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.

1 files changed, 6 insertions, 0 deletions

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