Preserve custom inspect on Delegator wrappers

lib/pp.rb

@@ -200,18 +200,38 @@ def pop_inspect_key(id)
     def pp(obj)
       # If obj is a Delegator then use the object being delegated to for cycle
       # detection
-      obj = obj.__getobj__ if defined?(::Delegator) and ::Delegator === obj
+      delegated = defined?(::Delegator) && ::Delegator === obj
+      key = delegated ? obj.__getobj__ : obj
 
-      if check_inspect_key(obj)
+      if check_inspect_key(key)
+        obj = key if delegated and !obj.respond_to?(:pretty_print_cycle)
         group {obj.pretty_print_cycle self}
         return
       end
 
-      guard_inspect(obj) do
+      guard_inspect(key) do
+        custom_inspect = false
+        if delegated
+          delegator_class = obj.class
+          unless delegator_class.public_method_defined?(:pretty_print)
+            singleton_methods = obj.singleton_methods(false)
+            custom_inspect =
+              !singleton_methods.include?(:pretty_print) &&
+              (delegator_class.public_method_defined?(:inspect) ||
+               singleton_methods.include?(:inspect))
+          end
+        end
+        obj = key if delegated && !custom_inspect && !obj.respond_to?(:pretty_print)
         group do
-          obj.pretty_print self
-        rescue NoMethodError
-          text Kernel.instance_method(:inspect).bind_call(obj)
+          if custom_inspect
+            text obj.inspect
+          else
+            begin
+              obj.pretty_print self
+            rescue NoMethodError
+              text Kernel.instance_method(:inspect).bind_call(obj)
+            end
+          end
         end
       end
     end

test/test_pp.rb

@@ -312,6 +312,24 @@ def test_direct_pp
 class PPDelegateTest < Test::Unit::TestCase
   class A < DelegateClass(Array); end
 
+  class Delegated < SimpleDelegator
+    def pretty_print(q)
+      q.text "<delegated>"
+    end
+  end
+
+  class Inspected < SimpleDelegator
+    def inspect
+      "<delegated inspect>"
+    end
+  end
+
+  class RaisingInspect < SimpleDelegator
+    def inspect
+      self.missing_from_inspect
+    end
+  end
+
   def test_delegate
     assert_equal("[]\n", A.new([]).pretty_inspect, "[ruby-core:25804]")
   end
@@ -327,6 +345,35 @@ def test_delegate_cycle
 
     assert_equal(cycle_pretty_inspect, delegator_cycle_pretty_inspect)
   end
+
+  def test_delegate_pretty_print
+    delegated = Delegated.new(HasPrettyPrint.new(nil))
+    assert_equal("<delegated>\n", PP.pp(delegated, ''.dup))
+  end
+
+  def test_delegate_inspect
+    delegated = Inspected.new(HasInspect.new(:target))
+    assert_equal("<delegated inspect>\n", PP.pp(delegated, ''.dup))
+  end
+
+  def test_delegate_singleton_inspect
+    delegated = SimpleDelegator.new(HasInspect.new(:target))
+    def delegated.inspect() "<delegated inspect>" end
+
+    assert_equal("<delegated inspect>\n", PP.pp(delegated, ''.dup))
+  end
+
+  def test_delegate_inspect_error
+    error = assert_raise(NoMethodError) do
+      PP.pp(RaisingInspect.new(HasInspect.new(:target)), ''.dup)
+    end
+    assert_equal(:missing_from_inspect, error.name)
+  end
+
+  def test_delegate_basic_object
+    delegated = SimpleDelegator.new(BasicObject.new)
+    assert_match(/\A#<BasicObject:0x[\da-f]+>\n\z/, PP.pp(delegated, ''.dup))
+  end
 end
 
 class PPFileStatTest < Test::Unit::TestCase