Bug: `no-multiple-h1` and `require-alt-text` miss errors after a HTML comment is closed

[ericcornelissen]

Environment

ESLint version: 9.31.0
@eslint/markdown version: 7.0.0
Node version: 22.15.0
npm version: 10.9.2
Operating System: Ubuntu 24.04

Which language are you using?

gfm

What did you do?

Configuration

import { defineConfig } from "eslint/config";
import markdown from "@eslint/markdown";

export default defineConfig({
  files: ["**/*.md"],
  plugins: { markdown },
  language: "markdown/gfm",
  rules: {
    "markdown/no-multiple-h1": "error",
    "markdown/require-alt-text": "error",
  },
});

# Heading 1

<h1>Reported</h1>
<!-- --> <h1>Not reported</h1>

---

<img src="reported.png" />
<!-- --> <img src="not-reported.png" />

What did you expect to happen?

With no-multiple-h1: error the substring <h1>Not reported</h1> should be reported.

With require-alt-text: error the substring <img src="not-reported.png" /> should be reported.

What actually happened?

Neither is reported.

Link to Minimal Reproducible Example

https://stackblitz.com/edit/stackblitz-starters-cttfryej?file=eslint.config.js,markdown.md&view=editor

Participation

• I am willing to submit a pull request for this issue.

Additional comments

For both this is due to the regular subexpression (?<!<!--[\s\S]*?)<, which does not end after the closing -->.

• markdown/src/rules/no-multiple-h1.js

  Line 27 in 56eb0ee

  const h1TagPattern = /(?<!<!--[\s\S]*?)<h1[^>]*>[\s\S]*?<\/h1>/giu;

• markdown/src/rules/require-alt-text.js

  Line 27 in 56eb0ee

  const imgTagPattern = /(?<!<!--[\s\S]*?)<img[^>]*>/giu;

[TKDev7]

I was able to reproduce this as well. I'll work on this.

[snitin315]

Good catch! Marking as accepted.