optimise updating document content in workspace

src/SharpIDE.Application/Features/Analysis/RoslynAnalysis.cs

@@ -603,10 +603,12 @@ public static class RoslynAnalysis
 	public static async Task<(ISymbol?, LinePositionSpan?)> LookupSymbol(SharpIdeFile fileModel, LinePosition linePosition)
 	{
 		await _solutionLoadedTcs.Task;
-		var (symbol, linePositionSpan) =
-			fileModel.IsRazorFile ? await LookupSymbolInRazor(fileModel, linePosition)
-			: fileModel.IsCsharpFile ? await LookupSymbolInCs(fileModel, linePosition)
-			: (null, null);
+		var (symbol, linePositionSpan) = fileModel switch
+		{
+			{ IsRazorFile: true } => await LookupSymbolInRazor(fileModel, linePosition),
+			{ IsCsharpFile: true } => await LookupSymbolInCs(fileModel, linePosition),
+			_ => (null, null)
+		};
 		return (symbol, linePositionSpan);
 	}
 
@@ -680,24 +682,37 @@ public static class RoslynAnalysis
 		return null;
 	}
 
-	public static void UpdateDocument(SharpIdeFile fileModel, string newContent)
+	public static async Task UpdateDocument(SharpIdeFile fileModel, string newContent)
 	{
 		Guard.Against.Null(fileModel, nameof(fileModel));
 		Guard.Against.NullOrEmpty(newContent, nameof(newContent));
 
 		var project = _workspace!.CurrentSolution.Projects.Single(s => s.FilePath == ((IChildSharpIdeNode)fileModel).GetNearestProjectNode()!.FilePath);
-		if (fileModel.IsRazorFile)
+
+		var sourceText = SourceText.From(newContent);
+		var document = fileModel switch
 		{
-			var razorDocument = project.AdditionalDocuments.Single(s => s.FilePath == fileModel.Path);
-			var newSolution = _workspace.CurrentSolution.WithAdditionalDocumentText(razorDocument.Id, SourceText.From(newContent));
-			_workspace.TryApplyChanges(newSolution);
-		}
-		else
+			{ IsRazorFile: true } => project.AdditionalDocuments.Single(s => s.FilePath == fileModel.Path),
+			{ IsCsharpFile: true } => project.Documents.Single(s => s.FilePath == fileModel.Path),
+			_ => throw new InvalidOperationException("UpdateDocument failed: File is not in workspace")
+		};
+
+		var oldText = await document.GetTextAsync();
+
+		// Compute minimal text changes
+		var changes = sourceText.GetChangeRanges(oldText);
+		if (changes.Count == 0)
+			return; // No changes, nothing to apply
+
+		var newText = oldText.WithChanges(sourceText.GetTextChanges(oldText));
+
+		var newSolution = fileModel switch
 		{
-			var document = project.Documents.Single(s => s.FilePath == fileModel.Path);
-			Guard.Against.Null(document, nameof(document));
-			var newSolution = _workspace.CurrentSolution.WithDocumentText(document.Id, SourceText.From(newContent));
-			_workspace.TryApplyChanges(newSolution);
-		}
+			{ IsRazorFile: true } => _workspace.CurrentSolution.WithAdditionalDocumentText(document.Id, newText),
+			{ IsCsharpFile: true } => _workspace.CurrentSolution.WithDocumentText(document.Id, newText),
+			_ => throw new ArgumentOutOfRangeException()
+		};
+
+		_workspace.TryApplyChanges(newSolution);
 	}
 }

src/SharpIDE.Application/Features/FilePersistence/IdeFileManager.cs

@@ -24,7 +24,7 @@ public class IdeFileManager
 	}
 
 	// Calling this assumes that the file is already open - may need to be revisited for code fixes and refactorings. I think all files involved in a multi-file fix/refactor shall just be saved to disk immediately.
-	public void UpdateFileTextInMemory(SharpIdeFile file, string newText)
+	public async Task UpdateFileTextInMemory(SharpIdeFile file, string newText)
 	{
 		if (!_openFiles.ContainsKey(file)) throw new InvalidOperationException("File is not open in memory.");
 
@@ -33,7 +33,7 @@ public class IdeFileManager
 		// Potentially should be event based?
 		if (file.IsRoslynWorkspaceFile)
 		{
-			RoslynAnalysis.UpdateDocument(file, newText);
+			await RoslynAnalysis.UpdateDocument(file, newText);
 		}
 	}
 
@@ -47,7 +47,7 @@ public class IdeFileManager
 		if (file.IsRoslynWorkspaceFile)
 		{
 			var text = await textTask;
-			RoslynAnalysis.UpdateDocument(file, text);
+			await RoslynAnalysis.UpdateDocument(file, text);
 		}
 	}
 
@@ -65,7 +65,7 @@ public class IdeFileManager
 	{
 		if (_openFiles.ContainsKey(file))
 		{
-			UpdateFileTextInMemory(file, newText);
+			await UpdateFileTextInMemory(file, newText);
 			await SaveFileAsync(file);
 		}
 		else