Dedupe Build and Live Diagnostics

[beccamc]

Currently build and live diagnostics are reported independently, causing duplicate errors and errors that don't go away until a re-build. The root cause of this problem is that DevKit extension reports build diagnostics and C# extension reports live diagnostics.

This change creates a separate build diagnostics collection, that filters the diagnostics reported by the build and only shows the ones that are not being shown by live.

1. On build complete, receive build diagnostics from DevKit extension via a brokered service
2. Check if any of the files with build diagnostics have live diagnostics. If they have live diagnostics, display "build-only" diagnostics (e.g. errors we know that will not be caught by live). If they have no diagnostics, shown, they display all of the diagnostics reported by the build.
3. When a file is opened, check to see if the build reported anything about it. If it did, display the build-only diagnostics. All other diagnostics should be shown by live.

Issue: #5728

[beccamc]

If anyone has testing thoughts, please share! I'm sure there are corner cases I am not aware of.

[dibarbet]

If anyone has testing thoughts, please share! I'm sure there are corner cases I am not aware of.

1. Making sure behavior makes sense with FSA on/off (seems like it does from the description)
2. Making sure the experience works if you turn FSA on or off (does that require a restart?)
3. Is it possible to somehow indicate which errors are build only? Perhaps we could use the diagnostic source? To potentially alleviate confusion on why some errors go away later.

[beccamc]

The source is set to "csharp-build"

[beccamc]

The experience with FSA and very large solutions isn't very good. With this change, FSA solutions don't show build errors that would be duplicates. This means, as David pointed out, you could build the solution but not see errors until FSA finishes. Manish is gathering telemetry on FSA solutions so we can understand how common this is. For now, waiting for feedback and tracking in this issue - #6606

[dibarbet]

I assume this change is safe to merge even if the devkit change is not in?

[beccamc]

Yes, this is safe without the DevKit change! CSharp extension will listen for any of the IBuildResultDiagnostics events, but it is not a problem that it doesn't receive any. On every file open it will check to see if there are build diagnostics in it's cache. There will be none and it'll skip doing any processing.

[mavasani]

This approach sounds good to me as a starting point. I think we should dogfood the experience to confirm if the delay between build completion and background analysis reporting live diagnostics for open files (FSA off) or closed files (FSA on) is acceptable for real world solutions with large number of open files across the solution. Especially if there are compiler errors in the files which we are deferring to background analysis to report diagnostics. Otherwise, we may have to introduce some handshake between this diagnostic source and the existing live diagnostic source such that we report all build reported diagnostics for a file here until live background analysis has analyzed that file and reported live diagnostics for it.