Add no-length-as-slice-end rule (#2400)

Co-authored-by: Sindre Sorhus <[email protected]>

Author: fisker

docs/rules/no-length-as-slice-end.md

@@ -0,0 +1,30 @@
+# Disallow using `.length` as the `end` argument of `{Array,String,TypedArray}#slice()`
+
+💼 This rule is enabled in the ✅ `recommended` [config](https://github.com/sindresorhus/eslint-plugin-unicorn#preset-configs-eslintconfigjs).
+
+🔧 This rule is automatically fixable by the [`--fix` CLI option](https://eslint.org/docs/latest/user-guide/command-line-interface#--fix).
+
+<!-- end auto-generated rule header -->
+<!-- Do not manually modify this header. Run: `npm run fix:eslint-docs` -->
+
+When calling `{String,Array,TypedArray}#slice(start, end)`, omitting the `end` argument defaults it to the object's `.length`. Passing it explicitly is unnecessary.
+
+## Fail
+
+```js
+const foo = string.slice(1, string.length);
+```
+
+```js
+const foo = array.slice(1, array.length);
+```
+
+## Pass
+
+```js
+const foo = string.slice(1);
+```
+
+```js
+const foo = bar.slice(1, baz.length);
+```

readme.md

@@ -142,6 +142,7 @@ If you don't use the preset, ensure you use the same `env` and `parserOptions` c
 | [no-invalid-fetch-options](docs/rules/no-invalid-fetch-options.md)                               | Disallow invalid options in `fetch()` and `new Request()`.                                                                                                                                                        | ✅  |    |    |
 | [no-invalid-remove-event-listener](docs/rules/no-invalid-remove-event-listener.md)               | Prevent calling `EventTarget#removeEventListener()` with the result of an expression.                                                                                                                             | ✅  |    |    |
 | [no-keyword-prefix](docs/rules/no-keyword-prefix.md)                                             | Disallow identifiers starting with `new` or `class`.                                                                                                                                                              |    |    |    |
+| [no-length-as-slice-end](docs/rules/no-length-as-slice-end.md)                                   | Disallow using `.length` as the `end` argument of `{Array,String,TypedArray}#slice()`.                                                                                                                            | ✅  | 🔧 |    |
 | [no-lonely-if](docs/rules/no-lonely-if.md)                                                       | Disallow `if` statements as the only statement in `if` blocks without `else`.                                                                                                                                     | ✅  | 🔧 |    |
 | [no-magic-array-flat-depth](docs/rules/no-magic-array-flat-depth.md)                             | Disallow a magic number as the `depth` argument in `Array#flat(…).`                                                                                                                                               | ✅  |    |    |
 | [no-negated-condition](docs/rules/no-negated-condition.md)                                       | Disallow negated conditions.                                                                                                                                                                                      | ✅  | 🔧 |    |

rules/no-length-as-slice-end.js

@@ -0,0 +1,53 @@
+'use strict';
+const {isMethodCall, isMemberExpression} = require('./ast/index.js');
+const {removeArgument} = require('./fix/index.js');
+const {isSameReference} = require('./utils/index.js');
+
+const MESSAGE_ID = 'no-length-as-slice-end';
+const messages = {
+	[MESSAGE_ID]: 'Passing `….length` as the `end` argument is unnecessary.',
+};
+
+/** @param {import('eslint').Rule.RuleContext} context */
+const create = context => {
+	context.on('CallExpression', callExpression => {
+		if (!isMethodCall(callExpression, {
+			method: 'slice',
+			argumentsLength: 2,
+			optionalCall: false,
+		})) {
+			return;
+		}
+
+		const secondArgument = callExpression.arguments[1];
+		const node = secondArgument.type === 'ChainExpression' ? secondArgument.expression : secondArgument;
+
+		if (
+			!isMemberExpression(node, {property: 'length', computed: false})
+			|| !isSameReference(callExpression.callee.object, node.object)
+		) {
+			return;
+		}
+
+		return {
+			node,
+			messageId: MESSAGE_ID,
+			/** @param {import('eslint').Rule.RuleFixer} fixer */
+			fix: fixer => removeArgument(fixer, secondArgument, context.sourceCode),
+		};
+	});
+};
+
+/** @type {import('eslint').Rule.RuleModule} */
+module.exports = {
+	create,
+	meta: {
+		type: 'suggestion',
+		docs: {
+			description: 'Disallow using `.length` as the `end` argument of `{Array,String,TypedArray}#slice()`.',
+			recommended: true,
+		},
+		fixable: 'code',
+		messages,
+	},
+};

