eng: add a basic 'must use result' and ensure assertSnapshot result is used

.eslintplugin/code-must-use-result.ts

@@ -0,0 +1,35 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the MIT License. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+import * as eslint from 'eslint';
+import { TSESTree } from '@typescript-eslint/experimental-utils';
+
+const VALID_USES = new Set<TSESTree.AST_NODE_TYPES | undefined>([
+	TSESTree.AST_NODE_TYPES.AwaitExpression,
+	TSESTree.AST_NODE_TYPES.VariableDeclarator,
+]);
+
+export = new class MustUseResults implements eslint.Rule.RuleModule {
+
+	create(context: eslint.Rule.RuleContext): eslint.Rule.RuleListener {
+
+		const config = <{ message: string, functions: string[] }[]>context.options[0];
+		const listener: eslint.Rule.RuleListener = {};
+
+		for (const { message, functions } of config) {
+			for (const fn of functions) {
+				const query = `CallExpression[callee.property.name='${fn}'], CallExpression[callee.name='${fn}']`
+				listener[query] = (node: any) => {
+					const cast: TSESTree.CallExpression = node;
+					if (!VALID_USES.has(cast.parent?.type)) {
+						context.report({ node, message });
+					}
+				}
+			}
+		}
+
+		return listener;
+	}
+};

.eslintrc.json

@@ -140,7 +140,18 @@
 			"rules": {
 				"local/code-no-test-only": "error",
 				"local/code-no-test-async-suite": "warn",
-				"local/code-no-unexternalized-strings": "off"
+				"local/code-no-unexternalized-strings": "off",
+				"local/code-must-use-result": [
+					"warn",
+					[
+						{
+							"message": "Expression must be awaited",
+							"functions": [
+								"assertSnapshot"
+							]
+						}
+					]
+				]
 			}
 		},
 		{

src/vs/workbench/contrib/chat/test/common/chatService.test.ts

@@ -257,7 +257,7 @@ suite('Chat', () => {
 		const model = testDisposables.add(testService.startSession(providerId, CancellationToken.None));
 		assert.strictEqual(model.getRequests().length, 0);
 
-		assertSnapshot(model.toExport());
+		await assertSnapshot(model.toExport());
 
 		const response = await testService.sendRequest(model.sessionId, 'test request');
 		assert(response);
@@ -266,7 +266,7 @@ suite('Chat', () => {
 
 		assert.strictEqual(model.getRequests().length, 1);
 
-		assertSnapshot(model.toExport());
+		await assertSnapshot(model.toExport());
 	});
 
 	test('can deserialize', async () => {
@@ -306,6 +306,6 @@ suite('Chat', () => {
 			dispose: () => testService2.clearSession(serializedChatData.sessionId)
 		});
 
-		assertSnapshot(chatModel2.toExport());
+		await assertSnapshot(chatModel2.toExport());
 	});
 });