made diagnostic tags to be removed faster and inserted slower.

src/EditorFeatures/Core/Implementation/Diagnostics/AbstractDiagnosticsTaggerProvider.TaggerProvider.cs

@@ -52,6 +52,11 @@ event EventHandler ITaggerEventSource.UIUpdatesResumed { add { } remove { } }
             void ITaggerEventSource.Connect() { }
             void ITaggerEventSource.Disconnect() { }
 
+            // we will show new tags to users very slowly. 
+            // don't confused this with data changed event which is for tag producer (which is set to NearImmediate).
+            // this delay is for letting editor know about newly added tags.
+            protected override TaggerDelay NewTagsNotificationDelay => TaggerDelay.OnIdle;
+
             protected override ITaggerEventSource CreateEventSource(ITextView textViewOpt, ITextBuffer subjectBuffer)
             {
                 // We act as a source of events ourselves.  When the diagnostics service tells
@@ -138,7 +143,11 @@ internal void OnDiagnosticsUpdated(DiagnosticsUpdatedArgs e, SourceText sourceTe
                     _latestSourceText = sourceText;
                     _latestEditorSnapshot = editorSnapshot;
                 }
-                this.Changed?.Invoke(this, new TaggerEventArgs(TaggerDelay.Medium));
+
+                // unlike any other tagger, actual work to produce data is done by other service rather than tag provider itself.
+                // so we don't need to do any big delay for diagnostic tagger (producer) to reduce doing expensive work repeatedly. that is already
+                // taken cared by the external service (diagnostic service).
+                this.Changed?.Invoke(this, new TaggerEventArgs(TaggerDelay.NearImmediate));
             }
         }
     }

src/EditorFeatures/Core/Tagging/AbstractAsynchronousTaggerProvider.TagSource.cs

@@ -75,7 +75,7 @@ private sealed partial class TagSource : ForegroundThreadAffinitizedObject
 
             #endregion
 
-            public event Action<ICollection<KeyValuePair<ITextBuffer, NormalizedSnapshotSpanCollection>>> TagsChangedForBuffer;
+            public event Action<ICollection<KeyValuePair<ITextBuffer, DiffResult>>> TagsChangedForBuffer;
 
             public event EventHandler Paused;
             public event EventHandler Resumed;
@@ -112,6 +112,9 @@ public TagSource(
                 RecalculateTagsOnChanged(new TaggerEventArgs(TaggerDelay.Short));
             }
 
+            public TaggerDelay NewTagsNotificationDelay => _dataSource.NewTagsNotificationDelay;
+            public TaggerDelay OldTagNotificationDelay => _dataSource.OldTagNotificationDelay;
+
             private ITaggerEventSource CreateEventSource()
             {
                 var eventSource = _dataSource.CreateEventSource(_textViewOpt, _subjectBuffer);
@@ -260,7 +263,7 @@ public void Disconnect()
                 _eventSource.Changed -= OnChanged;
             }
 
-            private void RaiseTagsChanged(ITextBuffer buffer, NormalizedSnapshotSpanCollection difference)
+            private void RaiseTagsChanged(ITextBuffer buffer, DiffResult difference)
             {
                 this.AssertIsForeground();
                 if (difference.Count == 0)
@@ -270,10 +273,10 @@ private void RaiseTagsChanged(ITextBuffer buffer, NormalizedSnapshotSpanCollecti
                 }
 
                 RaiseTagsChanged(SpecializedCollections.SingletonCollection(
-                    new KeyValuePair<ITextBuffer, NormalizedSnapshotSpanCollection>(buffer, difference)));
+                    new KeyValuePair<ITextBuffer, DiffResult>(buffer, difference)));
             }
 
-            private void RaiseTagsChanged(ICollection<KeyValuePair<ITextBuffer, NormalizedSnapshotSpanCollection>> collection)
+            private void RaiseTagsChanged(ICollection<KeyValuePair<ITextBuffer, DiffResult>> collection)
             {
                 TagsChangedForBuffer?.Invoke(collection);
             }
@@ -296,9 +299,12 @@ private static T NextOrDefault<T>(IEnumerator<T> enumerator)
             /// <summary>
             /// Return all the spans that appear in only one of "latestSpans" or "previousSpans".
             /// </summary>
-            private static IEnumerable<SnapshotSpan> Difference<T>(IEnumerable<ITagSpan<T>> latestSpans, IEnumerable<ITagSpan<T>> previousSpans, IEqualityComparer<T> comparer)
+            private static DiffResult Difference<T>(IEnumerable<ITagSpan<T>> latestSpans, IEnumerable<ITagSpan<T>> previousSpans, IEqualityComparer<T> comparer)
                 where T : ITag
             {
+                List<SnapshotSpan> added = null;
+                List<SnapshotSpan> removed = null;
+
                 var latestEnumerator = latestSpans.GetEnumerator();
                 var previousEnumerator = previousSpans.GetEnumerator();
                 try
@@ -313,12 +319,12 @@ private static IEnumerable<SnapshotSpan> Difference<T>(IEnumerable<ITagSpan<T>>
 
