Warn when extra parameters passed to SelectorQuery

lib/capybara/queries/selector_query.rb

@@ -11,14 +11,16 @@ module Capybara
         @options = if args.last.is_a?(Hash) then args.pop.dup else {} end
 
         if args[0].is_a?(Symbol)
-          @selector = Selector.all[args[0]]
-          @locator = args[1]
+          @selector = Selector.all[args.shift]
+          @locator = args.shift
         else
           @selector = Selector.all.values.find { |s| s.match?(args[0]) }
-          @locator = args[0]
+          @locator = args.shift
         end
         @selector ||= Selector.all[Capybara.default_selector]
 
+        warn "Unused parameters passed to #{self.class.name} : #{args.to_s}" unless args.empty?
+
         # for compatibility with Capybara 2.0
         if Capybara.exact_options and @selector == Selector.all[:option]
           @options[:exact] = true

lib/capybara/spec/session/has_selector_spec.rb

@@ -67,6 +67,11 @@ Capybara::SpecHelper.spec '#has_selector?' do
       expect(@session).to have_selector("//p//a", :text => /re[dab]i/i, :count => 1)
       expect(@session).not_to have_selector("//p//a", :text => /Red$/)
     end
+
+    it "should warn when extra parameters passed" do
+      expect_any_instance_of(Kernel).to receive(:warn).with(/extra/)
+      expect(@session).to have_selector(:css, "p a#foo", 'extra')
+    end
   end
 end