Implement equality semantics for async tagger tags.

src/EditorFeatures/Core.Wpf/InlineDiagnostics/InlineDiagnosticsTaggerProvider.cs

@@ -121,5 +121,19 @@ diagnostic.Severity is DiagnosticSeverity.Warning or DiagnosticSeverity.Error &&
                 return null;
             }
         }
+
+        /// <summary>
+        /// TODO: is there anything we can do better here? Inline diagnostic tags are not really data, but more UI
+        /// elements with specific constrols, positions and events attached to them.  There doesn't seem to be a safe
+        /// way to reuse any of these currently.  Ideally we could do something similar to inline-hints where there's a
+        /// data tagger portion (which is async and has clean equality semantics), and then the UI portion which just
+        /// translates those data-tags to the UI tags.
+        /// <para>
+        /// Doing direct equality means we'll always end up regenerating all tags.  But hopefully there won't be that
+        /// many in a document to matter.
+        /// </para>
+        /// </summary>
+        protected override bool TagEquals(InlineDiagnosticsTag tag1, InlineDiagnosticsTag tag2)
+            => tag1 == tag2;
     }
 }

src/EditorFeatures/Core.Wpf/LineSeparators/LineSeparatorTaggerProvider.cs

@@ -114,5 +114,12 @@ protected override async Task ProduceTagsAsync(
                     context.AddTag(new TagSpan<LineSeparatorTag>(span.ToSnapshotSpan(snapshotSpan.Snapshot), tag));
             }
         }
+
+        /// <summary>
+        /// We create and cache a separator tag to use (unless the format mapping changes).  So we can just use identity
+        /// comparisons here.
+        /// </summary>
+        protected override bool TagEquals(LineSeparatorTag tag1, LineSeparatorTag tag2)
+            => tag1 == tag2;
     }
 }

src/EditorFeatures/Core.Wpf/StringIndentation/StringIndentationTag.cs

@@ -2,27 +2,33 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+using System;
 using System.Collections.Immutable;
 using System.Windows.Media;
 using Microsoft.CodeAnalysis.Editor.Implementation.Adornments;
 using Microsoft.VisualStudio.Text;
 using Microsoft.VisualStudio.Text.Classification;
 using Microsoft.VisualStudio.Text.Editor;
+using Roslyn.Utilities;
 
 namespace Microsoft.CodeAnalysis.Editor.Implementation.StringIndentation
 {
     /// <summary>
     /// Tag that specifies how a string's content is indented.
     /// </summary>
-    internal class StringIndentationTag : BrushTag
+    internal class StringIndentationTag : BrushTag, IEquatable<StringIndentationTag>
     {
+        private readonly StringIndentationTaggerProvider _provider;
+
         public readonly ImmutableArray<SnapshotSpan> OrderedHoleSpans;
 
         public StringIndentationTag(
+            StringIndentationTaggerProvider provider,
             IEditorFormatMap editorFormatMap,
             ImmutableArray<SnapshotSpan> orderedHoleSpans)
             : base(editorFormatMap)
         {
+            _provider = provider;
             OrderedHoleSpans = orderedHoleSpans;
         }
 
@@ -31,5 +37,28 @@ public StringIndentationTag(
             var brush = view.VisualElement.TryFindResource("outlining.verticalrule.foreground") as SolidColorBrush;
             return brush?.Color;
         }
+
+        public override int GetHashCode()
+            => throw ExceptionUtilities.Unreachable();
+
+        public override bool Equals(object? obj)
+            => Equals(obj as StringIndentationTag);
+
+        public bool Equals(StringIndentationTag? other)
+        {
+            if (other is null)
+                return false;
+
+            if (this.OrderedHoleSpans.Length != other.OrderedHoleSpans.Length)
+                return false;
+
+            for (int i = 0, n = this.OrderedHoleSpans.Length; i < n; i++)
+            {
+                if (!_provider.SpanEquals(this.OrderedHoleSpans[i], other.OrderedHoleSpans[i]))
+                    return false;
+            }
+
+            return true;
+        }
     }
 }

src/EditorFeatures/Core.Wpf/StringIndentation/StringIndentationTaggerProvider.cs

@@ -69,7 +69,7 @@ public StringIndentationTaggerProvider(
         /// then the span of the tag will grow to the right and the line will immediately redraw in the correct position
         /// while we're in the process of recomputing the up to date tags.
         /// </summary>
-        protected override SpanTrackingMode SpanTrackingMode => SpanTrackingMode.EdgeInclusive;
+        public override SpanTrackingMode SpanTrackingMode => SpanTrackingMode.EdgeInclusive;
 