                         if (latestSpan.Start < previousSpan.Start)
                         {
-                            yield return latestSpan;
+                            AddToList(ref added, latestSpan);
                             latest = NextOrDefault(latestEnumerator);
                         }
                         else if (previousSpan.Start < latestSpan.Start)
                         {
-                            yield return previousSpan;
+                            AddToList(ref removed, previousSpan);
                             previous = NextOrDefault(previousEnumerator);
                         }
                         else
@@ -327,19 +333,19 @@ private static IEnumerable<SnapshotSpan> Difference<T>(IEnumerable<ITagSpan<T>>
                             // region to be conservative.
                             if (previousSpan.End > latestSpan.End)
                             {
-                                yield return previousSpan;
+                                AddToList(ref removed, previousSpan);
                                 latest = NextOrDefault(latestEnumerator);
                             }
                             else if (latestSpan.End > previousSpan.End)
                             {
-                                yield return latestSpan;
+                                AddToList(ref added, latestSpan);
                                 previous = NextOrDefault(previousEnumerator);
                             }
                             else
                             {
                                 if (!comparer.Equals(latest.Tag, previous.Tag))
                                 {
-                                    yield return latestSpan;
+                                    AddToList(ref added, latestSpan);
                                 }
 
                                 latest = NextOrDefault(latestEnumerator);
@@ -350,13 +356,13 @@ private static IEnumerable<SnapshotSpan> Difference<T>(IEnumerable<ITagSpan<T>>
 
                     while (latest != null)
                     {
-                        yield return latest.Span;
+                        AddToList(ref added, latest.Span);
                         latest = NextOrDefault(latestEnumerator);
                     }
 
                     while (previous != null)
                     {
-                        yield return previous.Span;
+                        AddToList(ref removed, previous.Span);
                         previous = NextOrDefault(previousEnumerator);
                     }
                 }
@@ -365,6 +371,14 @@ private static IEnumerable<SnapshotSpan> Difference<T>(IEnumerable<ITagSpan<T>>
                     latestEnumerator.Dispose();
                     previousEnumerator.Dispose();
                 }
+
+                return new DiffResult(added, removed);
+            }
+
+            private static void AddToList<T>(ref List<T> list, T item)
+            {
+                list = list ?? new List<T>();
+                list.Add(item);
             }
         }
     }

src/EditorFeatures/Core/Tagging/AbstractAsynchronousTaggerProvider.TagSource_ProduceTags.cs

@@ -90,10 +90,9 @@ private void RemoveAllTags()
 
                 var snapshot = _subjectBuffer.CurrentSnapshot;
                 var oldTagTree = GetTagTree(snapshot, oldTagTrees);
-                var newTagTree = GetTagTree(snapshot, this.CachedTagTrees);
-
-                var difference = ComputeDifference(snapshot, newTagTree, oldTagTree);
-                RaiseTagsChanged(snapshot.TextBuffer, difference);
+
+                // everything from old tree is removed.
+                RaiseTagsChanged(snapshot.TextBuffer, new DiffResult(added: null, removed: oldTagTree.GetSpans(snapshot).Select(s => s.Span)));
             }
 
             private void OnSubjectBufferChanged(object sender, TextContentChangedEventArgs e)
@@ -193,11 +192,13 @@ private void RemoveTagsThatIntersectEdit(TextContentChangedEventArgs e)
                 var oldTagTrees = this.CachedTagTrees;
                 this.CachedTagTrees = oldTagTrees.SetItem(snapshot.TextBuffer, newTagTree);
 
-                // Grab our old tags. We might not have any, so in this case we'll just pretend it's
-                // empty
-                var oldTagTree = GetTagTree(snapshot, oldTagTrees);
+                // Not sure why we are diffing when we already have tagsToRemove. is it due to _tagSpanComparer might return
+                // different result than GetIntersectingSpans?
+                //
+                // treeForBuffer basically points to oldTagTrees. case where oldTagTrees not exist is already taken cared by
+                // CachedTagTrees.TryGetValue.
+                var difference = ComputeDifference(snapshot, newTagTree, treeForBuffer);
 
