[Fix #106] Make Rails/ReflectionClassName aware of the use of strin…

…g with `to_s`

Follow #469

Fixes #106.

This PR makes `Rails/ReflectionClassName` aware of the use of string with `to_s`.

CHANGELOG.md

@@ -32,6 +32,7 @@
 * [#403](https://github.com/rubocop/rubocop-rails/pull/403): Mark `Rails/WhereEquals` 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][])
+* [#106](https://github.com/rubocop/rubocop-rails/issues/106): Make `Rails/ReflectionClassName` aware of the use of string with `to_s`. ([@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][])
 

lib/rubocop/cop/rails/reflection_class_name.rb

@@ -18,6 +18,7 @@ module Rails
       class ReflectionClassName < Base
         MSG = 'Use a string value for `class_name`.'
         RESTRICT_ON_SEND = %i[has_many has_one belongs_to].freeze
+        ALLOWED_REFLECTION_CLASS_TYPES = %i[dstr str sym].freeze
 
         def_node_matcher :association_with_reflection, <<~PATTERN
           (send nil? {:has_many :has_one :belongs_to} _ _ ?
@@ -26,14 +27,24 @@ class ReflectionClassName < Base
         PATTERN
 
         def_node_matcher :reflection_class_name, <<~PATTERN
-          (pair (sym :class_name) [!dstr !str !sym])
+          (pair (sym :class_name) #reflection_class_value?)
         PATTERN
 
         def on_send(node)
           association_with_reflection(node) do |reflection_class_name|
             add_offense(reflection_class_name.loc.expression)
           end
         end
+
+        private
+
+        def reflection_class_value?(class_value)
+          if class_value.send_type?
+            !class_value.method?(:to_s) || class_value.receiver.const_type?
+          else
+            !ALLOWED_REFLECTION_CLASS_TYPES.include?(class_value.type)
+          end
+        end
       end
     end
   end

spec/rubocop/cop/rails/reflection_class_name_spec.rb

@@ -16,6 +16,13 @@
       RUBY
     end
 
+    it '.to_s' do
+      expect_offense(<<~RUBY)
+        has_many :accounts, class_name: Account.to_s
+                            ^^^^^^^^^^^^^^^^^^^^^^^^ Use a string value for `class_name`.
+      RUBY
+    end
+
     it 'has_one' do
       expect_offense(<<~RUBY)
         has_one :account, class_name: Account
@@ -46,6 +53,12 @@
     RUBY
   end
 
+  it 'does not register an offense when using `class_name: do_something.to_s`' do
+    expect_no_offenses(<<~'RUBY')
+      has_many :accounts, class_name: do_something.to_s
+    RUBY
+  end
+
   it 'does not register an offense when using `foreign_key :account_id`' do
     expect_no_offenses(<<~RUBY)
       has_many :accounts, class_name: 'Account', foreign_key: :account_id