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Add regexp/no-standalone-backslash rule (#175)
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‎README.md

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@@ -104,6 +104,7 @@ The rules with the following star :star: are included in the `plugin:regexp/reco
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| [regexp/no-octal](https://ota-meshi.github.io/eslint-plugin-regexp/rules/no-octal.html) | disallow octal escape sequence | :star: |
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| [regexp/no-optional-assertion](https://ota-meshi.github.io/eslint-plugin-regexp/rules/no-optional-assertion.html) | disallow optional assertions | |
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| [regexp/no-potentially-useless-backreference](https://ota-meshi.github.io/eslint-plugin-regexp/rules/no-potentially-useless-backreference.html) | disallow backreferences that reference a group that might not be matched | |
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| [regexp/no-standalone-backslash](https://ota-meshi.github.io/eslint-plugin-regexp/rules/no-standalone-backslash.html) | disallow standalone backslashes (`\`) | |
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| [regexp/no-trivially-nested-assertion](https://ota-meshi.github.io/eslint-plugin-regexp/rules/no-trivially-nested-assertion.html) | disallow trivially nested assertions | :wrench: |
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| [regexp/no-trivially-nested-quantifier](https://ota-meshi.github.io/eslint-plugin-regexp/rules/no-trivially-nested-quantifier.html) | disallow nested quantifiers that can be rewritten as one quantifier | :wrench: |
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| [regexp/no-unused-capturing-group](https://ota-meshi.github.io/eslint-plugin-regexp/rules/no-unused-capturing-group.html) | disallow unused capturing group | |

‎docs/rules/README.md

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@@ -32,6 +32,7 @@ The rules with the following star :star: are included in the `plugin:regexp/reco
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| [regexp/no-octal](./no-octal.md) | disallow octal escape sequence | :star: |
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| [regexp/no-optional-assertion](./no-optional-assertion.md) | disallow optional assertions | |
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| [regexp/no-potentially-useless-backreference](./no-potentially-useless-backreference.md) | disallow backreferences that reference a group that might not be matched | |
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| [regexp/no-standalone-backslash](./no-standalone-backslash.md) | disallow standalone backslashes (`\`) | |
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| [regexp/no-trivially-nested-assertion](./no-trivially-nested-assertion.md) | disallow trivially nested assertions | :wrench: |
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| [regexp/no-trivially-nested-quantifier](./no-trivially-nested-quantifier.md) | disallow nested quantifiers that can be rewritten as one quantifier | :wrench: |
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| [regexp/no-unused-capturing-group](./no-unused-capturing-group.md) | disallow unused capturing group | |

‎docs/rules/no-standalone-backslash.md

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---
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pageClass: "rule-details"
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sidebarDepth: 0
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title: "regexp/no-standalone-backslash"
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description: "disallow standalone backslashes (`\\`)"
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---
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# regexp/no-standalone-backslash
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> disallow standalone backslashes (`\`)
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- :exclamation: <badge text="This rule has not been released yet." vertical="middle" type="error"> ***This rule has not been released yet.*** </badge>
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## :book: Rule Details
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This rule disallows backslash (`\`) without escape.
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E.g. the regular expression `/\c/` without the unicode (`u`) flag is the same pattern as `/\\c/`.
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In most cases, standalone backslashes are used by accident when a control escape sequence (`\cX`) or another escape sequence was intended. They are very confusing and should not be used intentionally.
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This behavior is described in [Annex B] of the ECMAScript specification.
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[Annex B]: https://tc39.es/ecma262/#sec-regular-expressions-patterns
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<eslint-code-block>
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```js
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/* eslint regexp/no-standalone-backslash: "error" */
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/* ✓ GOOD */
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var foo = /\cX/;
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/* ✗ BAD */
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var foo = /\c/;
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var foo = /\c-/;
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var foo = /[\c]/;
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```
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</eslint-code-block>
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## :wrench: Options
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Nothing.
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## :couple: Related rules
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- [regexp/no-useless-escape](./no-useless-escape.md)
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## :books: Further reading
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- [ECMAScript® 2022 Language Specification > Annex B > B.1.4 Regular Expressions Patterns](https://tc39.es/ecma262/#sec-regular-expressions-patterns)
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## :mag: Implementation
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- [Rule source](https://github.com/ota-meshi/eslint-plugin-regexp/blob/master/lib/rules/no-standalone-backslash.ts)
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- [Test source](https://github.com/ota-meshi/eslint-plugin-regexp/blob/master/tests/lib/rules/no-standalone-backslash.ts)

‎docs/rules/no-useless-escape.md

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@@ -54,10 +54,12 @@ var foo = /\u{[41]}/
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Nothing.
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## :books: Further reading
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## :couple: Related rules
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- [regexp/no-standalone-backslash]
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- [no-useless-escape]
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[regexp/no-standalone-backslash]: ./no-standalone-backslash.md
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[no-useless-escape]: https://eslint.org/docs/rules/no-useless-escape
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## :rocket: Version

