Create remote service and register etc.

eng/targets/Services.props

@@ -23,5 +23,6 @@
     <ServiceHubService Include="Microsoft.VisualStudio.Razor.UriPresentation" ClassName="Microsoft.CodeAnalysis.Remote.Razor.RemoteUriPresentationService+Factory" />
     <ServiceHubService Include="Microsoft.VisualStudio.Razor.FoldingRange" ClassName="Microsoft.CodeAnalysis.Remote.Razor.RemoteFoldingRangeService+Factory" />
     <ServiceHubService Include="Microsoft.VisualStudio.Razor.SignatureHelp" ClassName="Microsoft.CodeAnalysis.Remote.Razor.RemoteSignatureHelpService+Factory" />
+    <ServiceHubService Include="Microsoft.VisualStudio.Razor.DocumentHighlight" ClassName="Microsoft.CodeAnalysis.Remote.Razor.RemoteDocumentHighlightService+Factory" />
   </ItemGroup>
 </Project>

src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/Extensions/LinePositionExtensions.cs

@@ -4,6 +4,7 @@
 using Microsoft.CodeAnalysis.Razor.Logging;
 using Microsoft.CodeAnalysis.Text;
 using Microsoft.VisualStudio.LanguageServer.Protocol;
+using RLSP = Roslyn.LanguageServer.Protocol;
 
 namespace Microsoft.CodeAnalysis.Razor.Workspaces;
 
@@ -12,6 +13,9 @@ internal static class LinePositionExtensions
     public static Position ToPosition(this LinePosition linePosition)
         => new Position(linePosition.Line, linePosition.Character);
 
+    public static RLSP.Position ToRLSPPosition(this LinePosition linePosition)
+        => new RLSP.Position(linePosition.Line, linePosition.Character);
+
     public static bool TryGetAbsoluteIndex(this LinePosition position, SourceText sourceText, ILogger logger, out int absoluteIndex)
         => sourceText.TryGetAbsoluteIndex(position.Line, position.Character, logger, out absoluteIndex);
 

src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/Extensions/LinePositionSpanExtensions.cs

@@ -3,6 +3,7 @@
 
 using Microsoft.CodeAnalysis.Text;
 using Microsoft.VisualStudio.LanguageServer.Protocol;
+using RLSP = Roslyn.LanguageServer.Protocol;
 
 namespace Microsoft.CodeAnalysis.Razor.Workspaces;
 
@@ -15,6 +16,13 @@ internal static class LinePositionSpanExtensions
             End = linePositionSpan.End.ToPosition()
         };
 
+    public static RLSP.Range ToRLSPRange(this LinePositionSpan linePositionSpan)
+    => new RLSP.Range
+    {
+        Start = linePositionSpan.Start.ToRLSPPosition(),
+        End = linePositionSpan.End.ToRLSPPosition()
+    };
+
     public static TextSpan ToTextSpan(this LinePositionSpan linePositionSpan, SourceText sourceText)
         => sourceText.GetTextSpan(linePositionSpan.Start.Line, linePositionSpan.Start.Character, linePositionSpan.End.Line, linePositionSpan.End.Character);
 

src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/Extensions/PositionExtensions.cs

@@ -7,6 +7,7 @@ using Microsoft.AspNetCore.Razor.Language;
 using Microsoft.CodeAnalysis.Razor.Logging;
 using Microsoft.CodeAnalysis.Text;
 using Microsoft.VisualStudio.LanguageServer.Protocol;
+using RLSP = Roslyn.LanguageServer.Protocol;
 
 namespace Microsoft.CodeAnalysis.Razor.Workspaces;
 
@@ -15,6 +16,9 @@ internal static class PositionExtensions
     public static LinePosition ToLinePosition(this Position position)
         => new LinePosition(position.Line, position.Character);
 
+    public static LinePosition ToLinePosition(this RLSP.Position position)
+        => new LinePosition(position.Line, position.Character);
+
     public static bool TryGetAbsoluteIndex(this Position position, SourceText sourceText, ILogger? logger, out int absoluteIndex)
     {
         if (position is null)

src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/Extensions/RangeExtensions.cs

@@ -5,6 +5,7 @@ using System;
 using Microsoft.CodeAnalysis.Text;
 using Microsoft.VisualStudio.LanguageServer.Protocol;
 using Range = Microsoft.VisualStudio.LanguageServer.Protocol.Range;
+using RLSP = Roslyn.LanguageServer.Protocol;
 
 namespace Microsoft.CodeAnalysis.Razor.Workspaces;
 
@@ -110,6 +111,9 @@ internal static class RangeExtensions
     public static LinePositionSpan ToLinePositionSpan(this Range range)
         => new LinePositionSpan(range.Start.ToLinePosition(), range.End.ToLinePosition());
 
+    public static LinePositionSpan ToLinePositionSpan(this RLSP.Range range)
+        => new LinePositionSpan(range.Start.ToLinePosition(), range.End.ToLinePosition());
+
     public static bool IsUndefined(this Range range)
     {
         if (range is null)

src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/Protocol/DocumentHighlight/RemoteDocumentHighlight.cs

@@ -5,6 +5,7 @@ using System.Runtime.Serialization;
 using Microsoft.CodeAnalysis.Razor.Workspaces;
 using Microsoft.CodeAnalysis.Text;
 using Microsoft.VisualStudio.LanguageServer.Protocol;
+using RLSP = Roslyn.LanguageServer.Protocol;
 
 namespace Microsoft.CodeAnalysis.Razor.Protocol.DocumentHighlight;
 
