Add prefer-array-index-of rule (#920)

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

docs/rules/prefer-array-index-of.md

@@ -0,0 +1,58 @@
+# Prefer `Array#indexOf()` over `Array#findIndex()` when looking for the index of an item
+
+[`Array#findIndex()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/findIndex) is intended for more complex needs. If you are just looking for the index where the given item is present, then the code can be simplified to use [`Array#indexOf()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/indexOf). This applies to any search with a literal, a variable, or any expression that doesn't have any explicit side effects. However, if the expression you are looking for relies on an item related to the function (its arguments, the function self, etc.), the case is still valid.
+
+This rule is fixable, unless the search expression has side effects.
+
+## Fail
+
+```js
+const index = foo.findIndex(x => x === 'foo');
+```
+
+```js
+const index = foo.findIndex(x => 'foo' === x);
+```
+
+```js
+const index = foo.findIndex(x => {
+	return x === 'foo';
+});
+```
+
+## Pass
+
+```js
+const index = foo.indexOf('foo');
+```
+
+```js
+const index = foo.findIndex(x => x == undefined);
+```
+
+```js
+const index = foo.findIndex(x => x !== 'foo');
+```
+
+```js
+const index = foo.findIndex((x, index) => x === index);
+```
+
+```js
+const index = foo.findIndex(x => (x === 'foo') && isValid());
+```
+
+```js
+const index = foo.findIndex(x => y === 'foo');
+```
+
+```js
+const index = foo.findIndex(x => y.x === 'foo');
+```
+
+```js
+const index = foo.findIndex(x => {
+	const bar = getBar();
+	return x === bar;
+});
+```

index.js

@@ -81,6 +81,7 @@ module.exports = {
 				'unicorn/prefer-array-find': 'error',
 				// TODO: Enable this by default when targeting Node.js 12.
 				'unicorn/prefer-array-flat-map': 'off',
+				'unicorn/prefer-array-index-of': 'error',
 				'unicorn/prefer-array-some': 'error',
 				'unicorn/prefer-date-now': 'error',
 				'unicorn/prefer-default-parameters': 'error',

readme.md

@@ -73,6 +73,7 @@ Configure it in `package.json`.
 			"unicorn/prefer-add-event-listener": "error",
 			"unicorn/prefer-array-find": "error",
 			"unicorn/prefer-array-flat-map": "error",
+			"unicorn/prefer-array-index-of": "error",
 			"unicorn/prefer-array-some": "error",
 			"unicorn/prefer-date-now": "error",
 			"unicorn/prefer-default-parameters": "error",
@@ -147,6 +148,7 @@ Configure it in `package.json`.
 - [prefer-add-event-listener](docs/rules/prefer-add-event-listener.md) - Prefer `.addEventListener()` and `.removeEventListener()` over `on`-functions. *(partly fixable)*
 - [prefer-array-find](docs/rules/prefer-array-find.md) - Prefer `.find(…)` over the first element from `.filter(…)`. *(partly fixable)*
 - [prefer-array-flat-map](docs/rules/prefer-array-flat-map.md) - Prefer `.flatMap(…)` over `.map(…).flat()`. *(fixable)*
+- [prefer-array-index-of](docs/rules/prefer-array-index-of.md) - Prefer `Array#indexOf()` over `Array#findIndex()` when looking for the index of an item. *(partly fixable)*
 - [prefer-array-some](docs/rules/prefer-array-some.md) - Prefer `.some(…)` over `.find(…)`.
 - [prefer-date-now](docs/rules/prefer-date-now.md) - Prefer `Date.now()` to get the number of milliseconds since the Unix Epoch. *(fixable)*
 - [prefer-default-parameters](docs/rules/prefer-default-parameters.md) - Prefer default parameters over reassignment. *(fixable)*

