Cyclic project references can hang the IDE

[sharwell]

Version Used: 16.4 Preview 4

Steps to Reproduce:

1. Create a project with a <ProjectReference> to itself. This can also occur if the project contains a <Reference> to an assembly with the same name as the project, since the project system can implicitly convert this to a <ProjectReference> for use in the IDE.
2. Edit the project and attempt to use code fixes.

Expected Behavior:

An error is reported in the error list for the cyclic reference.

Actual Behavior:

The IDE hangs.

!dumpasync shows an asynchronous stack that attempts to recursively obtain a semaphore, and thus cannot make progress:

3083e57c <0> System.Threading.SemaphoreSlim+<WaitUntilCountOrTimeoutAsync>d__31 @ 72650098
..3083e644 <0> Roslyn.Utilities.SemaphoreSlimExtensions+<DisposableWaitAsync>d__1 @ 1213f390
..3083e700 <0> Microsoft.CodeAnalysis.SolutionState+CompilationTracker+<GetOrBuildCompilationInfoAsync>d__22 @ 12157df0
..3083e7cc <0> Microsoft.CodeAnalysis.SolutionState+CompilationTracker+<GetCompilationSlowAsync>d__19 @ 12157cb0
..3083e880 <0> Microsoft.CodeAnalysis.SolutionState+CompilationTracker+<GetMetadataReferenceAsync>d__32 @ 12159420
..3083e948 <1> Microsoft.CodeAnalysis.SolutionState+CompilationTracker+<FinalizeCompilationAsync>d__30 @ 12158e60
..3083ea20 <1> Microsoft.CodeAnalysis.SolutionState+CompilationTracker+<BuildFinalStateFromInProgressStateAsync>d__27 @ 12187610
..3083eae8 <1> Microsoft.CodeAnalysis.SolutionState+CompilationTracker+<GetOrBuildCompilationInfoAsync>d__22 @ 12157df0
..3083ebb4 <0> Microsoft.CodeAnalysis.SolutionState+CompilationTracker+<GetCompilationSlowAsync>d__19 @ 12157cb0
..3083ec68 <1> Microsoft.CodeAnalysis.Document+<GetSemanticModelAsync>d__23 @ 1215f720

[mavasani]

#40082 is another case of cyclic reference issue, which seems to cause corrupt project state instead of a hang, and subsequently causes tons of cascaded intellisense errors. We should ensure that we report a user friendly diagnostic in the error list for each such invalid input scenario.

[jasonmalinowski]

@tmat You added some additional guarding at the workspaces layer for this? Did we test if you end up creating a set of circular project files that the VS layer won't try to create a circularity or the VS bug still around (and potentially worse now if we're throwing more aggressively...)

[tmat]

I have not tested that specifically.