prefer-starts-ends-with: Add auto-fix (#711)

docs/rules/prefer-starts-ends-with.md

@@ -2,6 +2,7 @@
 
 There are several ways of checking whether a string starts or ends with a certain string, such as `string.indexOf('foo') === 0` or using a regex with `/^foo/` or `/foo$/`. ES2015 introduced simpler alternatives named [`String#startsWith()`](https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/String/startsWith) and [`String#endsWith()`](https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/String/endsWith). This rule enforces the use of those whenever possible.
 
+This rule is partly fixable.
 
 ## Fail
 
@@ -10,7 +11,6 @@ There are several ways of checking whether a string starts or ends with a certai
 /bar$/.test(foo);
 ```
 
-
 ## Pass
 
 ```js

readme.md

@@ -135,7 +135,7 @@ Configure it in `package.json`.
 - [prefer-replace-all](docs/rules/prefer-replace-all.md) - Prefer `String#replaceAll()` over regex searches with the global flag. *(fixable)*
 - [prefer-set-has](docs/rules/prefer-set-has.md) - Prefer `Set#has()` over `Array#includes()` when checking for existence or non-existence. *(fixable)*
 - [prefer-spread](docs/rules/prefer-spread.md) - Prefer the spread operator over `Array.from()`. *(fixable)*
-- [prefer-starts-ends-with](docs/rules/prefer-starts-ends-with.md) - Prefer `String#startsWith()` & `String#endsWith()` over more complex alternatives.
+- [prefer-starts-ends-with](docs/rules/prefer-starts-ends-with.md) - Prefer `String#startsWith()` & `String#endsWith()` over more complex alternatives. *(partly fixable)*
 - [prefer-string-slice](docs/rules/prefer-string-slice.md) - Prefer `String#slice()` over `String#substr()` and `String#substring()`. *(partly fixable)*
 - [prefer-text-content](docs/rules/prefer-text-content.md) - Prefer `.textContent` over `.innerText`. *(fixable)*
 - [prefer-trim-start-end](docs/rules/prefer-trim-start-end.md) - Prefer `String#trimStart()` / `String#trimEnd()` over `String#trimLeft()` / `String#trimRight()`. *(fixable)*

rules/prefer-starts-ends-with.js

@@ -1,5 +1,8 @@
 'use strict';
+const {isParenthesized} = require('eslint-utils');
 const getDocumentationUrl = require('./utils/get-documentation-url');
+const methodSelector = require('./utils/method-selector');
+const quoteString = require('./utils/quote-string');
 
 const MESSAGE_STARTS_WITH = 'prefer-starts-with';
 const MESSAGE_ENDS_WITH = 'prefer-ends-with';
@@ -11,54 +14,96 @@ const isSimpleString = string => doesNotContain(
 	['^', '$', '+', '[', '{', '(', '\\', '.', '?', '*']
 );
 
+const regexTestSelector = [
+	methodSelector({name: 'test', length: 1}),
+	'[callee.object.regex]'
+].join('');
+
+const stringMatchSelector = [
+	methodSelector({name: 'match', length: 1}),
+	'[arguments.0.regex]'
+].join('');
+
+const checkRegex = ({pattern, flags}) => {
+	if (flags.includes('i')) {
+		return;
+	}
+
+	if (pattern.startsWith('^')) {
+		const string = pattern.slice(1);
+
+		if (isSimpleString(string)) {
+			return {
+				messageId: MESSAGE_STARTS_WITH,
+				string
+			};
+		}
+	}
+
+	if (pattern.endsWith('$')) {
+		const string = pattern.slice(0, -1);
+
+		if (isSimpleString(string)) {
+			return {
+				messageId: MESSAGE_ENDS_WITH,
+				string
+			};
+		}
+	}
+};
+
 const create = context => {
-	return {
-		CallExpression(node) {
-			const {callee} = node;
-			const {property} = callee;
+	const sourceCode = context.getSourceCode();
 
-			if (!(property && callee.type === 'MemberExpression')) {
+	return {
+		[regexTestSelector](node) {
+			const regexNode = node.callee.object;
+			const {regex} = regexNode;
+			const result = checkRegex(regex);
+			if (!result) {
 				return;
 			}
 
-			const arguments_ = node.arguments;
-
-			let regex;
-			if (property.name === 'test' && callee.object.regex) {
-				({regex} = callee.object);
-			} else if (
-				property.name === 'match' &&
-				arguments_ &&
-				arguments_[0] &&
-				arguments_[0].regex
-			) {
-				({regex} = arguments_[0]);
-			} else {
-				return;
-			}
+			context.report({
+				node,
+				messageId: result.messageId,
+				fix: fixer => {
+					const method = result.messageId === MESSAGE_STARTS_WITH ? 'startsWith' : 'endsWith';
+					const [target] = node.arguments;
+					let targetString = sourceCode.getText(target);
+
+					if (
+						// If regex is parenthesized, we can use it, so we don't need add again
+						!isParenthesized(regexNode, sourceCode) &&
+						(isParenthesized(target, sourceCode) || target.type === 'AwaitExpression')
+					) {
+						targetString = `(${targetString})`;
+					}
 
