Restore old APi to make migration easier.

src/EditorFeatures/Core/EditorFeatures.csproj

@@ -165,6 +165,7 @@
     <Compile Include="Implementation\Intellisense\QuickInfo\Providers\LinkedFileDiscrepancyException.cs" />
     <Compile Include="Implementation\Intellisense\Completion\CompletionFilterReason.cs" />
     <Compile Include="Implementation\Intellisense\Completion\FilterResult.cs" />
+    <Compile Include="Implementation\ReferenceHighlighting\IDocumentHighlightsService.cs" />
     <Compile Include="Implementation\Structure\BlockTagState.cs" />
     <Compile Include="Implementation\Suggestions\ISuggestedActionCallback.cs" />
     <Compile Include="Implementation\Suggestions\SuggestedActionSetComparer.cs" />

src/EditorFeatures/Core/Implementation/ReferenceHighlighting/IDocumentHighlightsService.cs

+// Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
+
+using System;
+using System.Collections.Immutable;
+using System.Threading;
+using System.Threading.Tasks;
+using Microsoft.CodeAnalysis.Host;
+using Microsoft.CodeAnalysis.Text;
+
+namespace Microsoft.CodeAnalysis.Editor
+{
+    internal enum HighlightSpanKind
+    {
+        None,
+        Definition,
+        Reference,
+        WrittenReference,
+    }
+
+    internal struct HighlightSpan
+    {
+        public TextSpan TextSpan { get; }
+        public HighlightSpanKind Kind { get; }
+
+        public HighlightSpan(TextSpan textSpan, HighlightSpanKind kind) : this()
+        {
+            this.TextSpan = textSpan;
+            this.Kind = kind;
+        }
+    }
+
+    internal struct DocumentHighlights
+    {
+        public Document Document { get; }
+        public ImmutableArray<HighlightSpan> HighlightSpans { get; }
+
+        public DocumentHighlights(Document document, ImmutableArray<HighlightSpan> highlightSpans)
+        {
+            this.Document = document;
+            this.HighlightSpans = highlightSpans;
+        }
+    }
+
+    /// <summary>
+    /// Note: kept around for back compat until F# and TypeScript move over to 
+    /// <see cref="Microsoft.CodeAnalysis.DocumentHighlighting.IDocumentHighlightsService"/>.
+    /// </summary>
+    internal interface IDocumentHighlightsService : ILanguageService
+    {
+        Task<ImmutableArray<DocumentHighlights>> GetDocumentHighlightsAsync(
+            Document document, int position, IImmutableSet<Document> documentsToSearch, CancellationToken cancellationToken);
+    }
+}
\ No newline at end of file

src/EditorFeatures/Core/ReferenceHighlighting/ReferenceHighlightingViewTaggerProvider.cs

@@ -5,14 +5,17 @@
 using System.Collections.Immutable;
 using System.ComponentModel.Composition;
 using System.Linq;
+using System.Threading;
 using System.Threading.Tasks;
 using Microsoft.CodeAnalysis.DocumentHighlighting;
 using Microsoft.CodeAnalysis.Editor.Shared.Options;
 using Microsoft.CodeAnalysis.Editor.Shared.Tagging;
 using Microsoft.CodeAnalysis.Editor.Tagging;
+using Microsoft.CodeAnalysis.Host;
 using Microsoft.CodeAnalysis.Internal.Log;
 using Microsoft.CodeAnalysis.Notification;
 using Microsoft.CodeAnalysis.Options;
+using Microsoft.CodeAnalysis.Shared.Extensions;
 using Microsoft.CodeAnalysis.Shared.TestHooks;
 using Microsoft.CodeAnalysis.Text;
 using Microsoft.CodeAnalysis.Text.Shared.Extensions;
@@ -111,13 +114,12 @@ protected override Task ProduceTagsAsync(TaggerContext<NavigableHighlightTag> co
             }
 
