Don't allow virtual documents to go back in time

src/Razor/src/Microsoft.AspNetCore.Razor.LanguageServer/GeneratedDocumentPublisher.cs

@@ -72,14 +72,22 @@ public void PublishCSharp(ProjectKey projectKey, string filePath, SourceText sou
                 previouslyPublishedData = PublishData.Default;
             }
 
+            if (previouslyPublishedData.HostDocumentVersion > hostDocumentVersion)
+            {
+                // We've already published a newer version of this document. No-op.
+                Debug.Fail("C# document being published that is older than one we've previously published!");
+                _logger.LogWarning($"Skipping publish of C# for {filePath} because we've already published version {previouslyPublishedData.HostDocumentVersion}, and this request is for {hostDocumentVersion}.");
+                return;
+            }
+
             textChanges = SourceTextDiffer.GetMinimalTextChanges(previouslyPublishedData.SourceText, sourceText);
             if (textChanges.Count == 0 && hostDocumentVersion == previouslyPublishedData.HostDocumentVersion)
             {
                 // Source texts match along with host document versions. We've already published something that looks like this. No-op.
                 return;
             }
 
-            _logger.LogTrace(
+            _logger.LogDebug(
                 $"Updating C# buffer of {filePath} for project {documentKey.ProjectKey} to correspond with host document " +
                 $"version {hostDocumentVersion}. {previouslyPublishedData.SourceText.Length} -> {sourceText.Length} = Change delta of " +
                 $"{sourceText.Length - previouslyPublishedData.SourceText.Length} via {textChanges.Count} text changes.");
@@ -111,14 +119,22 @@ public void PublishHtml(ProjectKey projectKey, string filePath, SourceText sourc
                 previouslyPublishedData = PublishData.Default;
             }
 
+            if (previouslyPublishedData.HostDocumentVersion > hostDocumentVersion)
+            {
+                // We've already published a newer version of this document. No-op.
+                Debug.Fail("Html document being published that is older than one we've previously published!");
+                _logger.LogWarning($"Skipping publish of Html for {filePath} because we've already published version {previouslyPublishedData.HostDocumentVersion}, and this request is for {hostDocumentVersion}.");
+                return;
+            }
+
             textChanges = SourceTextDiffer.GetMinimalTextChanges(previouslyPublishedData.SourceText, sourceText);
             if (textChanges.Count == 0 && hostDocumentVersion == previouslyPublishedData.HostDocumentVersion)
             {
                 // Source texts match along with host document versions. We've already published something that looks like this. No-op.
                 return;
             }
 
-            _logger.LogTrace(
+            _logger.LogDebug(
                 $"Updating HTML buffer of {filePath} to correspond with host document version {hostDocumentVersion}. {previouslyPublishedData.SourceText.Length} -> {sourceText.Length} = Change delta of {sourceText.Length - previouslyPublishedData.SourceText.Length} via {textChanges.Count} text changes.");
 
             _publishedHtmlData[filePath] = new PublishData(sourceText, hostDocumentVersion);

src/Razor/src/Microsoft.VisualStudio.LanguageServices.Razor/LanguageClient/Endpoints/RazorCustomMessageTarget.cs

@@ -146,6 +146,8 @@ private async Task<SynchronizedResult<TVirtualDocumentSnapshot>> TrySynchronizeV
             return await TempForCohost_TrySynchronizeVirtualDocumentAsync<TVirtualDocumentSnapshot>(hostDocument, cancellationToken);
         }
 
+        _logger.LogDebug($"Trying to synchronize for {caller} to version {requiredHostDocumentVersion} of {hostDocument.Uri} for {hostDocument.GetProjectContext()?.Id ?? "(no project context)"}");
+
         // For Html documents we don't do anything fancy, just call the standard service
         // If we're not generating unique document file names, then we can treat C# documents the same way
         if (!_languageServerFeatureOptions.IncludeProjectKeyInGeneratedFilePath ||
@@ -154,8 +156,6 @@ private async Task<SynchronizedResult<TVirtualDocumentSnapshot>> TrySynchronizeV
             return await _documentSynchronizer.TrySynchronizeVirtualDocumentAsync<TVirtualDocumentSnapshot>(requiredHostDocumentVersion, hostDocument.Uri, cancellationToken).ConfigureAwait(false);
         }
 
-        _logger.LogDebug($"Trying to synchronize for {caller} to version {requiredHostDocumentVersion} of {hostDocument.Uri} for {hostDocument.GetProjectContext()?.Id ?? "(no project context)"}");
-
         var virtualDocument = FindVirtualDocument<TVirtualDocumentSnapshot>(hostDocument.Uri, hostDocument.GetProjectContext());
 
         if (virtualDocument is { ProjectKey.IsUnknown: true })

src/Razor/src/Microsoft.VisualStudio.LanguageServices.Razor/LanguageClient/Endpoints/RazorCustomMessageTarget_UpdateHtmlBuffer.cs

@@ -5,6 +5,7 @@
 using System.Linq;
 using System.Threading;
 using System.Threading.Tasks;
+using Microsoft.CodeAnalysis.Razor.Logging;
 using Microsoft.CodeAnalysis.Razor.Protocol;
 using StreamJsonRpc;
 
@@ -35,6 +36,9 @@ internal void UpdateHtmlBuffer(UpdateBufferRequest request)
         }
 
         var hostDocumentUri = new Uri(request.HostDocumentFilePath);
+
+        _logger.LogDebug($"UpdateHtmlBuffer for {request.HostDocumentVersion} of {hostDocumentUri} in {request.ProjectKeyId}");
+
         _documentManager.UpdateVirtualDocument<HtmlVirtualDocument>(
             hostDocumentUri,
             request.Changes.Select(change => change.ToVisualStudioTextChange()).ToArray(),