Don't unwrap wrapped DataObject inner data store (#12800)

src/System.Windows.Forms/src/System/Windows/Forms/OLE/DataObject.cs

@@ -45,11 +45,7 @@ public DataObject()
     /// </summary>
     public DataObject(object data)
     {
-        if (data is DataObject dataObject)
-        {
-            _innerData = dataObject._innerData;
-        }
-        else if (data is IDataObject iDataObject)
+        if (data is IDataObject iDataObject)
         {
             _innerData = Composition.CreateFromWinFormsDataObject(iDataObject);
         }

src/System.Windows.Forms/tests/UnitTests/System/Windows/Forms/ClipboardTests.cs

@@ -699,4 +699,33 @@ public void Clipboard_SetDataObject_Text()
         byte[] array = stream.ToArray();
         array.Should().BeEquivalentTo("Hello, World!\0"u8.ToArray());
     }
+
+    [WinFormsFact]
+    public void Clipboard_DerivedDataObject_DataPresent()
+    {
+        // https://github.com/dotnet/winforms/issues/12789
+        SomeDataObject data = new();
+
+        // This was provided as a workaround for the above and should not break, but should
+        // also work without it.
+        data.SetData(SomeDataObject.Format, data);
+
+        Clipboard.SetDataObject(data);
+        Clipboard.ContainsData(SomeDataObject.Format).Should().BeTrue();
+        Clipboard.GetDataObject()!.GetDataPresent(SomeDataObject.Format).Should().BeTrue();
+
+        data = new();
+        Clipboard.SetDataObject(data);
+        Clipboard.ContainsData(SomeDataObject.Format).Should().BeTrue();
+        Clipboard.GetDataObject()!.GetDataPresent(SomeDataObject.Format).Should().BeTrue();
+    }
+
+    public class SomeDataObject : DataObject
+    {
+        public static string Format => "SomeDataObjectId";
+        public override string[] GetFormats() => [Format];
+
+        public override bool GetDataPresent(string format, bool autoConvert)
+            => format == Format || base.GetDataPresent(format, autoConvert);
+    }
 }

src/System.Windows.Forms/tests/UnitTests/System/Windows/Forms/DataObjectTests.cs

@@ -2657,4 +2657,77 @@ public unsafe void DataObject_ComTypesIDataObject_MockRoundTrip_IsWrapped()
         IDataObject outData = dropTargetAccessor.CreateDelegate<CreateWinFormsDataObjectForOutgoingDropData>()(inDataPtr);
         outData.Should().BeSameAs(inData);
     }
+
+    [Fact]
+    public void DataObject_CreateFromDataObject_DoesNotUnwrapDataStore()
+    {
+        // The inner data should not have it's data store unwrapped.
+        DataObject dataObject = new();
+        DataObject wrapped = new(dataObject);
+        DataObject.Composition composition = wrapped.TestAccessor().Dynamic._innerData;
+        IDataObject original = composition.TestAccessor().Dynamic._winFormsDataObject;
+        original.Should().BeSameAs(dataObject);
+    }
+
+    [Fact]
+    public void DataObject_CreateFromDataObject_VirtualsAreCalled()
+    {
+        Mock<DataObject> mock = new(MockBehavior.Loose);
+        DataObject wrapped = new(mock.Object);
+
+        wrapped.GetData("Foo", false);
+        mock.Verify(o => o.GetData("Foo", false), Times.Once());
+        mock.VerifyNoOtherCalls();
+        mock.Reset();
+
+        wrapped.GetData("Foo");
+        mock.Verify(o => o.GetData("Foo", true), Times.Once());
+        mock.VerifyNoOtherCalls();
+        mock.Reset();
+
+        wrapped.GetData(typeof(string));
+        mock.Verify(o => o.GetData("System.String", true), Times.Once());
+        mock.VerifyNoOtherCalls();
+        mock.Reset();
+
+        wrapped.GetDataPresent("Foo", false);
+        mock.Verify(o => o.GetDataPresent("Foo", false), Times.Once());
+        mock.VerifyNoOtherCalls();
+        mock.Reset();
+
+        wrapped.GetDataPresent("Foo");
+        mock.Verify(o => o.GetDataPresent("Foo", true), Times.Once());
+        mock.VerifyNoOtherCalls();
+        mock.Reset();
+
+        wrapped.GetDataPresent(typeof(string));
+        mock.Verify(o => o.GetDataPresent("System.String", true), Times.Once());
+        mock.VerifyNoOtherCalls();
+        mock.Reset();
+
+        wrapped.GetFormats(false);
+        mock.Verify(o => o.GetFormats(false), Times.Once());
+        mock.VerifyNoOtherCalls();
+        mock.Reset();
+
+        wrapped.GetFormats();
+        mock.Verify(o => o.GetFormats(true), Times.Once());
+        mock.VerifyNoOtherCalls();
+        mock.Reset();
+
+        wrapped.SetData("Foo", "Bar");
+        mock.Verify(o => o.SetData("Foo", "Bar"), Times.Once());
+        mock.VerifyNoOtherCalls();
+        mock.Reset();
+
+        wrapped.SetData(typeof(string), "Bar");
+        mock.Verify(o => o.SetData(typeof(string), "Bar"), Times.Once());
+        mock.VerifyNoOtherCalls();
+        mock.Reset();
+
+        wrapped.SetData("Bar");
+        mock.Verify(o => o.SetData("Bar"), Times.Once());
+        mock.VerifyNoOtherCalls();
+        mock.Reset();
+    }
 }