Replace TravisCI with GitHub Actions

[anoadragon453]

Replaces TravisCI (which has officially been shut down) with Github Actions, which now runs the unit tests.

You can see the pipeline passing over on my repo: https://github.com/anoadragon453/matrix-content-scanner/runs/2718947043

Signed-off-by: Andrew Morgan <andrewm@element.io>

[callahad]

One nit, otherwise looks fine as a port of the Travis config.

More broadly, it might make sense to get out of Docker for running tests (speed, caching, etc.), but that's out of scope for this.

[callahad]

You probably want this to trigger on all pull requests, but only on pushes to the main branch. Otherwise a push to an open PR will trigger the workflow to run twice

[anoadragon453]

I think it would only run twice if I'd specified [push, pull_request] here? I tried making a PR and only had one test run occur: anoadragon453#1

[callahad]

Ah, what I mean is that you probably want it to run on pull_request as well, since otherwise I don't think PRs from external forks wouldn't trigger the workflow? And if you're running on pull_request, you'll need to limit the branches for the push rule.

But I could be wrong. Should we merge it and see?

[anoadragon453]

Aha, I didn't think about how pull wouldn't cover external repositories. I actually cribbed this behaviour from Sygnal: https://github.com/matrix-org/sygnal/blob/main/.github/workflows/pipeline.yml#L2

And it indeed looks like tests aren't being run on contributor PRs: matrix-org/sygnal#227 I'll PR a fix to Sygnal as well as update this PR.

[anoadragon453]

I think ideally I'd want to have tests run on a push to any branch on the repository, even if it's not part of a pull request. However, I'm not sure how to achieve that automatically without also triggering two jobs to run when pushing to a PR branch.

It also doesn't look like it's possible to manually run a workflow on an arbitrary branch alas.

[callahad]

Looks good to me :)