Predefined type 'System.Void' is not defined or imported during Visual Studio Online build of ASP.NET 5

Question

I get this error when I try to build the project in Visual Studio Online:

Frontend\src\Frontend\Startup.cs(65,49): Error CS0518: Predefined type 'System.Void' is not defined or imported C:\a\1\s\Frontend\src\Frontend\Startup.cs(65,49): DNXCore,Version=v5.0 error CS0518: Predefined type 'System.Void' is not defined or imported [C:\a\1\s\Frontend\src\Frontend\Frontend.xproj]

It seems that the error happens in the place where I reference another library (package class library).

P.S. I had some conversation about this here: Easy way to build and deploy (to Azure) ASP.NET 5 in Visual Studio Team Services, but there was no answer after all, so I still cannot build it...

Web project.json:

"dependencies": {
    "Microsoft.AspNet.IISPlatformHandler": "1.0.0-rc1-final",
    "Microsoft.AspNet.Mvc": "6.0.0-rc1-final",
    "Microsoft.AspNet.Mvc.TagHelpers": "6.0.0-rc1-final",
    "Microsoft.AspNet.Server.Kestrel": "1.0.0-rc1-final",
    "Microsoft.AspNet.StaticFiles": "1.0.0-rc1-final",
    "Microsoft.AspNet.Tooling.Razor": "1.0.0-rc1-final",
    "Microsoft.Extensions.Configuration.FileProviderExtensions": "1.0.0-rc1-final",
    "Microsoft.Extensions.Configuration.Json": "1.0.0-rc1-final",
    "Microsoft.Extensions.Configuration.UserSecrets": "1.0.0-rc1-final",
    "Microsoft.Extensions.Logging": "1.0.0-rc1-final",
    "Microsoft.Extensions.Logging.Console": "1.0.0-rc1-final",
    "Microsoft.Extensions.Logging.Debug": "1.0.0-rc1-final",
    "Web.Common": "1.0.0-*"
},

"frameworks": {
    "dnx451": { },
    "dnxcore50": { }
},

Library project.json

"frameworks": {
    "dnx451": { },
    "dnxcore50": {
        "dependencies": {
            "Microsoft.CSharp": "4.0.1-beta-23516",
            "System.Collections": "4.0.11-beta-23516",
            "System.Linq": "4.0.1-beta-23516",
            "System.Runtime": "4.0.21-beta-23516",
            "System.Threading": "4.0.11-beta-23516"
      }
    }
  },
"dependencies": {
    "Microsoft.AspNet.Mvc": "6.0.0-rc1-final"
  }

Update (problem and solution):

The problem was in the fact that my library reference was not in the same folder and the script by default does not run dnu-restore there, so I had to go one level up and start finding project.json recursively there

$SourceRoot = Split-Path -Path $PSScriptRoot -Parent

# run DNU restore on all project.json files in the src folder including 2>1 to redirect stderr to stdout for badly behaved tools
Get-ChildItem -Path $SourceRoot -Filter project.json -Recurse | ForEach-Object { & dnu restore $_.FullName 2>1 }

Thanks Eddie - MSFT for help!

I think you are missing a dependency on the "System.Runtime" package. — Pawel
Where should I have this dependency? It's not by default in project.json in web project and it exist for coreclr, but not for clr in the library. P.S. Everything builds locally in VS by the way — Ilya Chernomordik
Can you share the "dependencies" and "frameworks" section in project.json file? — Eddie Chen - MSFT
I have added it to the post, I have changed the library target framework to match the web one because of R# issues (it does not find them as the same otherwise), but I have tried changing it back and it did not help either. I guess it should work properly with these web targets anyway as they are only more restrictive as far as I understood. — Ilya Chernomordik

Eddie Chen - MSFT Eddie Chen - MSFT · Accepted Answer · 2016-01-07T02:48:02

I just reproduced this issue after updating the code in "PreBuild.ps1" script to only restore the "project.json" file for web project.

Original Code (Build Success):

Get-ChildItem -Path $PSScriptRoot\src -Filter project.json -Recurse | ForEach-Object { & dnu restore $_.FullName 2>1 }

Updated Code (Build fail with: Predefined type 'System.Void' is not defined or imported):

Get-ChildItem -Path $PSScriptRoot\src\WebProjectName -Filter project.json -Recurse | ForEach-Object { & dnu restore $_.FullName 2>1 }

So you need to check the PreBuild.ps1 script and the build logs for PowerShell step to check if the project.json files for Web project and Library project are both restored.

Predefined type 'System.Void' is not defined or imported during Visual Studio Online build of ASP.NET 5

Update (problem and solution):

6 Answers