Add no-unreadable-iife rule (#1765)

configs/recommended.js

@@ -52,6 +52,7 @@ module.exports = {
 		'unicorn/no-thenable': 'error',
 		'unicorn/no-this-assignment': 'error',
 		'unicorn/no-unreadable-array-destructuring': 'error',
+		'unicorn/no-unreadable-iife': 'error',
 		'unicorn/no-unsafe-regex': 'off',
 		'unicorn/no-unused-properties': 'off',
 		'unicorn/no-useless-fallback-in-spread': 'error',

docs/rules/no-unreadable-iife.md

@@ -0,0 +1,36 @@
+# Disallow unreadable IIFEs
+
+<!-- Do not manually modify RULE_NOTICE part. Run: `npm run generate-rule-notices` -->
+<!-- RULE_NOTICE -->
+✅ *This rule is part of the [recommended](https://github.com/sindresorhus/eslint-plugin-unicorn#recommended-config) config.*
+<!-- /RULE_NOTICE -->
+
+[IIFE](https://en.wikipedia.org/wiki/Immediately_invoked_function_expression) with parenthesized arrow function body is considered unreadable.
+
+## Fail
+
+```js
+const foo = (bar => (bar ? bar.baz : baz))(getBar());
+```
+
+```js
+const foo = ((bar, baz) => ({bar, baz}))(bar, baz);
+```
+
+## Pass
+
+```js
+const bar = getBar();
+const foo = bar ? bar.baz : baz;
+```
+
+```js
+const getBaz = bar => (bar ? bar.baz : baz);
+const foo = getBaz(getBar());
+```
+
+```js
+const foo = (bar => {
+	return bar ? bar.baz : baz;
+})(getBar());
+```

readme.md

@@ -93,6 +93,7 @@ Each rule has emojis denoting:
 | [no-thenable](docs/rules/no-thenable.md) | Disallow `then` property. | ✅ |  |  |
 | [no-this-assignment](docs/rules/no-this-assignment.md) | Disallow assigning `this` to a variable. | ✅ |  |  |
 | [no-unreadable-array-destructuring](docs/rules/no-unreadable-array-destructuring.md) | Disallow unreadable array destructuring. | ✅ | 🔧 |  |
+| [no-unreadable-iife](docs/rules/no-unreadable-iife.md) | Disallow unreadable IIFEs. | ✅ |  |  |
 | [no-unsafe-regex](docs/rules/no-unsafe-regex.md) | Disallow unsafe regular expressions. |  |  |  |
 | [no-unused-properties](docs/rules/no-unused-properties.md) | Disallow unused object properties. |  |  |  |
 | [no-useless-fallback-in-spread](docs/rules/no-useless-fallback-in-spread.md) | Disallow useless fallback when spreading in object literals. | ✅ | 🔧 |  |

rules/no-unreadable-iife.js

@@ -0,0 +1,48 @@
+'use strict';
+const {
+	isParenthesized,
+	getParenthesizedRange,
+} = require('./utils/parentheses.js');
+const toLocation = require('./utils/to-location.js');
+
+const MESSAGE_ID_ERROR = 'no-unreadable-iife';
+const messages = {
+	[MESSAGE_ID_ERROR]: 'IIFE with parenthesized arrow function body is considered unreadable.',
+};
+
+const selector = [
+	'CallExpression',
+	' > ',
+	'ArrowFunctionExpression.callee',
+	' > ',
+	':not(BlockStatement).body',
+].join('');
+
+/** @param {import('eslint').Rule.RuleContext} context */
+const create = context => ({
+	[selector](node) {
+		const sourceCode = context.getSourceCode();
+		if (!isParenthesized(node, sourceCode)) {
+			return;
+		}
+
+		return {
+			node,
+			loc: toLocation(getParenthesizedRange(node, sourceCode), sourceCode),
+			messageId: MESSAGE_ID_ERROR,
+		};
+	},
+});
+
+/** @type {import('eslint').Rule.RuleModule} */
+module.exports = {
+	create,
+	meta: {
+		type: 'suggestion',
+		docs: {
+			description: 'Disallow unreadable IIFEs.',
+		},
+		hasSuggestions: false,
+		messages,
+	},
+};

