CI: Autobuild job

[szepeviktor]

Motivation
When editing files here on GitHub one cannot run npm run build

Description
Please consider adding a CI job:

1. runs npm run build
2. commit the changes

[mAAdhaTTah]

The repo code powers download page of the website, which is served from github pages & uses the minified files in the repo, so we need to commit the built files so it works.

[szepeviktor]

@mAAdhaTTah That is what I'm suggesting! :)

1. User comes and edits a file here on GitHub web interface
2. CI auto-builds all those minified files and commits to the repo

[mAAdhaTTah]

Oh, hmm, I suspect it would only work if the author gives us editing rights. Interesting idea tho so I'll keep this open.

[szepeviktor]

PrismJS/prism has write access to PR branches!

[RunDevelopment]

PrismJS/prism has write access to PR branches!

Only if they don't deselect the "Allow edits from maintainers" option. It's on by default tho.

This actually has the nice side effect that users can actually opt-out of this feature, if implemented.

CI auto-builds all those minified files and commits to the repo

GitHub action workflows that commit code won't trigger the CI again. This is an explicit feature of GH actions.

This behavior isn't a problem for the test suite (it doesn't use minified files) but it is a problem for the bundle size bot. The bot itself can't build the PR branch since that means executing untrusted code. (The bot runs in pull_request_target scope, so it has full access to this repo.)

[szepeviktor]

Currently in the final CI step exit 1 makes the whole thing fail 🌧️
https://github.com/PrismJS/prism/blob/master/.github/workflows/test.yml#L43-L46

Instead we could commit those files.

Side-effect: node-version: [10.x, 12.x, 14.x] should run after each other to allow this procedure.

1. run on nodejs 14
2. check and optionally commit to the repo
3. run on nodejs 12 and 10

[RunDevelopment]

We could also ditch the older node versions. This has the disadvantage that version-specific bugs in node causing different build results might go undetected but it's a lot simpler.