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Add regexp/no-useless-flag rule (#139)
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‎README.md

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@@ -109,6 +109,7 @@ The rules with the following star :star: are included in the `plugin:regexp/reco
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| [regexp/no-useless-dollar-replacements](https://ota-meshi.github.io/eslint-plugin-regexp/rules/no-useless-dollar-replacements.html) | disallow useless `$` replacements in replacement string | |
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| [regexp/no-useless-escape](https://ota-meshi.github.io/eslint-plugin-regexp/rules/no-useless-escape.html) | disallow unnecessary escape characters in RegExp | |
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| [regexp/no-useless-exactly-quantifier](https://ota-meshi.github.io/eslint-plugin-regexp/rules/no-useless-exactly-quantifier.html) | disallow unnecessary exactly quantifier | :star: |
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| [regexp/no-useless-flag](https://ota-meshi.github.io/eslint-plugin-regexp/rules/no-useless-flag.html) | disallow unnecessary regex flags | :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-range](https://ota-meshi.github.io/eslint-plugin-regexp/rules/no-useless-range.html) | disallow unnecessary range of characters by using a hyphen | :wrench: |

‎docs/rules/README.md

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| [regexp/no-useless-dollar-replacements](./no-useless-dollar-replacements.md) | disallow useless `$` replacements in replacement string | |
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| [regexp/no-useless-escape](./no-useless-escape.md) | disallow unnecessary escape characters in RegExp | |
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| [regexp/no-useless-exactly-quantifier](./no-useless-exactly-quantifier.md) | disallow unnecessary exactly quantifier | :star: |
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| [regexp/no-useless-flag](./no-useless-flag.md) | disallow unnecessary regex flags | :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-range](./no-useless-range.md) | disallow unnecessary range of characters by using a hyphen | :wrench: |

‎docs/rules/no-useless-flag.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-flag"
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description: "disallow unnecessary regex flags"
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---
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# regexp/no-useless-flag
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> disallow unnecessary regex flags
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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 will point out present regex flags that do not change the pattern.
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### `i` flag (ignoreCase)
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The `i` flag is only necessary if the pattern contains any characters with case
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variations. If the pattern contains no such characters, the flag will be
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unnecessary. E.g. `/\.{3}/i`
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<eslint-code-block fix>
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```js
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/* eslint regexp/no-useless-flag: "error" */
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/* ✓ GOOD */
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var foo = /a|b/i;
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/* ✗ BAD */
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var foo = /\.{3}/i;
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var foo = /\w+/i;
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```
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</eslint-code-block>
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### `m` flag (multiline)
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The `m` flag changes the behavior of the `^` and `$` assertions. If the pattern
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doesn't contain these anchors, the `m` flag will be unnecessary. E.g. `/foo|[^\r\n]*/m`
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<eslint-code-block fix>
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```js
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/* eslint regexp/no-useless-flag: "error" */
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/* ✓ GOOD */
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var foo = /^foo$/m;
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/* ✗ BAD */
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var foo = /foo|[^\r\n]*/m;
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var foo = /a|b/m;
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```
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</eslint-code-block>
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### `s` flag (dotAll)
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The `s` flag makes the dot (`.`) match all characters instead of the usually
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non-line-terminator characters. If the pattern doesn't contain a dot
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character set, the `s` flag will be unnecessary. E.g. `/[.:]/s`
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<eslint-code-block fix>
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```js
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/* eslint regexp/no-useless-flag: "error" */
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/* ✓ GOOD */
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var foo = /a.*?b/s;
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/* ✗ BAD */
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var foo = /[.:]/s;
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var foo = /^foo$/s;
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```
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</eslint-code-block>
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### `g` flag (global)
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The `g` flag is used when you need to test a regular expression against all possible string match. If not, it will be unnecessary.
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<eslint-code-block fix>
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```js
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/* eslint regexp/no-useless-flag: "error" */
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/* ✓ GOOD */
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const regex1 = /foo/g;
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const str = 'table football, foosball';
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while ((array = regex1.exec(str)) !== null) {
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//
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}
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const regex2 = /foo/g;
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regex2.test(string);
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regex2.test(string);
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str.replace(/foo/g, 'bar');
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str.replaceAll(/foo/g, 'bar');
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/* ✗ BAD */
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/foo/g.test(string);
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const regex3 = /foo/g;
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regex3.test(string); // You have used it only once.
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/foo/g.exec(string);
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const regex4 = /foo/g;
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regex4.exec(string); // You have used it only once.
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new RegExp('foo', 'g').test(string);
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str.search(/foo/g);
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```
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</eslint-code-block>
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### other flags
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No other flags will be checked.
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## :wrench: Options
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```json5
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{
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"regexp/no-useless-flag": ["error",
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{
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"ignore": [] // An array of "i", "m", "s" and "g".
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}
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]
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}
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```
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- `ignore` ... An array of flags to ignore from the check.
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### `"ignore": ["s", "g"]`
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<eslint-code-block fix>
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```js
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/* eslint regexp/no-useless-flag: ["error", { "ignore": ["s", "g"] }] */
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/* ✓ GOOD */
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var foo = /\w/s;
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/foo/g.test(string);
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/* ✗ BAD */
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var foo = /\w/i;
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var foo = /\w/m;
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```
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</eslint-code-block>
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## :heart: Compatibility
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This rule is compatible with [clean-regex/no-unnecessary-flag] rule.
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[clean-regex/no-unnecessary-flag]: https://github.com/RunDevelopment/eslint-plugin-clean-regex/blob/master/docs/rules/no-unnecessary-flag.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-useless-flag.ts)
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- [Test source](https://github.com/ota-meshi/eslint-plugin-regexp/blob/master/tests/lib/rules/no-useless-flag.ts)

