NullReferenceException at GetCompletionsAsync on Roslyn

Question

I try to get code completion, but when I try to get completions async by CompletionService I get NullReferenceException.

Here is a piece of code:

public async Task<IList<ICompletionData>> GetCompletionData(String code, int offset)
    {
        IList<ICompletionData> completionData = null;

        if (_workspace != null)
        {
            _workspace.Dispose();
        }
        _workspace = new AdhocWorkspace();
        _project = _workspace.AddProject("Test", LanguageNames.CSharp);



        var sourceText = SourceText.From(code);
        var document = _workspace.AddDocument(_project.Id, "Compilation0", sourceText); 
        var completionService = CompletionService.GetService(document);
        var charCompletion = GetCompletionTrigger('.');
        var data = await completionService.GetCompletionsAsync(_document, offset,charCompletion,).ConfigureAwait(false);

        if (data == null || data.Items.Any() == false)
            return new List<ICompletionData>();

        completionData = data.Items.Select(item => new RoslynCodeCompletion(_document, item)).ToList<ICompletionData>();

        return completionData;
    }

Error at line:

var data = await completionService.GetCompletionsAsync(_document, offset,charCompletion,).ConfigureAwait(false);//NullReferenseException.

Script code codepletion triggers by '.' (dot) symbol:

var str="";
str. // here calls `GetCompletionData`

Full code snippet is on pastebin

Answer 1

This became a lot easier after Roslyn PR #14921 was merged. Before you had to a lot of manual MEF configuration, but now it should be enough to have the following nuget packages installed:

• Microsoft.CodeAnalysis
• Microsoft.CodeAnalysis.CSharp
• Microsoft.CodeAnalysis.Features
• Microsoft.CodeAnalysis.CSharp.Features

And Roslyn will do the required configuration.