better code completion apply

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

@@ -0,0 +1,17 @@
+using Microsoft.CodeAnalysis.Completion;
+using SharpIDE.Application.Features.FileWatching;
+using SharpIDE.Application.Features.SolutionDiscovery;
+
+namespace SharpIDE.Application.Features.Analysis;
+
+public class IdeCompletionService(RoslynAnalysis roslynAnalysis, FileChangedService fileChangedService)
+{
+	private readonly RoslynAnalysis _roslynAnalysis = roslynAnalysis;
+	private readonly FileChangedService _fileChangedService = fileChangedService;
+
+	public async Task ApplyCompletion(SharpIdeFile file, CompletionItem completionItem)
+	{
+		var (updatedDocumentText, newLinePosition) = await _roslynAnalysis.GetCompletionApplyChanges(file, completionItem);
+		await _fileChangedService.SharpIdeFileChanged(file, updatedDocumentText, FileChangeType.CompletionChange, newLinePosition);
+	}
+}

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

@@ -575,6 +575,37 @@ public class RoslynAnalysis
 		return completions;
 	}
 
+	public async Task<(string updatedText, SharpIdeFileLinePosition sharpIdeFileLinePosition)> GetCompletionApplyChanges(SharpIdeFile file, CompletionItem completionItem, CancellationToken cancellationToken = default)
+	{
+		var documentId = _workspace!.CurrentSolution.GetDocumentIdsWithFilePath(file.Path).Single();
+		var document = _workspace.CurrentSolution.GetRequiredDocument(documentId);
+		var completionService = CompletionService.GetService(document) ?? throw new InvalidOperationException("Completion service is not available for the document.");
+
+		var completionChange = await completionService.GetChangeAsync(document, completionItem, commitCharacter: '.', cancellationToken: cancellationToken);
+		var sourceText = await document.GetTextAsync(cancellationToken);
+		var newText = sourceText.WithChanges(completionChange.TextChange);
+		var newCaretPosition = completionChange.NewPosition ?? NewCaretPosition();
+		var linePosition = newText.Lines.GetLinePosition(newCaretPosition);
+		var sharpIdeFileLinePosition = new SharpIdeFileLinePosition
+		{
+			Line = linePosition.Line,
+			Column = linePosition.Character
+		};
+
+		return (newText.ToString(), sharpIdeFileLinePosition);
+
+		int NewCaretPosition()
+		{
+			var caretPosition = completionChange.TextChange.Span.Start + completionChange.TextChange.NewText!.Length;
+			// if change ends with (), place caret between the parentheses
+			if (completionChange.TextChange.NewText!.EndsWith("()"))
+			{
+				caretPosition -= 1;
+			}
+			return caretPosition;
+		}
+	}
+
 	/// Returns the list of files that would be modified by applying the code action. Does not apply the changes to the workspace sln
 	public async Task<List<(SharpIdeFile File, string UpdatedText)>> GetCodeActionApplyChanges(CodeAction codeAction)
 	{

src/SharpIDE.Application/Features/FileWatching/FileChangedService.cs

@@ -13,7 +13,8 @@ public enum FileChangeType
 	IdeSaveToDisk, // Apply to disk
 	IdeUnsavedChange, // Apply only in memory
 	ExternalChange, // Apply to disk, as well as in memory
-	CodeActionChange // Apply to disk, as well as in memory
+	CodeActionChange, // Apply to disk, as well as in memory
+	CompletionChange // Apply only in memory, as well as notify tabs of new content
 }
 
 public class FileChangedService(RoslynAnalysis roslynAnalysis, IdeOpenTabsFileManager openTabsFileManager)
@@ -59,7 +60,7 @@ public class FileChangedService(RoslynAnalysis roslynAnalysis, IdeOpenTabsFileMa
 	}
 
 	// All file changes should go via this service
-	public async Task SharpIdeFileChanged(SharpIdeFile file, string newContents, FileChangeType changeType)
+	public async Task SharpIdeFileChanged(SharpIdeFile file, string newContents, FileChangeType changeType, SharpIdeFileLinePosition? linePosition = null)
 	{
 		if (changeType is FileChangeType.ExternalChange)
 		{
@@ -67,13 +68,19 @@ public class FileChangedService(RoslynAnalysis roslynAnalysis, IdeOpenTabsFileMa
 			// Update any open tabs
 			// update in memory
 			await _openTabsFileManager.UpdateFileTextInMemory(file, newContents);
-			file.FileContentsChangedExternally.InvokeParallelFireAndForget();
+			file.FileContentsChangedExternally.InvokeParallelFireAndForget(linePosition);
 		}
 		else if (changeType is FileChangeType.CodeActionChange)
 		{
 			// update in memory, tabs and save to disk
 			await _openTabsFileManager.UpdateInMemoryIfOpenAndSaveAsync(file, newContents);
-			file.FileContentsChangedExternally.InvokeParallelFireAndForget();
+			file.FileContentsChangedExternally.InvokeParallelFireAndForget(linePosition);
+		}
+		else if (changeType is FileChangeType.CompletionChange)
+		{
+			// update in memory, tabs
+			await _openTabsFileManager.UpdateFileTextInMemory(file, newContents);
+			file.FileContentsChangedExternally.InvokeParallelFireAndForget(linePosition);
 		}
 		else if (changeType is FileChangeType.IdeSaveToDisk)
 		{

src/SharpIDE.Application/Features/SolutionDiscovery/SharpIdeFile.cs

@@ -1,6 +1,7 @@
 using System.Collections.Concurrent;
 using System.Diagnostics.CodeAnalysis;
 using R3;
+using SharpIDE.Application.Features.Analysis;
 using SharpIDE.Application.Features.Events;
 using SharpIDE.Application.Features.SolutionDiscovery.VsPersistence;
 
@@ -19,7 +20,7 @@ public class SharpIdeFile : ISharpIdeNode, IChildSharpIdeNode, IFileOrFolder
 	public required ReactiveProperty<bool> IsDirty { get; init; }
 	public required bool SuppressDiskChangeEvents { get; set; } // probably has concurrency issues
 	public required DateTimeOffset? LastIdeWriteTime { get; set; }
-	public EventWrapper<Task> FileContentsChangedExternally { get; } = new(() => Task.CompletedTask);
+	public EventWrapper<SharpIdeFileLinePosition?, Task> FileContentsChangedExternally { get; } = new((_) => Task.CompletedTask);
 
 	[SetsRequiredMembers]
 	internal SharpIdeFile(string fullPath, string name, IExpandableSharpIdeNode parent, ConcurrentBag<SharpIdeFile> allFiles)