Classifier.cs

using System;
using System.Collections.Generic;
using System.ComponentModel.Composition;
using System.Linq;
using System.Windows.Media;
using Microsoft.VisualStudio.ApplicationModel.Environments;
using Microsoft.VisualStudio.Text;
using Microsoft.VisualStudio.Text.Classification;
using Microsoft.VisualStudio.Utilities;

namespace ClassifyAllBut
{
    public static class TypeAndFormatExports
    {
        [Export(typeof(ClassificationTypeDefinition))]
        [Name("strike-out")]
        internal static ClassificationTypeDefinition StrikeOutType;

        [Export(typeof(EditorFormatDefinition))]
        [ClassificationType(ClassificationTypeNames = "strike-out")]
        [Name("Strike-out")]
        [DisplayName("Strike-out Text")]
        [UserVisible(true)]
        [Order(Before = Priority.High)]
        internal sealed class StrikeOutFormat : ClassificationFormatDefinition
        {
            public StrikeOutFormat()
            {
                this.TextDecorations = System.Windows.TextDecorations.Strikethrough;
            }
        }
    }

    [Export(typeof(IClassifierProvider))]
    [ContentType("CSharp")]
    internal sealed class GrayedOutClassifierProvider : IClassifierProvider
    {
        [Import]
        internal IClassificationTypeRegistryService TypeRegistry;
        [Import]
        internal IClassifierAggregatorService AggregatorService;

        internal static bool ignoreRequest = false;

        public IClassifier GetClassifier(ITextBuffer textBuffer, IEnvironment context)
        {
            if (ignoreRequest)
                return null;

            try
            {
                ignoreRequest = true;
                return textBuffer.Properties.GetOrCreateSingletonProperty(
                    () => new GrayedOutClassifier(AggregatorService.GetClassifier(textBuffer, context), TypeRegistry));
            }
            finally
            {
                ignoreRequest = false;
            }
        }
    }

    internal sealed class GrayedOutClassifier : IClassifier
    {
        private IClassifier aggregator;
        private IClassificationTypeRegistryService typeRegistry;

        public GrayedOutClassifier(IClassifier aggregator, IClassificationTypeRegistryService typeRegistry)
        {
            this.aggregator = aggregator;
            this.typeRegistry = typeRegistry;
        }

        public event EventHandler<ClassificationChangedEventArgs> ClassificationChanged;

        public IList<ClassificationSpan> GetClassificationSpans(SnapshotSpan span)
        {
            var classifiedSpans = from cspan in aggregator.GetClassificationSpans(span)
                                  let name = cspan.ClassificationType.Classification.ToLower()
                                  where name.Contains("string") || name.Contains("comment") || name.Contains("xml doc")
                                  select cspan.Span;

            NormalizedSnapshotSpanCollection ignored = new NormalizedSnapshotSpanCollection(classifiedSpans);
            NormalizedSnapshotSpanCollection request = new NormalizedSnapshotSpanCollection(span);

            var spansToStrikeOut = NormalizedSnapshotSpanCollection.Difference(request, ignored);

            IClassificationType type = typeRegistry.GetClassificationType("strike-out");

            return spansToStrikeOut.Select(s => new ClassificationSpan(s, type))
                                 .ToList();
        }
    }

}