Visual Studio SDK - IViewTagAggregatorFactoryService.CreateTagAggregator causes an exception

Question

I need to obtain classifications tags for ITextSnapshotLine lines in a current text view.

First, I get the active text view:

public static IWpfTextView GetTextView()
{
    var textManager = (IVsTextManager)ServiceProvider.GlobalProvider.GetService(typeof(SVsTextManager));
    IVsTextView vTextView = null;
    var mustHaveFocus = 1;
    textManager.GetActiveView(mustHaveFocus, null, out vTextView);
    var userData = vTextView as IVsUserData;
    if (userData != null)
    {
        IWpfTextViewHost viewHost;
        object holder;
        var guidViewHost = DefGuidList.guidIWpfTextViewHost;
        userData.GetData(ref guidViewHost, out holder);
        viewHost = (IWpfTextViewHost)holder;
        var textView = viewHost.TextView;
        return textView;
    }

    return null;
}

Then, I get the collection of ITextViewLine lines from the view and call GetClassificationTags method on each:

GetClassificationTags(new SnapshotSpan(line.Start, line.Length), textView)

The method looks like this:

public IEnumerable<IMappingTagSpan<IClassificationTag>> GetClassificationTags(SnapshotSpan span, ITextView textView)
{
    var snapshot = textView.TextSnapshot;

    var componentModel = (IComponentModel)ServiceProvider.GlobalProvider.GetService(typeof(SComponentModel));
    var exportProvider = componentModel.DefaultExportProvider;

    var viewTagAggregatorFactoryService = exportProvider.GetExportedValue<IViewTagAggregatorFactoryService>();

    var tagAggregator = viewTagAggregatorFactoryService.CreateTagAggregator<IClassificationTag>(textView);

    return tagAggregator.GetTags(span);
}

As a result I have everything classified correctly. However, Visual Studio throws an exception and logs it to the ActivityLog.xml file. This happens only after classifying all the lines for the first time. The information in log file says:

System.InvalidOperationException:
Unexpected false

at Roslyn.Utilities.Contract.ThrowIfFalse(Boolean condition, String message)

at Microsoft.CodeAnalysis.Editor.Implementation.Diagnostics.AbstractDiagnosticsTaggerProvider`1.CreateTagger[T](ITextBuffer buffer)

at Microsoft.CodeAnalysis.Editor.Implementation.Diagnostics.AbstractDiagnosticsTaggerProvider`1.Microsoft.VisualStudio.Text.Tagging.ITaggerProvider.CreateTagger[T](ITextBuffer buffer)

at Microsoft.VisualStudio.Text.Tagging.Implementation.TagAggregator`1.GatherTaggers(ITextBuffer textBuffer)

I noticed that the exception is not thrown after commenting out the line below:

var tagAggregator = viewTagAggregatorFactoryService.CreateTagAggregator<IClassificationTag>(textView);

Sometimes, there is also this exception in the log file:

System.InvalidOperationException: Unexpected false

at Roslyn.Utilities.Contract.ThrowIfFalse(Boolean condition, String message)

at Microsoft.CodeAnalysis.Editor.Tagging.AbstractAsynchronousTaggerProvider`1.TagSource.GetTagIntervalTreeForBuffer(ITextBuffer buffer)

at Microsoft.CodeAnalysis.Editor.Tagging.AbstractAsynchronousTaggerProvider`1.Tagger.GetTagsWorker(NormalizedSnapshotSpanCollection requestedSpans, Boolean accurate, CancellationToken cancellationToken)

at Microsoft.CodeAnalysis.Editor.Tagging.AbstractAsynchronousTaggerProvider`1.Tagger.GetTags(NormalizedSnapshotSpanCollection requestedSpans)

at Microsoft.VisualStudio.Text.Tagging.Implementation.TagAggregator`1.<GetTagsForBuffer>d__38.MoveNext()

My question is: what causes this exception and how can I get rid of it?

Answer 1

The code is open source, you can just take a look. My guess is you're trying that on a background thread.