Semantic Versioning

Semantic Versioning is a three tiered versioning system that increments version numbers based on the type of API change introduced to a releasable software component. It’s a standard way of communicating programmatic compatibility of a package or module for dependent consumers and API implementations. If a package is programmatically (i.e., semantically) incompatible with a project, Bnd (used when building modules) fails that project’s build immediately.

The semantic version format looks like this:

MAJOR.MINOR.MICRO

Certain events force each tier to be incremented:

  • MAJOR: an incompatible, API-breaking change is made
  • MINOR: a change that affects only providers of the API, or new backwards- compatible functionality is added
  • MICRO: a backwards-compatible bug fix is made

For more details on semantic versioning, see the official Semantic Versioning site and OSGi Alliance’s Semantic Versioning technical whitepaper.

All of Liferay DXP’s modules use Semantic Versioning.

Following Semantic Versioning is especially important because Liferay DXP is a modular platform containing hundreds of independent OSGi modules. With many independent modules containing a slew of dependencies, releasing new package versions can quickly become terrifying. With this complex intertwined system of dependencies, you must meticulously manage your own project’s API versions to ensure compatibility for those who leverage it. With Semantic Versioning’s straightforward system and the help of Liferay tooling, managing your project’s versions is easy.

Baselining Your Project

Following Semantic Versioning manually seems deceptively easy. There’s a sad history of good-intentioned developers updating their projects’ semantic versions manually, only to find out later they made a mistake. The truth is, it’s hard to anticipate the ramifications of a simple update. To avoid this, you can baseline your project after it has been updated. Baselining verifies that the Semantic Versioning rules are obeyed by your project. This can catch many obvious API changes that are not so obvious to humans. Care must always be taken, however, when making any kind of code change because this tool is not smart enough to identify compatibility changes not represented in the signatures of Java classes or interfaces, or in API use changes (e.g., assumptions about method call order, or changes to input and/or output encoding). Baseline, as the name implies, does give you a certain measure of baseline comfort that a large class of compatibility issues won’t sneak past you.

You can use Liferay’s Baseline Gradle plugin to provide baselining capabilities. Add it to your Gradle build configuration and execute the following command:

./gradlew baseline

See the Baseline Gradle Plugin article for configuration details. This plugin is not provided in Liferay Workspace by default.

When you run the baseline command, the plugin baselines your new module against the latest released non-snapshot module (i.e., the baseline). That is, it compares the public exported API of your new module with the baseline. If there are any changes, it uses the OSGi Semantic Versioning rules to calculate the minimum new version. If your new module has a lower version, errors are thrown.

With baselining, your project’s Semantic Versioning is as accurate as its API expresses.

Managing Artifact and Dependency Versions

There are two ways to track your project’s artifact and dependency versions with Semantic Versioning:

  • Range of versions
  • Exact version (one-to-one)

You should track a range of versions if you intend to build your project for multiple versions of Liferay DXP and maintain maximum compatibility. In other words, if several versions of a package work for an app, you can configure the app to use any of them. What’s more, Bnd automatically determines the semantically compatible range of each package a module depends on and records the range to the module’s manifest.

For help with version range syntax, see the OSGi Specifications.

A version range for imported packages in an OSGi bundle’s bnd.bnd looks like this:

Import-Package: com.liferay.docs.test; version="[1.0.0,2.0.0)"

Popular build tools also follow this syntax. In Gradle, a version range for a dependency looks like this:

compile group: "com.liferay.portal", name: "com.liferay.portal.test", version: "[1.0.0,2.0.0)"

In Maven, it looks like this:

<groupId>com.liferay.portal</groupId>
<artifactId>com.liferay.portal.test</artifactId>
<version>[1.0.0,2.0.0)</version>

Specifying the latest release version can also be considered a range of versions with no upper limit. For example, in Gradle, it’s specified as version: "latest.release". This can be done in Maven 2.x with the usage of the version marker RELEASE. This is not possible if you’re using Maven 3.x. See Gradle and Maven’s respective docs for more information.

Tracking a range of versions comes with a price. It’s hard to reproduce old builds when you’re debugging an issue. It also comes with the risk of differing behaviors depending on the version used. Also, relying on the latest release could break compatibility with your project if a major change is introduced. You should proceed with caution when specifying a range of versions and ensure your project is tested on all included versions.

Tracking a dependency’s exact version is much safer, but is less flexible. This might limit you to a specific version of Liferay DXP. You would also be locked in to APIs that only exist for that specific version. This means your module is much easier to test and has less chance for unexpected failures.

You now know the pros and cons for tracking dependencies as a range and as an exact match.

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