Can the new csproj file structure be used with a A

The new .csproj format includes some significant improvements over the classic files, including tight integration with NuGet package management and significantly less-verbose structure. I want to gain these benefits whilst still using the .NET Framework 4.6 and ASP.NET (because my project depends on Umbraco which has yet to produce a .NET Core version).

The biggest challenge would seem to be the debugging experience - an ASP.NET Core project expects to run a dotnet core application and set up a reverse proxy to an IIS instance. This process is completely alien to the .NET Framework model and I wouldn't know where to start trying to set up debugging in Visual Studio.

Is there any way to get these two project models to mix?

There is a bunch of open issues on GitHub regarding support of new csproj format for ASP.NET (non-Core) applications. Some of them:

Using the new .Csproj without .Net core #1688
Add support for ASP.NET (non-Core) projects #2670
Support for "classic" ASP.NET #1978

As you probably already understood, new csproj format is not yet supported for ASP.NET applications. It's possible to make it work, however it won't be smooth.

Some time ago I have tried to create ASP.NET MVC project in new csproj format, just for fun. I made it work, however I had not played with it a lot. So it will be interesting to know your experience.

The steps are following:

Remove old unrequired project files:
- MvcApplication.csproj
- MvcApplication.csproj.user
- packages.config

Create new MvcApplication.csproj with the following content:

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <TargetFramework>net461</TargetFramework>
  </PropertyGroup>

  <PropertyGroup>
    <AppendTargetFrameworkToOutputPath>false</AppendTargetFrameworkToOutputPath>
    <OutputPath>bin\</OutputPath>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="Antlr" version="3.4.1.9004" />
    <PackageReference Include="bootstrap" version="3.0.0" />
    <PackageReference Include="jQuery" version="1.10.2" />
    <PackageReference Include="jQuery.Validation" version="1.11.1" />
    <PackageReference Include="Microsoft.ApplicationInsights" version="2.2.0" />
    <PackageReference Include="Microsoft.ApplicationInsights.Agent.Intercept" version="2.0.6" />
    <PackageReference Include="Microsoft.ApplicationInsights.DependencyCollector" version="2.2.0" />
    <PackageReference Include="Microsoft.ApplicationInsights.PerfCounterCollector" version="2.2.0" />
    <PackageReference Include="Microsoft.ApplicationInsights.Web" version="2.2.0" />
    <PackageReference Include="Microsoft.ApplicationInsights.WindowsServer" version="2.2.0" />
    <PackageReference Include="Microsoft.ApplicationInsights.WindowsServer.TelemetryChannel" version="2.2.0" />
    <PackageReference Include="Microsoft.AspNet.Mvc" version="5.2.3" />
    <PackageReference Include="Microsoft.AspNet.Razor" version="3.2.3" />
    <PackageReference Include="Microsoft.AspNet.Web.Optimization" version="1.1.3" />
    <PackageReference Include="Microsoft.AspNet.WebPages" version="3.2.3" />
    <PackageReference Include="Microsoft.CodeDom.Providers.DotNetCompilerPlatform" version="1.0.5" />
    <PackageReference Include="Microsoft.CSharp" Version="4.4.1" />
    <PackageReference Include="Microsoft.jQuery.Unobtrusive.Validation" version="3.2.3" />
    <PackageReference Include="Microsoft.Net.Compilers" version="2.1.0" developmentDependency="true" />
    <PackageReference Include="Microsoft.Web.Infrastructure" version="1.0.0.0" />
    <PackageReference Include="Modernizr" version="2.6.2" />
    <PackageReference Include="Newtonsoft.Json" version="6.0.4" />
    <PackageReference Include="Respond" version="1.2.0" />
    <PackageReference Include="WebGrease" version="1.5.2" />
  </ItemGroup>

  <ItemGroup>
    <DotNetCliToolReference Include="Microsoft.VisualStudio.Web.CodeGeneration.Tools" Version="2.0.0" />
  </ItemGroup>

  <ItemGroup>
    <Reference Include="System.Web" />
  </ItemGroup>

  <ItemGroup>
    <Compile Update="Global.asax.cs">
      <DependentUpon>Global.asax</DependentUpon>
    </Compile>
  </ItemGroup>

  <ItemGroup>
    <Content Include="Web.config">
      <SubType>Designer</SubType>
    </Content>
    <Content Include="Web.*.config">
      <DependentUpon>Web.config</DependentUpon>
      <SubType>Designer</SubType>
    </Content>
  </ItemGroup>

</Project>

The long package list above includes default packages added for default ASP.NET MVC application. You should add other packages used by your application.

Don't forget to add the Microsoft.CSharp package, otherwise you'll get following compilation error on ViewBag assignments:

error CS0656: Missing compiler required member 'Microsoft.CSharp.RuntimeBinder.CSharpArgumentInfo.Create'

In ASP.NET projects, Microsoft.CSharp is added as reference to the project. But it's better to consume it as NuGet package.

The only direct reference that could not be avoided is a System.Web.

Debugging the project

You were right when said that debugging could be a pain. Since Visual Studio does not know it's an ASP.NET application, there is no instant method to start debugging session.

I see 2 possible solutions here:

a. Use IIS Express for debugging.

It's quite easy to configure debugging based on IIS Express executable. Just create the following debugging profile:

Corresponding launchSettings.json:
```
{
  "profiles": {
    "ASP.NET Old csproj": {
      "commandName": "Executable",
      "executablePath": "c:\\Program Files\\IIS Express\\iisexpress.exe",
      "commandLineArgs": "/path:\"$(SolutionDir)$(ProjectName)\" /port:12345"
    }
}
```
b. Use IIS for debugging.

In IIS Manager create application that points to directory with your project. Now you could debug your application by attaching to w3wp.exe process.

Here is Sample Project on GitHub. It is basically default ASP.NET MVC project migrated to new csproj format following above steps. It could be compiled, executed and debugged (profile for IIS Express included)