Prevent EditAndContinueFeedbackDiagnosticFileProvider from throwing an exception in Razor scenarios

[allisonchou]

This line in Razor's integration test logic throws an exception since one of the found providers is EditAndContinueFeedbackDiagnosticFileProvider, which seems to only account for Roslyn scenarios. This PR mitigates the issue by ensuring that we don't initialize a FileSystemWatcher (which threw the original exception) unless the provided directory is valid.

[tmat]

File watcher throws when the directory does not exist? What is the exact exception trace?
That'd be unfortunate since the intent was to detect when the file in that directory is created. The directory indeed might not exist at this time because VS Feedback didn't created it yet.

[allisonchou]

Integration tests are struggling to run locally on my machine right now (trying to figure it out) so I don't have the exact stack trace at the moment, but the exception was:

ArgumentException: The directory name C:\Users\allichou\AppData\Local\Temp\Microsoft\VSFeedbackCollector is invalid.

and it was definitely originating from trying to initialize EditAndContinueFeedbackDiagnosticFileProvider. Looking at the constructor code, it seems the most likely culprit is from FileSystemWatcher, as the documentation for the FileSystemWatcher constructor says it can throw:

        //   T:System.ArgumentException:
        //     The path parameter is an empty string (""). -or- The path specified through the
        //     path parameter does not exist.
        //

[tmat]

I see. ok.

[allisonchou]

Thanks for the review @tmat! To close out the convo, I was finally able to get integration tests running again, and the below was the more detailed exception:

Microsoft.VisualStudio.Composition.CompositionFailedException: 'An exception was thrown while initializing part "Microsoft.VisualStudio.LanguageServices.EditAndContinue.EditAndContinueFeedbackDiagnosticFileProvider".'

Inner Exception
ArgumentException: The directory name C:\Users\allichou\AppData\Local\Temp\Microsoft\VSFeedbackCollector is invalid.