NullReferenceException when OmniSharp server starts

[DustinCampbell]

From @sidecus on May 16, 2018 4:42

Environment data

dotnet --info output:

.NET Command Line Tools (2.0.0)
Runtime Environment:
 OS Name:     Windows
 OS Version:  6.3.9600
 OS Platform: Windows
 RID:         win81-x64

VS Code version: 1.23.1
C# Extension version: 1.15.2

Steps to reproduce

OmniSharp started and then throws exception:

System.NullReferenceException: Object reference not set to an instance of an object.
   at OmniSharp.MSBuild.Discovery.Providers.DevConsoleInstanceProvider.GetInstances()
   at OmniSharp.MSBuild.Discovery.MSBuildLocator.GetInstances()
   at OmniSharp.CompositionHostBuilder.RegisterMSBuildInstance(IMSBuildLocator msbuildLocator, ILogger logger)
   at OmniSharp.CompositionHostBuilder.Build()
   at OmniSharp.Stdio.Host..ctor(TextReader input, ISharedTextWriter writer, IOmniSharpEnvironment environment, IConfiguration configuration, IServiceProvider serviceProvider, CompositionHostBuilder compositionHostBuilder, ILoggerFactory loggerFactory, CancellationTokenSource cancellationTokenSource)
   at OmniSharp.Stdio.Driver.Program.<>c__DisplayClass0_1.<Main>b__1()
   at Microsoft.Extensions.CommandLineUtils.CommandLineApplication.Execute(String[] args)
   at OmniSharp.HostHelpers.Start(Func`1 action)
[ERROR] Error: OmniSharp server load timed out. Use the 'omnisharp.projectLoadTimeout' setting to override the default delay (one minute).

Copied from original issue: dotnet/vscode-csharp#2310

[DustinCampbell]

Thanks for reporting this failure! It looks to me like this can happen if the "VSINSTALLDIR" environment variable is set but "VSCMD_VER" is not. This could happen with older instances of Visual Studio when launching from a Developer Command Prompt or if you've set "VSINSTALLDIR" yourself.

I have fix for null-ref in PR. Once this PR is merged and CI is complete, you can use it in C# for VS Code by setting the following option in VS Code:

{
    "omnisharp.path": "latest"
}

Alternatively, you should be able workaround the issue by setting the "VSCMD_VER" environment variable to "".