:
+  Enabled: false
+
+# Not used by Mongoid
+Rails/RedundantPresenceValidationOnBelongsTo:
+  Enabled: false
+
+Style/Documentation:
+  Exclude:
+    - 'spec/**/*'

.rubocop_todo.yml

@@ -0,0 +1,7 @@
+# This configuration was generated by
+# `rubocop --auto-gen-config`
+# on 2023-02-10 19:24:10 UTC using RuboCop version 1.45.1.
+# 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.

gemfiles/standard.rb

@@ -15,10 +15,16 @@ def standard_dependencies
     # Evergreen configuration generation
     gem 'erubi'
     gem 'tilt'
+    gem 'solargraph'
   end
 
   group :development, :test do
     gem 'rspec-core', '~> 3.10'
+    gem 'rubocop', '~> 1.45.1'
+    gem 'rubocop-performance', '~> 1.16.0'
+    gem 'rubocop-rails', '~> 2.17.4'
+    gem 'rubocop-rake', '~> 0.6.0'
+    gem 'rubocop-rspec', '~> 2.18.1'
 
     platform :mri do
       gem 'byebug'