Change Rails/ApplicationRecord to ignore migrations

Author: fatkodima

changelog/change_application_record_to_ignore_migrations.md

@@ -0,0 +1 @@
+* [#1342](https://github.com/rubocop/rubocop-rails/issues/1342): Change `Rails/ApplicationRecord` to ignore migrations. ([@fatkodima][])

config/default.yml

@@ -212,7 +212,9 @@ Rails/ApplicationRecord:
   Enabled: true
   SafeAutoCorrect: false
   VersionAdded: '0.49'
-  VersionChanged: '2.5'
+  VersionChanged: '<<next>>'
+  Exclude:
+    - db/**/*.rb
 
 Rails/ArelStar:
   Description: 'Enforces `Arel.star` instead of `"*"` for expanded columns.'

lib/rubocop/cop/rails/application_record.rb

@@ -5,6 +5,10 @@ module Cop
     module Rails
       # Checks that models subclass `ApplicationRecord` with Rails 5.0.
       #
+      # It is a common practice to define models inside migrations in order to retain forward
+      # compatibility by avoiding loading any application code. And so migration files are excluded
+      # by default for this cop.
+      #
       # @safety
       #   This cop's autocorrection is unsafe because it may let the logic from `ApplicationRecord`
       #   sneak into an Active Record model that is not purposed to inherit logic common among other