Implement excerpt service so we can provide nice results in FAR and CodeLens etc.

Author: davidwengier

src/Razor/src/Microsoft.CodeAnalysis.Razor.CohostingShared/Microsoft.CodeAnalysis.Razor.CohostingShared.projitems

@@ -35,6 +35,7 @@
     <Compile Include="$(MSBuildThisFileDirectory)OnAutoInsert\CohostOnAutoInsertEndpoint.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)OnAutoInsert\CohostOnAutoInsertTriggerCharacterProviders.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)RazorAnalyzerAssemblyRedirector.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)RazorSourceGeneratedDocumentExcerptService.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)RazorSourceGeneratedDocumentSpanMappingService.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)RazorSourceGeneratorLocator.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Rename\CohostRenameEndpoint.cs" />

src/Razor/src/Microsoft.CodeAnalysis.Razor.CohostingShared/RazorSourceGeneratedDocumentExcerptService.cs

@@ -0,0 +1,54 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.ComponentModel.Composition;
+using System.Threading;
+using System.Threading.Tasks;
+using Microsoft.CodeAnalysis.ExternalAccess.Razor;
+using Microsoft.CodeAnalysis.Razor.DocumentExcerpt;
+using Microsoft.CodeAnalysis.Razor.Remote;
+using Microsoft.CodeAnalysis.Text;
+
+namespace Microsoft.CodeAnalysis.Razor.CohostingShared;
+
+[Export(typeof(IRazorSourceGeneratedDocumentExcerptService))]
+[method: ImportingConstructor]
+internal sealed class RazorSourceGeneratedDocumentExcerptService(IRemoteServiceInvoker remoteServiceInvoker) : IRazorSourceGeneratedDocumentExcerptService
+{
+    private readonly IRemoteServiceInvoker _remoteServiceInvoker = remoteServiceInvoker;
+
+    public async Task<RazorExcerptResult?> TryExcerptAsync(SourceGeneratedDocument document, TextSpan span, RazorExcerptMode mode, RazorClassificationOptionsWrapper options, CancellationToken cancellationToken)
+    {
+        if (!document.IsRazorSourceGeneratedDocument())
+        {
+            return null;
+        }
+
+        var result = await _remoteServiceInvoker.TryInvokeAsync<IRemoteSpanMappingService, RemoteExcerptResult?>(
+            document.Project.Solution,
+            (service, solutionInfo, cancellationToken) => service.TryExcerptAsync(solutionInfo, document.Id, span, mode, options, cancellationToken),
+            cancellationToken).ConfigureAwait(false);
+
+        if (result is null)
+        {
+            return null;
+        }
+
+        // Source text can't be sent back from OOP, so we have to do the translation here. Fortunately this doesn't need
+        // anything we can't access
+        var razorDocument = document.Project.GetAdditionalDocument(result.RazorDocumentId);
+        if (razorDocument is null)
+        {
+            return null;
+        }
+
+        var razorSourceText = await razorDocument.GetTextAsync(cancellationToken).ConfigureAwait(false);
+        var builder = result.ClassifiedSpans.ToBuilder();
+
+        var razorDocumentSpan = result.RazorDocumentSpan;
+        var excerptSpan = result.ExcerptSpan;
+        var excerptText = DocumentExcerptHelper.GetTranslatedExcerptText(razorSourceText, ref razorDocumentSpan, ref excerptSpan, builder);
+
+        return new RazorExcerptResult(excerptText, razorDocumentSpan, builder.ToImmutable(), document, span);
+    }
+}

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

@@ -22,4 +22,12 @@ ValueTask<ImmutableArray<RazorMappedSpanResult>> MapSpansAsync(
         DocumentId generatedDocumentId,
         ImmutableArray<TextSpan> spans,
         CancellationToken cancellationToken);
+
+    ValueTask<RemoteExcerptResult?> TryExcerptAsync(
+        RazorPinnedSolutionInfoWrapper solutionInfo,
+        DocumentId id,
+        TextSpan span,
+        RazorExcerptMode mode,
+        RazorClassificationOptionsWrapper options,
+        CancellationToken cancellationToken);
 }

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

@@ -0,0 +1,17 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Collections.Immutable;
+using System.Runtime.Serialization;
+using Microsoft.CodeAnalysis.Classification;
+using Microsoft.CodeAnalysis.Text;
+
+namespace Microsoft.CodeAnalysis.Razor.Remote;
+
+[DataContract]
+internal sealed record RemoteExcerptResult(
+    [property: DataMember(Order = 0)] DocumentId RazorDocumentId,
+    [property: DataMember(Order = 1)] TextSpan RazorDocumentSpan,
+    [property: DataMember(Order = 2)] TextSpan ExcerptSpan,
+    [property: DataMember(Order = 3)] ImmutableArray<ClassifiedSpan> ClassifiedSpans,
+    [property: DataMember(Order = 4)] TextSpan Span);

src/Razor/src/Microsoft.CodeAnalysis.Remote.Razor/WrapWithTag/RemoteSpanMappingService.cs renamed to src/Razor/src/Microsoft.CodeAnalysis.Remote.Razor/DocumentMapping/RemoteSpanMappingService.cs

