"Feature 'CodeLens references' is currently unavailable due to an internal error" when using SourceGenerator

[trampster]

Version Used:
Whatever is used by Visual studio 2019 Version 16.9.3

Steps to Reproduce:

1. Use StrongInject (source generator based IoC library) for dependency injection
2. Go to a class that does StrongInject source generation (Module or Container class)
   -> the IDE is spammed with yellow warnings:
   Feature "'CodeLens references' is currently unavailable due to an internal error."
   There is a blue 'i' icon on the left of the message. In my project I get five of these per at a time, so they stack up really fast. So I'm forever having to clear them.

The stack trace is as follows:

StreamJsonRpc.RemoteInvocationException: Object reference not set to an instance of an object.
   at StreamJsonRpc.JsonRpc.<InvokeCoreAsync>d__139`1.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Threading.Tasks.ValueTask`1.get_Result()
   at System.Runtime.CompilerServices.ConfiguredValueTaskAwaitable`1.ConfiguredValueTaskAwaiter.GetResult()
   at Microsoft.CodeAnalysis.Remote.BrokeredServiceConnection`1.<TryInvokeAsync>d__17`1.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at Microsoft.VisualStudio.Telemetry.WindowsErrorReporting.WatsonReport.GetClrWatsonExceptionInfo(Exception exceptionObject)
RPC server exception:
System.NullReferenceException: Object reference not set to an instance of an object.
      at Microsoft.CodeAnalysis.CodeLens.CodeLensReferencesService.<TryGetMethodDescriptorAsync>d__8.MoveNext()
   --- End of stack trace from previous location where exception was thrown ---
      at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
      at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
      at Microsoft.CodeAnalysis.CodeLens.CodeLensReferencesService.<>c__DisplayClass9_0.<<FindReferenceMethodsAsync>b__0>d.MoveNext()
   --- End of stack trace from previous location where exception was thrown ---
      at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
      at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
      at Microsoft.CodeAnalysis.CodeLens.CodeLensReferencesService.<FindAsync>d__1`1.MoveNext()
   --- End of stack trace from previous location where exception was thrown ---
      at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
      at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
      at Microsoft.CodeAnalysis.Remote.RemoteCodeLensReferencesService.<>c__DisplayClass5_0.<<FindReferenceMethodsAsync>b__0>d.MoveNext()
   --- End of stack trace from previous location where exception was thrown ---
      at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
      at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
      at System.Threading.Tasks.ValueTask`1.get_Result()
      at Microsoft.CodeAnalysis.Remote.BrokeredServiceBase.<RunServiceImplAsync>d__12`1.MoveNext()
   --- End of stack trace from previous location where exception was thrown ---
      at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
      at Microsoft.VisualStudio.Telemetry.WindowsErrorReporting.WatsonReport.GetClrWatsonExceptionInfo(Exception exceptionObject)

Expected Behavior:
Can use SourceGenerators without getting spammed with this error

Actual Behavior:
Get spammed with the error.
The CodeLens feature is broken for these pages, the references count doesn't update.

I raised this with the StrongInject github project and the author suggested raising it with Roslyn. YairHalberstadt/stronginject#120

[Youssef1313]

cc @CyrusNajmabadi

[Youssef1313]

This was already fixed in 16.10 per #52558 (comment).