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Add regexp/no-lazy-ends rule (#96)
* Add `regexp/no-lazy-ends` rule * update
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‎README.md

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@@ -95,6 +95,7 @@ The rules with the following star :star: are included in the `plugin:regexp/reco
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| [regexp/no-empty-lookarounds-assertion](https://ota-meshi.github.io/eslint-plugin-regexp/rules/no-empty-lookarounds-assertion.html) | disallow empty lookahead assertion or empty lookbehind assertion | :star: |
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| [regexp/no-escape-backspace](https://ota-meshi.github.io/eslint-plugin-regexp/rules/no-escape-backspace.html) | disallow escape backspace (`[\b]`) | :star: |
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| [regexp/no-invisible-character](https://ota-meshi.github.io/eslint-plugin-regexp/rules/no-invisible-character.html) | disallow invisible raw character | :star::wrench: |
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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-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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| [regexp/no-empty-lookarounds-assertion](./no-empty-lookarounds-assertion.md) | disallow empty lookahead assertion or empty lookbehind assertion | :star: |
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| [regexp/no-escape-backspace](./no-escape-backspace.md) | disallow escape backspace (`[\b]`) | :star: |
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| [regexp/no-invisible-character](./no-invisible-character.md) | disallow invisible raw character | :star::wrench: |
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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-unused-capturing-group](./no-unused-capturing-group.md) | disallow unused capturing group | |

‎docs/rules/no-lazy-ends.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-lazy-ends"
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description: "disallow lazy quantifiers at the end of an expression"
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---
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# regexp/no-lazy-ends
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> disallow lazy quantifiers at the end of an expression
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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 a lazily quantified element is the last element matched by an expression
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(e.g. the `a{2,3}?` in `b+a{2,3}?`), we know that the lazy quantifier will
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always only match the element the minimum number of times. The maximum is
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completely ignored because the expression can accept after the minimum was
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reached.
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If the minimum of the lazy quantifier is 0, we can even remove the quantifier
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and the quantified element without changing the meaning of the pattern. E.g.
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`a+b*?` and `a+` behave the same.
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If the minimum is 1, we can remove the quantifier. E.g. `a+b+?` and `a+b` behave
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the same.
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If the minimum is greater than 1, we can replace the quantifier with a constant,
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greedy quantifier. E.g. `a+b{2,4}?` and `a+b{2}` behave the same.
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<eslint-code-block>
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```js
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/* eslint regexp/no-lazy-ends: "error" */
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/* ✓ GOOD */
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var foo = /a+?b*/
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var foo = /a??(?:ba+?|c)*/
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var foo = /ba*?$/
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/* ✗ BAD */
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var foo = /a??/
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var foo = /a+b+?/
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var foo = /a(?:c|ab+?)?/
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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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## :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-lazy-ends] rule.
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[eslint-plugin-clean-regex]: https://github.com/RunDevelopment/eslint-plugin-clean-regex
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[clean-regex/no-lazy-ends]: https://github.com/RunDevelopment/eslint-plugin-clean-regex/blob/master/docs/rules/no-lazy-ends.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-lazy-ends.ts)
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- [Test source](https://github.com/ota-meshi/eslint-plugin-regexp/blob/master/tests/lib/rules/no-lazy-ends.ts)

