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Add regexp/no-potentially-useless-backreference rule (#136)
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‎README.md

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@@ -98,6 +98,7 @@ The rules with the following star :star: are included in the `plugin:regexp/reco
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| [regexp/no-lazy-ends](https://ota-meshi.github.io/eslint-plugin-regexp/rules/no-lazy-ends.html) | disallow lazy quantifiers at the end of an expression | |
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| [regexp/no-legacy-features](https://ota-meshi.github.io/eslint-plugin-regexp/rules/no-legacy-features.html) | disallow legacy RegExp features | |
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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-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-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-unused-capturing-group](https://ota-meshi.github.io/eslint-plugin-regexp/rules/no-unused-capturing-group.html) | disallow unused capturing group | |
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| [regexp/no-useless-backreference](https://ota-meshi.github.io/eslint-plugin-regexp/rules/no-useless-backreference.html) | disallow useless backreferences in regular expressions | :star: |

‎docs/rules/README.md

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| [regexp/no-lazy-ends](./no-lazy-ends.md) | disallow lazy quantifiers at the end of an expression | |
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| [regexp/no-legacy-features](./no-legacy-features.md) | disallow legacy RegExp features | |
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| [regexp/no-octal](./no-octal.md) | disallow octal escape sequence | :star: |
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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-trivially-nested-assertion](./no-trivially-nested-assertion.md) | disallow trivially nested assertions | :wrench: |
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| [regexp/no-unused-capturing-group](./no-unused-capturing-group.md) | disallow unused capturing group | |
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| [regexp/no-useless-backreference](./no-useless-backreference.md) | disallow useless backreferences in regular expressions | :star: |

‎docs/rules/no-potentially-useless-backreference.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-potentially-useless-backreference"
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description: "disallow backreferences that reference a group that might not be matched"
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---
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# regexp/no-potentially-useless-backreference
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> disallow backreferences that reference a group that might not be matched
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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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If the referenced group of a backreference is not matched because some other path leads to the backreference, the backreference will trivially accept (e.g. `/(?:(a)|b)\1/`). The same will happen if the captured text of the referenced group was reset before reaching the backreference.
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This will not handle backreferences that always trivially accept. Use [regexp/no-useless-backreference] for that.
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<eslint-code-block>
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```js
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/* eslint regexp/no-potentially-useless-backreference: "error" */
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/* ✓ GOOD */
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var foo = /(a+)b\1/;
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var foo = /(a+)b|\1/; // this will be done by regexp/no-useless-backreference
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/* ✗ BAD */
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var foo = /(?:(a)|b)\1/;
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var foo = /(a)?b\1/;
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var foo = /((a)|c)+b\2/;
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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-backreference]
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[regexp/no-useless-backreference]: ./no-useless-backreference.md
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## :heart: Compatibility
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This rule was taken from [eslint-plugin-clean-regex].
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This rule is compatible with [clean-regex/no-potentially-empty-backreference] rule.
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[eslint-plugin-clean-regex]: https://github.com/RunDevelopment/eslint-plugin-clean-regex
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[clean-regex/no-potentially-empty-backreference]: https://github.com/RunDevelopment/eslint-plugin-clean-regex/blob/master/docs/rules/no-potentially-empty-backreference.md
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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-potentially-useless-backreference.ts)
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- [Test source](https://github.com/ota-meshi/eslint-plugin-regexp/blob/master/tests/lib/rules/no-potentially-useless-backreference.ts)

