Git-Based Semantic Versioning

This action produces a semantic version for a repository using the repository's git history without ever requiring a human to choose or manually assign the version number.

This action is designed to facilitate assigning version numbers during a build automatically while publishing version that only increment by one value per release. To accomplish this, the next version number is calculated along with a commit increment indicating the number of commits for this version. The commit messages are inspected to determine the type of version change the next version represents. Including the term (MAJOR) or (MINOR) in the commit message alters the type of change the next version will represent.

Background

Automatic versioning during a build presents a chicken-and-egg problem--we want the version to increase by a single value between each release, but we usually do not know at build time whether a new build will be released or not. Generally a build is tagged as part of a release step after passing testing and other quality controls, so if we want to use the version number in the build itself, especially for a build triggered by a commit, we cannot rely on having a proper tag for the build. Most CI systems offer a "build number", but this does not correspond to our semantic version and relies on the state of the CI tool. It is with this in mind that this tool was developed with the following goals:

Allow the version to be injected into the build
Derive the version only from the git repository itself
Do not require the version to be maintained by hand
Resolve the version deterministically for a given commit (see caveats below)
Provide an easy mechanism for incrementing major and minor versions by developers

To solve this problem, this action calculates the next implied version based on the most recently tagged version and the commit messages. An additional value called the "increment" tracks the count of commits since the last version change, allowing a label to be created to mark pre-release versions. The version produced by this action is always the_implied version (unless bump_each_commit is set to true). Subsequently tagging a commit that is chosen as the implied version is what bumps the version for future commits.

Unless the current commit is already tagged, the version produced by this action will be one value ahead of the last tag.

Major and Minor Versions

The commit messages for the span of commits from the last tag are checked for the presence of the designated terms ((MAJOR) or (MINOR) by default), if a term is encountered that commit is treated as the start of a major or minor version instead of the default patch level. As with normal commits the implied version will only increment by one value since the last tag regardless of how many major or minor commits are encountered. Major commits override minor commits, so a set of commits containing both major and minor tags will result in a major version increment.

Tags on Previous Commits

Adding a tag to an older commit changes the implicit version of commits since the tagged commit. If a tag is assigned to an older commit, the commits that come after it will be given the new version if the build were to be retriggered, for example:

Usage

- uses: iautom8things/semantic-version@v4.0.5
  with:
    # The prefix to use to identify tags
    tag_prefix: "v"
    # A string which, if present in a git commit, indicates that a change represents a
    # major (breaking) change, supports regular expressions wrapped with '/'
    major_pattern: "(MAJOR)"
    # Same as above except indicating a minor change, supports regular expressions wrapped with '/'
    minor_pattern: "(MINOR)"
    # A string to determine the format of the version output
    format: "${major}.${minor}.${patch}-prerelease${increment}"
    # Optional path to check for changes. If any changes are detected in the path the
    # 'changed' output will true. Enter multiple paths separated by spaces.
    change_path: "src/my-service"
    # Named version, will be used as suffix for name version tag
    namespace: project-b
    # Indicate whether short tags like 'v1' should be supported. If false only full
    # tags like 'v1.0.0' will be recognized.
    short_tags: true
    # If this is set to true, *every* commit will be treated as a new version.
    bump_each_commit: false
    # If this is set to true, patterns will be applied to the `test_value` instead of git commit messages
    use_test_value: false
    # test major/minor patterns against this value.  This example shows how you can test against a PR's branch name
    test_value: ${{ github.event.pull_request.head.ref }}

Outputs

major, minor, and patch provide the version numbers that have been determined for this commit
increment is an additional value indicating the number of commits for the current version, starting at zero. This can be used as part of a pre-release label.
version is a formatted version string created using the format input. This is a convenience value to provide a preformatted representation of the data generated by this action.
version_tag is a string identifier that would be used to tag the current commit as the "released" version. Typically this would only be used to generate a Git tag name.
changed indicates whether there was a change since the last version if change_path was specified. If no change_path was specified this value will always be true since the entire repo is considered. (It is possible to create a commit with no changes, but the Git cli rejects this by default and this case is not considered here)

There are two types of "version" string, one is the semantic version output that can be used to identify a build and can include prerelease data and metadata specific to the commit such as v2.0.1-pre001+cf6e75 (you would produce this string yourself using the version information from this action plus whatever metadata you wanted to add), the other is the tag version string, which identifies a specific commit as being a specific version.

Using Multiple Versions in the Same Repository

It is possible to create additional versions for multiple project co-existing in one repository, for example you may have a Helm chart, database migration, or simply be hosting multiple projects in the same repository and want them to be versioned independently. There are a few settings that can be used to accomplish this:

First, you can set the change_path input to specify a path that will be inspected for changes. Commits which do no change any files in this path will not increase the increment output. In addition, if there are no changes in a given commit with this path specified, the changed value will be false.

Second, the input namespace can be set to create an additional named version. If this value is set, it will be appended (separated by a hyphen) to the end of tags for the version, and only tags with this value appended will be considered when determining the version. The namespace will be pruned from the string output as "version" within the action.

Finally, set different values for major_pattern and minor_pattern than the other projects in order to be able to mark these commits independently.

To use secondary versions in a workflow, simply create additional steps in a job referencing semantic version multiple times. For example, a project tagged like v1.2.3+0-db could be configured like this:

- name: Application Version
  id: version
  uses: iautom8things/semantic-version@v4.0.5
  with:
    change_path: "src/service"
- name: Database Version
  id: db-version
  uses: iatuom8things/semantic-version@v4.0.5
  with:
    major_pattern: "(MAJOR-DB)"
    minor_pattern: "(MINOR-DB)"
    change_path: "src/migrations"
    namespace: db

Important Note Regarding the Checkout action

Beginning in v2, actions/checkout does not include tags/history by default. This history is required to determine the version correctly. To include the history and tags, specify the fetch-depth parameter in your checkout action declaration. Specify zero to pull the full history and tags.

  - name: Checkout
    uses: actions/checkout@v2
    with:
      fetch-depth: 0

License

iautom8things/semantic-version

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