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sbt-version-policy

sbt-version-policy helps library maintainers to follow the recommended versioning scheme. This plugin:

Install

Make sure your project uses a version of sbt higher than 1.5.0.

Add to your project/plugins.sbt:

addSbtPlugin("ch.epfl.scala" % "sbt-version-policy" % "<version>")

The latest version is Scaladex.

sbt-version-policy depends on MiMa, so that you don't need to explicitly depend on it.

Use

The plugin supports multiple types of workflow. It can validate that pull requests don’t break the binary compatibility or source compatibility, it can assess the compatibility level of a project compared to a previous release, and it can be used in combination with release plugins such as sbt-ci-release or sbt-release.

How to check that a project does not violate the desired compatibility level?

The main use case in sbt-version-policy is to check that incoming pull requests don’t break the intended level of compatibility. For instance, a contribution targeting a branch that accepts only bug fixes should not introduce binary incompatibilities nor source incompatibilities.

To achieve this, you need to set the intended level of compatibility of the project with the setting versionPolicyIntention, to set the next release version with the setting version, and to run the task versionPolicyCheck in your continuous integration system.

1. Set versionPolicyIntention

The setting versionPolicyIntention can take the following three values:

2. Run versionPolicyCheck

The task versionPolicyCheck will report any incompatibilities beyond the intended compatibility level. You typically want to run this task in your CI pipeline to fail it when the changes in a pull request violate the intended compatibility level.

sbt versionPolicyCheck

The task versionPolicyCheck checks that the dependencies of the module did not change in an incompatible way (for instance, if the intended compatibility level is BinaryCompatible, you cannot bump a dependency of your module to a new major version, otherwise the classpath would end up not being binary compatible), and that the code changes in the module itself do not violate the intended compatibility level (ie, it checks that the type signatures of existing public methods stay unchanged if the compatibility level is BinaryCompatible). More details.

The plugin uses MiMa to check for incompatibilities with the previous release. To achieve this, it has to know what was the previous release version. By default, the previous release version is automatically computed from the current value of the version key in your build (more details here). This means that you have to set this key to the next version you want to release:

// Next version will be 1.1.0
ThisBuild / version := "1.1.0"

In practice, the way the version is defined in your build depends on your release process. For instance, if you use a plugin like sbt-dynver or sbt-ci-release, which automatically set the version based on the Git status, read below. If you use sbt-release, read the corresponding section.

Alternatively, you can define your own logic to compute the previous version (e.g. to not require the version to be set) by redefining the setting versionPolicyPreviousVersions.

Note that versionPolicyCheck fails if it finds incompatibilities that violate the intended compatibility level. If you want to find such incompatibilities without failing, use the task versionPolicyFindIssues.

How to check that the release version is valid with respect to the compatibility guarantees it provides?

Some release processes require you to manually set the release version. This is the case for all the release processes triggered by pushing a Git tag, such as sbt-ci-release.

In such a case, your release process should check that the version you set is valid with respect to the compatibility guarantees of the release (as defined by versionPolicyIntention). For instance, a release that breaks the binary compatibility should bump the major version number.

You can check that by running the task versionCheck in your release process:

  1. set the version to the new release version (e.g., "1.2.3"),
  2. make sure versionPolicyIntention is set to the intended compatibility level of the release,
  3. run sbt versionCheck before publishing your module artifacts.

The task versionCheck checks that the release version number is consistent with the intended compatibility level as per versionPolicyIntention. For instance, if your intention is to publish a release that breaks binary compatibility, the task versionCheck will fail if you didn’t bump the major version number.

See below how to integrate with sbt-ci-release or with sbt-release for instructions specific to these release processes.

How to assess the compatibility level of a project?

In case you don’t want to force a compatibility level but are interested in knowing the current level of compatibility of the project compared to its previous version, you can use the task versionPolicyAssessCompatibility:

  1. do not assign a value to versionPolicyIntention,
  2. set the version to the next release version,
  3. use the task versionPolicyAssessCompatibility to compute the compatibility level.

The reason why you need to set the version to the next release version before running versionPolicyAssessCompatiblity is because we use it to compute the previous release version, against which assess the compatibility level. Alternatively, you can manually define the previous release version by redefining the setting versionPolicyPreviousVersions.

