Add `ActiveModel::Errors#of_kind?`

Related to https://github.com/rails/rails/pull/34817#issuecomment-451508668

1 files changed, 30 insertions, 9 deletions

diff --git a/activemodel/lib/active_model/errors.rb b/activemodel/lib/active_model/errors.rb
index 969effdc20..9fd6f2d89c 100644
--- a/activemodel/lib/active_model/errors.rb
+++ b/activemodel/lib/active_model/errors.rb
@@ -328,15 +328,15 @@ module ActiveModel
     #   person.errors.added? :name, :blank           # => true
     #   person.errors.added? :name, "can't be blank" # => true
     #
-    # If the error message requires an option, then it returns +true+ with
-    # the correct option, or +false+ with an incorrect or missing option.
-    #
-    #  person.errors.add :name, :too_long, { count: 25 }
-    #  person.errors.added? :name, :too_long, count: 25                     # => true
-    #  person.errors.added? :name, "is too long (maximum is 25 characters)" # => true
-    #  person.errors.added? :name, :too_long, count: 24                     # => false
-    #  person.errors.added? :name, :too_long                                # => false
-    #  person.errors.added? :name, "is too long"                            # => false
+    # If the error message requires options, then it returns +true+ with
+    # the correct options, or +false+ with incorrect or missing options.
+    #
+    #   person.errors.add :name, :too_long, { count: 25 }
+    #   person.errors.added? :name, :too_long, count: 25                     # => true
+    #   person.errors.added? :name, "is too long (maximum is 25 characters)" # => true
+    #   person.errors.added? :name, :too_long, count: 24                     # => false
+    #   person.errors.added? :name, :too_long                                # => false
+    #   person.errors.added? :name, "is too long"                            # => false
     def added?(attribute, message = :invalid, options = {})
       message = message.call if message.respond_to?(:call)
 
@@ -347,6 +347,27 @@ module ActiveModel
       end
     end
 
+    # Returns +true+ if an error on the attribute with the given message is
+    # present, or +false+ otherwise. +message+ is treated the same as for +add+.
+    #
+    #   person.errors.add :age
+    #   person.errors.add :name, :too_long, { count: 25 }
+    #   person.errors.of_kind? :age                                            # => true
+    #   person.errors.of_kind? :name                                           # => false
+    #   person.errors.of_kind? :name, :too_long                                # => true
+    #   person.errors.of_kind? :name, "is too long (maximum is 25 characters)" # => true
+    #   person.errors.of_kind? :name, :not_too_long                            # => false
+    #   person.errors.of_kind? :name, "is too long"                            # => false
+    def of_kind?(attribute, message = :invalid)
+      message = message.call if message.respond_to?(:call)
+
+      if message.is_a? Symbol
+        details[attribute.to_sym].map { |e| e[:error] }.include? message
+      else
+        self[attribute].include? message
+      end
+    end
+
     # Returns all the full error messages in an array.
     #
     #   class Person