Fix compact class CI errors (facebook#293)

Summary:
Note: this based on top of the shipit sync PR facebook#292

Pull Request resolved: facebook#293

Differential Revision: D70406994

fbshipit-source-id: 80bcbe374c647c90142c73feda098e9885f7e0c7

Author: dafyddcrosby

.cookstyle.yml

@@ -11,6 +11,14 @@ AllCops:
 Lint/Syntax:
   Enabled: true
 
+# Generally speaking, we don't want to use compact class definitions in Chef
+# because it opens the codebase to runtime constant-load failures. However, we
+# control the load path of Cookstyle, and the deep nesting of class definitions
+# make readability difficult.
+Style/ClassAndModuleChildren:
+  Exclude:
+    - !ruby/regexp /^.*\/cookstyle\/.*\.rb$/
+
 Chef/Correctness/BlockGuardWithOnlyString:
   Enabled: true
 Chef/Correctness/ChefApplicationFatal:

cookstyle/helpers.rb

@@ -17,3 +17,16 @@
 def fb_msg(msg)
   "#{msg} (https://github.com/facebook/chef-cookbooks)".freeze
 end
+
+# Predefine modules for compact style, cannot be compact
+module RuboCop # rubocop:disable Chef/Meta/CookstyleCompactClassStyle
+  module Cop
+    module Chef
+      module Meta
+        class Base < RuboCop::Cop::Base
+          prepend RuboCop::Cop
+        end
+      end
+    end
+  end
+end