‎lib/rules/no-potentially-useless-backreference.ts

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import type { Expression } from "estree"
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import type { RegExpVisitor } from "regexpp/visitor"
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import { createRule, defineRegexpVisitor, getRegexpLocation } from "../utils"
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import {
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isEmptyBackreference,
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isStrictBackreference,
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} from "regexp-ast-analysis"
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export default createRule("no-potentially-useless-backreference", {
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meta: {
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docs: {
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description:
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"disallow backreferences that reference a group that might not be matched",
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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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default: "warn",
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},
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schema: [],
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messages: {
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potentiallyUselessBackreference:
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"Some paths leading to the backreference do not go through the referenced capturing group or the captured text might be reset before reaching the backreference.",
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},
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type: "problem",
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},
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create(context) {
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const sourceCode = context.getSourceCode()
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/**
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* Create visitor
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* @param node
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*/
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function createVisitor(node: Expression): RegExpVisitor.Handlers {
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return {
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onBackreferenceEnter(backreference) {
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if (isEmptyBackreference(backreference)) {
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// handled by regexp/no-useless-backreference
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return
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}
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if (!isStrictBackreference(backreference)) {
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context.report({
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node,
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loc: getRegexpLocation(
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sourceCode,
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node,
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backreference,
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),
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messageId: "potentiallyUselessBackreference",
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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/utils/rules.ts

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@@ -14,6 +14,7 @@ import noInvisibleCharacter from "../rules/no-invisible-character"
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import noLazyEnds from "../rules/no-lazy-ends"
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import noLegacyFeatures from "../rules/no-legacy-features"
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import noOctal from "../rules/no-octal"
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import noPotentiallyUselessBackreference from "../rules/no-potentially-useless-backreference"
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import noTriviallyNestedAssertion from "../rules/no-trivially-nested-assertion"
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import noUnusedCapturingGroup from "../rules/no-unused-capturing-group"
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import noUselessBackreference from "../rules/no-useless-backreference"
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noLazyEnds,
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noLegacyFeatures,
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noOctal,
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noPotentiallyUselessBackreference,
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noTriviallyNestedAssertion,
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noUnusedCapturingGroup,
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noUselessBackreference,

‎tests/lib/rules/no-potentially-useless-backreference.ts

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import { RuleTester } from "eslint"
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import rule from "../../../lib/rules/no-potentially-useless-backreference"
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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-potentially-useless-backreference", rule as any, {
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valid: [
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String.raw`/()\1/`,
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String.raw`/(a*)(?:a|\1)/`,
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String.raw`/(a)+\1/`,
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String.raw`/(?=(a))\1/`,
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// done by regexp/no-useless-backreference
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String.raw`/(a+)b|\1/`,
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],
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invalid: [
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{
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code: String.raw`
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var foo = /(a+)b\1/;
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var foo = /(a)?b\1/;
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var foo = /((a)|c)+b\2/;`,
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errors: [
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{
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message:
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"Some paths leading to the backreference do not go through the referenced capturing group or the captured text might be reset before reaching the backreference.",
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line: 4,
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column: 29,
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},
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{
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message:
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"Some paths leading to the backreference do not go through the referenced capturing group or the captured text might be reset before reaching the backreference.",
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line: 5,
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column: 33,
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},
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],
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},
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{
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code: String.raw`/(a)?\1/`,
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errors: [
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{
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message:
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"Some paths leading to the backreference do not go through the referenced capturing group or the captured text might be reset before reaching the backreference.",
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line: 1,
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column: 6,
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},
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],
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},
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{
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code: String.raw`/(a)*\1/`,
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errors: [
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{
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message:
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"Some paths leading to the backreference do not go through the referenced capturing group or the captured text might be reset before reaching the backreference.",
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line: 1,
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column: 6,
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},
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],
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},
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{
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code: String.raw`/(?:(a)|b)\1/`,
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errors: [
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{
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message:
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"Some paths leading to the backreference do not go through the referenced capturing group or the captured text might be reset before reaching the backreference.",
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line: 1,
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column: 11,
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},
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],
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},
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{
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code: String.raw`/(?:(a)|b)+\1/`,
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errors: [
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{
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message:
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"Some paths leading to the backreference do not go through the referenced capturing group or the captured text might be reset before reaching the backreference.",
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line: 1,
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column: 12,
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},
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],
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},
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],
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})

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