How to debug when the CompletionService.GetService return null

[WeihanLi]

Hello experts, I'm trying to implement auto-completion with CompletionService.GetService(document).GetCompletionsAsync(), while the CompletionService.GetService(document) seemed always return null, while in a minimal sample, it would not be null, is there some guide to debug?

The code used for completion is here:
https://github.com/WeihanLi/dotnet-exec/blob/c148f7c0bad9b36efd3b49ff04a4cd31652d7949/src/dotnet-exec/Services/Repl.cs#L134

or

https://github.com/WeihanLi/dotnet-exec/blob/f679d834d8a8f136fdbd1a2822a24f625e4db2ab/src/dotnet-exec/Services/ScriptCompletionService.cs#L24

Thanks very much

[333fred]

You're not populating the MEF cache at all: https://github.com/WeihanLi/dotnet-exec/blob/c148f7c0bad9b36efd3b49ff04a4cd31652d7949/src/dotnet-exec/Services/Repl.cs#L140. Both the examples you linked right above used a different manner of creating the MEF catalog.

[WeihanLi]

does the creating the MEF catalog you mention mean

var host = MefHostServices.Create(MefHostServices.DefaultAssemblies);
var workspace = new AdhocWorkspace(host);

?

I tried this way also but either not working

[333fred]

I guess I'd start stepping through the code. Make sure that the mef host actually has all the c# assemblies in it. Maybe @sharwell has a better idea.

[WeihanLi]

think it may be a dependency issue, I could run this test case pass in linqpad, while the test case failed in the project

https://github.com/WeihanLi/dotnet-exec/blob/f679d834d8a8f136fdbd1a2822a24f625e4db2ab/tests/UnitTest/ScriptCompletionServiceTest.cs#L35

full linqpad script

<Query Kind="Statements">
  <NuGetReference>Microsoft.CodeAnalysis.CSharp.Features</NuGetReference>
  <NuGetReference>ReferenceResolver</NuGetReference>
  <NuGetReference>WeihanLi.Common</NuGetReference>
  <Namespace>WeihanLi.Common</Namespace>
  <Namespace>WeihanLi.Common.Helpers</Namespace>
  <Namespace>WeihanLi.Common.Http</Namespace>
  <Namespace>WeihanLi.Extensions</Namespace>
  <Namespace>ReferenceResolver</Namespace>
  <Namespace>System.Threading.Tasks</Namespace>
</Query>

using System;
using Microsoft.CodeAnalysis;
using Microsoft.CodeAnalysis.Completion;
using Microsoft.CodeAnalysis.CSharp;
using Microsoft.CodeAnalysis.Host.Mef;
using Microsoft.CodeAnalysis.Text;

var usings = FrameworkReferenceResolver.GetImplicitUsings(FrameworkReferenceResolver.FrameworkNames.Default);
var defaultReferences = await FrameworkReferenceResolver.ResolveDefaultReferences("net8.0");
var metadataReferences = defaultReferences.Select(r => 
{
	try
	{	        
		_ = AssemblyName.GetAssemblyName(r);
		return MetadataReference.CreateFromFile(r);
	}
	catch
	{
		return null;
	}
}).WhereNotNull().ToArray();
using var workspace = new AdhocWorkspace(MefHostServices.DefaultHost);
var compilationOptions = new CSharpCompilationOptions(OutputKind.DynamicallyLinkedLibrary, nullableContextOptions: NullableContextOptions.Annotations)
	.WithUsings(usings.Select(u => u.TrimStart("global::")))
	;

var projectInfo = ProjectInfo.Create(
	ProjectId.CreateNewId(),
	VersionStamp.Create(),
	"dotnet-exec-repl",
	"dotnet-exec-repl",
	LanguageNames.CSharp,
	isSubmission: true)
	.WithMetadataReferences(
	   metadataReferences
	)
	.WithCompilationOptions(compilationOptions)
	;
var project = workspace.AddProject(projectInfo);

var code = "Guid.";

var documentInfo = DocumentInfo.Create(
	DocumentId.CreateNewId(project.Id), "__Script.cs",
	sourceCodeKind: SourceCodeKind.Script,
	loader: new PlainTextLoader(code));
var document = workspace.AddDocument(documentInfo);

var completionService = CompletionService.GetService(document);
if (completionService is null)
{
	Console.WriteLine("CompletionService is null");
	return;
}

var completions = await completionService.GetCompletionsAsync(document, code.Length);
if (completions.ItemsList.Count is 0)
{
	Console.WriteLine("Completion ItemsList is empty");
	return;
}

Console.WriteLine("Completion list:");
foreach (var completion in completions.ItemsList)
{
	Console.WriteLine(completion.DisplayText);
}

public sealed class PlainTextLoader(string text) : TextLoader
{
	private readonly TextAndVersion _textAndVersion = TextAndVersion.Create(SourceText.From(text), VersionStamp.Default);

	public override Task<TextAndVersion> LoadTextAndVersionAsync(LoadTextOptions options, CancellationToken cancellationToken)
	{
		return Task.FromResult(_textAndVersion);
	}
}

[WeihanLi]

It turned out that the dependencies were not correct, Microsoft.CodeAnalysis.Features was used in the project while in the sample it used Microsoft.CodeAnalysis.CSharp.Features,

it works when update the Microsoft.CodeAnalysis.Features reference to Microsoft.CodeAnalysis.CSharp.Features