‎lib/rules/no-lazy-ends.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 type { Alternative, Quantifier } from "regexpp/ast"
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import { createRule, defineRegexpVisitor, getRegexpLocation } from "../utils"
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/**
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* Extract lazy end quantifiers
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*/
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function* extractLazyEndQuantifiers(
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alternatives: Alternative[],
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): IterableIterator<Quantifier> {
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for (const { elements } of alternatives) {
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if (elements.length > 0) {
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const last = elements[elements.length - 1]
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switch (last.type) {
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case "Quantifier":
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if (!last.greedy && last.min !== last.max) {
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yield last
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} else if (last.max === 1) {
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const element = last.element
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if (
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element.type === "Group" ||
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element.type === "CapturingGroup"
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) {
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yield* extractLazyEndQuantifiers(
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element.alternatives,
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)
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}
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}
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break
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case "CapturingGroup":
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case "Group":
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yield* extractLazyEndQuantifiers(last.alternatives)
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break
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default:
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break
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}
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}
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}
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}
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export default createRule("no-lazy-ends", {
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meta: {
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docs: {
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description:
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"disallow lazy quantifiers at the end of an expression",
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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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uselessElement:
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"The quantifier and the quantified element can be removed because the quantifier is lazy and has a minimum of 0.",
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uselessQuantifier:
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"The quantifier can be removed because the quantifier is lazy and has a minimum of 1.",
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uselessRange:
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"The quantifier can be replaced with '{{{min}}}' because the quantifier is lazy and has a minimum of {{min}}.",
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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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onPatternEnter(pNode) {
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for (const lazy of extractLazyEndQuantifiers(
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pNode.alternatives,
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)) {
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if (lazy.min === 0) {
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context.report({
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node,
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loc: getRegexpLocation(sourceCode, node, lazy),
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messageId: "uselessElement",
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})
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} else if (lazy.min === 1) {
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context.report({
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node,
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loc: getRegexpLocation(sourceCode, node, lazy),
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messageId: "uselessQuantifier",
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})
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} else {
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context.report({
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node,
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loc: getRegexpLocation(sourceCode, node, lazy),
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messageId: "uselessRange",
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data: {
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min: String(lazy.min),
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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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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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@@ -11,6 +11,7 @@ import noEmptyGroup from "../rules/no-empty-group"
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import noEmptyLookaroundsAssertion from "../rules/no-empty-lookarounds-assertion"
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import noEscapeBackspace from "../rules/no-escape-backspace"
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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 noUnusedCapturingGroup from "../rules/no-unused-capturing-group"
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noEmptyLookaroundsAssertion,
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noEscapeBackspace,
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noInvisibleCharacter,
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noLazyEnds,
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noLegacyFeatures,
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noOctal,
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noUnusedCapturingGroup,

‎tests/lib/rules/no-lazy-ends.ts

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import { RuleTester } from "eslint"
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import rule from "../../../lib/rules/no-lazy-ends"
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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-lazy-ends", rule as any, {
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valid: [
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`/a+?b*/`,
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`/a??(?:ba+?|c)*/`,
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`/ba*?$/`,
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`/a{3}?/`, // uselessly lazy but that's not for this rule to correct
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],
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invalid: [
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{
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code: `/a??/`,
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errors: [
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{
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message:
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"The quantifier and the quantified element can be removed because the quantifier is lazy and has a minimum of 0.",
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line: 1,
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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: `/a*?/`,
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errors: [
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{
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message:
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"The quantifier and the quantified element can be removed because the quantifier is lazy and has a minimum of 0.",
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line: 1,
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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: `/a+?/`,
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errors: [
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{
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message:
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"The quantifier can be removed because the quantifier is lazy and has a minimum of 1.",
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line: 1,
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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: `/a{3,7}?/`,
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errors: [
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{
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message:
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"The quantifier can be replaced with '{3}' because the quantifier is lazy and has a minimum of 3.",
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line: 1,
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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: `/a{3,}?/`,
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errors: [
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{
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message:
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"The quantifier can be replaced with '{3}' because the quantifier is lazy and has a minimum of 3.",
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line: 1,
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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: `/(?:a|b(c+?))/`,
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errors: [
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{
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message:
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"The quantifier can be removed because the quantifier is lazy and has a minimum of 1.",
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line: 1,
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column: 9,
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},
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],
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},
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{
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code: `/a(?:c|ab+?)?/`,
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errors: [
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{
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message:
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"The quantifier can be removed because the quantifier is lazy and has a minimum of 1.",
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line: 1,
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column: 9,
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},
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],
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},
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],
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})

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