add ICompletionExtension2 accepting CompletionList as parameter (microsoft#1258)

* add ICompletionExtension2 accepting CompletionList as parameter

* refactoring using switch pattern matching

Author: felixhao28

src/LanguageServer/Impl/Extensibility/ICompletionExtension.cs

@@ -18,9 +18,15 @@
 using Microsoft.Python.Analysis;
 using Microsoft.Python.Core.Text;
 using Microsoft.Python.LanguageServer.Completion;
+using Microsoft.Python.LanguageServer.Protocol;
 
 namespace Microsoft.Python.LanguageServer.Extensibility {
     public interface ICompletionExtension {
         Task HandleCompletionAsync(IDocumentAnalysis analysis, SourceLocation location, CompletionItemEx[] completions, CancellationToken token);
+
+    }
+
+    public interface ICompletionExtension2 {
+        Task HandleCompletionAsync(IDocumentAnalysis analysis, SourceLocation location, CompletionList completions, CancellationToken token);
     }
 }

src/LanguageServer/Impl/Implementation/Server.Editor.cs

@@ -42,8 +42,20 @@ public async Task<CompletionList> Completion(CompletionParams @params, Cancellat
                 var result = _completionSource.GetCompletions(analysis, @params.position);
                 res.items = result?.Completions?.ToArray() ?? Array.Empty<CompletionItem>();
 
-                await InvokeExtensionsAsync((ext, token)
-                    => (ext as ICompletionExtension)?.HandleCompletionAsync(analysis, @params.position, res.items.OfType<CompletionItemEx>().ToArray(), cancellationToken), cancellationToken);
+                await InvokeExtensionsAsync(async (ext, token)
+                    => {
+                        switch (ext) {
+                            case ICompletionExtension2 e:
+                                await e.HandleCompletionAsync(analysis, @params.position, res, cancellationToken);
+                                break;
+                            case ICompletionExtension e:
+                                await e.HandleCompletionAsync(analysis, @params.position, res.items.OfType<CompletionItemEx>().ToArray(), cancellationToken);
+                                break;
+                            default:
+                                // ext is not a completion extension, ignore it.
+                                break;
+                        }
+                    }, cancellationToken);
             }
 
             return res;