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272 changes: 272 additions & 0 deletions docs/content/rules/sort-regexp.mdx
Original file line number Diff line number Diff line change
@@ -0,0 +1,272 @@
---
title: sort-regexp
description: Keep regular expressions predictable by sorting flags, character classes, and alternation branches. This ESLint rule helps you avoid subtle regex bugs and improves readability
shortDescription: Enforce sorted regular expressions
keywords:
- eslint
- regex sorting
- regular expressions
- eslint rule
- code quality
- javascript linting
---

import CodeExample from '../../components/CodeExample.svelte'
import CodeTabs from '../../components/CodeTabs.svelte'
import dedent from 'dedent'

Enforce consistent ordering in regular expressions: flags, character-class elements, and alternation branches inside capture groups or the top-level pattern.

Large patterns become easier to maintain when related branches are grouped and repeatedly used flags or character classes follow the same order. This rule helps you spot missing alternatives, avoid duplicated work, and keeps refactors safer by applying one sorting strategy across your codebase.

The rule is **safe** – it only reorders elements without changing their meaning.
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@hugop95 hugop95 Oct 28, 2025

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@azat-io

Honestly, I'm not confident that we can 100% ensure full safety here at this stage. I would even say that regex re-ordering probably has more weird edge cases that any other rules we have (which already have complex edge cases due to dependency ordering).

I expect bugs related to ordering that change the behavior when the rule is launched. It might be OK in 95% of the cases, but I have doubt about the remaining complex cases.

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I've added additional safeguards in the latest commits:

  • ES2024 /v flag guard - skips character class sorting to avoid breaking set operations (&&, --)
  • More backreference tests - covers named groups and complex scenarios
  • Existing shadowing detection - already handles /(ab|a)/ cases

The rule is conservative - it skips sorting when it detects potentially unsafe patterns. That said, I agree 100% safety is hard to guarantee with regex.


Comment on lines +22 to +23
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@coderabbitai coderabbitai bot Oct 18, 2025

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⚠️ Potential issue | 🟠 Major

Docs overstate safety; add caveat and guidance

Reordering alternations is not universally safe (e.g., shared prefixes like (ab|a)), and numeric backreferences can also change behavior if group numbering shifts after reordering.

- The rule is **safe** – it only reorders elements without changing their meaning.
+ Important: Reordering can change behavior in specific cases (e.g., alternatives that share a prefix like `(ab|a)`, or patterns whose numeric backreferences depend on the textual order of capturing groups). The rule avoids such changes when it detects risk; otherwise, prefer `type: 'unsorted'` or disable the rule locally for those patterns.
📝 Committable suggestion

‼️ IMPORTANT
Carefully review the code before committing. Ensure that it accurately replaces the highlighted code, contains no missing lines, and has no issues with indentation. Thoroughly test & benchmark the code to ensure it meets the requirements.

Suggested change
The rule is **safe**it only reorders elements without changing their meaning.
Important: Reordering can change behavior in specific cases (e.g., alternatives that share a prefix like `(ab|a)`, or patterns whose numeric backreferences depend on the textual order of capturing groups). The rule avoids such changes when it detects risk; otherwise, prefer `type: 'unsorted'` or disable the rule locally for those patterns.
🤖 Prompt for AI Agents
In docs/content/rules/sort-regexp.mdx around lines 22-23, the claim "The rule is
**safe** – it only reorders elements without changing their meaning." overstates
safety; update the text to add a short caveat and guidance: state that
reordering alternations can change behavior for patterns with shared prefixes
(e.g., (ab|a)) and when numeric capture group indices are relied upon by
backreferences, and advise when the rule is safe to apply (alternations are
independent, use non-capturing groups (?:...) or named captures to preserve
backreference semantics) and when to avoid it; include one minimal example of a
problematic case and a recommended fix or workaround (use non-capturing groups
or reorder/escape to preserve intended match) so readers know when to
enable/disable the rule.

