nobu	2015-12-30 11:18:44 +0900 (Wed, 30 Dec 2015)

  New Revision: 53381

  http://svn.ruby-lang.org/cgi-bin/viewvc.cgi?view=revision&revision=53381

  Log:
    Forwardable: Fix delegating to 'args' and 'block'
    
    * lib/forwardable.rb (def_instance_delegator) fix delegating to
      'args' and 'block', clashing with local variables in generated
      methods.  [ruby-core:72579] [Bug #11916]
    
    * lib/forwardable.rb (def_single_delegator): ditto.
    
    If you have a class that uses Forwardable to delegate a method to
    another object, and the method that returns the delegate object is
    called `args` or `block`, then Forwardable will fail to work.
    
    Here's a simple example:
    
        class ModelCreator
          extend Forwardable
    
          attr_reader :args
    
          def_delegator :args, :model_name
    
          def initialize(args)
            @args = args
          end
        end
    
        ModelCreator.new.model_name
    
    If you run the last line above, then you'll get:
    
        NoMethodError: undefined method `model_name' for []:Array
    
    This error occurs because `def_delegator` -- as it is written in Ruby --
    uses metaprogramming to add methods to the class that will then delegate
    to the delegate object. So it's as if we had written:
    
        class ModelCreator
          extend Forwardable
    
          attr_reader :args
    
          def model_name(*args, &block)
            args.model_name(*args, &block)
          end
    
          def initialize(args)
            @args = args
          end
        end
    
    As you can see, `def_delegator` will not only forward the method call
    onto the delegate object, it will also forward any arguments provided as
    well. It is here that the bug arises: it splats all of the arguments
    into a variable which is called `args`, and because of how variable
    scope works in Ruby, it then attempts to call `model_name` on *this*
    variable and *not* our delegate object method.
    
    The fix is to call the delegate object method manually using `__send__`.
    (This assumes, of course, that the given receiver is, in fact, the name
    of a method and not the name of an instance variable, which is also a
    possibility.) We use `__send__` because the delegate object method could
    be private.
    
    So, that looks like this:
    
        def model_name(*args, &block)
          __send__(:args).model_name(*args, &block)
        end
    
    Because `def_delegators` and `delegate` use `def_delegator` internally,
    they also get this fix as well.

  Modified files:
    trunk/ChangeLog
    trunk/lib/forwardable.rb
Index: ChangeLog
===================================================================
--- ChangeLog	(revision 53380)
+++ ChangeLog	(revision 53381)
@@ -1,3 +1,11 @@ https://github.com/ruby/ruby/blob/trunk/ChangeLog#L1
+Wed Dec 30 11:18:42 2015  Elliot Winkler  <elliot.winkler@g...>
+
+	* lib/forwardable.rb (def_instance_delegator) fix delegating to
+	  'args' and 'block', clashing with local variables in generated
+	  methods.  [ruby-core:72579] [Bug #11916]
+
+	* lib/forwardable.rb (def_single_delegator): ditto.
+
 Wed Dec 30 09:58:56 2015  Nobuyoshi Nakada  <nobu@r...>
 
 	* object.c (rb_class_inherited_p): search the corresponding
Index: lib/forwardable.rb
===================================================================
--- lib/forwardable.rb	(revision 53380)
+++ lib/forwardable.rb	(revision 53381)
@@ -178,6 +178,10 @@ module Forwardable https://github.com/ruby/ruby/blob/trunk/lib/forwardable.rb#L178
   #   q.push 23  #=> NoMethodError
   #
   def def_instance_delegator(accessor, method, ali = method)
+    if method_defined?(accessor) || private_method_defined?(accessor)
+      accessor = "#{accessor}()"
+    end
+
     line_no = __LINE__; str = %{
       def #{ali}(*args, &block)
         begin
@@ -270,7 +274,11 @@ module SingleForwardable https://github.com/ruby/ruby/blob/trunk/lib/forwardable.rb#L274
   # the method of the same name in _accessor_).  If _new_name_ is
   # provided, it is used as the name for the delegate method.
   def def_single_delegator(accessor, method, ali = method)
-    str = %{
+    if method_defined?(accessor) || private_method_defined?(accessor)
+      accessor = "#{accessor}()"
+    end
+
+    line_no = __LINE__; str = %{
       def #{ali}(*args, &block)
         begin
           #{accessor}.__send__(:#{method}, *args, &block)
@@ -281,7 +289,7 @@ module SingleForwardable https://github.com/ruby/ruby/blob/trunk/lib/forwardable.rb#L289
       end
     }
 
-    instance_eval(str, __FILE__, __LINE__)
+    instance_eval(str, __FILE__, line_no)
   end
 
   alias delegate single_delegate

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