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Calculate minimal diffs before updating Html buffer #12256

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Merged
davidwengier merged 1 commit into from
Sep 23, 2025
Merged

Calculate minimal diffs before updating Html buffer #12256

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15 changes: 12 additions & 3 deletions ...rosoft.VisualStudio.LanguageServices.Razor/LanguageClient/Cohost/HtmlDocumentPublisher.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -2,6 +2,7 @@
// The .NET Foundation licenses this file to you under the MIT license.

using System;
using System.Collections.Immutable;
using System.ComponentModel.Composition;
using System.Diagnostics;
using System.Threading;
Expand All @@ -10,6 +11,8 @@
using Microsoft.CodeAnalysis;
using Microsoft.CodeAnalysis.ExternalAccess.Razor;
using Microsoft.CodeAnalysis.Razor.Logging;
using Microsoft.CodeAnalysis.Razor.TextDifferencing;
using Microsoft.CodeAnalysis.Text;
using Microsoft.VisualStudio.LanguageServer.ContainedLanguage;
using Microsoft.VisualStudio.Threading;

Expand Down Expand Up @@ -44,7 +47,7 @@ public async Task PublishAsync(TextDocument document, SynchronizationResult sync
return;
}

_logger.LogDebug($"The html document for {document.FilePath} is {uri}");
_logger.LogDebug($"The html document for {document.FilePath} is {htmlDocument.Uri}");

await _joinableTaskContext.Factory.SwitchToMainThreadAsync(cancellationToken);

Expand All @@ -53,9 +56,15 @@ public async Task PublishAsync(TextDocument document, SynchronizationResult sync
return;
}

VisualStudioTextChange[] changes = [new(0, htmlDocument.Snapshot.Length, htmlText)];
// We have a string for the Html text here, so its tempting to just overwrite the whole buffer, but that causes issues with
// the editors span tracking, which is used by the Html server to map diagnostic ranges. Updating with minimal changes helps
// the editor understand what is actually happening to the virtual buffer.
var currentHtmlSourceText = htmlDocument.Snapshot.AsText();
var newHtmlSourceText = SourceText.From(htmlText, currentHtmlSourceText.Encoding, currentHtmlSourceText.ChecksumAlgorithm);
var textChanges = SourceTextDiffer.GetMinimalTextChanges(currentHtmlSourceText, newHtmlSourceText);
var changes = textChanges.SelectAsArray(c => new VisualStudioTextChange(c.Span.Start, c.Span.Length, c.NewText.AssumeNotNull()));
_documentManager.UpdateVirtualDocument<HtmlVirtualDocument>(uri, changes, documentSnapshot.Version, state: synchronizationResult.Checksum);

_logger.LogDebug($"Finished Html document generation for {document.FilePath} (into {uri})");
_logger.LogDebug($"Finished Html document generation for {document.FilePath} (into {htmlDocument.Uri})");
}
}