Allow links to point to the top of the document

[loilo]

This PR enables linking to the top of a document on GitHub and Gitlab.

Both services have an anchor called #readme at the beginning of a rendered markdown document. This is useful for skipping the (potentially long) file list above it and it's heavily used in production (for example by npm init which appends it automatically if your package homepage is a GitHub repo).

BitBucket has no equivalent to this anchor, so this PR implements the feature as an environment-specific configuration.

I'll open this as a draft PR since I need clarification on the tests: I added a link pointing to #readme to each the github.md and the gitlab.md. They work as expected, however I added the same link to bitbucket.md, expecting it to fail, but it passed because it was tested as being in a GitHub environment.

Is there any mechanism in place to simulate BitBucket for tests?

[wooorm]

Hmm, the reason Bitbucket doesn’t warn about #top or #readme and the like (which I think you’re asking, right?), is that Bitbucket uses #markdown-header- as a heading prefix, and we ignore all anchor links that don’t use the heading prefix.

Because GH and GL use # as a heading prefix, in those environments, every anchor fails if it isn’t know. In case of BB, we ignore everything that doesn’t start with #markdown-header- silently.

[loilo]

Ah, alright. 👍
Then this is ready to review I guess. 🙂

[loilo]

Hey @wooorm, just for a bit of planning — when is the next minor release of this package scheduled? Having this thing solved would spare me a couple dozen noisy messages on my lint runs. 🙂

[wooorm]

Thanks, released!

[loilo]

Weee, thanks! 😄