‎lib/rules/match-any.ts

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getRegexpRange,
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fixerApplyEscape,
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parseFlags,
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isRegexpLiteral,
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} from "../utils"
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import type { ReadonlyFlags } from "regexp-ast-analysis"
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import { matchesAllCharacters } from "regexp-ast-analysis"
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* Fix source code
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* @param fixer
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*/
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function fix(
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function* fix(
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fixer: Rule.RuleFixer,
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node: Expression,
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regexpNode: RegExpNode,
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flags: ReadonlyFlags,
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) {
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if (!preference) {
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return null
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return
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}
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if (preference === OPTION_DOTALL && !flags.dotAll) {
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// since we can't just add flags, we cannot fix this
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return null
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if (preference === OPTION_DOTALL) {
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if (!flags.dotAll) {
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// since we can't just add flags, we cannot fix this
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return
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}
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if (!isRegexpLiteral(node)) {
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// Flag conflicts may be unavoidable and will not be autofix.
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return
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}
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}
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const range = getRegexpRange(sourceCode, node, regexpNode)
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if (range == null) {
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return null
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return
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}
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if (
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regexpNode.type === "CharacterClass" &&
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preference.startsWith("[") &&
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preference.endsWith("]")
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) {
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return fixer.replaceTextRange(
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yield fixer.replaceTextRange(
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[range[0] + 1, range[1] - 1],
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fixerApplyEscape(preference.slice(1, -1), node),
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)
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return
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}
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const replacement = preference === OPTION_DOTALL ? "." : preference
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return fixer.replaceTextRange(
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yield fixer.replaceTextRange(
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range,
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fixerApplyEscape(replacement, node),
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)
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if (preference === OPTION_DOTALL) {
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// Autofix to dotAll depends on the flag.
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// Modify the entire regular expression literal to avoid conflicts due to flag changes.
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// Mark regular expression flag changes to avoid conflicts due to flag changes.
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const afterRange: [number, number] = [range[1], node.range![1]]
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yield fixer.replaceTextRange(
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afterRange,
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sourceCode.text.slice(...afterRange),
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)
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}
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}
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/**

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