Some progress.

shared/src/contract.ts

@@ -1,4 +1,10 @@
-import { contract, notificationContract, types } from "@hediet/typed-json-rpc";
+import {
+	contract,
+	notificationContract,
+	types,
+	requestContract,
+	JSONObject,
+} from "@hediet/typed-json-rpc";
 import {
 	DataExtractionResult,
 	DataExtractorId,
@@ -22,6 +28,57 @@ export type DataExtractionState =
 			result: DataExtractionResult;
 	  };
 
+// https://microsoft.github.io/debug-adapter-protocol/specification#CompletionItem
+type CompletionItemType =
+	| "method"
+	| "function"
+	| "constructor"
+	| "field"
+	| "variable"
+	| "class"
+	| "interface"
+	| "module"
+	| "property"
+	| "unit"
+	| "value"
+	| "enum"
+	| "keyword"
+	| "snippet"
+	| "text"
+	| "color"
+	| "file"
+	| "reference"
+	| "customcolor";
+
+export interface CompletionItem {
+	/**
+	 * The label of this completion item. By default this is also the text that is inserted when selecting this completion.
+	 */
+	label: string;
+
+	/**
+	 * If text is not falsy then it is inserted instead of the label.
+	 */
+	text?: string;
+
+	/**
+	 * The item's type. Typically the client uses this information to render the item in the UI with an icon.
+	 */
+	type?: CompletionItemType;
+
+	/**
+	 * This value determines the location (in the CompletionsRequest's 'text' attribute) where the completion text is added.
+	 * If missing the text is added at the location specified by the CompletionsRequest's 'column' attribute.
+	 */
+	start?: number;
+
+	/**
+	 * This value determines how many characters are overwritten by the completion text.
+	 * If missing the value 0 is assumed which results in the completion text being inserted.
+	 */
+	length?: number;
+}
+
 export const debugVisualizerUIContract = contract({
 	client: {
 		updateState: notificationContract({
@@ -43,5 +100,15 @@ export const debugVisualizerUIContract = contract({
 		}),
 		refresh: notificationContract({}),
 		openInBrowser: notificationContract({}),
+
+		getCompletions: requestContract({
+			params: types.type({
+				text: types.string,
+				column: types.number,
+			}),
+			result: types.type({
+				completions: types.array(unchecked<CompletionItem>()),
+			}),
+		}),
 	},
 });