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@azat-io

There are indeed dangers with the current state:

image

but

image

I don't think we should include this rule in the recommended, they are very likely other edge cases we will be missing.

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Seems like the humans are having a chat. I'll hop back into my burrow for now. If you need me again, just tag @coderabbitai in a new comment, and I'll come hopping out!

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@hugop95 I fixed it

## Try it out

<CodeExample
alphabetical={dedent`
const patterns = {
alternatives: /(apple|banana|orange|pear)/,
alias: /(?<role>administrator|guest|user)/,
characterClass: /[0-9A-Za-fz]/,
flags: /pattern/gimsuy,
}
`}
lineLength={dedent`
const patterns = {
alternatives: /(banana|orange|apple|pear)/,
alias: /(?<role>administrator|guest|user)/,
characterClass: /[0-9A-Za-fz]/,
flags: /pattern/yusmig,
}
`}
initial={dedent`
const patterns = {
alternatives: /(pear|apple|orange|banana)/,
alias: /(?<role>user|administrator|guest)/,
characterClass: /[z0-9a-fA-Z]/,
flags: /pattern/yusmig,
}
`}
client:load
lang="tsx"
/>

## Options

This rule accepts an options object with the following properties:

### type

<sub>default: `'alphabetical'`</sub>

Specifies the sorting strategy applied to matches (flags, character-class elements, and alternation branches).

- `'alphabetical'` — Sort values alphabetically using [`localeCompare`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/localeCompare).
- `'natural'` — Sort values in [natural](https://github.com/yobacca/natural-orderby) order (e.g., `(?=2)` comes before `(?=10)`).
- `'line-length'` — Sort values by their textual length.
- `'custom'` — Sort values according to a custom alphabet defined in [`alphabet`](#alphabet).
- `'unsorted'` — Do not reorder values. [`groups`](#groups) and [`customGroups`](#customgroups) are still applied.

### order

<sub>default: `'asc'`</sub>

Specifies the direction of sorting.

- `'asc'` — Ascending order (shorter to longer, A to Z).
- `'desc'` — Descending order (longer to shorter, Z to A).

### fallbackSort

<sub>
type:
```ts
{
type: 'alphabetical' | 'natural' | 'line-length' | 'custom' | 'unsorted'
order?: 'asc' | 'desc'
}
```
</sub>
<sub>default: `{ type: 'unsorted' }`</sub>

Used when the primary [`type`](#type) considers two values equal. For example, rely on alphabetical order when two branches share the same length.

### alphabet

<sub>default: `''`</sub>

Defines the custom alphabet for `'custom'` sorting. Use the [`Alphabet` helper](https://perfectionist.dev/alphabet) to build consistent alphabets quickly.

### locales

<sub>default: `'en-US'`</sub>

Locales passed to `localeCompare` when alphabetical comparisons are required.

### ignoreCase

<sub>default: `true`</sub>

Whether comparisons should be case-insensitive.

- `true` — Treat upper- and lowercase branches as equal (default).
- `false` — Preserve case sensitivity.

### specialCharacters

<sub>default: `'keep'`</sub>

Controls how special characters are handled before comparison.

- `'keep'` — Keep them (default).
- `'trim'` — Trim leading special characters.
- `'remove'` — Remove all special characters.

### ignoreAlias

<sub>default: `false`</sub>

Determines whether named capturing group aliases (e.g., `(?<role>...)`) are considered during comparison.

- `false` — Sort by `alias: pattern` (default).
- `true` — Ignore the alias and only compare the branch content.

This is useful when you only care about the pattern and not how it is aliased.

### customGroups
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@azat-io

For other rules, this section is after Groups, so I would do the same here for consistency.