Integrate with your release process

Some release processes require you to define the release version beforehand (e.g., sbt-ci-release), and some of them compute the release version as part of the process (e.g., sbt-release). That difference impacts the integration with sbt-version-policy.

How to integrate with sbt-ci-release?

sbt-ci-release uses Git tags to compute the project version. You can integrate sbt-version-policy into a project that uses sbt-ci-release as follows:

Since sbt-ci-release uses sbt-dynver under the hood, please read over the next section.

Examples

sbt-version-policy itself uses sbt-version-policy and sbt-ci-release. You can have a look at our Github workflow as an example of integration.

You can also have a look at the test example-sbt-ci-release for a minimalistic sbt project using both sbt-version-policy and sbt-ci-release.

How to integrate with sbt-dynver?

sbt-dynver generates version numbers looking like 1.2.3+4-abcd1234 when the Git history contains commits, or changes, after the last tag.

Supporting multi-projects builds

The version numbers generated by sbt-dynver are usually not a problem, except when checking for dependency issues between projects of the current build (e.g., if a project a depends on another project b in the current build). In such a case, sbt-version-policy might report a false incompatibility when checking the dependencies of a (because the project b now has a non-normalized version number, from which we are unable to draw any conclusions).

To solve this issue, you can tell sbt-version-policy to ignore the dependencies to internal projects when their version number matches some regular expression:

// Ignore dependencies to internal modules whose version is like `1.2.3+4...`
ThisBuild / versionPolicyIgnoredInternalDependencyVersions := Some("^\\d+\\.\\d+\\.\\d+\\+\\d+".r)

Unsupported custom dynverSeparator

When sbt-version-policy computes the previous version of the release, it only supports "+" as a dynverSeparator. This can be an issue in case you changed this setting to use a more portable version string.

In the specific case of Docker usage, a workaround is to keep the default dynverSeparator value ("+"), and to tweak the Docker / version:

Docker / version := version.value.replace('+', '-')

Example

You can have a look at the test example-sbt-dynver for a minimalistic sbt project using both sbt-version-policy and sbt-dynver.

How to integrate with sbt-release?

sbt-release is able to run sophisticated release pipelines including running the tests, setting the release version, publishing the artifacts, and pushing a Git tag named after the release version.

There are two ways to use sbt-version-policy along with sbt-release:

Constrained compatibility level

In this mode, you can use sbt-version-policy to check that incoming pull requests do not violate the intended compatibility level, and to compute the next release version according to the compatibility level.

Example

You can have a look at the test example-sbt-release for an example of sbt project using both sbt-version-policy and sbt-release.

In that example, we also automatically reset the intended compatibility level to BinaryAndSourceCompatible as the last step of the release process.

Unconstrained compatibility level

In this mode, you can use sbt-version-policy to assess the incompatibilities introduced in the project since the last release and compute the new release version accordingly (ie, to bump the major version number if you introduced binary incompatibilities):

  1. make sure versionPolicyIntention is not set
  2. define releaseVersion from the compatibility level returned by versionPolicyAssessCompatibility:
    import sbtversionpolicy.withsbtrelease.ReleaseVersion
    
    releaseVersion := {
      ReleaseVersion.fromAssessedCompatibilityWithLatestRelease().value
    }
    
    Alternatively, if your project contains multiple modules, you want to use the aggregated assessed compatibility level:
    import sbtversionpolicy.withsbtrelease.ReleaseVersion
    
    releaseVersion := {
      ReleaseVersion.fromAggregatedAssessedCompatibilityWithLatestRelease().value
    }
    
    In both cases, the releaseVersion function sets the release version according to the compatibility level with the latest release. Optionally, you can also define a qualifier to append to the release version by setting the environment variable VERSION_POLICY_RELEASE_QUALIFIER (e.g., VERSION_POLICY_RELEASE_QUALIFIER="-RC1").

Note that for the first release you have to set the release version yourself via the file version.sbt (e.g., set 1.0.0-SNAPSHOT or 0.1.0-SNAPSHOT). This is because sbt-version-policy needs a previous release to exist to be able to assess the compatibility level of the current state of the project with that release.

Example

We demonstrate the “unconstrained” mode in this example.

How to generate compatibility reports?

You can export the compatibility reports in JSON format with the task versionPolicyExportCompatibilityReport.