@@ -15,8 +16,8 @@ internal readonly record struct RemoteDocumentHighlight(
     [property: DataMember(Order = 0)] LinePositionSpan Position,
     [property: DataMember(Order = 1)] DocumentHighlightKind Kind)
 {
-    public static RemoteDocumentHighlight FromLspDocumentHighlight(DocumentHighlight h)
-        => new RemoteDocumentHighlight(h.Range.ToLinePositionSpan(), h.Kind);
+    public static RemoteDocumentHighlight FromRLSPDocumentHighlight(RLSP.DocumentHighlight h)
+        => new RemoteDocumentHighlight(h.Range.ToLinePositionSpan(), (DocumentHighlightKind)h.Kind);
 
     public static DocumentHighlight ToLspDocumentHighlight(RemoteDocumentHighlight r)
         => new DocumentHighlight

src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/Remote/RazorServices.cs

@@ -19,7 +19,8 @@ internal static class RazorServices
             (typeof(IRemoteSemanticTokensService), null),
             (typeof(IRemoteHtmlDocumentService), null),
             (typeof(IRemoteUriPresentationService), null),
-            (typeof(IRemoteFoldingRangeService), null)
+            (typeof(IRemoteFoldingRangeService), null),
+            (typeof(IRemoteDocumentHighlightService), null),
         ];
 
     // Internal for testing

src/Razor/src/Microsoft.CodeAnalysis.Remote.Razor/DocumentHighlight/RemoteDocumentHighlightService.cs

@@ -0,0 +1,88 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the MIT license. See License.txt in the project root for license information.
+
+using System.Linq;
+using System.Threading;
+using System.Threading.Tasks;
+using Microsoft.AspNetCore.Razor.Language;
+using Microsoft.CodeAnalysis.ExternalAccess.Razor;
+using Microsoft.CodeAnalysis.ExternalAccess.Razor.Cohost.Handlers;
+using Microsoft.CodeAnalysis.Razor.DocumentMapping;
+using Microsoft.CodeAnalysis.Razor.Protocol;
+using Microsoft.CodeAnalysis.Razor.Protocol.DocumentHighlight;
+using Microsoft.CodeAnalysis.Razor.Remote;
+using Microsoft.CodeAnalysis.Razor.Workspaces;
+using Microsoft.CodeAnalysis.Remote.Razor.ProjectSystem;
+using Microsoft.CodeAnalysis.Text;
+
+namespace Microsoft.CodeAnalysis.Remote.Razor;
+
+internal sealed partial class RemoteDocumentHighlightService(in ServiceArgs args) : RazorDocumentServiceBase(in args), IRemoteDocumentHighlightService
+{
+    internal sealed class Factory : FactoryBase<IRemoteDocumentHighlightService>
+    {
+        protected override IRemoteDocumentHighlightService CreateService(in ServiceArgs args)
+            => new RemoteDocumentHighlightService(in args);
+    }
+
+    private readonly IRazorDocumentMappingService _documentMappingService = args.ExportProvider.GetExportedValue<IRazorDocumentMappingService>();
+    private readonly IFilePathService _filePathService = args.ExportProvider.GetExportedValue<IFilePathService>();
+
+    public ValueTask<RemoteDocumentHighlight[]?> GetHighlightsAsync(
+        RazorPinnedSolutionInfoWrapper solutionInfo,
+        DocumentId razorDocumentId,
+        LinePosition position,
+        CancellationToken cancellationToken)
+        => RunServiceAsync(
+            solutionInfo,
+            razorDocumentId,
+            context => GetHighlightsAsync(context, position, cancellationToken),
+            cancellationToken);
+
+    private async ValueTask<RemoteDocumentHighlight[]?> GetHighlightsAsync(
+        RemoteDocumentContext context,
+        LinePosition position,
+        CancellationToken cancellationToken)
+    {
+        var sourceText = await context.GetSourceTextAsync(cancellationToken).ConfigureAwait(false);
+        if (!sourceText.TryGetAbsoluteIndex(position.Line, position.Character, out var index))
+        {
+            return null;
+        }
+
+        var codeDocument = await context.GetCodeDocumentAsync(cancellationToken).ConfigureAwait(false);
+
+        var languageKind = _documentMappingService.GetLanguageKind(codeDocument, index, rightAssociative: true);
+        if (languageKind is RazorLanguageKind.Html)
+        {
+            // Returning null indicates we have nothing to say, so go to Html
+            return null;
+        }
+        else if (languageKind is RazorLanguageKind.CSharp)
+        {
+            var csharpDocument = codeDocument.GetCSharpDocument();
+            if (_documentMappingService.TryMapToGeneratedDocumentPosition(csharpDocument, index, out var mappedPosition, out _))
+            {
+                var generatedDocument = await context.GetGeneratedDocumentAsync(_filePathService, cancellationToken).ConfigureAwait(false);
+
+                var highlights = await DocumentHighlights.GetHighlightsAsync(generatedDocument, mappedPosition, cancellationToken).ConfigureAwait(false);
+
+                if (highlights is not null)
+                {
+                    foreach (var highlight in highlights)
+                    {
+                        if (_documentMappingService.TryMapToHostDocumentRange(csharpDocument, highlight.Range.ToLinePositionSpan(), out var mappedRange))
+                        {
+                            highlight.Range = mappedRange.ToRLSPRange();
+                        }
+                    }
+
+                    return highlights.Select(RemoteDocumentHighlight.FromRLSPDocumentHighlight).ToArray();
+                }
+            }
+        }
+
+        // We don't do anything for Razor, but we return an empty array so the caller knows not to bother asking Html
+        return [];
+    }
+}