<sub>
type: `Array<CustomGroupDefinition | CustomGroupAnyOfDefinition>`
</sub>
<sub>default: `[]`</sub>

Define custom groups to control how alternatives are organized before sorting.

```ts
interface CustomGroupDefinition {
groupName: string
selector?: 'alias' | 'pattern'
elementNamePattern?: string | string[] | { pattern: string; flags?: string } | { pattern: string; flags?: string }[]
elementValuePattern?: string | string[] | { pattern: string; flags?: string } | { pattern: string; flags?: string }[]
type?: 'alphabetical' | 'natural' | 'line-length' | 'custom' | 'unsorted'
order?: 'asc' | 'desc'
fallbackSort?: { type: string; order?: 'asc' | 'desc' }
}

interface CustomGroupAnyOfDefinition {
groupName: string
anyOf: Array<{
selector?: 'alias' | 'pattern'
elementNamePattern?: string | string[] | { pattern: string; flags?: string } | { pattern: string; flags?: string }[]
elementValuePattern?: string | string[] | { pattern: string; flags?: string } | { pattern: string; flags?: string }[]
}>
type?: 'alphabetical' | 'natural' | 'line-length' | 'custom' | 'unsorted'
order?: 'asc' | 'desc'
fallbackSort?: { type: string; order?: 'asc' | 'desc' }
}
```

Attributes:

- `groupName` — Identifier referenced in [`groups`](#groups).
- `selector` — Filter by element type:
- `'alias'` — Named capturing group alternatives.
- `'pattern'` — Plain alternatives without aliases.
- `elementNamePattern` — Regex applied to the alias (if present).
- `elementValuePattern` — Regex applied to the branch content.
- `type`, `order`, `fallbackSort` — Override the respective global options for the group.

Custom groups are evaluated in order; the first match wins and overrides predefined groups.

### groups
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@azat-io

I would take the same sub sections as for other rules for consistency as well, even if this feature probably won't likely be used for this rule in particular:

### groups
<sub>
type:
```ts
Array<
| string
| string[]
| { newlinesBetween: number }
| {
group: string | string[];
type?: 'alphabetical' | 'natural' | 'line-length' | 'custom' | 'unsorted';
order?: 'asc' | 'desc';
}
>
```
</sub>
<sub>default: `[]`</sub>


<sub>
type: `Array<string | string[]>`
</sub>
<sub>default: `[]`</sub>

Controls the order in which groups are evaluated. Use the selectors from [`customGroups`](#customgroups) or custom group names. When an element does not match any provided group, it falls back to the implicit `unknown` group at the end of the list.

You can combine multiple groups by wrapping them in an array; all members will be sorted together using the global or overridden options.

## Usage

<CodeTabs
code={[
{
source: dedent`
// eslint.config.js
import perfectionist from 'eslint-plugin-perfectionist'
export default [
{
plugins: {
perfectionist,
},
rules: {
'perfectionist/sort-regexp': [
'error',
{
type: 'alphabetical',
order: 'asc',
fallbackSort: { type: 'unsorted' },
ignoreCase: true,
ignoreAlias: false,
specialCharacters: 'keep',
locales: 'en-US',
alphabet: '',
groups: [],
customGroups: [],
},
],
},
},
]
`,
name: 'Flat Config',
value: 'flat',
},
{
source: dedent`
// .eslintrc.js
module.exports = {
plugins: [
'perfectionist',
],
rules: {
'perfectionist/sort-regexp': [
'error',
{
type: 'alphabetical',
order: 'asc',
fallbackSort: { type: 'unsorted' },
ignoreCase: true,
ignoreAlias: false,
specialCharacters: 'keep',
locales: 'en-US',
alphabet: '',
groups: [],
customGroups: [],
},
],
},
}
`,
name: 'Legacy Config',
value: 'legacy',
},
]}
type="config-type"
client:load
lang="tsx"
/>

## Version

This rule was introduced in [v5.0.0](https://github.com/azat-io/eslint-plugin-perfectionist/releases/tag/v5.0.0).

