Add optimal-quantifier-concatenation rule (#207)

* Add `optimal-quantifier-concatenation` rule

* Improved detection

Author: RunDevelopment

README.md

@@ -139,6 +139,7 @@ The rules with the following star :star: are included in the `plugin:regexp/reco
 | [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: |
 | [regexp/no-zero-quantifier](https://ota-meshi.github.io/eslint-plugin-regexp/rules/no-zero-quantifier.html) | disallow quantifiers with a maximum of zero |  |
 | [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 |  |
+| [regexp/optimal-quantifier-concatenation](https://ota-meshi.github.io/eslint-plugin-regexp/rules/optimal-quantifier-concatenation.html) | require optimal quantifiers for concatenated quantifiers | :wrench: |
 | [regexp/prefer-escape-replacement-dollar-char](https://ota-meshi.github.io/eslint-plugin-regexp/rules/prefer-escape-replacement-dollar-char.html) | enforces escape of replacement `$` character (`$$`). |  |
 | [regexp/prefer-predefined-assertion](https://ota-meshi.github.io/eslint-plugin-regexp/rules/prefer-predefined-assertion.html) | prefer predefined assertion over equivalent lookarounds | :wrench: |
 | [regexp/prefer-quantifier](https://ota-meshi.github.io/eslint-plugin-regexp/rules/prefer-quantifier.html) | enforce using quantifier | :wrench: |

docs/rules/README.md

@@ -53,6 +53,7 @@ The rules with the following star :star: are included in the `plugin:regexp/reco
 | [regexp/no-useless-two-nums-quantifier](./no-useless-two-nums-quantifier.md) | disallow unnecessary `{n,m}` quantifier | :star::wrench: |
 | [regexp/no-zero-quantifier](./no-zero-quantifier.md) | disallow quantifiers with a maximum of zero |  |
 | [regexp/optimal-lookaround-quantifier](./optimal-lookaround-quantifier.md) | disallow the alternatives of lookarounds that end with a non-constant quantifier |  |
+| [regexp/optimal-quantifier-concatenation](./optimal-quantifier-concatenation.md) | require optimal quantifiers for concatenated quantifiers | :wrench: |
 | [regexp/prefer-escape-replacement-dollar-char](./prefer-escape-replacement-dollar-char.md) | enforces escape of replacement `$` character (`$$`). |  |
 | [regexp/prefer-predefined-assertion](./prefer-predefined-assertion.md) | prefer predefined assertion over equivalent lookarounds | :wrench: |
 | [regexp/prefer-quantifier](./prefer-quantifier.md) | enforce using quantifier | :wrench: |

docs/rules/optimal-quantifier-concatenation.md

@@ -0,0 +1,51 @@
+---
+pageClass: "rule-details"
+sidebarDepth: 0
+title: "regexp/optimal-quantifier-concatenation"
+description: "require optimal quantifiers for concatenated quantifiers"
+---
+# regexp/optimal-quantifier-concatenation
+
+> require optimal quantifiers for concatenated quantifiers
+
+- :exclamation: <badge text="This rule has not been released yet." vertical="middle" type="error"> ***This rule has not been released yet.*** </badge>
+- :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.
+
+## :book: Rule Details
+
+If two quantified characters, character classes, or characters are concatenated, the quantifiers can be optimized if either of the characters elements is a subset of the other.
+
+Let's take `\d+\w+` as an example. <br>
+This can be optimized to the equivalent pattern `\d\w+`. Not only is the optimized pattern simpler, it is also faster because the first pattern might take up to _O(n^2)_ steps to fail while the optimized pattern will fail after at most _O(n)_ steps. Generally, the optimized pattern will take less backtracking steps to fail.
+
+Choosing optimal quantifiers does not only make your patterns simpler but also faster and most robust against ReDoS attacks.
+
+<eslint-code-block fix>
+
+```js
+/* eslint regexp/optimal-quantifier-concatenation: "error" */
+
+/* ✓ GOOD */
+var foo = /\w+\d{4}/;
+var foo = /\w{3,5}\d*/;
+var foo = /a+b+c+d+[abc]+/;
+var foo = /a\w*/;
+
+/* ✗ BAD */
+var foo = /\w+\d+/;
+var foo = /\w+\d?/;
+var foo = /\w?\w/;
+var foo = /[ab]*(?:a|b)/;
+var foo = /\w+(?:(a)|b)*/;
+```
+
+</eslint-code-block>
+
+## :wrench: Options
+
+Nothing.
+
+## :mag: Implementation
+
+- [Rule source](https://github.com/ota-meshi/eslint-plugin-regexp/blob/master/lib/rules/optimal-quantifier-concatenation.ts)
+- [Test source](https://github.com/ota-meshi/eslint-plugin-regexp/blob/master/tests/lib/rules/optimal-quantifier-concatenation.ts)