New Rule: check for broken links

[fibo]

Rule details

A set of rules that check links, for example internal links in a markdown file or cross links from between two markdown files would be a huge value added. I am already using those rules via markdownlint and they are so useful. I saw many projects where the links in the markdown docs are broken. I am excited about using ESLint to lint also JSON, CSS, markdown etc. and having rules to check for broken links is the main criteria that would convince me to adopt ESLint for markdown.

What type of rule is this?

Warns about a potential problem

Example code

The same feature is implemented by the following packages as markdownlint custom rules:

- markdownlint-rule-github-internal-links
- markdownlint-rule-relative-links

Participation

• I am willing to submit a pull request to implement this rule.

Additional comments

No response

[nzakas]

Can you please explain exactly what you mean by "check for broken links"?

What is considered a "broken link"?

[fibo]

Sure @nzakas , thanks for you answer!!

Examples

Internal links

First of all, there are internal links.

# My project

[Installation](#installation) | [Usage](#usaage) | [Lincense](#license)

## Installation

    npm install my-project

## Usage

The link to this section in the Table of contents is broken.

## License

MIT

Cross links

Then there are links across different documents.

For example here the second link is broken.

# ESLint markdown

Rules:

- [`fenced-code-language`](docs/rules/fenced-code-language.md)
- [`heading-increment`](docs/rules/heading-increement.md)

Furthermore you can also have broken links cause one section was renamed or removed like

Install Node with proper version, see [requirements here](docs/requirements.md#node)

Counter example

On the other side, checking for external links within a tool like ESLint does not make sense to me. First of all because it depends a network connection. But also because there is no easy way to determine if a link is actually broken.

Conclusion and feedback

I hope it is clear, otherwise feel free to ping me.
I am really looking forward to use ESLint for Markdown as well as for CSS.
I am already experimenting with ESLint stylistic to replace prettier.
Also there, it is a tool not ready yet (especially for TypeScript) but very promising.
But the non plus ultra IMO would be an HTML linter that takes advantage of CSS, JS and possibly other linters to check mixed code in a page.
Sorry, I diverged.

I am also available to help implementing or testing the "broken links" rule.