Add registered callback for extension modules [#148]

The "registered" message is sent to extension modules immediately
after the module is mixed into a Sinatra::Base class. This can be
used to initialize the class with options, add templates, define
error handlers, etc.

lib/sinatra/base.rb

@@ -716,13 +716,16 @@ module Sinatra
 
     public
       def helpers(*extensions, &block)
-        class_eval(&block) if block_given?
-        include *extensions
+        class_eval(&block)  if block_given?
+        include *extensions if extensions.any?
       end
 
       def register(*extensions, &block)
-        extensions << Module.new(&block) if block
-        extend *extensions
+        extensions << Module.new(&block) if block_given?
+        extensions.each do |extension|
+          extend extension
+          extension.registered(self) if extension.respond_to?(:registered)
+        end
       end
 
       def development? ; environment == :development ; end

test/extensions_test.rb

@@ -60,4 +60,25 @@ describe 'Registering extensions' do
     assert !Sinatra::Base.respond_to?(:baz)
     assert Sinatra::Default.respond_to?(:baz)
   end
+
+  module BizzleExtension
+    def bizzle
+      bizzle_option
+    end
+
+    def self.registered(base)
+      fail "base should be BizzleApp" unless base == BizzleApp
+      fail "base should have already extended BizzleExtension" unless base.respond_to?(:bizzle)
+      base.set :bizzle_option, 'bizzle!'
+    end
+  end
+
+  class BizzleApp < Sinatra::Base
+  end
+
+  it 'sends .registered to the extension module after extending the class' do
+    BizzleApp.register BizzleExtension
+    assert_equal 'bizzle!', BizzleApp.bizzle_option
+    assert_equal 'bizzle!', BizzleApp.bizzle
+  end
 end