Xamarin.Forms ViewCell / Visual Studio 2019 - "Partial declarations of 'someType' must not specify different base classes"

Question

In my Xamarin.Forms project I am attempting to create a reusable ViewCell. I can't figure out, though, why when I simply create a ViewCell XAML and CS file using the VS-supplied template, it will not compile due to the following error:

"Partial declarations of 'DateViewCell' must not specify different base classes"

This error pops the second I create the file (as you'll see in the code below, I haven't added any code yet and this is all boilerplate) and I have a fully functional Xamarin.Forms project that compiles with no issues if I remove the extension.

DateViewCell.xaml:

<?xml version="1.0" encoding="UTF-8"?>
<ViewCell xmlns="http://xamarin.com/schemas/2014/forms" 
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:d="http://xamarin.com/schemas/2014/forms/design"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
             mc:Ignorable="d"
             x:Class="HelloWorld.Extensions.DateViewCell">
  <ViewCell.View>
      <StackLayout>
          <Label Text="Hello Xamarin.Forms!" />
      </StackLayout>
  </ViewCell.View>
</ViewCell>

DateViewCell.xaml.cs:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

using Xamarin.Forms;
using Xamarin.Forms.Xaml;

namespace HelloWorld.Extensions
{
    [XamlCompilation(XamlCompilationOptions.Compile)]
    public partial class DateViewCell : ViewCell
    {
        public DateViewCell()
        {
            InitializeComponent();
        }
    }
}

DateViewCell.xaml.g.cs:

//------------------------------------------------------------------------------
// <auto-generated>
//     This code was generated by a tool.
//     Runtime Version:4.0.30319.42000
//
//     Changes to this file may cause incorrect behavior and will be lost if
//     the code is regenerated.
// </auto-generated>
//------------------------------------------------------------------------------

[assembly: global::Xamarin.Forms.Xaml.XamlResourceIdAttribute("HelloWorld.Extensions.DateViewCell.xaml", "Extensions/DateViewCell.xaml", typeof(global::HelloWorld.Extensions.DateViewCell))]

namespace HelloWorld.Extensions {


    [global::Xamarin.Forms.Xaml.XamlFilePathAttribute("Extensions\\DateViewCell.xaml")]
    public partial class DateViewCell : global::Xamarin.Forms.ViewCell {

        [global::System.CodeDom.Compiler.GeneratedCodeAttribute("Xamarin.Forms.Build.Tasks.XamlG", "2.0.0.0")]
        private void InitializeComponent() {
            global::Xamarin.Forms.Xaml.Extensions.LoadFromXaml(this, typeof(DateViewCell));
        }
    }
}

Sort of at a dead end here. I tried creating this "DateViewCell" extension manually and I get the same error that I did when I let VS create the file for me. I'm starting to wonder if this is a bug in Xamarin.

Anyone have any suggestions? The SO articles I could find that referenced this particular error didn't really apply and I'm out of ideas on better ways to search this... Thanks everybody.