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Add no-useless-quantifier rule (#197)
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‎README.md‎

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@@ -132,6 +132,7 @@ The rules with the following star :star: are included in the `plugin:regexp/reco
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| [regexp/no-useless-lazy](https://ota-meshi.github.io/eslint-plugin-regexp/rules/no-useless-lazy.html) | disallow unnecessarily non-greedy quantifiers | :wrench: |
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| [regexp/no-useless-non-capturing-group](https://ota-meshi.github.io/eslint-plugin-regexp/rules/no-useless-non-capturing-group.html) | disallow unnecessary Non-capturing group | :wrench: |
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| [regexp/no-useless-non-greedy](https://ota-meshi.github.io/eslint-plugin-regexp/rules/no-useless-non-greedy.html) | disallow unnecessarily non-greedy quantifiers | :wrench: |
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| [regexp/no-useless-quantifier](https://ota-meshi.github.io/eslint-plugin-regexp/rules/no-useless-quantifier.html) | disallow quantifiers that can be removed | :wrench: |
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| [regexp/no-useless-range](https://ota-meshi.github.io/eslint-plugin-regexp/rules/no-useless-range.html) | disallow unnecessary range of characters by using a hyphen | :wrench: |
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| [regexp/no-useless-two-nums-quantifier](https://ota-meshi.github.io/eslint-plugin-regexp/rules/no-useless-two-nums-quantifier.html) | disallow unnecessary `{n,m}` quantifier | :star::wrench: |
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| [regexp/optimal-lookaround-quantifier](https://ota-meshi.github.io/eslint-plugin-regexp/rules/optimal-lookaround-quantifier.html) | disallow the alternatives of lookarounds that end with a non-constant quantifier | |

‎docs/rules/README.md‎

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@@ -46,6 +46,7 @@ The rules with the following star :star: are included in the `plugin:regexp/reco
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| [regexp/no-useless-lazy](./no-useless-lazy.md) | disallow unnecessarily non-greedy quantifiers | :wrench: |
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| [regexp/no-useless-non-capturing-group](./no-useless-non-capturing-group.md) | disallow unnecessary Non-capturing group | :wrench: |
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| [regexp/no-useless-non-greedy](./no-useless-non-greedy.md) | disallow unnecessarily non-greedy quantifiers | :wrench: |
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| [regexp/no-useless-quantifier](./no-useless-quantifier.md) | disallow quantifiers that can be removed | :wrench: |
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| [regexp/no-useless-range](./no-useless-range.md) | disallow unnecessary range of characters by using a hyphen | :wrench: |
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| [regexp/no-useless-two-nums-quantifier](./no-useless-two-nums-quantifier.md) | disallow unnecessary `{n,m}` quantifier | :star::wrench: |
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| [regexp/optimal-lookaround-quantifier](./optimal-lookaround-quantifier.md) | disallow the alternatives of lookarounds that end with a non-constant quantifier | |

‎docs/rules/no-useless-quantifier.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-useless-quantifier"
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description: "disallow quantifiers that can be removed"
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---
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# regexp/no-useless-quantifier
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> disallow quantifiers that can be removed
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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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- :wrench: The `--fix` option on the [command line](https://eslint.org/docs/user-guide/command-line-interface#fixing-problems) can automatically fix some of the problems reported by this rule.
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## :book: Rule Details
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This rule reports quantifiers that can trivially be removed without affecting the pattern.
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This rule only fixes constant one quantifiers (e.g. `a{1}`). All other reported useless quantifiers hint at programmer oversight or fundamental problems with the pattern.
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Examples:
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- `a{1}`
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It's clear that the `{1}` quantifier can be removed.
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- `(?:a+b*|c*)?`
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It might not very obvious that the `?` quantifier can be removed. Without this quantifier, that pattern can still match the empty string by choosing 0 many `c`s in the `c*` alternative.
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- `(?:\b)+`
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The `+` quantifier can be removed because its quantified element doesn't consume characters.
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<eslint-code-block fix>
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```js
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/* eslint regexp/no-useless-quantifier: "error" */
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/* ✓ GOOD */
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var foo = /a*/;
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var foo = /(?:a|b?)??/;
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var foo = /(?:\b|(?!a))*/;
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/* ✗ BAD */
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var foo = /a{1}/;
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var foo = /(?:\b)+/;
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var foo = /(?:a+b*|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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## :mag: Implementation
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- [Rule source](https://github.com/ota-meshi/eslint-plugin-regexp/blob/master/lib/rules/no-useless-quantifier.ts)
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- [Test source](https://github.com/ota-meshi/eslint-plugin-regexp/blob/master/tests/lib/rules/no-useless-quantifier.ts)

