[Fix #106] Mark Rails/ReflectionClassName as unsafe

Fixes #106.

This PR marks `Rails/ReflectionClassName` as unsafe.

And it would be possible to exclude `to_s` call other than constants.
I will consider opening it as a separate PR.

CHANGELOG.md

@@ -30,6 +30,7 @@
 * [#451](https://github.com/rubocop/rubocop-rails/issues/451): Make `Rails/RelativeDateConstant` aware of `yesterday` and `tomorrow` methods. ([@koic][])
 * [#454](https://github.com/rubocop/rubocop-rails/pull/454): Mark `Rails/WhereExists` as unsafe auto-correction. ([@koic][])
 * [#379](https://github.com/rubocop/rubocop-rails/issues/379): Mark `Rails/DynamicFindBy` as unsafe. ([@koic][])
+* [#106](https://github.com/rubocop/rubocop-rails/issues/106): Mark `Rails/ReflectionClassName` as unsafe. ([@koic][])
 * [#456](https://github.com/rubocop/rubocop-rails/pull/456): Drop Ruby 2.4 support. ([@koic][])
 * [#462](https://github.com/rubocop/rubocop-rails/pull/462): Require RuboCop 1.7 or higher. ([@koic][])
 

config/default.yml

@@ -563,7 +563,9 @@ Rails/RedundantReceiverInWithOptions:
 Rails/ReflectionClassName:
   Description: 'Use a string for `class_name` option value in the definition of a reflection.'
   Enabled: true
+  Safe: false
   VersionAdded: '0.64'
+  VersionChanged: '2.10'
 
 Rails/RefuteMethods:
   Description: 'Use `assert_not` methods instead of `refute` methods.'

docs/modules/ROOT/pages/cops_rails.adoc

@@ -3163,14 +3163,16 @@ end
 | Enabled by default | Safe | Supports autocorrection | VersionAdded | VersionChanged
 
 | Enabled
-| Yes
+| No
 | No
 | 0.64
-| -
+| 2.10
 |===
 
 This cop checks if the value of the option `class_name`, in
 the definition of a reflection is a string.
+It is marked as unsafe because it cannot be determined whether
+constant or method return value specified to `class_name` is a string.
 
 === Examples
 

lib/rubocop/cop/rails/reflection_class_name.rb

@@ -5,6 +5,8 @@ module Cop
     module Rails
       # This cop checks if the value of the option `class_name`, in
       # the definition of a reflection is a string.
+      # It is marked as unsafe because it cannot be determined whether
+      # constant or method return value specified to `class_name` is a string.
       #
       # @example
       #   # bad