Add `ActiveModel::Errors#of_kind?`

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

activemodel/CHANGELOG.md

@@ -1,3 +1,7 @@
+*   Add `ActiveModel::Errors#of_kind?`.
+
+    *bogdanvlviv*, *Rafael Mendonça França*
+
 *   Fix numericality equality validation of `BigDecimal` and `Float`
     by casting to `BigDecimal` on both ends of the validation.
 

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.
+    # 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
+    #   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

activemodel/test/cases/errors_test.rb

@@ -209,6 +209,8 @@ class ErrorsTest < ActiveModel::TestCase
     person.errors.add(:name, "cannot be blank")
     person.errors.add(:name, "is invalid")
     assert person.errors.added?(:name, "cannot be blank")
+    assert person.errors.added?(:name, "is invalid")
+    assert_not person.errors.added?(:name, "incorrect")
   end
 
   test "added? returns false when no errors are present" do
@@ -222,7 +224,7 @@ class ErrorsTest < ActiveModel::TestCase
     assert_not person.errors.added?(:name, "cannot be blank")
   end
 
-  test "added? returns false when checking for an error, but not providing message arguments" do
+  test "added? returns false when checking for an error, but not providing message argument" do
     person = Person.new
     person.errors.add(:name, "cannot be blank")
     assert_not person.errors.added?(:name)
@@ -233,6 +235,7 @@ class ErrorsTest < ActiveModel::TestCase
     person.errors.add :name, :too_long, count: 25
 
     assert person.errors.added? :name, :too_long, count: 25
+    assert person.errors.added? :name, "is too long (maximum is 25 characters)"
     assert_not person.errors.added? :name, :too_long, count: 24
     assert_not person.errors.added? :name, :too_long
     assert_not person.errors.added? :name, "is too long"
@@ -243,6 +246,81 @@ class ErrorsTest < ActiveModel::TestCase
     person = Person.new
     person.errors.add(:name, :wrong)
     assert_not person.errors.added?(:name, :used)
+    assert person.errors.added?(:name, :wrong)
+  end
+
+  test "of_kind? returns false when checking for an error, but not providing message argument" do
+    person = Person.new
+    person.errors.add(:name, "cannot be blank")
+    assert_not person.errors.of_kind?(:name)
+  end
+
+  test "of_kind? returns false when checking a nonexisting error and other errors are present for the given attribute" do
+    person = Person.new
+    person.errors.add(:name, "is invalid")
+    assert_not person.errors.of_kind?(:name, "cannot be blank")
+  end
+
+  test "of_kind? returns false when no errors are present" do
+    person = Person.new
+    assert_not person.errors.of_kind?(:name)
+  end
+
+  test "of_kind? matches the given message when several errors are present for the same attribute" do
+    person = Person.new
+    person.errors.add(:name, "cannot be blank")
+    person.errors.add(:name, "is invalid")
+    assert person.errors.of_kind?(:name, "cannot be blank")
+    assert person.errors.of_kind?(:name, "is invalid")
+    assert_not person.errors.of_kind?(:name, "incorrect")
+  end
+
+  test "of_kind? defaults message to :invalid" do
+    person = Person.new
+    person.errors.add(:name)
+    assert person.errors.of_kind?(:name)
+  end
+
+  test "of_kind? handles proc messages" do
+    person = Person.new
+    message = Proc.new { "cannot be blank" }
+    person.errors.add(:name, message)
+    assert person.errors.of_kind?(:name, message)
+  end
+
+  test "of_kind? returns true when string attribute is used with a symbol message" do
+    person = Person.new
+    person.errors.add(:name, :blank)
+    assert person.errors.of_kind?("name", :blank)
+  end
+
+  test "of_kind? handles symbol message" do
+    person = Person.new
+    person.errors.add(:name, :blank)
+    assert person.errors.of_kind?(:name, :blank)
+  end
+
+  test "of_kind? detects indifferent if a specific error was added to the object" do
+    person = Person.new
+    person.errors.add(:name, "cannot be blank")
+    assert person.errors.of_kind?(:name, "cannot be blank")
+    assert person.errors.of_kind?("name", "cannot be blank")
+  end
+
+  test "of_kind? ignores options" do
+    person = Person.new
+    person.errors.add :name, :too_long, count: 25
+
+    assert person.errors.of_kind? :name, :too_long
+    assert person.errors.of_kind? :name, "is too long (maximum is 25 characters)"
+  end
+
+  test "of_kind? returns false when checking for an error by symbol and a different error with same message is present" do
+    I18n.backend.store_translations("en", errors: { attributes: { name: { wrong: "is wrong", used: "is wrong" } } })
+    person = Person.new
+    person.errors.add(:name, :wrong)
+    assert_not person.errors.of_kind?(:name, :used)
+    assert person.errors.of_kind?(:name, :wrong)
   end
 
   test "size calculates the number of error messages" do