Automate GitHub Pages generation

[dan-zheng]

Task

We can use GitHub Actions to automate GitHub Pages updates: running make docs and pushing the output to gh-pages branch. So far, we've been updating gh-pages branch manually.

Automation suggested here: #472 (comment)

Considerations

• gh-pages branch currently has some hardcoded stop-gap HTML redirection pages, added in Add HTML redirection pages. #392. We should consider what to do with those - maybe we're okay with dropping those pages by now.

[oxinabox]

possible duplicate of #291

[srush]

You could just check those pages into docs/

[apaszke]

I'll close this since it's a duplicate. About checking in to docs/, I don't see how this simplifies things. Checking in to main is equally hard as checking in to gh-pages, with the latter also having the benefit of being accessible via a URL that skips the GitHub UI.

[srush]

Oh I just meant if there were a fixed set of extra static landing pages you could check them in somewhere.

The main suggestion was to use GitHub actions to generate the gh-pages. GitHub actions could also generate these static pages as well.

[apaszke]

I'm not sure if I follow. gh-pages is already the branch that contains the check in of those static pages.

[srush]

If we move to a world where gh-pages is an automatically built branch, then one setup would be to just deploy clean to it every time master is updated by rebuilding the html pages in GitHub actions.

@dan-zheng was worried that this would make it difficult to also have manually created html pages there.

One solution would be to move those manual pages somewhere else, another would be to only update the non manual part of the branch, a final solution would be to have no manual pages and just autogen placeholders.

This is not an interesting problem.