-                var difference = ComputeDifference(snapshot, newTagTree, oldTagTree);
                 RaiseTagsChanged(snapshot.TextBuffer, difference);
             }
 
@@ -594,7 +595,7 @@ private void ProcessNewTagTrees(
                 object newState,
                 CancellationToken cancellationToken)
             {
-                var bufferToChanges = new Dictionary<ITextBuffer, NormalizedSnapshotSpanCollection>();
+                var bufferToChanges = new Dictionary<ITextBuffer, DiffResult>();
                 using (Logger.LogBlock(FunctionId.Tagger_TagSource_ProcessNewTags, cancellationToken))
                 {
                     foreach (var latestBuffer in newTagTrees.Keys)
@@ -609,8 +610,7 @@ private void ProcessNewTagTrees(
                         else
                         {
                             // It's a new buffer, so report all spans are changed
-                            var allSpans = new NormalizedSnapshotSpanCollection(newTagTrees[latestBuffer].GetSpans(snapshot).Select(t => t.Span));
-                            bufferToChanges[latestBuffer] = allSpans;
+                            bufferToChanges[latestBuffer] = new DiffResult(added: newTagTrees[latestBuffer].GetSpans(snapshot).Select(t => t.Span), removed: null);
                         }
                     }
 
@@ -619,8 +619,7 @@ private void ProcessNewTagTrees(
                         if (!newTagTrees.ContainsKey(oldBuffer))
                         {
                             // This buffer disappeared, so let's notify that the old tags are gone
-                            var allSpans = new NormalizedSnapshotSpanCollection(oldTagTrees[oldBuffer].GetSpans(oldBuffer.CurrentSnapshot).Select(t => t.Span));
-                            bufferToChanges[oldBuffer] = allSpans;
+                            bufferToChanges[oldBuffer] = new DiffResult(added: null, removed: oldTagTrees[oldBuffer].GetSpans(oldBuffer.CurrentSnapshot).Select(t => t.Span));
                         }
                     }
                 }
@@ -640,7 +639,7 @@ private void ProcessNewTagTrees(
 
             private void UpdateStateAndReportChanges(
                 ImmutableDictionary<ITextBuffer, TagSpanIntervalTree<TTag>> newTagTrees,
-                Dictionary<ITextBuffer, NormalizedSnapshotSpanCollection> bufferToChanges,
+                Dictionary<ITextBuffer, DiffResult> bufferToChanges,
                 object newState)
             {
                 _workQueue.AssertIsForeground();
@@ -673,13 +672,12 @@ private void UpdateStateAndReportChanges(
                 RaiseTagsChanged(bufferToChanges);
             }
 
-            private NormalizedSnapshotSpanCollection ComputeDifference(
+            private DiffResult ComputeDifference(
                 ITextSnapshot snapshot,
                 TagSpanIntervalTree<TTag> latestSpans,
                 TagSpanIntervalTree<TTag> previousSpans)
             {
-                return new NormalizedSnapshotSpanCollection(
-                    Difference(latestSpans.GetSpans(snapshot), previousSpans.GetSpans(snapshot), _dataSource.TagComparer));
+                return Difference(latestSpans.GetSpans(snapshot), previousSpans.GetSpans(snapshot), _dataSource.TagComparer);
             }
 
             /// <summary>

src/EditorFeatures/Core/Tagging/AbstractAsynchronousTaggerProvider.Tagger.cs

@@ -4,6 +4,7 @@
 using System.Collections.Generic;
 using System.Linq;
 using System.Threading;
+using Microsoft.CodeAnalysis.Editor.Shared.Tagging;
 using Microsoft.CodeAnalysis.Shared.TestHooks;
 using Microsoft.VisualStudio.Text;
 using Microsoft.VisualStudio.Text.Tagging;
@@ -77,7 +78,7 @@ private void OnResumed(object sender, EventArgs e)
                 _batchChangeNotifier.Resume();
             }
 
-            private void OnTagsChangedForBuffer(ICollection<KeyValuePair<ITextBuffer, NormalizedSnapshotSpanCollection>> changes)
+            private void OnTagsChangedForBuffer(ICollection<KeyValuePair<ITextBuffer, DiffResult>> changes)
             {
                 _tagSource.AssertIsForeground();
 
@@ -94,10 +95,27 @@ private void OnTagsChangedForBuffer(ICollection<KeyValuePair<ITextBuffer, Normal
                     }
 