rules/prefer-array-index-of.js

@@ -0,0 +1,156 @@
+'use strict';
+const {hasSideEffect, isParenthesized, findVariable} = require('eslint-utils');
+const getDocumentationUrl = require('./utils/get-documentation-url');
+const methodSelector = require('./utils/method-selector');
+const getVariableIdentifiers = require('./utils/get-variable-identifiers');
+
+const MESSAGE_ID_FIND_INDEX = 'findIndex';
+const MESSAGE_ID_REPLACE = 'replaceFindIndex';
+const messages = {
+	[MESSAGE_ID_FIND_INDEX]: 'Use `.indexOf()` instead of `.findIndex()` when looking for the index of an item.',
+	[MESSAGE_ID_REPLACE]: 'Replace `.findIndex()` with `.indexOf()`.'
+};
+
+const getBinaryExpressionSelector = path => [
+	`[${path}.type="BinaryExpression"]`,
+	`[${path}.operator="==="]`,
+	`:matches([${path}.left.type="Identifier"], [${path}.right.type="Identifier"])`
+].join('');
+const getFunctionSelector = path => [
+	`[${path}.generator=false]`,
+	`[${path}.async=false]`,
+	`[${path}.params.length=1]`,
+	`[${path}.params.0.type="Identifier"]`
+].join('');
+const selector = [
+	methodSelector({
+		name: 'findIndex',
+		length: 1
+	}),
+	`:matches(${
+		[
+			// Matches `foo.findIndex(bar => bar === baz)`
+			[
+				'[arguments.0.type="ArrowFunctionExpression"]',
+				getFunctionSelector('arguments.0'),
+				getBinaryExpressionSelector('arguments.0.body')
+			].join(''),
+			// Matches `foo.findIndex(bar => {return bar === baz})`
+			// Matches `foo.findIndex(function (bar) {return bar === baz})`
+			[
+				':matches([arguments.0.type="ArrowFunctionExpression"], [arguments.0.type="FunctionExpression"])',
+				getFunctionSelector('arguments.0'),
+				'[arguments.0.body.type="BlockStatement"]',
+				'[arguments.0.body.body.length=1]',
+				'[arguments.0.body.body.0.type="ReturnStatement"]',
+				getBinaryExpressionSelector('arguments.0.body.body.0.argument')
+			].join('')
+		].join(', ')
+	})`
+].join('');
+
+const isIdentifierNamed = ({type, name}, expectName) => type === 'Identifier' && name === expectName;
+
+function isVariablesInCallbackUsed(scopeManager, callback, parameterInBinaryExpression) {
+	const scope = scopeManager.acquire(callback);
+
+	// `parameter` is used on somewhere else
+	const [parameter] = callback.params;
+	if (
+		getVariableIdentifiers(findVariable(scope, parameter))
+			.some(identifier => identifier !== parameter && identifier !== parameterInBinaryExpression)
+	) {
+		return true;
+	}
+
+	if (callback.type === 'FunctionExpression') {
+		// `this` is used
+		if (scope.thisFound) {
+			return true;
+		}
+
+		// The function name is used
+		if (
+			callback.id &&
+			getVariableIdentifiers(findVariable(scope, callback.id))
+				.some(identifier => identifier !== callback.id)
+		) {
+			return true;
+		}
+
+		// `arguments` is used
+		if (scope.references.some(({identifier: {name}}) => name === 'arguments')) {
+			return true;
+		}
+	}
+}
+
+const create = context => {
+	const sourceCode = context.getSourceCode();
+	const {scopeManager} = sourceCode;
+
+	return {
+		[selector](node) {
+			const [callback] = node.arguments;
+			const binaryExpression = callback.body.type === 'BinaryExpression' ?
+				callback.body :
+				callback.body.body[0].argument;
+			const [parameter] = callback.params;
+			const {left, right} = binaryExpression;
+			const {name} = parameter;
+
+			let searchValueNode;
+			let parameterInBinaryExpression;
+			if (isIdentifierNamed(left, name)) {
+				searchValueNode = right;
+				parameterInBinaryExpression = left;
+			} else if (isIdentifierNamed(right, name)) {
+				searchValueNode = left;
+				parameterInBinaryExpression = right;
+			} else {
+				return;
+			}
+
+			if (isVariablesInCallbackUsed(scopeManager, callback, parameterInBinaryExpression)) {
+				return;
+			}
+
+			const method = node.callee.property;
+			const problem = {
+				node: method,
+				messageId: MESSAGE_ID_FIND_INDEX,
+				suggest: []
+			};
+
+			function * fix(fixer) {
+				let text = sourceCode.getText(searchValueNode);
+				if (isParenthesized(searchValueNode, sourceCode) && !isParenthesized(callback, sourceCode)) {
+					text = `(${text})`;
+				}
+
+				yield fixer.replaceText(method, 'indexOf');
+				yield fixer.replaceText(callback, text);
+			}
+
+			if (hasSideEffect(searchValueNode, sourceCode)) {
+				problem.suggest.push({messageId: MESSAGE_ID_REPLACE, fix});
+			} else {
+				problem.fix = fix;
+			}
+
+			context.report(problem);
+		}
+	};
+};
+
+module.exports = {
+	create,
+	meta: {
+		type: 'suggestion',
+		docs: {
+			url: getDocumentationUrl(__filename)
+		},
+		fixable: 'code',
+		messages
+	}
+};