Add workflow to check for expected @wordpress/components CHANGELOG updates

[chad1008]

What?

Adds an automated check to PRs editing the @wordpress/components package to ensure the CHANGELOG has been updated.

Why?

This is an easy step to miss, and a common part of reviews, so it makes sense to automate it.

How?

The new check will only be run on PRs that change files in the packages/components/** directory, but not if all of those files are stories or unit tests, as those changes don't need to be entered in the changelog.

If any files outside of tests and stories are modified, a git diff is run to confirm that /packages/components/CHANGELOG.md is included in the files changed by the PR. If it isn't, the check fails with an error message asking the author to add an entry.

Testing Instructions

1. After checking out this PR, create a new branch off of it. Create a PR of your own from that branch.
2. Modify a story file for any component. Commit that change to your test branch and push, updating your PR.
3. Wait for the checks to run and confirm that Verify @wordpress/components CHANGELOG update was NOT run.
4. Modify a unit test for any component. Commit that change to your test branch and push, updating your PR again.
5. Wait again for the checks and confirm that Verify @wordpress/components CHANGELOG update still was NOT run.
6. Modify a component file (any component, anything that isn't a unit test or story file). Commit and push.
7. Wait for the checks. Confirm that this time Verify @wordpress/components CHANGELOG update IS run.
8. Confirm that the check fails, because you didn't update the changelog. When clicking details on the check, you should see output asking you to add a CHANGELOG entry.
9. Update the CHANGELOG file. The check isn't picky about what you do, it only looks for the file to have been changed. Commit and push one last time.
10. Wait once more for the checks, confirm that this time Verify @wordpress/components CHANGELOG update runs and passes.

[github-actions]

Flaky tests detected in 4c8bea2.
Some tests passed with failed attempts. The failures may not be related to this commit but are still reported for visibility. See the documentation for more information.

🔍 Workflow run URL: https://github.com/WordPress/gutenberg/actions/runs/4620681022
📝 Reported issues:

• [Flaky Test] Keeps focus in place on undo in template parts #49386 in /test/e2e/specs/site-editor/template-part.spec.js
• [Flaky Test] prevent the removal of locked column block from the column count change UI #49534 in /test/e2e/specs/editor/blocks/columns.spec.js

[ciampo]

Not sure if I'm reading this correctly, but it looks like the search for changes to the CHANGELOG file is done against the latest trunk (ie. from the origin remote). I wonder what happens if the CHANGELOG file is changed on trunk?

In my mental model, we should check for differences against the commit that the current PR is based off (something similar to what described in this article), and not against latest origin / trunk

[chad1008]

Good point, and thanks for the example, it helped a lot.

I've reworked the PR so it should now check against the PR's base commit. While changing this, I also realized I didn't like that we were fetching all of origin/trunk when we really only need to go back as far as the base commit, so I've made the fetch depth dynamic to only pull what the given PR needs.

[ciampo]

Tested in #49619, works as per testing instructions 🚀

[geriux]

Hey there 👋 I'm having issues in this PR where the Verify @wordpress/components CHANGELOG update / Check CHANGELOG diff check fails. @chad1008 do you have any ideas why is it failing? Thanks!

[geriux]

I see it is because I'm making changes to some files within the components folder but it's for native files, I think we should exclude this check for .native files 🤔

[chad1008]

Thanks for pointing that out @geriux. Proposed a change to the check in #49688 🙂