test/no-unreadable-iife.mjs

@@ -0,0 +1,52 @@
+import outdent from 'outdent';
+import {getTester} from './utils/test.mjs';
+
+const {test} = getTester(import.meta);
+
+test.snapshot({
+	valid: [
+		'const foo = (bar => bar)();',
+		outdent`
+			const foo = (() => {
+				return a ? b : c
+			})();
+		`,
+	],
+	invalid: [
+		'const foo = (() => (a ? b : c))();',
+		outdent`
+			const foo = (() => (
+				a ? b : c
+			))();
+		`,
+		outdent`
+			const foo = (
+				() => (
+					a ? b : c
+				)
+			)();
+		`,
+		outdent`
+			const foo = (() => (
+				a, b
+			))();
+		`,
+		outdent`
+			const foo = (() => ({
+				a: b,
+			}))();
+		`,
+		'const foo = (bar => (bar))();',
+		outdent`
+			(async () => ({
+				bar,
+			}))();
+		`,
+		outdent`
+			const foo = (async (bar) => ({
+				bar: await baz(),
+			}))();
+		`,
+		'(async () => (( {bar} )))();',
+	],
+});

test/snapshots/no-unreadable-iife.mjs.md

@@ -0,0 +1,135 @@
+# Snapshot report for `test/no-unreadable-iife.mjs`
+
+The actual snapshot is saved in `no-unreadable-iife.mjs.snap`.
+
+Generated by [AVA](https://avajs.dev).
+
+## Invalid #1
+      1 | const foo = (() => (a ? b : c))();
+
+> Error 1/1
+
+    `␊
+    > 1 | const foo = (() => (a ? b : c))();␊
+        |                    ^^^^^^^^^^^ IIFE with parenthesized arrow function body is considered unreadable.␊
+    `
+
+## Invalid #2
+      1 | const foo = (() => (
+      2 | 	a ? b : c
+      3 | ))();
+
+> Error 1/1
+
+    `␊
+    > 1 | const foo = (() => (␊
+        |                    ^␊
+    > 2 | 	a ? b : c␊
+        | ^^^^^^^^^^␊
+    > 3 | ))();␊
+        | ^^ IIFE with parenthesized arrow function body is considered unreadable.␊
+    `
+
+## Invalid #3
+      1 | const foo = (
+      2 | 	() => (
+      3 | 		a ? b : c
+      4 | 	)
+      5 | )();
+
+> Error 1/1
+
+    `␊
+      1 | const foo = (␊
+    > 2 | 	() => (␊
+        | 	      ^␊
+    > 3 | 		a ? b : c␊
+        | ^^^^^^^^^^^␊
+    > 4 | 	)␊
+        | ^^^ IIFE with parenthesized arrow function body is considered unreadable.␊
+      5 | )();␊
+    `
+
+## Invalid #4
+      1 | const foo = (() => (
+      2 | 	a, b
+      3 | ))();
+
+> Error 1/1
+
+    `␊
+    > 1 | const foo = (() => (␊
+        |                    ^␊
+    > 2 | 	a, b␊
+        | ^^^^^␊
+    > 3 | ))();␊
+        | ^^ IIFE with parenthesized arrow function body is considered unreadable.␊
+    `
+
+## Invalid #5
+      1 | const foo = (() => ({
+      2 | 	a: b,
+      3 | }))();
+
+> Error 1/1
+
+    `␊
+    > 1 | const foo = (() => ({␊
+        |                    ^^␊
+    > 2 | 	a: b,␊
+        | ^^^^^^␊
+    > 3 | }))();␊
+        | ^^^ IIFE with parenthesized arrow function body is considered unreadable.␊
+    `
+
+## Invalid #6
+      1 | const foo = (bar => (bar))();
+
+> Error 1/1
+
+    `␊
+    > 1 | const foo = (bar => (bar))();␊
+        |                     ^^^^^ IIFE with parenthesized arrow function body is considered unreadable.␊
+    `
+
+## Invalid #7
+      1 | (async () => ({
+      2 | 	bar,
+      3 | }))();
+
+> Error 1/1
+
+    `␊
+    > 1 | (async () => ({␊
+        |              ^^␊
+    > 2 | 	bar,␊
+        | ^^^^^␊
+    > 3 | }))();␊
+        | ^^^ IIFE with parenthesized arrow function body is considered unreadable.␊
+    `
+
+## Invalid #8
+      1 | const foo = (async (bar) => ({
+      2 | 	bar: await baz(),
+      3 | }))();
+
+> Error 1/1
+
+    `␊
+    > 1 | const foo = (async (bar) => ({␊
+        |                             ^^␊
+    > 2 | 	bar: await baz(),␊
+        | ^^^^^^^^^^^^^^^^^^␊
+    > 3 | }))();␊
+        | ^^^ IIFE with parenthesized arrow function body is considered unreadable.␊
+    `
+
+## Invalid #9
+      1 | (async () => (( {bar} )))();
+
+> Error 1/1
+
+    `␊
+    > 1 | (async () => (( {bar} )))();␊
+        |              ^^^^^^^^^^^ IIFE with parenthesized arrow function body is considered unreadable.␊
+    `