False positives in `no-empty-alternative` and `prefer-character-class` after updating eslint utils

[kachkaev]

Information:

• ESLint version: 9.25.1
• eslint-plugin-regexp version: 2.7.0

Description

After updating transient dependencies, I noticed new violations of regexp/no-empty-alternative and regexp/prefer-character-class rules.

This was related to updating @eslint-community/eslint-utils from 4.6.1 to 4.7.0. Both versions are within the dependency range:

eslint-plugin-regexp/package.json

Line 122 in 14ac3d8

"@eslint-community/eslint-utils": "^4.2.0",

This upstream PR looks relevant: eslint-community/eslint-utils#255

Here is an MWE:

const a = ["x", "y"] as const;
const b = ["x", "y", ""] as const;
const c = ["x", "y", "z"] as const;

const r1 = new RegExp(`^(${a.join("|")})$`);
const r2 = new RegExp(`^(${b.join("|")})$`);
const r3 = new RegExp(`^(${c.join("|")})$`);

Before @eslint-community/eslint-utils was updated, no errors were triggered for the above code. But now I see this:

const r1 = new RegExp(`^(${a.join("|")})$`);
const r2 = new RegExp(`^(${b.join("|")})$`); // This empty alternative might be a mistake. If not, use a quantifier instead. eslint(regexp/no-empty-alternative)
const r3 = new RegExp(`^(${c.join("|")})$`); // Unexpected the disjunction of single element alternatives. Use character class '[...]' instead. eslint(regexp/prefer-character-class)

I believe that these are false positives. If a RegExp is built from the variables, it is impossible to meet the rules without introducing multiple sources of truth.

[ota-meshi]

I think the rule is working correctly, and because eslint-utils now understands as const, the rule work better.
If you have source code where the rule is giving a false positive, can you provide an example and a repository where it can be reproduced?