                     // Now report them back to the UI on the main thread.
-                    _batchChangeNotifier.EnqueueChanges(change.Value);
+
+                    // We ask to update UI immediately for removed tags
+                    NotifyEditors(change.Value.Removed, _tagSource.OldTagNotificationDelay);
+                    NotifyEditors(change.Value.Added, _tagSource.NewTagsNotificationDelay);
                 }
             }
 
+            private void NotifyEditors(NormalizedSnapshotSpanCollection changes, TaggerDelay delay)
+            {
+                if (delay == TaggerDelay.NearImmediate)
+                {
+                    // if delay is immediate, we let notifier knows about the change right away
+                    _batchChangeNotifier.EnqueueChanges(changes);
+                    return;
+                }
+
+                // if delay is anything more than that, we let notifier knows about the change after given delay
+                // event notification is not cancellable.
+                _tagSource.RegisterNotification(() => _batchChangeNotifier.EnqueueChanges(changes), (int)delay.ComputeTimeDelay(_subjectBuffer).TotalMilliseconds, CancellationToken.None);
+            }
+
             public IEnumerable<ITagSpan<TTag>> GetTags(NormalizedSnapshotSpanCollection requestedSpans)
             {
                 return GetTagsWorker(requestedSpans, accurate: false, cancellationToken: CancellationToken.None);

src/EditorFeatures/Core/Tagging/AbstractAsynchronousTaggerProvider.cs

@@ -70,6 +70,16 @@ internal abstract partial class AbstractAsynchronousTaggerProvider<TTag> : Foreg
         protected virtual IEnumerable<Option<bool>> Options => SpecializedCollections.EmptyEnumerable<Option<bool>>();
         protected virtual IEnumerable<PerLanguageOption<bool>> PerLanguageOptions => SpecializedCollections.EmptyEnumerable<PerLanguageOption<bool>>();
 
+        /// <summary>
+        /// This controls what delay tagger will use to let editor know about newly inserted tags
+        /// </summary>
+        protected virtual TaggerDelay NewTagsNotificationDelay => TaggerDelay.NearImmediate;
+
+        /// <summary>
+        /// This controls what delay tagger will use to let editor know about just deleted tags.
+        /// </summary>
+        protected virtual TaggerDelay OldTagNotificationDelay => TaggerDelay.NearImmediate;
+
 #if DEBUG
         public readonly string StackTrace;
 #endif
@@ -212,5 +222,19 @@ protected virtual Task ProduceTagsAsync(TaggerContext<TTag> context, DocumentSna
         {
             return SpecializedTasks.EmptyTask;
         }
+
+        private struct DiffResult
+        {
+            public NormalizedSnapshotSpanCollection Added { get; }
+            public NormalizedSnapshotSpanCollection Removed { get; }
+
+            public DiffResult(IEnumerable<SnapshotSpan> added, IEnumerable<SnapshotSpan> removed)
+            {
+                Added = added != null ? new NormalizedSnapshotSpanCollection(added) : NormalizedSnapshotSpanCollection.Empty;
+                Removed = removed != null ? new NormalizedSnapshotSpanCollection(removed) : NormalizedSnapshotSpanCollection.Empty;
+            }
+
+            public int Count => Added.Count + Removed.Count;
+        }
     }
 }

src/Features/Core/Portable/SolutionCrawler/InternalSolutionCrawlerOptions.cs

@@ -9,7 +9,7 @@ internal static class InternalSolutionCrawlerOptions
         public const string OptionName = "SolutionCrawler";
 
         public static readonly Option<bool> SolutionCrawler = new Option<bool>("FeatureManager/Components", "Solution Crawler", defaultValue: true);
-        public static readonly Option<int> ActiveFileWorkerBackOffTimeSpanInMS = new Option<int>(OptionName, "Active file worker backoff timespan in ms", defaultValue: 800);
+        public static readonly Option<int> ActiveFileWorkerBackOffTimeSpanInMS = new Option<int>(OptionName, "Active file worker backoff timespan in ms", defaultValue: 400);
         public static readonly Option<int> AllFilesWorkerBackOffTimeSpanInMS = new Option<int>(OptionName, "All files worker backoff timespan in ms", defaultValue: 1500);
         public static readonly Option<int> EntireProjectWorkerBackOffTimeSpanInMS = new Option<int>(OptionName, "Entire project analysis worker backoff timespan in ms", defaultValue: 5000);
         public static readonly Option<int> SemanticChangeBackOffTimeSpanInMS = new Option<int>(OptionName, "Semantic change backoff timespan in ms", defaultValue: 100);