check for valid options in validate method

This change prevents a certain class of user error which results when
mistakenly using the `validate` class method instead of the `validates`
class method.

Only apply when all arguments are symbols, because some validations use
the `validate` method and pass in additional options, namely the
`LenghValidator` via the `ActiveMode::Validations::validates_with`
method.

3 files changed, 18 insertions, 0 deletions

diff --git a/activemodel/CHANGELOG.md b/activemodel/CHANGELOG.md
index 555cd259d2..c8ee8ad7de 100644
--- a/activemodel/CHANGELOG.md
+++ b/activemodel/CHANGELOG.md
@@ -1,3 +1,9 @@
+*   Validate options passed to `ActiveModel::Validations::validate`
+
+    Preventing, in many cases, the simple mistake of using `validate` instead of `validate`.
+
+    *Sonny Michaud*
+
 *   Deprecate `reset_#{attribute}` in favor of `restore_#{attribute}`.
 
     These methods may cause confusion with the `reset_changes` that behaves differently
diff --git a/activemodel/lib/active_model/validations.rb b/activemodel/lib/active_model/validations.rb
index cf97f45dba..b3d345c8ca 100644
--- a/activemodel/lib/active_model/validations.rb
+++ b/activemodel/lib/active_model/validations.rb
@@ -141,6 +141,11 @@ module ActiveModel
       #   value.
       def validate(*args, &block)
         options = args.extract_options!
+
+        if args.all? { |arg| arg.is_a?(Symbol) }
+          options.assert_valid_keys(%i(on if unless))
+        end
+
         if options.key?(:on)
           options = options.dup
           options[:if] = Array(options[:if])
@@ -148,6 +153,7 @@ module ActiveModel
             Array(options[:on]).include?(o.validation_context)
           }
         end
+
         args << options
         set_callback(:validate, *args, &block)
       end
diff --git a/activemodel/test/cases/validations_test.rb b/activemodel/test/cases/validations_test.rb
index 4fee704ef5..948efd0f0a 100644
--- a/activemodel/test/cases/validations_test.rb
+++ b/activemodel/test/cases/validations_test.rb
@@ -167,6 +167,12 @@ class ValidationsTest < ActiveModel::TestCase
     end
   end
 
+  def test_invalid_options_to_validate
+    assert_raises(ArgumentError) do
+      Topic.validate :title, presence: true
+    end
+  end
+
   def test_errors_conversions
     Topic.validates_presence_of %w(title content)
     t = Topic.new