Intellisense doesn't work on my solution

[frblondin]

Version Used: VS2017 15.3.1 & 15.3.2

Steps to Reproduce:
Note that these steps are only reproductible on a particular solution. The same steps are not failing on other solutions

1. Add a new Class1.cs type, make it implementing IDisposable (add : IDisposable)
2. Quick action is empty and doesn't provide any action (Implement Interface...)
   This is reproductible on other computers. I have tried the following:
   • VS repair
   • VS settings reset
   • Deletion of .vs folder
   • Deletion of all obj folders

Interestingly, the autompletion for adding a namespace contains 3 library names out of four. This seems to prove that the cache update gets interrupted, preventing the intellisense to work as expected.
I don't know what I can do (log) to provide more meaningful information. Please advise. The solution I'm working on cannot be shared outside my company.

Expected Behavior:
I'd expect intellisens to be working.

Actual Behavior:
More generally almost all intellisense features are broken:

• Intellisense is not detecting any code issue (wrong method name...), only detecting when compiling
• Not able to make missing using proposals
• No quick action such as Extract method or such

[Pilchie]

What does the drop down at the top left of the file say? Does it say "Miscellaneous files"? If it does, are there any errors/warnings in your error list? Can you try diagnosing a design-time build failure as described at https://github.com/dotnet/project-system/blob/master/docs/design-time-builds.md?

[frblondin]

The correct drop down list value is displayed. I could enable the design time logs and there is no error... despite the intellisense continues failing (no "Implement Interface..." action).

[xxx.Server.xxx_Compile_4bd3d94e.designtime.log.txt]

[Pilchie]

Hmm - that is perplexing indeed. @CyrusNajmabadi - any ideas here?

[frblondin]

I was able to debug Roslyn and find some interesting stuff.

First my solution contains many projects but only two projects are really involved in the issue.

Flow of issues:

• Executor.SemanticAnalysisEnabled(...) is returning false. This prevents intellisense features to work correctly
• The reason is that CompilationTracker.FinalizeCompilationAsync(...) checks the status of each referenced project
• ... and asks for the metadataReference by calling SolutionState.GetMetadataReferenceAsync(...) which fails because MetadataOnlyReference.GetOrBuildReference(...) returns a null reference. As image.IsEmpty returns true a null reference is returned.

So... I tried to understand why the image is empty for this referenced project. It is empty because the function Compilation.FilterAndAppendDiagnostics(...) encounters some warnings (GetHashCode not implemented whereas Equals is overridden...) that are treated as errors, because TreatWarningsAsErrors is set to true. The problem is that a project rebuild doesn't show any warning. This Warning (that will be treated as an error) is ignored using a pragma. The problem is that there is another file for this type that completes the definition of X using a partial class. This other file doesn't use the pragmas. That is why in the end the warnings are simply ignored but Roslyn badly assumes that the project is in an error state.

There are two issues:

1. If a referenced project has warnings treated as errors this should not prevent the other projects depending on it to work
2. Warnings treated as errors are not displayed in VS or in the build result for my project whereas there are still active internally in the roslyn analysis results.

I tried to create a lightweight solution so you can reproduce the issue. I reproduced this simple organization where there are two projects, and the project (being referenced) having a partial class with pragma-ignored warnings. For some reason I couldn't reproduce the error and I can't spend too much time on this anylonger...

I hope that, thanks to the call flow description above, you will be able to better understand what can cause the problem.

[Pilchie]

Thanks for the debugging! One thing you might try is enabling Full solution analysis from Tools/Options/Text Editor/C#/Advanced. It should hopefully show you the IDE errors for closed files as well.

@jasonmalinowski / @jcouv - looks like another skeleton assembly issue, maybe some part of the pragma stuff is skipped? We should probably always ignore warnaserror?

[frblondin]

We are disabling Full solution analysis because of performance issues. Next time we are getting such errors we will try to enable it before debugging roslyn, hehe.

[jasonmalinowski]

Yeah, we should most definitely not be applying warn-as-error to skeleton assembly builds. That's...very not good. Awesome debugging job @frblondin!

I guess the fix is to amend this line, maybe? I admit I don't know what Emit does for warn-as-error here. Clearly the "Succeeded" is coming back false (which makes sense), but did it still do an emit to the stream anyways? Put another way, if we stop looking at Succeeded and actually look at the diagnostics to see if there were any 'real' errors, is that sufficient? Or do we have to turn of warn as error in the options before we even call emit? I'm hoping the former is the case, because otherwise that compilation for with new options might get more expensive, not sure.

@mavasani or @jaredpar or maybe @gafter, any idea what the contract is there?

[frblondin]

FYI I disabled all warn as errors but I'm still having the intellisense broken for other types/projects. The reason is that there are false positives in the diagnostics of type error BC30002: Type 'IClassExplorer' is not defined.

Having these false positives should be another issue that I will post separately, but this shows that creating the image even if there are errors (even real errors, not only warn-as-error types) for skeleton assembly is absolutely required. At this stage, I edit my type as if I was using a simple text editor without intellisense :-(

Can you possibly fix this issue in the current release (15.3), not in 15.5?

[jaredpar]

CC @jcouv

[CyrusNajmabadi]

Why are these errors being created? Can you just fix the error? The way skeletons work is that we should keep using the last successfully built skeleton until we can successfully make a new one. If we can't even make one, then there's going to be problems.