Making the switch to Semantic Versioning

Just in time for the new year...

After years of talking about it, we’re finally ready to make the switch to Semantic Versioning in Asciidoctor. This switch will happen as part of the next major release for each participating project.

What follows is a cross post from the blog at https://asciidoctor.org/news/2018/12/31/making-the-switch-to-semver/.

Semantic Versioning (or SemVer, for short) is a logical system for selecting version numbers based on a simple MAJOR.MINOR.PATCH sequence.

* A MAJOR version is for introducing incompatible changes (large or small).
* A MINOR version is for adding backward-compatible functionality.
* A PATCH version is for making bug fixes (backward compatible, of course).

There’s also room for a prerelease version via build metadata. You can learn more at https://semver.org.

In our current system, patch releases are indistinguishable from major and minor releases and there’s only a single release line. Experience has taught us (the hard way) that this situation is neither clear or sustainable. For us, SemVer is about having better communication and room to grow. It’s a system based on shared expectations and trust. Although it may not be perfect, SemVer should help to understand what a version number entails and when to upgrade. We can’t expect it to prevent breaking something, but at least you’ll know when it might.

Switching to SemVer also means that, for the first time, the Asciidoctor projects will be versioned independently, namely Asciidoctor, AsciidoctorJ, and Asciidoctor.js. Other projects in the ecosystem will likely start versioning independently as well (in fact, some already have).

AsciidoctorJ and Asciidoctor.js have both reached a point where the projects are much more than a redistribution of the Asciidoctor RubyGem. They have their own API, extensions model, custom features, and platform integration. And that warrants having their own version line. An independent version line will also allow users to better understand what to expect in each release.

After speaking with Robert (AsciidoctorJ lead) and Guillaume (Asciidoctor.js lead), here’s the system we agreed on:

1. The core processors (Asciidoctor, AsciidoctorJ, and Asciidoctor.js) will move to semantic versioning starting with the 2.0.0 release. We plan for all three projects to make this major version shift at roughly the same time to minimize confusion.

2. If Asciidoctor.js or AsciidoctorJ need a change in Asciidoctor, they can force Asciidoctor to be released. This means Asciidoctor will need to be “release ready” at all times. A patch or minor release won’t need much discussion, but a major release, of course, will.

3. We will not attempt to align the version numbers between the three projects after 2.0.0. Guillaume laid out a strong case that trying to align the version numbers would work against semantic versioning and thus result in the version numbers losing their meaning. This does introduce the complexity of having to document the version of Asciidoctor that Asciidoctor.js or AsciidoctorJ provides. However, both AsciidoctorJ and Asciidoctor.js provide an API for accessing the version of the underlying Asciidoctor release. The release number is also available via the asciidoctor-version document attribute.

We considered ways to lock Asciidoctor, AsciidoctorJ, and Asciidoctor.js to the same version while still adhering to SemVer. However, we reached the conclusion that doing that would only perpetuate the situation that’s caused the backup of releases we’ve seen. It’s best if the projects have the freedom to release when the time is right to release. And with three version number segments (MAJOR.MINOR.PATCH), we finally have enough space for those releases to happen!

We’ll start by repackaging the Asciidoctor 1.5.8 release as 2.0.0, with some minor adjustments to drop unsupported versions of Ruby. AsciidoctorJ and Asciidoctor.js will then follow with their 2.0.0 releases. At that point, we’ll stick to versioning according to SemVer rules as outlined above.

Cheers and Happy New Year!

-Dan

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