Semantic Versioning

Semantic versioning is not exactly a Git topic. But since you will need to bump the version of the application after each release and tag the master branch, you need to learn how to properly update it following the Semantic versioning principles.

Given a version number MAJOR.MINOR.PATCH, increment the:

• MAJOR version when you make incompatible API changes,
• MINOR version when you add functionality in a backwards compatible manner,
• PATCH version when you make backwards compatible bug fixes.

Additional labels for pre-release and build metadata are available as extensions to the MAJOR.MINOR.PATCH format.

The bigger a system grows and the more packages integrated into a software, the more we need a solid versioning process.

In systems with many dependencies, releasing new package versions needs to be carefully handled.

To prevent any version issue we use a global set of rules and requirements that dictate how version numbers are assigned and incremented.

Consider a version format of X.Y.Z (Major.Minor.Patch).

• Bug fixes not affecting the application increment the patch version
• Backwards compatible application additions/changes increment the minor version
• Backwards incompatible application changes increment the major version

Under this scheme, version numbers and the way they change convey meaning about the underlying code and what has been modified from one version to the next.

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
• Z is the patch version. Each element MUST increase numerically. For instance: 1.9.0 -> 1.10.0 -> 1.11.0.

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.

• Major version zero (0.y.z) is for initial development. Anything MAY change at any time. The application SHOULD NOT be considered stable.

• Version 1.0.0 defines the first release in production. The way in which the version number is incremented after this release is dependent on the application and how it changes.

• 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.

• Minor version Y (x.Y.z | x > 0) MUST be incremented if new, backwards compatible functionality is introduced to the application. It MUST be incremented if any application 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.

• Major version X (X.y.z | X > 0) MUST be incremented if any backwards incompatible changes are introduced to the application. It MAY also include minor and patch level changes. Patch and minor version MUST be reset to 0 when major version is incremented.

• 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.

• Build metadata MAY be denoted by appending a plus sign and a series of dot separated identifiers immediately following the patch or pre-release version. Identifiers MUST comprise only ASCII alphanumerics and hyphens [0-9A-Za-z-]. Identifiers MUST NOT be empty. Build metadata MUST be ignored when determining version precedence. Thus two versions that differ only in the build metadata, have the same precedence. Examples: 1.0.0-alpha+001, 1.0.0+20130313144700, 1.0.0-beta+exp.sha.5114f85, 1.0.0+21AF26D3—-117B344092BD.

Precedence refers to how versions are compared to each other when ordered.

It MUST be calculated by separating the version into major, minor, patch and pre-release identifiers in that order (Build metadata does not figure into precedence).

It is determined by the first difference when comparing each of these identifiers from left to right as follows: Major, minor, and patch versions are always compared numerically.

Example: 1.0.0 < 2.0.0 < 2.1.0 < 2.1.1.

When major, minor, and patch are equal, a pre-release version has lower precedence than a normal version:

Example: 1.0.0-alpha < 1.0.0

Precedence for two pre-release versions with the same major, minor, and patch version MUST be determined by comparing each dot separated identifier from left to right until a difference is found as follows:

Identifiers consisting of only digits are compared numerically.

Identifiers with letters or hyphens are compared lexically in ASCII sort order.

Numeric identifiers always have lower precedence than non-numeric identifiers.

A larger set of pre-release fields has a higher precedence than a smaller set, if all of the preceding identifiers are equal.

1.0.0-alpha < 1.0.0-alpha.1 < 1.0.0-alpha.beta < 1.0.0-beta < 1.0.0-beta.2 < 1.0.0-beta.11 < 1.0.0-rc.1 < 1.0.0.

Start your initial development release at 0.1.0 and then increment the minor version for each subsequent release.

If your software is being used in production, it should probably already be 1.0.0. If you have a stable application on which users have come to depend, you should be 1.0.0. If you’re worrying a lot about backwards compatibility, you should probably already be 1.0.0. If you’re changing the application every day you should either still be in version 0.y.z or on a separate development branch working on the next major version.

This is a question of responsible development and foresight. Incompatible changes should not be introduced lightly to software that has a lot of dependent code. The cost that must be incurred to upgrade can be significant. Having to bump major versions to release incompatible changes means you’ll think through the impact of your changes, and evaluate the cost/benefit ratio involved.

As soon as you realize that you’ve broken the Semantic Versioning spec, fix the problem and release a new minor version that corrects the problem and restores backwards compatibility. Even under this circumstance, it is unacceptable to modify versioned releases. If it’s appropriate, document the offending version and inform your users of the problem so that they are aware of the offending version.

That would be considered compatible since it does not affect the application. Software that explicitly depends on the same dependencies as your package should have their own dependency specifications and the author will notice any conflicts. Determining whether the change is a patch level or minor level modification depends on whether you updated your dependencies in order to fix a bug or introduce new functionality. In which case it’s a minor level increment.

(i.e. the code incorrectly introduces a major breaking change in a patch release)

Use your best judgment. If you have a huge audience that will be drastically impacted by changing the behavior back to what the public API intended, then it may be best to perform a major version release, even though the fix could strictly be considered a patch release. Remember, Semantic Versioning is all about conveying meaning by how the version number changes. If these changes are important to your users, use the version number to inform them.

Deprecating existing functionality is a normal part of software development and is often required to make forward progress. When you deprecate part of your public API, you should do two things: (1) update your documentation to let users know about the change, (2) issue a new minor release with the deprecation in place. Before you completely remove the functionality in a new major release there should be at least one minor release that contains the deprecation so that users can smoothly transition to the new API.

Use good judgment. A 255 character version string is overkill and unreadable.

“v1.2.3” is not a semantic version. However, prefixing a semantic version with a “v” is a common way (in English) to indicate it is a version number. Abbreviating “version” as “v” is often seen with version control. Example: git tag v1.2.3 -m “Release version 1.2.3”, in which case “v1.2.3” is a tag name and the semantic version is “1.2.3”.