         protected override ITaggerEventSource CreateEventSource(
             ITextView? textView, ITextBuffer subjectBuffer)
@@ -113,9 +113,13 @@ protected override async Task ProduceTagsAsync(
                 context.AddTag(new TagSpan<StringIndentationTag>(
                     region.IndentSpan.ToSnapshotSpan(snapshot),
                     new StringIndentationTag(
+                        this,
                         _editorFormatMap,
                         region.OrderedHoleSpans.SelectAsArray(s => s.ToSnapshotSpan(snapshot)))));
             }
         }
+
+        protected override bool TagEquals(StringIndentationTag tag1, StringIndentationTag tag2)
+            => tag1.Equals(tag2);
     }
 }

src/EditorFeatures/Core/BraceMatching/BraceHighlightTag.cs

@@ -2,13 +2,13 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
-#nullable disable
-
+using System;
 using Microsoft.VisualStudio.Text.Tagging;
+using Roslyn.Utilities;
 
 namespace Microsoft.CodeAnalysis.BraceMatching
 {
-    internal class BraceHighlightTag : TextMarkerTag
+    internal sealed class BraceHighlightTag : TextMarkerTag
     {
         public static readonly BraceHighlightTag StartTag = new(navigateToStart: true);
         public static readonly BraceHighlightTag EndTag = new(navigateToStart: false);

src/EditorFeatures/Core/BraceMatching/BraceHighlightingViewTaggerProvider.cs

@@ -174,5 +174,9 @@ private static void AddBraces(
                 context.AddTag(snapshot.GetTagSpan(braces.Value.RightSpan.ToSpan(), BraceHighlightTag.EndTag));
             }
         }
+
+        // Safe to directly compare as BraceHighlightTag uses singleton instances.
+        protected override bool TagEquals(BraceHighlightTag tag1, BraceHighlightTag tag2)
+            => tag1 == tag2;
     }
 }

src/EditorFeatures/Core/Classification/Semantic/AbstractSemanticOrEmbeddedClassificationViewTaggerProvider.cs

@@ -20,6 +20,7 @@
 using Microsoft.VisualStudio.Text;
 using Microsoft.VisualStudio.Text.Editor;
 using Microsoft.VisualStudio.Text.Tagging;
+using Newtonsoft.Json;
 using Roslyn.Utilities;
 
 namespace Microsoft.CodeAnalysis.Classification
@@ -124,5 +125,8 @@ protected sealed override Task ProduceTagsAsync(
             return ClassificationUtilities.ProduceTagsAsync(
                 context, spanToTag, classificationService, _typeMap, classificationOptions, _type, cancellationToken);
         }
+
+        protected override bool TagEquals(IClassificationTag tag1, IClassificationTag tag2)
+            => tag1.ClassificationType.Classification == tag2.ClassificationType.Classification;
     }
 }

src/EditorFeatures/Core/Diagnostics/AbstractDiagnosticsAdornmentTaggerProvider.RoslynErrorTag.cs

