build: annotate markdown lint failures in pull requests

[richardlau]

Add a problem matcher for output from remark-lint to our lint-md GitHub
Actions CI workflow so that any markdown linter failures are annotated
in the pull request in the web UI.

Refs: https://github.com/actions/toolkit/blob/master/docs/problem-matchers.md
Refs: https://github.com/actions/toolkit/blob/master/docs/commands.md#problem-matchers

Checklist

• commit message follows commit guidelines

[richardlau]

An example annotation:

[Trott]

I won't pretend to have looked at those regular expressions carefully, but rubber-stamp LGTM.

[gengjiawen]

Any thought on doc the regexp ?

[mmarchini]

RSLGTM (also love it, by far the simplest solution to annotate code I've seen).

One concern though: add-matcher doesn't seem to be documented (I would expect to see it here). Do you know if this is a stable API, or if there's any chance they'll pull it out in the near future?

[richardlau]

RSLGTM (also love it, by far the simplest solution to annotate code I've seen).

One concern though: add-matcher doesn't seem to be documented (I would expect to see it here). Do you know if this is a stable API, or if there's any chance they'll pull it out in the near future?

There’s no mention of problem matchers or annotations at all on that page (or any other help page for GitHub actions). The two referenced links are to the actions toolkit (https://github.com/actions/toolkit) where it’s documented. As to the stability of that your guess is as good as mine. If this does stop working it’s not the end of the world to lose the annotations — we would be back to where we are now without this PR.

Any thought on doc the regexp ?

What are you looking for? The regexps are trying to extract from the output of our markdown linting into the fields detailed in the first referenced link. Sample output to parse:

README.md
15:130 warning Line must be at most 80 characters maximum-line-length remark-lint
27:3-27:46 warning Marker style should be `*` unordered-list-marker-style remark-lint

[richardlau]

Landed in f467b9b.