-			if (regex.flags && regex.flags.includes('i')) {
+					// The regex literal always starts with `/` or `(`, so we don't need check ASI
+
+					return [
+						// Replace regex with string
+						fixer.replaceText(regexNode, targetString),
+						// `.test` => `.startsWith` / `.endsWith`
+						fixer.replaceText(node.callee.property, method),
+						// Replace argument with result.string
+						fixer.replaceText(target, quoteString(result.string))
+					];
+				}
+			});
+		},
+		[stringMatchSelector](node) {
+			const {regex} = node.arguments[0];
+			const result = checkRegex(regex);
+			if (!result) {
 				return;
 			}
 
-			const {pattern} = regex;
-			if (
-				pattern.startsWith('^') &&
-				isSimpleString(pattern.slice(1))
-			) {
-				context.report({
-					node,
-					messageId: MESSAGE_STARTS_WITH
-				});
-			} else if (
-				pattern.endsWith('$') &&
-				isSimpleString(pattern.slice(0, -1))
-			) {
-				context.report({
-					node,
-					messageId: MESSAGE_ENDS_WITH
-				});
-			}
+			context.report({
+				node,
+				messageId: result.messageId
+			});
 		}
 	};
 };
@@ -73,6 +118,7 @@ module.exports = {
 		messages: {
 			[MESSAGE_STARTS_WITH]: 'Prefer `String#startsWith()` over a regex with `^`.',
 			[MESSAGE_ENDS_WITH]: 'Prefer `String#endsWith()` over a regex with `$`.'
-		}
+		},
+		fixable: 'code'
 	}
 };

test/prefer-starts-ends-with.js

@@ -1,4 +1,5 @@
 import test from 'ava';
+import {outdent} from 'outdent';
 import avaRuleTester from 'eslint-ava-rule-tester';
 import rule from '../rules/prefer-starts-ends-with';
 
@@ -53,14 +54,78 @@ ruleTester.run('prefer-starts-ends-with', rule, {
 	],
 	invalid: [
 		...invalidRegex.map(re => {
-			const code = `${re}.test(bar)`;
-			const messageId = re.source.startsWith('^') ? MESSAGE_STARTS_WITH : MESSAGE_ENDS_WITH;
+			let messageId = MESSAGE_STARTS_WITH;
+			let method = 'startsWith';
+			let string = re.source;
+
+			if (string.startsWith('^')) {
+				string = string.slice(1);
+			} else {
+				messageId = MESSAGE_ENDS_WITH;
+				method = 'endsWith';
+				string = string.slice(0, -1);
+			}
+
 			return {
-				code,
-				output: code,
+				code: `${re}.test(bar)`,
+				output: `bar.${method}('${string}')`,
 				errors: [{messageId}]
 			};
 		}),
+		// Parenthesized
+		{
+			code: '/^b/.test(("a"))',
+			output: '("a").startsWith((\'b\'))',
+			errors: [{messageId: MESSAGE_STARTS_WITH}]
+		},
+		{
+			code: '(/^b/).test(("a"))',
+			output: '("a").startsWith((\'b\'))',
+			errors: [{messageId: MESSAGE_STARTS_WITH}]
+		},
+		{
+			code: 'const fn = async () => /^b/.test(await foo)',
+			output: 'const fn = async () => (await foo).startsWith(\'b\')',
+			errors: [{messageId: MESSAGE_STARTS_WITH}]
+		},
+		{
+			code: 'const fn = async () => (/^b/).test(await foo)',
+			output: 'const fn = async () => (await foo).startsWith(\'b\')',
+			errors: [{messageId: MESSAGE_STARTS_WITH}]
+		},
+		// Comments
+		{
+			code: outdent`
+				if (
+					/* comment 1 */
+					/^b/
+					/* comment 2 */
+					.test
+					/* comment 3 */
+					(
+						/* comment 4 */
+						foo
+						/* comment 5 */
+					)
+				) {}
+			`,
+			output: outdent`
+				if (
+					/* comment 1 */
+					foo
+					/* comment 2 */
+					.startsWith
+					/* comment 3 */
+					(
+						/* comment 4 */
+						'b'
+						/* comment 5 */
+					)
+				) {}
+			`,
+			errors: [{messageId: MESSAGE_STARTS_WITH}]
+		},
+
 		...invalidRegex.map(re => {
 			const code = `bar.match(${re})`;
 			const messageId = re.source.startsWith('^') ? MESSAGE_STARTS_WITH : MESSAGE_ENDS_WITH;