@@ -0,0 +1,69 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using Microsoft.CodeAnalysis.Classification;
+using Microsoft.CodeAnalysis.Editor.Implementation.IntelliSense.QuickInfo;
+using Microsoft.VisualStudio.Text.Adornments;
+using Microsoft.VisualStudio.Text.Tagging;
+using Roslyn.Utilities;
+
+namespace Microsoft.CodeAnalysis.Diagnostics
+{
+    internal partial class AbstractDiagnosticsAdornmentTaggerProvider<TTag>
+    {
+        protected sealed class RoslynErrorTag : ErrorTag, IEquatable<RoslynErrorTag>
+        {
+            private readonly DiagnosticData _data;
+
+            public RoslynErrorTag(string errorType, Workspace workspace, DiagnosticData data)
+                : base(errorType, CreateToolTipContent(workspace, data))
+            {
+                _data = data;
+            }
+
+            private static object CreateToolTipContent(Workspace workspace, DiagnosticData diagnostic)
+            {
+                Action? navigationAction = null;
+                string? tooltip = null;
+                if (workspace != null)
+                {
+                    var helpLinkUri = diagnostic.GetValidHelpLinkUri();
+                    if (helpLinkUri != null)
+                    {
+                        navigationAction = new QuickInfoHyperLink(workspace, helpLinkUri).NavigationAction;
+                        tooltip = diagnostic.HelpLink;
+                    }
+                }
+
+                var diagnosticIdTextRun = navigationAction is null
+                    ? new ClassifiedTextRun(ClassificationTypeNames.Text, diagnostic.Id)
+                    : new ClassifiedTextRun(ClassificationTypeNames.Text, diagnostic.Id, navigationAction, tooltip);
+
+                return new ContainerElement(
+                    ContainerElementStyle.Wrapped,
+                    new ClassifiedTextElement(
+                        diagnosticIdTextRun,
+                        new ClassifiedTextRun(ClassificationTypeNames.Punctuation, ":"),
+                        new ClassifiedTextRun(ClassificationTypeNames.WhiteSpace, " "),
+                        new ClassifiedTextRun(ClassificationTypeNames.Text, diagnostic.Message)));
+            }
+
+            public override bool Equals(object? obj)
+                => Equals(obj as RoslynErrorTag);
+
+            public bool Equals(RoslynErrorTag? other)
+            {
+                return other != null &&
+                    this.ErrorType == other.ErrorType &&
+                    this._data.GetValidHelpLinkUri() == other._data.GetValidHelpLinkUri() &&
+                    this._data.Id == other._data.Id &&
+                    this._data.Message == other._data.Message;
+            }
+
+            public override int GetHashCode()
+                => throw ExceptionUtilities.Unreachable();
+        }
+    }
+}

src/EditorFeatures/Core/Diagnostics/AbstractDiagnosticsAdornmentTaggerProvider.cs

@@ -3,19 +3,16 @@
 // See the LICENSE file in the project root for more information.
 
 using System;
-using Microsoft.CodeAnalysis.Classification;
-using Microsoft.CodeAnalysis.Editor.Implementation.IntelliSense.QuickInfo;
 using Microsoft.CodeAnalysis.Editor.Shared.Utilities;
 using Microsoft.CodeAnalysis.Options;
 using Microsoft.CodeAnalysis.Shared.TestHooks;
 using Microsoft.CodeAnalysis.Workspaces;
 using Microsoft.VisualStudio.Text;
-using Microsoft.VisualStudio.Text.Adornments;
 using Microsoft.VisualStudio.Text.Tagging;
 
 namespace Microsoft.CodeAnalysis.Diagnostics
 {
-    internal abstract class AbstractDiagnosticsAdornmentTaggerProvider<TTag> :
+    internal abstract partial class AbstractDiagnosticsAdornmentTaggerProvider<TTag> :
         AbstractDiagnosticsTaggerProvider<TTag>
         where TTag : class, ITag
     {
@@ -48,33 +45,6 @@ protected AbstractDiagnosticsAdornmentTaggerProvider(
             return new TagSpan<TTag>(adjustedSpan, errorTag);
         }
 
-        protected static object CreateToolTipContent(Workspace workspace, DiagnosticData diagnostic)
-        {
-            Action? navigationAction = null;
-            string? tooltip = null;
-            if (workspace != null)
-            {
-                var helpLinkUri = diagnostic.GetValidHelpLinkUri();
-                if (helpLinkUri != null)
-                {
-                    navigationAction = new QuickInfoHyperLink(workspace, helpLinkUri).NavigationAction;
-                    tooltip = diagnostic.HelpLink;
-                }
-            }
-
-            var diagnosticIdTextRun = navigationAction is null
-                ? new ClassifiedTextRun(ClassificationTypeNames.Text, diagnostic.Id)
-                : new ClassifiedTextRun(ClassificationTypeNames.Text, diagnostic.Id, navigationAction, tooltip);
-
-            return new ContainerElement(
-                ContainerElementStyle.Wrapped,
-                new ClassifiedTextElement(
-                    diagnosticIdTextRun,
-                    new ClassifiedTextRun(ClassificationTypeNames.Punctuation, ":"),
-                    new ClassifiedTextRun(ClassificationTypeNames.WhiteSpace, " "),
-                    new ClassifiedTextRun(ClassificationTypeNames.Text, diagnostic.Message)));
-        }
-
         // By default, tags must have at least length '1' so that they can be visible in the UI layer.
         protected virtual SnapshotSpan AdjustSnapshotSpan(SnapshotSpan span)
             => AdjustSnapshotSpan(span, minimumLength: 1, maximumLength: int.MaxValue);