             // Otherwise, we need to go produce all tags.
-            return ProduceTagsAsync(context, caretPosition, workspace, document);
+            return ProduceTagsAsync(context, caretPosition, document);
         }
 
         internal async Task ProduceTagsAsync(
             TaggerContext<NavigableHighlightTag> context,
             SnapshotPoint position,
-            Workspace workspace,
             Document document)
         {
             var cancellationToken = context.CancellationToken;
@@ -128,25 +130,73 @@ protected override Task ProduceTagsAsync(TaggerContext<NavigableHighlightTag> co
             {
                 if (document != null)
                 {
-                    var documentHighlightsService = document.Project.LanguageServices.GetService<IDocumentHighlightsService>();
-                    if (documentHighlightsService != null)
+                    // As we transition to the new API (defined at the Features layer) we support
+                    // calling into both it and the old API (defined at the EditorFeatures layer).
+                    //
+                    // Once TypeScript and F# can move over, then we can remove the calls to the old
+                    // API.
+                    await TryNewServiceAsync(context, position, document).ConfigureAwait(false);
+                    await TryOldServiceAsync(context, position, document).ConfigureAwait(false);
+                }
+            }
+        }
+
+        private Task TryOldServiceAsync(TaggerContext<NavigableHighlightTag> context, SnapshotPoint position, Document document)
+        {
+            return TryServiceAsync<IDocumentHighlightsService>(
+                context, position, document, 
+                (s, d, p, ds, c) => s.GetDocumentHighlightsAsync(d, p, ds, c));
+        }
+
+        private Task TryNewServiceAsync(
+            TaggerContext<NavigableHighlightTag> context, SnapshotPoint position, Document document)
+        {
+            return TryServiceAsync<DocumentHighlighting.IDocumentHighlightsService>(
+                context, position, document,
+                async (service, doc, point, documents, cancellation) =>
+                {
+                    // Call into the new service.
+                    var newHighlights = await service.GetDocumentHighlightsAsync(doc, point, documents, cancellation).ConfigureAwait(false);
+
+                    // then convert the result to the form the old service would return.
+                    return ConvertHighlights(newHighlights);
+                });
+        }
+
+        private async Task TryServiceAsync<T>(
+            TaggerContext<NavigableHighlightTag> context, SnapshotPoint position, Document document,
+            Func<T, Document, SnapshotPoint, ImmutableHashSet<Document>, CancellationToken, Task<ImmutableArray<DocumentHighlights>>> getDocumentHighlightsAsync)
+            where T : class, ILanguageService
+        {
+            var cancellationToken = context.CancellationToken;
+            var documentHighlightsService = document.GetLanguageService<T>();
+            if (documentHighlightsService != null)
+            {
+                // We only want to search inside documents that correspond to the snapshots
+                // we're looking at
+                var documentsToSearch = ImmutableHashSet.CreateRange(context.SpansToTag.Select(vt => vt.Document).WhereNotNull());
+                var documentHighlightsList = await getDocumentHighlightsAsync(
+                    documentHighlightsService, document, position, documentsToSearch, cancellationToken).ConfigureAwait(false);
+                if (documentHighlightsList != null)
+                {
+                    foreach (var documentHighlights in documentHighlightsList)
                     {
-                        // We only want to search inside documents that correspond to the snapshots
-                        // we're looking at
-                        var documentsToSearch = ImmutableHashSet.CreateRange(context.SpansToTag.Select(vt => vt.Document).WhereNotNull());
-                        var documentHighlightsList = await documentHighlightsService.GetDocumentHighlightsAsync(document, position, documentsToSearch, cancellationToken).ConfigureAwait(false);
-                        if (documentHighlightsList != null)
-                        {
-                            foreach (var documentHighlights in documentHighlightsList)
-                            {
-                                await AddTagSpansAsync(context, solution, documentHighlights).ConfigureAwait(false);
-                            }
-                        }
+                        await AddTagSpansAsync(
+                            context, document.Project.Solution, documentHighlights).ConfigureAwait(false);
                     }
                 }
             }
         }
 
+        private ImmutableArray<DocumentHighlights> ConvertHighlights(ImmutableArray<DocumentHighlighting.DocumentHighlights> newHighlights)
+            => newHighlights.SelectAsArray(
+                documentHighlights => new DocumentHighlights(
+                    documentHighlights.Document,
+                    documentHighlights.HighlightSpans.SelectAsArray(
+                        highlightSpan => new HighlightSpan(
+                            highlightSpan.TextSpan,
+                            (HighlightSpanKind)highlightSpan.Kind))));
+
         private async Task AddTagSpansAsync(
             TaggerContext<NavigableHighlightTag> context,
             Solution solution,