Turn off closed files diagnostic analysis & fix creating IncrementalBuilder when a file opens

[vasily-kirichenko]

This fixes #2389

In short, Roslyn by default performs "closed files diagnostic" analysis, which means it calls all DocumentDiagnosticsAnalyzer derivatives for all file in current project, opened and closed, even if a single file changed. This resulted with calling ParseAndCheckFileInProject for all files, which in turn made parseAndCheckFileInProjectCache useless.

• use predefined BlockForCompletionItems option instead of hand made one. Now completion feels really non-blocking.

This also fixes #2324

1. LanguageService.SetupProjectFile is called every time a file is opening https://github.com/Microsoft/visualfsharp/blob/master/vsintegration/src/FSharp.Editor/Common/LanguageService.fs#L298
2. It unconditionally called UpdateProjectInfo https://github.com/Microsoft/visualfsharp/blob/master/vsintegration/src/FSharp.Editor/Common/LanguageService.fs#L307
3. The latter, in turn, called Checker.InvalidateConfiguration https://github.com/Microsoft/visualfsharp/blob/master/vsintegration/src/FSharp.Editor/Common/LanguageService.fs#L117
4. It recreated IncrementalBuilder https://github.com/Microsoft/visualfsharp/blob/master/src/fsharp/vs/service.fs#L2716 and replaced the old one.

I'm surprised anything worked at all :(

[Pilchie]

LGTM, but also tagging @heejaechang to take a look.

[dsyme]

@Pilchie @cartermp @vasily-kirichenko This feels like it might cause considerable pain on VS2017 RTM?

[dsyme]

@vasily-kirichenko I think this also addresses #1856? What do you think? thanks

[vasily-kirichenko]

Yes, it's a very annoying. Having your CPU busy all time is not what you like to have.

I'm not sure it turns off ProjectDiagnosticsAnalyzer (yes, it's commented out, but we will want to turn it on at some point).

[cartermp]

@dsyme Do you mean this PR, or the symptom it's addressing? Closed File Diagnostics are off by default in C# as well, so I think this is a good change.

[dsyme]

@cartermp #1856 is not very clear and I didn't record a repro, I will close it since I think you guys are much clearer on the exact work that needs to be done :)

[heejaechang]

👍 and yes, it turns off ProjectDiagnosticAnalyzer now, but I am planning to turn it on soon.

[vasily-kirichenko]

:)

[dsyme]

@vasily-kirichenko That's fantastic!

[vasily-kirichenko]

@dsyme yeah, a couple of lines of code changes, but the effect is huge :)