Fix SimpleDelegator respond_to? regression

In 2.6, SimpleDelegator would always use the target `respond_to?`

In 2.7.0 it doesn't if the target does not inherit from Object.

This breaks compatibility for delegated objects that inherit
from BasicObject and redefine `respond_to?`.

2 files changed, 22 insertions, 1 deletions

diff --git a/lib/delegate.rb b/lib/delegate.rb
index b7d48effb4..e3b3488c16 100644
--- a/lib/delegate.rb
+++ b/lib/delegate.rb
@@ -103,13 +103,20 @@ class Delegator < BasicObject
     r
   end
 
+  KERNEL_RESPOND_TO = ::Kernel.instance_method(:respond_to?)
+  private_constant :KERNEL_RESPOND_TO
+
   # Handle BasicObject instances
   private def target_respond_to?(target, m, include_private)
     case target
     when Object
       target.respond_to?(m, include_private)
     else
-      ::Kernel.instance_method(:respond_to?).bind_call(target, m, include_private)
+      if KERNEL_RESPOND_TO.bind_call(target, :respond_to?)
+        target.respond_to?(m, include_private)
+      else
+        KERNEL_RESPOND_TO.bind_call(target, m, include_private)
+      end
     end
   end
 
diff --git a/test/test_delegate.rb b/test/test_delegate.rb
index 9c47743888..4a3445f121 100644
--- a/test/test_delegate.rb
+++ b/test/test_delegate.rb
@@ -344,6 +344,20 @@ class TestDelegateClass < Test::Unit::TestCase
     assert_raise(NoMethodError, /undefined method `foo' for/) { delegate.foo }
   end
 
+  def test_basicobject_respond_to
+    o = BasicObject.new
+    def o.bar
+      nil
+    end
+
+    def o.respond_to?(method, include_private=false)
+      return false if method == :bar
+      ::Kernel.instance_method(:respond_to?).bind_call(self, method, include_private)
+    end
+    delegate = SimpleDelegator.new(o)
+    refute delegate.respond_to?(:bar)
+  end
+
   def test_keyword_argument
     k = EnvUtil.labeled_class("Target") do
       def test(a, k:) [a, k]; end