Ensure only delegations to methods can have an automatic prefix. [#1235 state:resolved]

Signed-off-by: Pratik Naik <pratiknaik@gmail.com>

activesupport/lib/active_support/core_ext/module/delegation.rb

@@ -78,6 +78,10 @@ class Module
       raise ArgumentError, "Delegation needs a target. Supply an options hash with a :to key as the last argument (e.g. delegate :hello, :to => :greeter)."
     end
 
+    if options[:prefix] == true && options[:to].to_s =~ /^[^a-z_]/
+      raise ArgumentError, "Can only automatically set the delegation prefix when delegating to a method."
+    end
+
     prefix = options[:prefix] && "#{options[:prefix] == true ? to : options[:prefix]}_"
 
     methods.each do |method|

activesupport/test/core_ext/module_test.rb

@@ -106,6 +106,17 @@ class ModuleTest < Test::Unit::TestCase
     assert_equal invoice.customer_city, "Chicago"
   end
 
+  def test_delegation_prefix_with_instance_variable
+    assert_raise ArgumentError do
+      Class.new do
+        def initialize(client)
+          @client = client
+        end
+        delegate :name, :address, :to => :@client, :prefix => true
+      end
+    end
+  end
+
   def test_parent
     assert_equal Yz::Zy, Yz::Zy::Cd.parent
     assert_equal Yz, Yz::Zy.parent