diff --git a/client/src/common/completion.ts b/client/src/common/completion.ts
index 79ffb7de9..d455571bd 100644
--- a/client/src/common/completion.ts
+++ b/client/src/common/completion.ts
@@ -91,7 +91,7 @@ export class CompletionItemFeature extends TextDocumentLanguageFeature<Completio
 		completion.completionItemKind = { valueSet: SupportedCompletionItemKinds };
 		completion.completionList = {
 			itemDefaults: [
-				'commitCharacters', 'editRange', 'insertTextFormat', 'insertTextMode'
+				'commitCharacters', 'editRange', 'insertTextFormat', 'insertTextMode', 'data'
 			]
 		};
 	}
diff --git a/testbed/server/src/server.ts b/testbed/server/src/server.ts
index d99db1531..385e35ef5 100644
--- a/testbed/server/src/server.ts
+++ b/testbed/server/src/server.ts
@@ -17,7 +17,7 @@ import {
 	TextEdit, ProposedFeatures, DiagnosticTag, InsertTextFormat, SelectionRangeRequest, SelectionRange, InsertReplaceEdit,
 	SemanticTokensClientCapabilities, SemanticTokensLegend, SemanticTokensBuilder, SemanticTokensRegistrationType,
 	SemanticTokensRegistrationOptions, ProtocolNotificationType, ChangeAnnotation, WorkspaceChange, CompletionItemKind, DiagnosticSeverity,
-	DocumentDiagnosticReportKind, WorkspaceDiagnosticReport, NotebookDocuments
+	DocumentDiagnosticReportKind, WorkspaceDiagnosticReport, NotebookDocuments, CompletionList, DocumentLinkResolveRequest
 } from 'vscode-languageserver/node';
 
 import {
@@ -126,7 +126,7 @@ connection.onInitialize((params, cancel, progress): Thenable<InitializeResult> |
 				completionProvider: {
 					triggerCharacters: ['.'],
 					allCommitCharacters: [';'],
-					resolveProvider: false,
+					resolveProvider: true,
 				},
 				signatureHelpProvider: {
 				},
@@ -372,7 +372,7 @@ connection.languages.diagnostics.onWorkspace(async (params, token, _, resultProg
 	return { items: [] };
 });
 
-connection.onCompletion((params, token): CompletionItem[] => {
+connection.onCompletion((params, token): CompletionList => {
 	const result: CompletionItem[] = [];
 	let item = CompletionItem.create('foo');
 	result.push(item);
@@ -407,7 +407,9 @@ connection.onCompletion((params, token): CompletionItem[] => {
 	item.kind = CompletionItemKind.Field;
 	result.push(item);
 
-	return result;
+	const list = CompletionList.create(result, true);
+	list.itemDefaults = { data: 'abc' };
+	return list;
 });
 
 connection.onCompletionResolve((item): CompletionItem => {