Add minAlternatives option for prefer-character-class (#462)

* Add `minAlternatives` option for `prefer-character-class`

* Update docs/rules/prefer-character-class.md

Co-authored-by: Eric Cornelissen <[email protected]>

Co-authored-by: Eric Cornelissen <[email protected]>

Author: RunDevelopment

docs/rules/prefer-character-class.md

@@ -44,7 +44,22 @@ var foo = /(\w|\d)+:/
 
 ## :wrench: Options
 
-Nothing.
+```json5
+{
+  "regexp/prefer-character-class": [
+    "error",
+    {
+        "minAlternatives": 3
+    }
+  ]
+}
+```
+
+### `minAlternatives: integer`
+
+This number controls how many character alternatives have to be present for them to be merged. By default, there need to be at least 3 alternatives.
+
+Note that this option does not affect character alternatives where the characters overlap. These alternatives will always be merged to prevent excessive backtracking.
 
 ## :rocket: Version
 

lib/rules/prefer-character-class.ts

@@ -423,14 +423,28 @@ export default createRule("prefer-character-class", {
             recommended: true,
         },
         fixable: "code",
-        schema: [],
+        schema: [
+            {
+                type: "object",
+                properties: {
+                    minAlternatives: {
+                        type: "integer",
+                        minimum: 2,
+                    },
+                },
+                additionalProperties: false,
+            },
+        ],
         messages: {
             unexpected:
                 "Unexpected the disjunction of single element alternatives. Use character class '[...]' instead.",
         },
         type: "suggestion", // "problem",
     },
     create(context) {
+        const minCharacterAlternatives: number =
+            context.options[0]?.minAlternatives ?? 3
+
         /**
          * Create visitor
          */
@@ -515,7 +529,7 @@ export default createRule("prefer-character-class", {
                 const parsedAlts = parseRawAlts(alts, flags)
 
                 if (
-                    characterAltsCount >= 3 ||
+                    characterAltsCount >= minCharacterAlternatives ||
                     containsCharacterClass(alts) ||
                     totalIsAll(alts, regexpContext) ||
                     findNonDisjointAlt(parsedAlts)

tests/lib/rules/prefer-character-class.ts

@@ -19,6 +19,7 @@ tester.run("prefer-character-class", rule as any, {
         String.raw`/(?:[ab]|c\b)/`,
         String.raw`/(?:[ab]|cd)/`,
         String.raw`/(?:[ab]|(c))/`,
+        { code: String.raw`/a|b|c|\d/`, options: [{ minAlternatives: 5 }] },
     ],
     invalid: [
         {
@@ -285,5 +286,13 @@ tester.run("prefer-character-class", rule as any, {
                 },
             ],
         },
+
+        // minAlternatives option
+        {
+            code: String.raw`/(?:a|b)/`,
+            output: String.raw`/(?:[ab])/`,
+            options: [{ minAlternatives: 2 }],
+            errors: 1,
+        },
     ],
 })