<ItemGroup>
    <PackageReference Include="MessagePack.Annotations" Version="2.5.124" />
    <PackageReference Include="MessagePackAnalyzer" Version="2.5.124">
      <PrivateAssets>all</PrivateAssets>
      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
    </PackageReference>
  </ItemGroup>

using MessagePack;

namespace XYZ;

[MessagePackObject]
public class Foo
{
    [Key(0)]
    public int Foo1 { get; set; }

    // NOTE: No diagnostic reported!
    public int Foo2 { get; set; }
}