‎lib/rules/no-standalone-backslash.ts

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import type { RegExpVisitor } from "regexpp/visitor"
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import type { RegExpContext } from "../utils"
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import { createRule, defineRegexpVisitor, CP_BACK_SLASH } from "../utils"
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export default createRule("no-standalone-backslash", {
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meta: {
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docs: {
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description: "disallow standalone backslashes (`\\`)",
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// TODO Switch to recommended in the major version.
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// recommended: true,
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recommended: false,
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},
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schema: [],
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messages: {
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unexpected:
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"Unexpected standalone backslash (`\\`). It looks like an escape sequence, but it's a single `\\` character pattern.",
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},
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type: "suggestion", // "problem",
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},
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create(context) {
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/**
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* Create visitor
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*/
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function createVisitor({
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node,
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getRegexpLocation,
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}: RegExpContext): RegExpVisitor.Handlers {
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return {
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onCharacterEnter(cNode) {
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if (cNode.value === CP_BACK_SLASH && cNode.raw === "\\") {
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context.report({
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node,
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loc: getRegexpLocation(cNode),
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messageId: "unexpected",
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})
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}
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},
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}
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}
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return defineRegexpVisitor(context, {
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createVisitor,
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})
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},
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})

‎lib/rules/no-useless-escape.ts

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@@ -121,24 +121,6 @@ export default createRule("no-useless-escape", {
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}
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report(cNode, 0, char)
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}
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// else if (cNode.value === CP_BACK_SLASH) {
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// // Invalid escape for /\c/
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// if (cNode.raw === "\\") {
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// const parent = cNode.parent
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// if (
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// parent.type === "Alternative" ||
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// parent.type === "CharacterClass"
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// ) {
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// const next =
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// parent.elements[
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// parent.elements.indexOf(cNode) + 1
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// ]
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// if (next && next.raw.length === 1) {
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// report(cNode, 0, next.raw)
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// }
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// }
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// }
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// }
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}
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},
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}

‎lib/utils/rules.ts

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@@ -20,6 +20,7 @@ import noObscureRange from "../rules/no-obscure-range"
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import noOctal from "../rules/no-octal"
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import noOptionalAssertion from "../rules/no-optional-assertion"
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import noPotentiallyUselessBackreference from "../rules/no-potentially-useless-backreference"
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import noStandaloneBackslash from "../rules/no-standalone-backslash"
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import noTriviallyNestedAssertion from "../rules/no-trivially-nested-assertion"
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import noTriviallyNestedQuantifier from "../rules/no-trivially-nested-quantifier"
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import noUnusedCapturingGroup from "../rules/no-unused-capturing-group"
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noOctal,
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noOptionalAssertion,
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noPotentiallyUselessBackreference,
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noStandaloneBackslash,
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noTriviallyNestedAssertion,
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noTriviallyNestedQuantifier,
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noUnusedCapturingGroup,

‎tests/lib/rules/no-standalone-backslash.ts

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import { RuleTester } from "eslint"
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import rule from "../../../lib/rules/no-standalone-backslash"
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const tester = new RuleTester({
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parserOptions: {
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ecmaVersion: 2020,
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sourceType: "module",
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},
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})
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tester.run("no-standalone-backslash", rule as any, {
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valid: [String.raw`/\cX/`],
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invalid: [
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{
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code: String.raw`/\c/`,
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errors: [
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{
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message:
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"Unexpected standalone backslash (`\\`). It looks like an escape sequence, but it's a single `\\` character pattern.",
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column: 2,
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},
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],
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},
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{
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code: String.raw`/\c-/`,
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errors: [
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{
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message:
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"Unexpected standalone backslash (`\\`). It looks like an escape sequence, but it's a single `\\` character pattern.",
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column: 2,
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},
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],
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},
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{
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code: String.raw`/\c1/`,
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errors: [
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{
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message:
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"Unexpected standalone backslash (`\\`). It looks like an escape sequence, but it's a single `\\` character pattern.",
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column: 2,
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},
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],
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},
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{
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code: String.raw`/[\c]/`,
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errors: [
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{
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message:
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"Unexpected standalone backslash (`\\`). It looks like an escape sequence, but it's a single `\\` character pattern.",
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column: 3,
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},
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],
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},
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],
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})

‎tests/lib/rules/no-useless-escape.ts

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"Unnecessary escape character: \\P.",
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],
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},
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// {
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// code: String.raw`/\c1/`,
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// errors: [
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// {
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// message: "Unnecessary escape character: \\c.",
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// line: 1,
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// column: 2,
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// endLine: 1,
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// endColumn: 3,
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// },
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// ],
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// },
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// {
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// code: String.raw`/[\c]/`,
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// errors: [
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// {
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// message: "Unnecessary escape character: \\c.",
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// line: 1,
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// column: 3,
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// endLine: 1,
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// endColumn: 4,
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// },
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// ],
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// },
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],
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})

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