@@ -7,8 +7,10 @@
 using System.Threading;
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.Razor;
+using Microsoft.AspNetCore.Razor.Language;
 using Microsoft.AspNetCore.Razor.PooledObjects;
 using Microsoft.CodeAnalysis.ExternalAccess.Razor;
+using Microsoft.CodeAnalysis.Razor.DocumentExcerpt;
 using Microsoft.CodeAnalysis.Razor.DocumentMapping;
 using Microsoft.CodeAnalysis.Razor.Protocol;
 using Microsoft.CodeAnalysis.Razor.Remote;
@@ -30,6 +32,54 @@ protected override IRemoteSpanMappingService CreateService(in ServiceArgs args)
     private readonly IDocumentMappingService _documentMappingService = args.ExportProvider.GetExportedValue<IDocumentMappingService>();
     private readonly ITelemetryReporter _telemetryReporter = args.ExportProvider.GetExportedValue<ITelemetryReporter>();
 
+    public ValueTask<RemoteExcerptResult?> TryExcerptAsync(RazorPinnedSolutionInfoWrapper solutionInfo, DocumentId generatedDocumentId, TextSpan span, RazorExcerptMode mode, RazorClassificationOptionsWrapper options, CancellationToken cancellationToken)
+        => RunServiceAsync(
+            solutionInfo,
+            solution => TryExcerptAsync(solution, generatedDocumentId, span, mode, options, cancellationToken),
+            cancellationToken);
+
+    private async ValueTask<RemoteExcerptResult?> TryExcerptAsync(Solution solution, DocumentId generatedDocumentId, TextSpan span, RazorExcerptMode mode, RazorClassificationOptionsWrapper options, CancellationToken cancellationToken)
+    {
+        var generatedDocument = await solution.GetSourceGeneratedDocumentAsync(generatedDocumentId, cancellationToken).ConfigureAwait(false);
+        if (generatedDocument is null)
+        {
+            return null;
+        }
+
+        var razorDocument = await TryGetRazorDocumentForGeneratedDocumentAsync(generatedDocument, cancellationToken).ConfigureAwait(false);
+        if (razorDocument is null)
+        {
+            return null;
+        }
+
+        var documentSnapshot = _snapshotManager.GetSnapshot(razorDocument);
+        var codeDocument = await documentSnapshot.GetGeneratedOutputAsync(cancellationToken).ConfigureAwait(false);
+
+        var mappedSpans = MapSpans(codeDocument, [span]);
+        if (mappedSpans is not [{ IsDefault: false } mappedSpan])
+        {
+            return null;
+        }
+
+        var razorDocumentText = await razorDocument.GetTextAsync(cancellationToken).ConfigureAwait(false);
+        var razorDocumentSpan = razorDocumentText.GetTextSpan(mappedSpan.LinePositionSpan);
+
+        // First compute the range of text we want to we to display relative to the primary document.
+        var excerptSpan = DocumentExcerptHelper.ChooseExcerptSpan(razorDocumentText, razorDocumentSpan, (ExcerptModeInternal)mode);
+
+        // Then we'll classify the spans based on the primary document, since that's the coordinate
+        // space that our output mappings use.
+        var mappings = codeDocument.GetRequiredCSharpDocument().SourceMappings;
+        var classifiedSpans = await DocumentExcerptHelper.ClassifyPreviewAsync(
+            excerptSpan,
+            generatedDocument,
+            mappings,
+            options,
+            cancellationToken).ConfigureAwait(false);
+
+        return new RemoteExcerptResult(razorDocument.Id, razorDocumentSpan, excerptSpan, classifiedSpans.ToImmutable(), span);
+    }
+
     public ValueTask<ImmutableArray<RazorMappedSpanResult>> MapSpansAsync(RazorPinnedSolutionInfoWrapper solutionInfo, DocumentId generatedDocumentId, ImmutableArray<TextSpan> spans, CancellationToken cancellationToken)
        => RunServiceAsync(
             solutionInfo,
@@ -45,12 +95,17 @@ private async ValueTask<ImmutableArray<RazorMappedSpanResult>> MapSpansAsync(Sol
         }
 
         var documentSnapshot = _snapshotManager.GetSnapshot(razorDocument);
-        var output = await documentSnapshot.GetGeneratedOutputAsync(cancellationToken).ConfigureAwait(false);
+        var codeDocument = await documentSnapshot.GetGeneratedOutputAsync(cancellationToken).ConfigureAwait(false);
+
+        return MapSpans(codeDocument, spans);
+    }
 
-        var source = output.Source.Text;
+    private static ImmutableArray<RazorMappedSpanResult> MapSpans(RazorCodeDocument codeDocument, ImmutableArray<TextSpan> spans)
+    {
+        var source = codeDocument.Source.Text;
 
-        var csharpDocument = output.GetRequiredCSharpDocument();
-        var filePath = output.Source.FilePath.AssumeNotNull();
+        var csharpDocument = codeDocument.GetRequiredCSharpDocument();
+        var filePath = codeDocument.Source.FilePath.AssumeNotNull();
 
         using var results = new PooledArrayBuilder<RazorMappedSpanResult>();
 
@@ -118,6 +173,11 @@ private async ValueTask<ImmutableArray<RazorMappedEditResult>> MapTextChangesAsy
             return null;
         }
 
+        return await TryGetRazorDocumentForGeneratedDocumentAsync(generatedDocument, cancellationToken).ConfigureAwait(false);
+    }
+
+    private async Task<TextDocument?> TryGetRazorDocumentForGeneratedDocumentAsync(SourceGeneratedDocument generatedDocument, CancellationToken cancellationToken)
+    {
         var identity = RazorGeneratedDocumentIdentity.Create(generatedDocument);
         if (!identity.IsRazorSourceGeneratedDocument())
         {