Some progress.

extension/src/DataSource/DataSource.ts

@@ -1,5 +1,8 @@
 import { DataExtractorId } from "@hediet/debug-visualizer-data-extraction";
-import { DataExtractionState } from "@hediet/debug-visualizer-vscode-shared";
+import {
+	DataExtractionState,
+	CompletionItem,
+} from "@hediet/debug-visualizer-vscode-shared";
 
 export interface EvaluationWatcherOptions {
 	preferredDataExtractor?: DataExtractorId | undefined;
@@ -10,6 +13,7 @@ export interface DataSource {
 		expression: string,
 		options: EvaluationWatcherOptions
 	): EvaluationWatcher;
+	getCompletions(text: string, column: number): Promise<CompletionItem[]>;
 }
 
 export interface EvaluationWatcher {