tools: add linting rule for async IIFEs

The result of an async IIFE should always be handled in our tests,
typically by adding `.then(common.mustCall())` to verify that the
async function actually finishes executing at some point.

PR-URL: #34363
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

Author: addaleax

test/.eslintrc.yaml

@@ -53,6 +53,7 @@ rules:
   node-core/prefer-common-mustsucceed: error
   node-core/crypto-check: error
   node-core/eslint-check: error
+  node-core/async-iife-no-unused-result: error
   node-core/inspector-check: error
   ## common module is mandatory in tests
   node-core/required-modules:

test/parallel/test-eslint-async-iife-no-unused-result.js

@@ -0,0 +1,49 @@
+'use strict';
+const common = require('../common');
+if (!common.hasCrypto)
+  common.skip('missing crypto');
+common.skipIfEslintMissing();
+
+const RuleTester = require('../../tools/node_modules/eslint').RuleTester;
+const rule = require('../../tools/eslint-rules/async-iife-no-unused-result');
+
+const message = 'The result of an immediately-invoked async function needs ' +
+  'to be used (e.g. with `.then(common.mustCall())`)';
+
+const tester = new RuleTester({ parserOptions: { ecmaVersion: 8 } });
+tester.run('async-iife-no-unused-result', rule, {
+  valid: [
+    '(() => {})()',
+    '(async () => {})',
+    '(async () => {})().then()',
+    '(async () => {})().catch()',
+    '(function () {})()',
+    '(async function () {})',
+    '(async function () {})().then()',
+    '(async function () {})().catch()',
+  ],
+  invalid: [
+    {
+      code: '(async () => {})()',
+      errors: [{ message }],
+      output: '(async () => {})()',
+    },
+    {
+      code: '(async function() {})()',
+      errors: [{ message }],
+      output: '(async function() {})()',
+    },
+    {
+      code: "const common = require('../common');(async () => {})()",
+      errors: [{ message }],
+      output: "const common = require('../common');(async () => {})()" +
+        '.then(common.mustCall())',
+    },
+    {
+      code: "const common = require('../common');(async function() {})()",
+      errors: [{ message }],
+      output: "const common = require('../common');(async function() {})()" +
+        '.then(common.mustCall())',
+    },
+  ]
+});

tools/eslint-rules/async-iife-no-unused-result.js

@@ -0,0 +1,40 @@
+'use strict';
+const { isCommonModule } = require('./rules-utils.js');
+
+function isAsyncIIFE(node) {
+  const { callee: { type, async } } = node;
+  const types = ['FunctionExpression', 'ArrowFunctionExpression'];
+  return types.includes(type) && async;
+}
+
+const message =
+  'The result of an immediately-invoked async function needs to be used ' +
+  '(e.g. with `.then(common.mustCall())`)';
+
+module.exports = {
+  meta: {
+    fixable: 'code'
+  },
+  create: function(context) {
+    let hasCommonModule = false;
+    return {
+      CallExpression: function(node) {
+        if (isCommonModule(node) && node.parent.type === 'VariableDeclarator') {
+          hasCommonModule = true;
+        }
+
+        if (!isAsyncIIFE(node)) return;
+        if (node.parent && node.parent.type === 'ExpressionStatement') {
+          context.report({
+            node,
+            message,
+            fix: (fixer) => {
+              if (hasCommonModule)
+                return fixer.insertTextAfter(node, '.then(common.mustCall())');
+            }
+          });
+        }
+      }
+    };
+  }
+};