Visual studio 2017 : nesting files in a class library project

Question

In web projects you have the option of nesting files

 + startup.cs
   +--startup.internals.cs
   +--startup.configuration.cs

Is there any

Answer 1

I believe you can do this in your csproj file.

<Compile Include="startup.cs">
    <DependentUpon>startup.internals.xaml</DependentUpon>
    <DependentUpon>startup.configureation.xaml</DependentUpon>
</Compile>

Answer 2

To answer your Updates : Partially solved:

Something similar to this issue. DependentUpon is the correct element to use to achieve the nesting that you want.

But, your value cannot be expression that includes wildcards. It must be a single file that is under the same folder or a sub-folder. If your file exists in a sub-folder, you must specify the file via a relative path. So the content of your ItemGroup should be like this:

<Compile Include="Folder_A\Folder_A1\startup.cs" />
<Compile Include="Folder_A\Folder_A1\startup.configuration.cs">
  <DependentUpon>startup.cs</DependentUpon>
</Compile>
<Compile Include="Folder_A\Folder_A1\startup.internals.cs">
  <DependentUpon>startup.cs</DependentUpon>
</Compile>

And after my check, I think you need to use the Include attribute instead of Update if you are building a .NET FX class library project.

Update: The Update attribute is available only for .NET Core projects according to this doc.

And if in a .NET Core project, like what you indicated in a comment, maybe Update is more suitable:

<Compile Update="Folder_A\Folder_A1\startup.internals.cs">
  <DependentUpon>startup.cs</DependentUpon>
</Compile>