  1. It does not matter whether versionPolicyIntention is set or not. If it is set, the report will list the incompatibilities that violate the intended compatibility level. If it is not set, all the incompatibilities will be reported.

  2. Invoke the task versionPolicyExportCompatibilityReport on the module you want to generate a report for. For example, for the default root module:

    sbt versionPolicyExportCompatibilityReport
    

    The task automatically aggregates the compatibility reports of all its aggregated submodules.

  3. Read the file target/scala-2.13/compatibility-report.json (or target/scala-3/compatibility-report.json). You can see an example of compatibility report here.

    Here are examples of how to read some specific fields of the compatibility report with jq:

    # Get the highest compatibility level satisfied by all the aggregated modules.
    # Returns either 'incompatible', 'binary-compatible', or 'binary-and-source-compatible'.
    cat compatibility-report.json | jq '.aggregated.compatibility.value'
    
    # Get a human-readable description of the highest compatibility level sastisfied
    # by all the aggregated modules.
    cat compatibility-report.json | jq '.aggregated.compatibility.label'
    
    # Get the version of the project against which the compatibility level
    # was assessed.
    cat compatibility-report.json | jq '.aggregated.modules[0]."previous-version"'
    # Or, in the case of a single module report (no aggregated submodules):
    cat compatibility-report.json | jq '."previous-version"'
    

How does versionPolicyCheck work?

The versionPolicyCheck task:

The task versionPolicyCheck fails if any of these checks fails.

Automatic previous version calculation

sbt-version-policy automatically sets mimaPreviousArtifacts, depending on the current value of version, kind of like sbt-mima-version-check does. The previously compatible version is computed from version the following way:

You can see the value of the previous version computed by the plugin by inspecting the key versionPolicyPreviousVersions.

Source incompatibilities detection

MiMa can only detect binary incompatibilities. To detect source incompatibilities, this plugin uses MiMa in forward mode as an approximation. This is not always correct and may lead to false positives or false negatives. This is a known limitation of the current implementation.

Incompatibilities caused by removed or bumped dependencies

The subtask versionPolicyReportDependencyIssues checks that you did not remove or bump your dependencies in an incompatible way. For instance, if your intention for the next release is to keep binary compatibility, you can only bump your dependencies to binary compatible versions.

versionPolicyReportDependencyIssues compares the dependencies of versionPolicyPreviousArtifacts to the current ones.

By default, versionPolicyPreviousArtifacts relies on mimaPreviousArtifacts from sbt-mima, so that only setting / changing mimaPreviousArtifacts is enough for both sbt-mima and sbt-version-policy.

Dependency compatibility adjustments

Set libraryDependencySchemes to specify the versioning scheme used by your libraries. For instance:

libraryDependencySchemes += "org.scala-lang" % "scala-compiler" % "strict"

The following compatibility types are available:

If no rules for a module are found in libraryDependencySchemes, versionPolicyDefaultScheme is used as a compatibility type. Its default value is VersionCompatibility.PackVer (package versioning policy).

Disable the tasks versionPolicyCheck or versionCheck on a specific project

You can disable the tasks versionPolicyCheck and versionCheck at the project level by using the skip key.

By default, both versionPolicyCheck / skip and versionCheck / skip are initialized to (publish / skip).value. So, to disable both tasks on a given project, set the following:

publish / skip := true

Or, if you need more fine-grained control:

versionPolicyCheck / skip := true
versionCheck / skip := true

Custom parsing of version numbers, versionPolicyModuleVersionExtractor

You can specify custom logic for parsing version numbers on a per-dependency basis. This is useful when artifact providers use their own version naming scheme.

For example, say you have this dependency

libraryDependencies += "com.google.apis" % "google-api-services-iam" % "v1-rev20211104-1.32.1"

Google's version scheme is to include the target REST API version, v1-rev20211104 with the Java API version, 1.32.1.

In order to tell sbt-version-policy how to parse this version number, you can bind versionPolicyModuleVersionExtractor:

versionPolicyModuleVersionExtractor := {
  case m if m.name.startsWith("google-api-services") => m.revision.split('-').last
}

Acknowledgments

<img src="https://scala.epfl.ch/resources/img/scala-center-swirl.png" width="40px" />

sbt-version-policy is funded by the Scala Center.