Fix: Reduce false positives by only detecting ESM function-style rules when function returns an object

Author: bmish

lib/utils.js

@@ -1,6 +1,7 @@
 'use strict';
 
 const { getStaticValue } = require('eslint-utils');
+const estraverse = require('estraverse');
 
 /**
 * Determines whether a node is a 'normal' (i.e. non-async, non-generator) function expression.
@@ -102,6 +103,23 @@ function collectInterestingProperties (properties, interestingKeys) {
   }, {});
 }
 
+/**
+ * Check if there is a return statement that returns an object somewhere inside the given node.
+ * @param {Node} node
+ * @returns {boolean}
+ */
+function hasObjectReturn (node) {
+  let foundMatch = false;
+  estraverse.traverse(node, {
+    enter (child) {
+      if (child.type === 'ReturnStatement' && child.argument && child.argument.type === 'ObjectExpression') {
+        foundMatch = true;
+      }
+    },
+  });
+  return foundMatch;
+}
+
 /**
  * Helper for `getRuleInfo`. Handles ESM and TypeScript rules.
  */
@@ -114,8 +132,8 @@ function getRuleExportsESM (ast) {
       if (node.type === 'ObjectExpression') {
         // Check `export default { create() {}, meta: {} }`
         return collectInterestingProperties(node.properties, INTERESTING_RULE_KEYS);
-      } else if (isNormalFunctionExpression(node)) {
-        // Check `export default function() {}`
+      } else if (isNormalFunctionExpression(node) && hasObjectReturn(node)) {
+        // Check `export default function() { return { ... }; }`
         return { create: node, meta: null, isNewStyle: false };
       } else if (
         node.type === 'CallExpression' &&

package.json

@@ -30,7 +30,8 @@
   },
   "homepage": "https://github.com/not-an-aardvark/eslint-plugin-eslint-plugin#readme",
   "dependencies": {
-    "eslint-utils": "^3.0.0"
+    "eslint-utils": "^3.0.0",
+    "estraverse": "^5.2.0"
   },
   "nyc": {
     "branches": 98,
@@ -51,7 +52,6 @@
     "eslint-plugin-unicorn": "^37.0.0",
     "eslint-scope": "^6.0.0",
     "espree": "^9.0.0",
-    "estraverse": "^5.0.0",
     "lodash": "^4.17.2",
     "markdownlint-cli": "^0.28.1",
     "mocha": "^9.1.2",

tests/lib/utils.js

@@ -46,6 +46,15 @@ describe('utils', () => {
         'export default { foo: {} }',
         'const foo = {}; export default foo',
 
+        // Exports function but not default export.
+        'export function foo () { return {}; }',
+
+        // Exports function but no object return inside function.
+        'export default function () { }',
+        'export default function () { return; }',
+        'export default function () { return 123; }',
+        'export default function () { return FOO; }',
+
         // Incorrect TypeScript helper structure:
         'export default foo()({ create() {}, meta: {} });',
         'export default foo().bar({ create() {}, meta: {} });',
@@ -255,12 +264,17 @@ describe('utils', () => {
         },
 
         // ESM (function style)
-        'export default function () {}': {
+        'export default function () { return {}; }': {
+          create: { type: 'FunctionDeclaration' },
+          meta: null,
+          isNewStyle: false,
+        },
+        'export default function () { if (foo) { return {}; } }': {
           create: { type: 'FunctionDeclaration' },
           meta: null,
           isNewStyle: false,
         },
-        'export default () => {}': {
+        'export default () => { return {}; }': {
           create: { type: 'ArrowFunctionExpression' },
           meta: null,
           isNewStyle: false,