Add no-empty-file rule (#1506)

Co-authored-by: fisker Cheung <lionkay@gmail.com>
Co-authored-by: Sindre Sorhus <sindresorhus@gmail.com>

Author: 3 people

configs/recommended.js

@@ -24,6 +24,7 @@ module.exports = {
 		'unicorn/no-array-reduce': 'error',
 		'unicorn/no-console-spaces': 'error',
 		'unicorn/no-document-cookie': 'error',
+		'unicorn/no-empty-file': 'error',
 		'unicorn/no-for-loop': 'error',
 		'unicorn/no-hex-escape': 'error',
 		'unicorn/no-instanceof-array': 'error',

docs/rules/no-empty-file.md

@@ -0,0 +1,65 @@
+# Disallow empty files
+
+Meaningless files clutter a codebase.
+
+Disallow any files only containing the following:
+
+- Whitespace
+- Comments
+- Directives
+- Empty statements
+- Empty block statements
+- Hashbang
+
+## Fail
+
+```js
+
+```
+
+```js
+// Comment
+```
+
+```js
+/* Comment */
+```
+
+```js
+'use strict';
+```
+
+```js
+;
+```
+
+```js
+{
+}
+```
+
+```js
+#!/usr/bin/env node
+```
+
+## Pass
+
+```js
+const x = 0;
+```
+
+```js
+'use strict';
+const x = 0;
+```
+
+```js
+;;
+const x = 0;
+```
+
+```js
+{
+	const x = 0;
+}
+```

readme.md

@@ -57,6 +57,7 @@ Configure it in `package.json`.
 			"unicorn/no-array-reduce": "error",
 			"unicorn/no-console-spaces": "error",
 			"unicorn/no-document-cookie": "error",
+			"unicorn/no-empty-file": "error",
 			"unicorn/no-for-loop": "error",
 			"unicorn/no-hex-escape": "error",
 			"unicorn/no-instanceof-array": "error",
@@ -180,6 +181,7 @@ Each rule has emojis denoting:
 | [no-array-reduce](docs/rules/no-array-reduce.md) | Disallow `Array#reduce()` and `Array#reduceRight()`. | ✅ |  |  |
 | [no-console-spaces](docs/rules/no-console-spaces.md) | Do not use leading/trailing space between `console.log` parameters. | ✅ | 🔧 |  |
 | [no-document-cookie](docs/rules/no-document-cookie.md) | Do not use `document.cookie` directly. | ✅ |  |  |
+| [no-empty-file](docs/rules/no-empty-file.md) | Disallow empty files. | ✅ |  |  |
 | [no-for-loop](docs/rules/no-for-loop.md) | Do not use a `for` loop that can be replaced with a `for-of` loop. | ✅ | 🔧 |  |
 | [no-hex-escape](docs/rules/no-hex-escape.md) | Enforce the use of Unicode escapes instead of hexadecimal escapes. | ✅ | 🔧 |  |
 | [no-instanceof-array](docs/rules/no-instanceof-array.md) | Require `Array.isArray()` instead of `instanceof Array`. | ✅ | 🔧 |  |

rules/no-empty-file.js

@@ -0,0 +1,47 @@
+'use strict';
+
+const MESSAGE_ID = 'no-empty-file';
+const messages = {
+	[MESSAGE_ID]: 'Empty files are not allowed.',
+};
+
+const isEmpty = node =>
+	(
+		(node.type === 'Program' || node.type === 'BlockStatement')
+		&& node.body.every(currentNode => isEmpty(currentNode))
+	)
+	|| node.type === 'EmptyStatement'
+	|| (node.type === 'ExpressionStatement' && 'directive' in node);
+
+const create = context => {
+	const filename = context.getPhysicalFilename().toLowerCase();
+
+	if (!/\.(?:js|mjs|cjs|ts|mts|cts)$/.test(filename)) {
+		return {};
+	}
+
+	return {
+		Program(node) {
+			if (!isEmpty(node)) {
+				return;
+			}
+
+			return {
+				node,
+				messageId: MESSAGE_ID,
+			};
+		},
+	};
+};
+
+module.exports = {
+	create,
+	meta: {
+		type: 'suggestion',
+		docs: {
+			description: 'Disallow empty files.',
+		},
+		schema: [],
+		messages,
+	},
+};

test/no-empty-file.mjs

@@ -0,0 +1,74 @@
+import outdent from 'outdent';
+import {getTester} from './utils/test.mjs';
+
+const {test} = getTester(import.meta);
+
+test.snapshot({
+	valid: [
+		...[
+			'const x = 0;',
+			';; const x = 0;',
+			'{{{;;const x = 0;}}}',
+			outdent`
+				'use strict';
+				const x = 0;
+			`,
+			';;\'use strict\';',
+			'{\'use strict\';}',
+			'("use strict")',
+			'`use strict`',
+			'({})',
+			outdent`
+				#!/usr/bin/env node
+				console.log('done');
+			`,
+			'false',
+			'("")',
+			'NaN',
+			'undefined',
+			'null',
+			'[]',
+			'(() => {})()',
+		].map(code => ({code, filename: 'example.js'})),
+		'',
+		...[
+			'md',
+			'vue',
+			'svelte',
+			'tsx',
+		].map(extension => ({code: '', filename: `example.${extension}`})),
+	],
+	invalid: [
+		...[
+			'',
+			'\uFEFF',
+			' ',
+			'\t',
+			'\n',
+			'\r',
+			'\r\n',
+			outdent`
+
+			`,
+			'// comment',
+			'/* comment */',
+			'#!/usr/bin/env node',
+			'\'use asm\';',
+			'\'use strict\';',
+			'"use strict"',
+			'""',
+			';',
+			';;',
+			'{}',
+			'{;;}',
+			'{{}}',
+		].map(code => ({code, filename: 'example.js'})),
+		...[
+			'mjs',
+			'cjs',
+			'ts',
+			'mts',
+			'cts',
+		].map(extension => ({code: '{}', filename: `example.${extension}`})),
+	],
+});