src/EditorFeatures/Core/Diagnostics/DiagnosticsClassificationTaggerProvider.cs

@@ -99,5 +99,8 @@ protected internal override ImmutableArray<DiagnosticDataLocation> GetLocationsT
             // Default to the base implementation for the diagnostic data
             return base.GetLocationsToTag(diagnosticData);
         }
+
+        protected override bool TagEquals(ClassificationTag tag1, ClassificationTag tag2)
+            => tag1.ClassificationType.Classification == tag2.ClassificationType.Classification;
     }
 }

src/EditorFeatures/Core/Diagnostics/DiagnosticsSquiggleTaggerProvider.cs

@@ -15,9 +15,11 @@
 using Microsoft.CodeAnalysis.Options;
 using Microsoft.CodeAnalysis.Shared.TestHooks;
 using Microsoft.CodeAnalysis.Workspaces;
+using Microsoft.VisualStudio.Text;
 using Microsoft.VisualStudio.Text.Adornments;
 using Microsoft.VisualStudio.Text.Tagging;
 using Microsoft.VisualStudio.Utilities;
+using Roslyn.Utilities;
 
 namespace Microsoft.CodeAnalysis.Diagnostics
 {
@@ -73,7 +75,7 @@ protected internal override bool IncludeDiagnostic(DiagnosticData diagnostic)
                 return null;
             }
 
-            return new ErrorTag(errorType, CreateToolTipContent(workspace, diagnostic));
+            return new RoslynErrorTag(errorType, workspace, diagnostic);
         }
 
         private static string? GetErrorTypeFromDiagnostic(DiagnosticData diagnostic)
@@ -126,5 +128,12 @@ protected internal override bool IncludeDiagnostic(DiagnosticData diagnostic)
                     return PredefinedErrorTypeNames.OtherError;
             }
         }
+
+        protected override bool TagEquals(IErrorTag tag1, IErrorTag tag2)
+        {
+            Contract.ThrowIfFalse(tag1 is RoslynErrorTag);
+            Contract.ThrowIfFalse(tag2 is RoslynErrorTag);
+            return tag1.Equals(tag2);
+        }
     }
 }

src/EditorFeatures/Core/Diagnostics/DiagnosticsSuggestionTaggerProvider.cs

@@ -17,6 +17,7 @@
 using Microsoft.VisualStudio.Text.Adornments;
 using Microsoft.VisualStudio.Text.Tagging;
 using Microsoft.VisualStudio.Utilities;
+using Roslyn.Utilities;
 
 namespace Microsoft.CodeAnalysis.Diagnostics
 {
@@ -56,14 +57,19 @@ protected internal override bool SupportsDignosticMode(DiagnosticMode mode)
         }
 
         protected override IErrorTag CreateTag(Workspace workspace, DiagnosticData diagnostic)
-            => new ErrorTag(
-                PredefinedErrorTypeNames.HintedSuggestion,
-                CreateToolTipContent(workspace, diagnostic));
+            => new RoslynErrorTag(PredefinedErrorTypeNames.HintedSuggestion, workspace, diagnostic);
 
         protected override SnapshotSpan AdjustSnapshotSpan(SnapshotSpan snapshotSpan)
         {
             // We always want suggestion tags to be two characters long.
             return AdjustSnapshotSpan(snapshotSpan, minimumLength: 2, maximumLength: 2);
         }
+
+        protected override bool TagEquals(IErrorTag tag1, IErrorTag tag2)
+        {
+            Contract.ThrowIfFalse(tag1 is RoslynErrorTag);
+            Contract.ThrowIfFalse(tag2 is RoslynErrorTag);
+            return tag1.Equals(tag2);
+        }
     }
 }

src/EditorFeatures/Core/EditAndContinue/ActiveStatementTaggerProvider.cs

@@ -3,6 +3,7 @@
 // See the LICENSE file in the project root for more information.
 
 using System;
+using System.Collections.Generic;
 using System.Collections.Immutable;
 using System.ComponentModel.Composition;
 using System.Diagnostics;
@@ -101,5 +102,11 @@ protected override async Task ProduceTagsAsync(
             // Let the context know that this was the span we actually tried to tag.
             context.SetSpansTagged(ImmutableArray.Create(spanToTag.SnapshotSpan));
         }
+
+        protected override bool TagEquals(ITextMarkerTag tag1, ITextMarkerTag tag2)
+        {
+            Contract.ThrowIfFalse(tag1 == tag2, "ActiveStatementTag is a supposed to be a singleton");
+            return true;
+        }
     }
 }