Add instance_methods to class generated by DelegateClass

Also, make DelegateClass.instance_method fallback to superclass.

Fixes [Bug #16982]

lib/delegate.rb

@@ -422,6 +422,21 @@ def DelegateClass(superclass, &block)
   klass.define_singleton_method :protected_instance_methods do |all=true|
     super(all) | superclass.protected_instance_methods
   end
+  klass.define_singleton_method :instance_methods do |all=true|
+    super(all) | superclass.instance_methods
+  end
+  klass.define_singleton_method :public_instance_method do |name|
+    super(name)
+  rescue NameError
+    raise unless self.public_instance_methods.include?(name)
+    superclass.public_instance_method(name)
+  end
+  klass.define_singleton_method :instance_method do |name|
+    super(name)
+  rescue NameError
+    raise unless self.instance_methods.include?(name)
+    superclass.instance_method(name)
+  end
   klass.module_eval(&block) if block
   return klass
 end

test/test_delegate.rb

@@ -106,6 +106,10 @@ class TestDelegateClass < Test::Unit::TestCase
     protected
 
     def parent_protected; end
+
+    private
+
+    def parent_private; end
   end
 
   class Child < DelegateClass(Parent)
@@ -117,6 +121,10 @@ class TestDelegateClass < Test::Unit::TestCase
     protected
 
     def parent_protected_added; end
+
+    private
+
+    def parent_private_added; end
   end
 
   def test_public_instance_methods
@@ -131,6 +139,32 @@ class TestDelegateClass < Test::Unit::TestCase
     assert_equal([:parent_protected, :parent_protected_added], (Child.new(Parent.new).protected_methods - ignores).sort)
   end
 
+  def test_instance_methods
+    ignores = Object.instance_methods | Delegator.instance_methods
+    assert_equal([:parent_protected, :parent_protected_added, :parent_public, :parent_public_added], (Child.instance_methods - ignores).sort)
+    assert_equal([:parent_protected, :parent_protected_added, :parent_public, :parent_public_added], (Child.new(Parent.new).methods - ignores).sort)
+  end
+
+  def test_DelegateClass_instance_method
+    assert_instance_of UnboundMethod, Child.instance_method(:parent_public)
+    assert_instance_of UnboundMethod, Child.instance_method(:parent_public_added)
+    assert_instance_of UnboundMethod, Child.instance_method(:parent_protected)
+    assert_instance_of UnboundMethod, Child.instance_method(:parent_protected_added)
+    assert_raise(NameError) { Child.instance_method(:parent_private) }
+    assert_raise(NameError) { Child.instance_method(:parent_private_added) }
+    assert_instance_of UnboundMethod, Child.instance_method(:to_s)
+  end
+
+  def test_DelegateClass_public_instance_method
+    assert_instance_of UnboundMethod, Child.public_instance_method(:parent_public)
+    assert_instance_of UnboundMethod, Child.public_instance_method(:parent_public_added)
+    assert_raise(NameError) { Child.public_instance_method(:parent_protected) }
+    assert_raise(NameError) { Child.public_instance_method(:parent_protected_added) }
+    assert_raise(NameError) { Child.instance_method(:parent_private) }
+    assert_raise(NameError) { Child.instance_method(:parent_private_added) }
+    assert_instance_of UnboundMethod, Child.public_instance_method(:to_s)
+  end
+
   class IV < DelegateClass(Integer)
     attr_accessor :var