Replace Jenkins with GitHub Actions

[benthorner]

Depends on: alphagov/govuk-puppet#10315

This is largely based on the workflow for Jenkins [1]. Note that
that our release process is somewhat bespoke:

- We avoid pushing a gem version if it already exists
- We use the version in the gemspec to auto-create a tag

This makes it's difficult to reuse a 3rd party GitHub Action, which
we should avoid anyway due to the secret API token.

Other notes:

- The API token is automatically masked by GitHub in the log
output: "GEM_HOST_API_KEY: ***".

- We only need to trigger our tests on 'push' events, which
includes manual pushes (even before a PR is opened), as well
as merge commits to the master branch.

- We want to run tests (again) before releasing, since other
commits on the master branch may still cause an issue when a PR is
merged, even if there are no conflicts.

- Since the 'release' job only occurs on the master branch (outside of a
  PR), you need to look at the 'Actions' tab to debug it [2].

[1]: https://github.com/alphagov/govuk-jenkinslib/blob/master/vars/govuk.groovy
[2]: https://github.com/alphagov/rubocop-govuk/actions

[issyl0]

I really like this - thanks! I don't know why I made it so verbose. 😅

[huwd]

Guess this proves the usefulness:

[benthorner]

@huwd to be fair, it's hard for Jenkins to run without a Jenkinsfile 👀

[issyl0]

Looks good to me. Thanks again, Ben.

[kevindew]

This looks good to me 👍

I've been wondering whether we want to use matrix builds for gems or not (as we used to but don't really do on Jenkins) since the .ruby-version of the gem isn't actually that relevant once distributed. I had a quick go here: 93caf38

[benthorner]

@kevindew I agree that's a good idea. I'd prefer to do that in a different PR, since this gem doesn't have a minimum version requirement, so it's unclear what the version matrix should be.

[benthorner]

@kevindew I've also added a comment here, after trying it on alphagov/govuk-connect#11 (comment).

I've pushed a commit to try this, but it turns out we have a problem with conflicting gem versions. Normally one has one Gemfile for each Ruby version.

I'd like to suggest the minimum version is more of an 'indicator' than something we officially support. The extra testing and maintenance of the matrix doesn't seem worth it.

[kevindew]

@kevindew I've also added a comment here, after trying it on alphagov/govuk-connect#11 (comment).

I've pushed a commit to try this, but it turns out we have a problem with conflicting gem versions. Normally one has one Gemfile for each Ruby version.
I'd like to suggest the minimum version is more of an 'indicator' than something we officially support. The extra testing and maintenance of the matrix doesn't seem worth it.

Oh bummer - what gem(s) caused you a problem? I didn't see it on the commit I pushed: 93caf38

It's normally only a dire situation that you need to have different gemfiles for different Ruby versions, nearly all gems manage to avoid it. I certainly wouldn't enjoy managing a gem with multiple gemfiles 😬

[benthorner]

Sorry, I should have given more info: this was for Ruby 2.4 with govuk-connect. Since govuk-connect has this as its minimum Ruby version, it made sense to include that as part of the matrix.

While this repo doesn't have a minimum version (yet), I'm worried that using a matrix will become a problematic pattern, partly for versioning, but also if people forget to maintain it.

I'm wondering if it's easier to avoid any commitment to support multi Ruby versions, since doing that properly involves putting in more effort than we have with Jenkins.

[kevindew]

Sorry, I should have given more info: this was for Ruby 2.4 with govuk-connect. Since govuk-connect has this as its minimum Ruby version, it made sense to include that as part of the matrix.

While this repo doesn't have a minimum version (yet), I'm worried that using a matrix will become a problematic pattern, partly for versioning, but also if people forget to maintain it.

I'm wondering if it's easier to avoid any commitment to support multi Ruby versions, since doing that properly involves putting in more effort than we have with Jenkins.

It's worth bearing in mind that the Jenkins effort only recently slipped away: alphagov/govuk-jenkinslib@f7e00f3

Yeah, it's always a problem if it's not maintained. I think it also slips the other way though that for a gem only testing on the one ruby version in .ruby-version isn't particularly safe as that has no effect on how the gem is used. It does seem a bit of a bummer for example that if any of our apps start using Ruby 2.7 none of our gems are tested against it.

Oh I see the problem in govuk-connect is because the Gemfile.lock is commited. If it's a gem we shouldn't be committing that, then it should be able to resolve to an earlier activesupport.

[benthorner]

@kevindew oops, that was me. Here's a PR to fix it and add matrix builds: alphagov/govuk-connect#14. I did try to get act working, but it seems to be quite brittle, compared to GitHub.