Add missing absence validations to Rails/Validation

CHANGELOG.md

@@ -12,6 +12,7 @@
 
 * Do not annotate message with cop name in JSON output. ([@elebow][])
 * [#6914](https://github.com/rubocop-hq/rubocop/issues/6914): [Fix #6914] Fix an error for `Rails/RedundantAllowNil` when with interpolations. ([@Blue-Pix][])
+* [#6941](https://github.com/rubocop-hq/rubocop/issues/6941): Add missing absence validations to `Rails/Validation`. ([@jmanian][])
 
 ### Changes
 
@@ -3946,3 +3947,4 @@
 [@thomthom]: https://github.com/thomthom
 [@Blue-Pix]: https://github.com/Blue-Pix
 [@Mange]: https://github.com/Mange
+[@jmanian]: https://github.com/jmanian

lib/rubocop/cop/rails/validation.rb

@@ -15,6 +15,7 @@ module Rails
       #   validates_length_of :foo
       #   validates_numericality_of :foo
       #   validates_presence_of :foo
+      #   validates_absence_of :foo
       #   validates_size_of :foo
       #   validates_uniqueness_of :foo
       #
@@ -27,6 +28,7 @@ module Rails
       #   validates :foo, length: true
       #   validates :foo, numericality: true
       #   validates :foo, presence: true
+      #   validates :foo, absence: true
       #   validates :foo, size: true
       #   validates :foo, uniqueness: true
       #
@@ -43,6 +45,7 @@ class Validation < Cop
           length
           numericality
           presence
+          absence
           size
           uniqueness
         ].freeze

manual/cops_rails.md

@@ -2350,6 +2350,7 @@ validates_inclusion_of :foo
 validates_length_of :foo
 validates_numericality_of :foo
 validates_presence_of :foo
+validates_absence_of :foo
 validates_size_of :foo
 validates_uniqueness_of :foo
 
@@ -2362,6 +2363,7 @@ validates :foo, inclusion: true
 validates :foo, length: true
 validates :foo, numericality: true
 validates :foo, presence: true
+validates :foo, absence: true
 validates :foo, size: true
 validates :foo, uniqueness: true
 ```