Visual Studio Code: Roslyn and OmniSharp with the C# compiler on Windows

(A month is a long time in .Net, right now. Looking back at this, it clearly predates my getting to grips with project.json. I’m leaving it here as I find it instructive to leave my naive attempts in place.)

  • Visual Studio 2015: I abbreviate this to VS
  • Visual Studio Code: I abbreviate this to VSC

Summary

This is aimed at C# programmers on Windows, who are used to doing all their editing and dev compilation in VS. In VSC, you can edit existing .cs files which are already part of a parent .sln file. Doing this, you will get Intellisense and a whole bunch of richness. However if you create new .cs files, then to get Intellisense etc, you must first go to VS and add that new file to a .csproj and .sln (or write some command line transformer to add the .cs files… or a Task in VS). With a little one-off effort, you can compile inside VSC. 

If you are using VSC on Windows, and you are writing C#, and you want OmniSharp and Intellisense to work… then you must have a VS Solution in place. I emphasise that, because I first did not entirely digest this point here:

OmniSharp01

As a C# programmer, just heed the stuff in the orange borders. As ever, some screenshots illustrate the point. Firstly, this is what happens if you naively open a .cs file in VSC that does not ultimately have a parent .sln file:

OmniSharp02

After typing [System.] above, I pressed [ctrl-space], which returns [No suggestion]. That is because App1.cs is standalone, and has no VS Solution context. It is however perfectly valid C#  (once I fix the syntax):

OmniSharp03

But if in VS I now create a simple console app, and therefore get a .sln file, with the simple .cs existing in the context of that Solution, we see this in VS:

OmniSharp04

I then locate the solution in VSC:

OmniSharp05

, and open the program file. We then get all the Intellisense and OmniSharp checks:

OmniSharp06

Doing a bit more editing shows that you get:

  • IntelliSense (as said)
  • Redundant Usings warnings
  • A summary of warnings
  • snippet/auto completion (I haven’t yet worked out where it gets these), but e.g. CW does the right thing
  • Code formatting (I haven’t worked out how you set this to your standards)
  • Code Lens

OmniSharp07

So all in all, I THINK it was worth the pain… my use-case is that for the trade-off of creating at least a skeleton project in VS, I can edit on a non-full-power box. But right now, I see this being more for a scratchpad or POC application, rather than an enterprise-size application. That might not be true for an AngularJS app – I suspect it is not true given all the passion on Twitter etc for this from JavaScript people. But it does have a very small footprint. I have a Linx 2GB/32GB Windows 10 tablet, and whereas it struggled to cope with a full VS environment, I’m sure this will be easy for it. That is the use-case I guess (note I am specifically talking about C# usage, not JavaScript etc)

And note that you don’t somehow download OmniSharp, or direct VSC to find it as an extension. No, it is evidently part of VSC, on Windows anyway.

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