C# 从Roslyn完成API获取函数参数

我试图使用完成API来构建自动完成功能。结果是正确的，但我无法获得方法签名。 例如：如果我键入“string.”，API将返回所有方法，如“Format”，“Compare”，但在“string.Format”（之后，它不会返回所有可能的方法签名，如Format（string，Object），Format（string，Object[]）等。有人能帮我实现这一目标吗

var expression = "String.";
var code = String.Format(CultureInfo.InvariantCulture,
                           @"
                               Imports System

                               Sub Main(args As String[])
                                     Dim typeUnderInvestigation As String = {0}
                                End sub
                             ", expression);

var projectInfo = ProjectInfo.Create(ProjectId.CreateNewId(), VersionStamp.Create(), "MyProject", "MyProject", LanguageNames.VisualBasic)
                             .WithMetadataReferences(new[] 
                             {
                                  MetadataReference.CreateFromFile(typeof(object).Assembly.Location)
                             });

var project = workspace.AddProject(projectInfo);
var document = workspace.AddDocument(project.Id, "MyFile.cs", SourceText.From(code));

// position is the last occurrence of "Guid." in our test code
// in real life scenarios the editor surface should inform us
// about the current cursor position
var position = code.LastIndexOf(expression, StringComparison.InvariantCulture) + expression.Length;

var completionService = CompletionService.GetService(document);
var results = await completionService.GetCompletionsAsync(document, position);