Write C# LSIF indexer

[mrnugget]

I discussed this with @efritz and @chrismwendt: I'm going to help out the @sourcegraph/code-intel team by trying to write an LSIF indexer.

Spec: https://github.com/microsoft/language-server-protocol/blob/master/indexFormat/specification.md

I'll update this ticket in the future with more information.

[mrnugget]

Removing it from the 3.13 milestone because I clearly won't be working on it.

[shrouxm]

Leaving notes here about maria and i's attempt to use Roslyn's C# LSIF indexer.

Context: there is an unpublished module in Roslyn's (the C# compiler) tree for LSIF generation: https://github.com/dotnet/roslyn/tree/master/src/Features/Lsif/Generator. We know from the language tooling summit that Microsoft is using this to upload LSIF indexes to their consumer. Maria and I did an ultimately unsuccessful timeboxed investigation to see if we could get it to run ourselves, noting our learnings here:

After much ado, running out of the box seemed generally impossible. using the following command from the project's root

dotnet run -p src/Features/Lsif/Generator/Microsoft.CodeAnalysis.LanguageServerIndexFormat.Generator.csproj --solution Roslyn.sln

would yield the following error

System.ComponentModel.Win32Exception (2): No such file or directory
   at System.Diagnostics.Process.ForkAndExecProcess(String filename, String[] argv, String[] envp, String cwd, Boolean redirectStdin, Boolean redirectStdout, Boolean redirectStderr, Boolean setCredentials, UInt32 userId, UInt32 groupId, UInt32[] groups, Int32& stdinFd, Int32& stdoutFd, Int32& stderrFd, Boolean usesTerminal, Boolean throwOnNoExec)
   at System.Diagnostics.Process.StartCore(ProcessStartInfo startInfo)
   at System.Diagnostics.Process.Start()
   at Microsoft.DotNet.Cli.Utils.Command.Execute(Action`1 processStarted)
   at Microsoft.DotNet.Cli.Utils.Command.Execute()
   at Microsoft.DotNet.Tools.Run.RunCommand.Execute()
   at Microsoft.DotNet.Tools.Run.RunCommand.Run(String[] args)
   at Microsoft.DotNet.Cli.Program.ProcessArgs(String[] args, ITelemetry telemetryClient)
   at Microsoft.DotNet.Cli.Program.Main(String[] args)

After asking around on the repo: dotnet/roslyn#50290, I got a tip to change a the TargetFramework in Microsoft.CodeAnalysis.LanguageServerIndexFormat.Generator.csproj to net5.0 from net472, as net472 is windows only.

That yielded the following error:

/usr/share/dotnet/sdk/5.0.101/Sdks/Microsoft.NET.Sdk/targets/Microsoft.NET.Sdk.DefaultItems.targets(362,5): error NETSDK1136: The target platform must be set to Windows (usually by including '-windows' in the TargetFramework property) when using Windows Forms or WPF, or referencing projects or packages that do so. [src/Features/Lsif/Generator/Microsoft.CodeAnalysis.LanguageServerIndexFormat.Generator.csproj]

The build failed. Fix the build errors and run again.

I posted about that in the same thread but got no reply. Future directions for investigation when we allot more time to this:

• try running it on windows, which if it works might be good enough. interested users are probably developing on windows anyway.
• ping the LSIF people we know at microsoft directly to ask about this
• wait til this tool is released publicly in any capacity

[tomdegoede]

@gbrik I actually tried running that on Windows a few days back and was able to get some result. I was however not able to get it working in the VS Code extension and validating it with lsif-util raised many issues (found both of them mentioned here).

[shrouxm]

@tomdegoede thanks for sharing! that also points towards the tool being in a very experimental state.

probably not worth revisiting this until Microsoft does more work or we decide to invest in rolling our own.

[macraig]

Archiving for now, will reopen when we revisit C# support.