[Fix rubocop#1295] Covers validates_comparison_of in Rails/Validations

Rails/Validations should include all old-style validation helpers,
including validates_comparison_of.

changelog/change_1295_covers_validates_comparison_of_in.md

@@ -0,0 +1 @@
+* [#1295](https://github.com/rubocop/rubocop-rails/issues/1295): Covers validates_comparison_of in Rails/Validations. ([@ChaelCodes][])

lib/rubocop/cop/rails/validation.rb

@@ -8,6 +8,7 @@ module Rails
       # @example
       #   # bad
       #   validates_acceptance_of :foo
+      #   validates_comparison_of :foo
       #   validates_confirmation_of :foo
       #   validates_exclusion_of :foo
       #   validates_format_of :foo
@@ -22,6 +23,7 @@ module Rails
       #   # good
       #   validates :foo, acceptance: true
       #   validates :foo, confirmation: true
+      #   validates :foo, comparison: true
       #   validates :foo, exclusion: true
       #   validates :foo, format: true
       #   validates :foo, inclusion: true
@@ -39,6 +41,7 @@ class Validation < Base
 
         TYPES = %w[
           acceptance
+          comparison
           confirmation
           exclusion
           format

spec/rubocop/cop/rails/validation_spec.rb

@@ -159,6 +159,18 @@
       include_examples 'autocorrects'
     end
 
+    context 'with a proc' do
+      let(:autocorrected_source) do
+        'validates :a, :b, comparison: { greater_than: -> { Time.zone.today } }'
+      end
+
+      let(:source) do
+        'validates_comparison_of :a, :b, greater_than: -> { Time.zone.today }'
+      end
+
+      include_examples 'autocorrects'
+    end
+
     context 'with splat' do
       let(:autocorrected_source) do
         'validates :a, *b, numericality: true'