test/no-length-as-slice-end.mjs

@@ -0,0 +1,33 @@
+import {getTester} from './utils/test.mjs';
+
+const {test} = getTester(import.meta);
+
+test.snapshot({
+	valid: [
+		'foo.slice?.(1, foo.length)',
+		'foo.slice(foo.length, 1)',
+		'foo.slice()',
+		'foo.slice(1)',
+		'foo.slice(1, foo.length - 1)',
+		'foo.slice(1, foo.length, extraArgument)',
+		'foo.slice(...[1], foo.length)',
+		'foo.notSlice(1, foo.length)',
+		'new foo.slice(1, foo.length)',
+		'slice(1, foo.length)',
+		'foo.slice(1, foo.notLength)',
+		'foo.slice(1, length)',
+		'foo[slice](1, foo.length)',
+		'foo.slice(1, foo[length])',
+		'foo.slice(1, bar.length)',
+		// `isSameReference` consider they are not the same reference
+		'foo().slice(1, foo().length)',
+	],
+	invalid: [
+		'foo.slice(1, foo.length)',
+		'foo?.slice(1, foo.length)',
+		'foo.slice(1, foo.length,)',
+		'foo.slice(1, (( foo.length )))',
+		'foo.slice(1, foo?.length)',
+		'foo?.slice(1, foo?.length)',
+	],
+});

test/snapshots/no-length-as-slice-end.mjs.md

@@ -0,0 +1,131 @@
+# Snapshot report for `test/no-length-as-slice-end.mjs`
+
+The actual snapshot is saved in `no-length-as-slice-end.mjs.snap`.
+
+Generated by [AVA](https://avajs.dev).
+
+## invalid(1): foo.slice(1, foo.length)
+
+> Input
+
+    `␊
+      1 | foo.slice(1, foo.length)␊
+    `
+
+> Output
+
+    `␊
+      1 | foo.slice(1)␊
+    `
+
+> Error 1/1
+
+    `␊
+    > 1 | foo.slice(1, foo.length)␊
+        |              ^^^^^^^^^^ Passing \`….length\` as the \`end\` argument is unnecessary.␊
+    `
+
+## invalid(2): foo?.slice(1, foo.length)
+
+> Input
+
+    `␊
+      1 | foo?.slice(1, foo.length)␊
+    `
+
+> Output
+
+    `␊
+      1 | foo?.slice(1)␊
+    `
+
+> Error 1/1
+
+    `␊
+    > 1 | foo?.slice(1, foo.length)␊
+        |               ^^^^^^^^^^ Passing \`….length\` as the \`end\` argument is unnecessary.␊
+    `
+
+## invalid(3): foo.slice(1, foo.length,)
+
+> Input
+
+    `␊
+      1 | foo.slice(1, foo.length,)␊
+    `
+
+> Output
+
+    `␊
+      1 | foo.slice(1,)␊
+    `
+
+> Error 1/1
+
+    `␊
+    > 1 | foo.slice(1, foo.length,)␊
+        |              ^^^^^^^^^^ Passing \`….length\` as the \`end\` argument is unnecessary.␊
+    `
+
+## invalid(4): foo.slice(1, (( foo.length )))
+
+> Input
+
+    `␊
+      1 | foo.slice(1, (( foo.length )))␊
+    `
+
+> Output
+
+    `␊
+      1 | foo.slice(1)␊
+    `
+
+> Error 1/1
+
+    `␊
+    > 1 | foo.slice(1, (( foo.length )))␊
+        |                 ^^^^^^^^^^ Passing \`….length\` as the \`end\` argument is unnecessary.␊
+    `
+
+## invalid(5): foo.slice(1, foo?.length)
+
+> Input
+
+    `␊
+      1 | foo.slice(1, foo?.length)␊
+    `
+
+> Output
+
+    `␊
+      1 | foo.slice(1)␊
+    `
+
+> Error 1/1
+
+    `␊
+    > 1 | foo.slice(1, foo?.length)␊
+        |              ^^^^^^^^^^^ Passing \`….length\` as the \`end\` argument is unnecessary.␊
+    `
+
+## invalid(6): foo?.slice(1, foo?.length)
+
+> Input
+
+    `␊
+      1 | foo?.slice(1, foo?.length)␊
+    `
+
+> Output
+
+    `␊
+      1 | foo?.slice(1)␊
+    `
+
+> Error 1/1
+
+    `␊
+    > 1 | foo?.slice(1, foo?.length)␊
+        |               ^^^^^^^^^^^ Passing \`….length\` as the \`end\` argument is unnecessary.␊
+    `