Add support to a checker for markdown links

[jenkin]

Problem

Links in markdown (ie. [anchor](absolute url or relative local path)) can be broken. Raneto doesn't have a built-in link checker or doesn't support custom plugins.

Requirements

A link checker validating both external links (ie. https://...) and relative local path (ie. ../dir/page.md) with anchors (ie. ../dir/page.md#chapter-1).

Proposed solution

There are many tools available to validate links in html or markdown files, ie. markdown-link-validator. We can integrate it in Makefile.

check:
    npx --yes markdown-link-validator ./content

So we can check all links running make check.

Output.

/home/jenkin/Progetti/sparkfabrik/company-playbook/content/tools-and-policies/access-to-the-office-during-covid19-pandemic.md
✔ https://calendar.google.com/calendar/u/1/embed?src=agavee.com_1eaeflfo4q9siffm4bj6umkpuk@group.calendar.google.com&ctz=Europe/Rome
✖ https://calendar.google.com/calendar/ical/agavee.com_1eaeflfo4q9siffm4bj6umkpuk%40group.calendar.google.com/private-999297412c557aade34f6654b5e2b923/basic.ics:17:232
✔ https://www.gazzettaufficiale.it/atto/serie_generale/caricaDettaglioAtto/originario?atto.dataPubblicazioneGazzetta=2020-10-07&atto.codiceRedazionale=20G00144&elenco30giorni=false
✔ #responsible-for-security

Found 4 links:
    3 valid
    1 invalid

Drawbacks

For markdown-link-validator a valid internal link should have a relative path (no leading /) and a .md extension (see https://github.com/webhintio/markdown-link-validator/blob/main/src/lib/mdfile.ts#L178).

Alternatives

• markdown-link-check: same drawbacks of markdown-link-validator, no built-in support for directory recursive (see docs), it compiles markdown to html using markdown-link-extractor and extracts links from it using html-link-extractor
• remark-validate-links: to be tested

[stickgrinder]

This is a great idea. One thing that we may want to do is providing a git-hook which runs the check before commit or push events, because being Raneto a running service, you make it once and it reflects the markdown files on the fly. This would rule out the check after the first make issuing.

[jenkin]

@stickgrinder I added a drawbacks section and published a working experiment in 167-exp-link-checker branch.

[stickgrinder]

can you please open a draft PR with your work so I can review it with ease?

[jenkin]

Here is my enhanced fork of markdown-link-validator: https://github.com/jenkin/markdown-link-validator/tree/feature/sparkfabrik-enhancements. All fixes merged in #170 come from that enhanced version.

[jenkin]

All fixes proposed in #172 come from enhanced version of markdown-link-validator.

In #173 it is integrated in playbook Makefile.

[stickgrinder]

@jenkin I merged this, will try and do some testing adding stuff to the pages you created, before closing the card.