FCS caches does not work when a file opens

[vasily-kirichenko]

1. Open FCS solution
2. Open service.fs
3. Wait until colorization appears
4. Close the file
5. Reopen it
6. It takes equally long time for colorization and even structure to appear

The same behavior is observed when another file, even small one, is opened after the first one is fully checked. Looks like https://github.com/Microsoft/visualfsharp/blob/master/src/fsharp/vs/service.fs#L2413 checks all files laying prior to the current every time (however, I've not looked at it closely yet).

[dsyme]

Looks like https://github.com/Microsoft/visualfsharp/blob/master/src/fsharp/vs/service.fs#L2413 checks all files laying prior to the current every time (however, I've not looked at it closely yet).

This fetches the results cached by the IncrementalBuilder (i.e. the background build process). I believe we have quite a lot of tests checking that re-checking doesn't happen (counting the number of checks).

That's not to say there isn't some kind of bug. For the repro steps above I would expect considerably less time on second opening, as long as the project itself has not been closed.

[vasily-kirichenko]

I've investigated it. Create a hello world app, open a file, wait for coloring, close it, reopen.
It turns out, this https://github.com/Microsoft/visualfsharp/blob/master/src/fsharp/vs/service.fs#L2530 returns None, digging into it shows this path: https://github.com/Microsoft/visualfsharp/blob/master/src/fsharp/vs/IncrementalBuild.fs#L1704 => https://github.com/Microsoft/visualfsharp/blob/master/src/fsharp/vs/IncrementalBuild.fs#L840 => https://github.com/Microsoft/visualfsharp/blob/master/src/fsharp/vs/IncrementalBuild.fs#L413

I know nothing about this vectors stuff. @dsyme any ideas what's going wrong?

[vasily-kirichenko]

It looks like GetCheckResultsBeforeFileInProject does not return cached background check result for any just opened file. It means that everything up to a opening file is rechecked (in one fat Reactor op, but it's a different issue).

I think it's a huge bug.

[vasily-kirichenko]

Fixed.

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 :(

[vasily-kirichenko]

Fixed in #2395

[cartermp]

Moving to VS Updates now 😄