‎lib/rules/no-useless-quantifier.ts‎

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import type { Rule } from "eslint"
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import type { RegExpVisitor } from "regexpp/visitor"
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import type { Quantifier } from "regexpp/ast"
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import type { RegExpContext } from "../utils"
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import { canUnwrapped, createRule, defineRegexpVisitor } from "../utils"
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import { isEmpty, isPotentiallyEmpty, isZeroLength } from "regexp-ast-analysis"
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export default createRule("no-useless-quantifier", {
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meta: {
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docs: {
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description: "disallow quantifiers that can be removed",
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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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fixable: "code",
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schema: [],
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messages: {
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constOne: "Unexpected useless quantifier.",
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empty:
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"Unexpected useless quantifier. The quantified element doesn't consume or assert characters.",
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emptyQuestionMark:
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"Unexpected useless quantifier. The quantified element can already accept the empty string, so this quantifier is redundant.",
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zeroLength:
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"Unexpected useless quantifier. The quantified element doesn't consume characters.",
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// suggestions
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remove: "Remove the '{{quant}}' quantifier.",
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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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regexpContext: RegExpContext,
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): RegExpVisitor.Handlers {
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const { node, getRegexpLocation, fixReplaceNode } = regexpContext
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/**
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* Returns a fix that replaces the given quantifier with its
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* quantified element
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*/
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function fixRemoveQuant(qNode: Quantifier) {
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return fixReplaceNode(qNode, () => {
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const text = qNode.element.raw
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return canUnwrapped(qNode, text) ? text : null
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})
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}
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/**
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* Returns a suggestion that replaces the given quantifier with its
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* quantified element
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*/
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function suggestRemoveQuant(
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qNode: Quantifier,
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): Rule.SuggestionReportDescriptor {
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const quant = qNode.raw.slice(qNode.element.end - qNode.start)
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return {
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messageId: "remove",
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data: { quant },
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fix: fixReplaceNode(qNode, () => {
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const text = qNode.element.raw
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return canUnwrapped(qNode, text) ? text : null
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}),
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}
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}
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return {
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onQuantifierEnter(qNode) {
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// trivial case
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// e.g. a{1}
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if (qNode.min === 1 && qNode.max === 1) {
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context.report({
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node,
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loc: getRegexpLocation(qNode),
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messageId: "constOne",
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fix: fixRemoveQuant(qNode),
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})
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return
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}
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// the quantified element already accepts the empty string
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// e.g. (||)*
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if (isEmpty(qNode.element)) {
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context.report({
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node,
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loc: getRegexpLocation(qNode),
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messageId: "empty",
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suggest: [suggestRemoveQuant(qNode)],
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})
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return
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}
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// the quantified element already accepts the empty string
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// e.g. (a?)?
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if (
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qNode.min === 0 &&
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qNode.max === 1 &&
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qNode.greedy &&
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isPotentiallyEmpty(qNode.element)
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) {
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context.report({
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node,
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loc: getRegexpLocation(qNode),
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messageId: "emptyQuestionMark",
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suggest: [suggestRemoveQuant(qNode)],
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})
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return
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}
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// the quantified is zero length
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// e.g. (\b){5}
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if (qNode.min >= 1 && isZeroLength(qNode.element)) {
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context.report({
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node,
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loc: getRegexpLocation(qNode),
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messageId: "zeroLength",
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suggest: [suggestRemoveQuant(qNode)],
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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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@@ -34,6 +34,7 @@ import noUselessFlag from "../rules/no-useless-flag"
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import noUselessLazy from "../rules/no-useless-lazy"
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import noUselessNonCapturingGroup from "../rules/no-useless-non-capturing-group"
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import noUselessNonGreedy from "../rules/no-useless-non-greedy"
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import noUselessQuantifier from "../rules/no-useless-quantifier"
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import noUselessRange from "../rules/no-useless-range"
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import noUselessTwoNumsQuantifier from "../rules/no-useless-two-nums-quantifier"
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import optimalLookaroundQuantifier from "../rules/optimal-lookaround-quantifier"
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noUselessLazy,
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noUselessNonCapturingGroup,
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noUselessNonGreedy,
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noUselessQuantifier,
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noUselessRange,
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noUselessTwoNumsQuantifier,
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optimalLookaroundQuantifier,