## Resources

- [Rule source](https://github.com/azat-io/eslint-plugin-perfectionist/blob/main/rules/sort-regexp.ts)
- [Test source](https://github.com/azat-io/eslint-plugin-perfectionist/blob/main/test/rules/sort-regexp.test.ts)
1 change: 1 addition & 0 deletions docs/public/llms.txt
Original file line number Diff line number Diff line change
Expand Up @@ -44,6 +44,7 @@ Key features:
- [sort-named-imports](https://perfectionist.dev/rules/sort-named-imports): Sort named imports
- [sort-object-types](https://perfectionist.dev/rules/sort-object-types): Sort TypeScript object type properties
- [sort-objects](https://perfectionist.dev/rules/sort-objects): Sort object properties
- [sort-regexp](https://perfectionist.dev/rules/sort-regexp): Sort regular expressions
- [sort-sets](https://perfectionist.dev/rules/sort-sets): Sort Set elements
- [sort-switch-case](https://perfectionist.dev/rules/sort-switch-case): Sort switch statement cases
- [sort-union-types](https://perfectionist.dev/rules/sort-union-types): Sort TypeScript union types
Expand Down
3 changes: 3 additions & 0 deletions index.ts
Original file line number Diff line number Diff line change
Expand Up @@ -20,6 +20,7 @@ import sortImports from './rules/sort-imports'
import sortExports from './rules/sort-exports'
import sortObjects from './rules/sort-objects'
import sortModules from './rules/sort-modules'
import sortRegexp from './rules/sort-regexp'
import sortEnums from './rules/sort-enums'
import sortMaps from './rules/sort-maps'
import sortSets from './rules/sort-sets'
Expand All @@ -45,6 +46,7 @@ interface PluginConfig {
'sort-imports': Rule.RuleModule
'sort-exports': Rule.RuleModule
'sort-objects': Rule.RuleModule
'sort-regexp': Rule.RuleModule
'sort-enums': Rule.RuleModule
'sort-sets': Rule.RuleModule
'sort-maps': Rule.RuleModule
Expand Down Expand Up @@ -92,6 +94,7 @@ export let rules = {
'sort-imports': sortImports,
'sort-exports': sortExports,
'sort-objects': sortObjects,
'sort-regexp': sortRegexp,
'sort-enums': sortEnums,
'sort-sets': sortSets,
'sort-maps': sortMaps,
Expand Down
1 change: 1 addition & 0 deletions package.json
Original file line number Diff line number Diff line change
Expand Up @@ -57,6 +57,7 @@
"test:unit": "vitest --run --coverage"
},
"dependencies": {
"@eslint-community/regexpp": "^4.12.1",
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@azat-io

For information:

Just something to keep in mind based on the adoption of the rule.

"@typescript-eslint/utils": "^8.46.2",
"natural-orderby": "^5.0.0"
},
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3 changes: 3 additions & 0 deletions pnpm-lock.yaml

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1 change: 1 addition & 0 deletions readme.md
Original file line number Diff line number Diff line change
Expand Up @@ -193,6 +193,7 @@ module.exports = {
| [sort-named-imports](https://perfectionist.dev/rules/sort-named-imports) | Enforce sorted named imports | 🔧 |
| [sort-object-types](https://perfectionist.dev/rules/sort-object-types) | Enforce sorted object types | 🔧 |
| [sort-objects](https://perfectionist.dev/rules/sort-objects) | Enforce sorted objects | 🔧 |
| [sort-regexp](https://perfectionist.dev/rules/sort-regexp) | Enforce sorted regular expressions | 🔧 |
| [sort-sets](https://perfectionist.dev/rules/sort-sets) | Enforce sorted Set elements | 🔧 |
| [sort-switch-case](https://perfectionist.dev/rules/sort-switch-case) | Enforce sorted switch case statements | 🔧 |
| [sort-union-types](https://perfectionist.dev/rules/sort-union-types) | Enforce sorted union types | 🔧 |
Expand Down
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