Merge pull request #20993 from CyrusNajmabadi/emptySpansToTag

Be resilient to getting back no spans to tag.

src/EditorFeatures/Core/ReferenceHighlighting/ReferenceHighlightingViewTaggerProvider.cs

@@ -69,6 +69,8 @@ protected override ITaggerEventSource CreateEventSource(ITextView textView, ITex
 
         protected override IEnumerable<SnapshotSpan> GetSpansToTag(ITextView textViewOpt, ITextBuffer subjectBuffer)
         {
+            // Note: this may return no snapshot spans.  We have to be resilient to that
+            // when processing the TaggerContext<>.SpansToTag below.
             return textViewOpt.BufferGraph.GetTextBuffers(b => IsSupportedContentType(b.ContentType))
                               .Select(b => b.CurrentSnapshot.GetFullSpan())
                               .ToList();
@@ -91,7 +93,8 @@ protected override Task ProduceTagsAsync(TaggerContext<NavigableHighlightTag> co
                 return SpecializedTasks.EmptyTask;
             }
 
-            var document = context.SpansToTag.First(vt => vt.SnapshotSpan.Snapshot == caretPosition.Snapshot).Document;
+            // GetSpansToTag may have produced no actual spans to tag.  Be resilient to that.
+            var document = context.SpansToTag.FirstOrDefault(vt => vt.SnapshotSpan.Snapshot == caretPosition.Snapshot).Document;
             if (document == null)
             {
                 return SpecializedTasks.EmptyTask;

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

@@ -335,7 +335,7 @@ private CancellationToken GetCancellationToken(bool initialTags)
                     ? _initialComputationCancellationTokenSource.Token
                     : _workQueue.CancellationToken;
 
-            private List<DocumentSnapshotSpan> GetSpansAndDocumentsToTag()
+            private ImmutableArray<DocumentSnapshotSpan> GetSpansAndDocumentsToTag()
             {
                 _workQueue.AssertIsForeground();
 
@@ -356,9 +356,8 @@ private List<DocumentSnapshotSpan> GetSpansAndDocumentsToTag()
 
                     // document can be null if the buffer the given span is part of is not part of our workspace.
                     return new DocumentSnapshotSpan(document, span);
-                }).ToList();
+                }).ToImmutableArray();
 
-                Debug.Assert(spansAndDocumentsToTag.Count > 0);
                 return spansAndDocumentsToTag;
             }
 
@@ -573,7 +572,7 @@ private IEnumerable<ITagSpan<TTag>> GetNonIntersectingTagSpans(IEnumerable<Snaps
                 object oldState,
                 SnapshotPoint? caretPosition,
                 TextChangeRange? textChangeRange,
-                List<DocumentSnapshotSpan> spansToTag,
+                ImmutableArray<DocumentSnapshotSpan> spansToTag,
                 ImmutableDictionary<ITextBuffer, TagSpanIntervalTree<TTag>> oldTagTrees,
                 bool initialTags,
                 CancellationToken cancellationToken)
@@ -618,7 +617,7 @@ private void ProduceTagsSynchronously(TaggerContext<TTag> context)
             }
 
             private void ProcessContext(
-                List<DocumentSnapshotSpan> spansToTag,
+                ImmutableArray<DocumentSnapshotSpan> spansToTag,
                 ImmutableDictionary<ITextBuffer, TagSpanIntervalTree<TTag>> oldTagTrees,
                 TaggerContext<TTag> context,
                 bool initialTags)
@@ -636,7 +635,7 @@ private void ProduceTagsSynchronously(TaggerContext<TTag> context)
             }
 
             private void ProcessNewTagTrees(
-                List<DocumentSnapshotSpan> spansToTag,
+                ImmutableArray<DocumentSnapshotSpan> spansToTag,
                 ImmutableDictionary<ITextBuffer, TagSpanIntervalTree<TTag>> oldTagTrees,
                 ImmutableDictionary<ITextBuffer, TagSpanIntervalTree<TTag>> newTagTrees,
                 object newState,

src/EditorFeatures/Core/Tagging/TaggerContext.cs

@@ -20,7 +20,7 @@ internal class TaggerContext<TTag> where TTag : ITag
         internal IEnumerable<DocumentSnapshotSpan> _spansTagged;
         internal ImmutableArray<ITagSpan<TTag>>.Builder tagSpans = ImmutableArray.CreateBuilder<ITagSpan<TTag>>();
 
-        public IEnumerable<DocumentSnapshotSpan> SpansToTag { get; }
+        public ImmutableArray<DocumentSnapshotSpan> SpansToTag { get; }
         public SnapshotPoint? CaretPosition { get; }
 
         /// <summary>
@@ -47,14 +47,14 @@ internal class TaggerContext<TTag> where TTag : ITag
             SnapshotPoint? caretPosition = null,
             TextChangeRange? textChangeRange = null,
             CancellationToken cancellationToken = default)
-            : this(null, new[] { new DocumentSnapshotSpan(document, snapshot.GetFullSpan()) },
+            : this(null, ImmutableArray.Create(new DocumentSnapshotSpan(document, snapshot.GetFullSpan())),
                   caretPosition, textChangeRange, null, cancellationToken)
         {
         }
 
         internal TaggerContext(
             object state,
-            IEnumerable<DocumentSnapshotSpan> spansToTag,
+            ImmutableArray<DocumentSnapshotSpan> spansToTag,
             SnapshotPoint? caretPosition,
             TextChangeRange? textChangeRange,
             ImmutableDictionary<ITextBuffer, TagSpanIntervalTree<TTag>> existingTags,