‎tests/lib/rules/no-useless-quantifier.ts‎

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import { RuleTester } from "eslint"
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import rule from "../../../lib/rules/no-useless-quantifier"
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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-useless-quantifier", rule as any, {
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valid: [
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String.raw`/a*/`,
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String.raw`/(?:a)?/`,
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String.raw`/(?:a|b?)??/`,
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String.raw`/(?:\b|a)?/`,
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String.raw`/(?:\b)*/`,
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String.raw`/(?:\b|(?!a))*/`,
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String.raw`/(?:\b|(?!))*/`,
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String.raw`/#[\da-z]+|#(?:-|([+/\\*~<>=@%|&?!])\1?)|#(?=\()/`,
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],
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invalid: [
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// trivial
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{
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code: String.raw`/a{1}/`,
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output: String.raw`/a/`,
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errors: ["Unexpected useless quantifier."],
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},
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{
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code: String.raw`/a{1,1}?/`,
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output: String.raw`/a/`,
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errors: ["Unexpected useless quantifier."],
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},
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// empty quantified element
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{
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code: String.raw`/(?:)+/`,
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output: null,
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errors: [
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{
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messageId: "empty",
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suggestions: [
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{ messageId: "remove", output: String.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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code: String.raw`/(?:|(?:)){5,9}/`,
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output: null,
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errors: [
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{
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messageId: "empty",
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suggestions: [
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{
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messageId: "remove",
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output: String.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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code: String.raw`/(?:|()()())*/`,
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output: null,
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errors: [
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{
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messageId: "empty",
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suggestions: [
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{
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messageId: "remove",
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output: String.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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// unnecessary optional quantifier (?) because the quantified element is potentially empty
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{
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code: String.raw`/(?:a+b*|c*)?/`,
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output: null,
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errors: [
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{
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messageId: "emptyQuestionMark",
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suggestions: [
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{
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messageId: "remove",
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output: String.raw`/(?:a+b*|c*)/`,
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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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code: String.raw`/(?:a|b?c?d?e?f?)?/`,
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output: null,
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errors: [
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{
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messageId: "emptyQuestionMark",
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suggestions: [
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{
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messageId: "remove",
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output: String.raw`/(?:a|b?c?d?e?f?)/`,
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},
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],
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},
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],
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},
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// quantified elements which do not consume characters
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{
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code: String.raw`/(?:\b)+/`,
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output: null,
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errors: [
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{
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messageId: "zeroLength",
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suggestions: [
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{ messageId: "remove", output: String.raw`/(?:\b)/` },
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],
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},
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],
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},
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{
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code: String.raw`/(?:\b){5,100}/`,
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output: null,
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errors: [
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{
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messageId: "zeroLength",
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suggestions: [
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{ messageId: "remove", output: String.raw`/(?:\b)/` },
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],
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},
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],
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},
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{
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code: String.raw`/(?:\b|(?!a))+/`,
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output: null,
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errors: [
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{
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messageId: "zeroLength",
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suggestions: [
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{
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messageId: "remove",
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output: String.raw`/(?:\b|(?!a))/`,
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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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code: String.raw`/(?:\b|(?!)){6}/`,
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output: null,
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errors: [
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{
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messageId: "zeroLength",
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suggestions: [
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{
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messageId: "remove",
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output: String.raw`/(?:\b|(?!))/`,
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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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})

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