ClassicPress Plugin Development: Semantic Versioning 2.0

This post is part of the ClassicPress Plugin Development series in which I am going to look at both best practice for developing plugins and how I approach some requirements as well as some of the functions I commonly use.

When developing plugins for ClassicPress, you need to develop using semantic versioning (or semver) as this will be a requirement of the ClassicPress Directory.

Semantic Versioning is a versioning scheme for using meaningful version numbers which can be used to avoid incompatibilities.

semver version numbering works using three segments:

1. MAJOR version when you make breaking changes where users will need to take some action during an upgrade.
2. MINOR version when you add functionality in a backwards compatible manner which users can simply apply without taking any other action.
3. PATCH version when you make backwards compatible bug fixes which, like MINOR versions users can apply without taking any other action.

One key point to note when using semver, is that when a versioned release has been made, nothing in that release can be changed; a new version with incremented number must be released instead.

Additional labels for pre-release and build metadata are available as extensions to the MAJOR.MINOR.PATCH format; pre-release versions often have a MAJOR version number of 0. When a plugin is ready for release to production it should be released as version 1.0.0.

The full specification for semver can be found here, but for how I develop the key points from the specification are:

2. A normal version number MUST take the form X.Y.Z where X, Y, and Z are non-negative integers, and MUST NOT contain leading zeroes. X is the major version, Y is the minor version, and Z is the patch version. Each element MUST increase numerically. For instance: 1.9.0 -> 1.10.0 -> 1.11.0.
3. Once a versioned package has been released, the contents of that version MUST NOT be modified. Any modifications MUST be released as a new version.
4. Major version zero (0.y.z) is for initial development. Anything MAY change at any time. The public API SHOULD NOT be considered stable.
5. Version 1.0.0 defines the public API. The way in which the version number is incremented after this release is dependent on this public API and how it changes.
6. Patch version Z (x.y.Z | x > 0) MUST be incremented if only backwards compatible bug fixes are introduced. A bug fix is defined as an internal change that fixes incorrect behavior.
7. Minor version Y (x.Y.z | x > 0) MUST be incremented if new, backwards compatible functionality is introduced to the public API. It MUST be incremented if any public API functionality is marked as deprecated. It MAY be incremented if substantial new functionality or improvements are introduced within the private code. It MAY include patch level changes. Patch version MUST be reset to 0 when minor version is incremented.
8. Major version X (X.y.z | X > 0) MUST be incremented if any backwards incompatible changes are introduced to the public API. It MAY also include minor and patch level changes. Patch and minor version MUST be reset to 0 when major version is incremented.
9. A pre-release version MAY be denoted by appending a hyphen and a series of dot separated identifiers immediately following the patch version. Identifiers MUST comprise only ASCII alphanumerics and hyphens [0-9A-Za-z-]. Identifiers MUST NOT be empty. Numeric identifiers MUST NOT include leading zeroes. Pre-release versions have a lower precedence than the associated normal version. A pre-release version indicates that the version is unstable and might not satisfy the intended compatibility requirements as denoted by its associated normal version. Examples: 1.0.0-alpha, 1.0.0-alpha.1, 1.0.0-0.3.7, 1.0.0-x.7.z.92, 1.0.0-x-y-z.—.