Generate changelog with semantic-release

[shawnbot]

This adds a script that uses semantic-release under the hood to generate the next release's changelog entry. I couldn't figure out how to work with any of the existing semantic-release plugins, so (natch) I wrote my own that implements two "steps":

1. analyzeCommits() gets a list of commits (from semantic-release 🎉), finds the merge commits that reference PR numbers, grabs the corresponding PR data from the GitHub API, and looks at the labels for each to determine which, if any:

   • correspond to a semver release type (patch, minor, or major) and
   • map to one of our predefined change categories (breaking, enhancement, bug fix, polish, or internal)

   This function then returns the release type (major, minor, or patch — I haven't tested the noop case yet) for semantic-release to manage.

2. generateNotes() gets the same list of commits, figures out which ones were marked as relevant merge commits in the previous step (and which grouping they belong to), then generates a hunk of raw Markdown text to drop into the changelog.

Caveats

• I thought that I could get away with stashing the metadata on the commit objects in the first step, but it wasn't available in the second one. I tried using a WeakMap for the metadata (map.set(commit, metadata)), but none of the commit objects in the second step were found in the map. This suggests that the objects are being recreated (or deep copied?) in between steps, but I'd need to look closer at the source to know for sure.

  Anyway, sharing state with in a Map by commit SHA feels icky, but it works and the keys are guaranteed unique, so 🤷‍♂

• It would probably be better to generate the changelog Markdown using an AST builder like remark.

Without further ado, here's the output, copied from this actions run:

13.2.0

🚀 Enhancements

• #959 More buttons
• #950 Add Diffstat component
• #913 Importing TimelineItem from .com and creating matching docs
• #953 Add IssueLabel component

🐛 Bug fixes

• #945 Add [role=tab][aria-selected=true] to .UnderlineNav-item.selected

📝 Documentation

• #939 Fix Box--overlay example
• #943 Fix broken links to typography utilities

🏠 Internal

• #946 Add TODO@version stylelint rule (local)

Committers

• @MohamedElidrissi
• @jonrohan
• @shawnbot
• @simurai

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[simurai]

The output looks pretty good. ✨ Like hand made.

[shawnbot]

Let's test this out on the 14.0 release!