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

• configures MiMa to check for binary or source incompatibilities,
• ensures that none of your dependencies are bumped or removed in an incompatible way,
• reports incompatibilities with previous releases,
• sets the versionScheme of the project to "early-semver".

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 .

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

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.

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.

The setting versionPolicyIntention can take the following three values:

• // Your next release will provide no compatibility guarantees with the
  // previous one (ie, it will be a major release).
  ThisBuild / versionPolicyIntention := Compatibility.None

• // Your next release will be binary compatible with the previous one,
  // but it may not be source compatible (ie, it will be a minor release).
  ThisBuild / versionPolicyIntention := Compatibility.BinaryCompatible

• // Your next release will be both binary compatible and source compatible
  // with the previous one (ie, it will be a patch release).
  ThisBuild / versionPolicyIntention := Compatibility.BinaryAndSourceCompatible

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.

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.

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.

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.

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:

• check that incoming pull requests do not violate the intended compatibility level (detailed documentation)
  1. if your project contains multiple sub-projects, set versionPolicyIgnoredInternalDependencyVersions as explained in the sbt-dynver integration:

     versionPolicyIgnoredInternalDependencyVersions := Some("^\\d+\\.\\d+\\.\\d+\\+\\d+".r)

  2. set the intended compatibility level of the next release with the setting versionPolicyIntention
  3. run sbt versionPolicyCheck in your CI pipeline:

     steps
       - name: Check compatibility
         run: sbt versionPolicyCheck

• check that a new release version is valid with respect to its compatibility guarantees (detailed documentation)
  1. run sbt versionCheck in your CI pipeline before running ci-release:

     steps
       - name: Release
         run: sbt versionCheck ci-release

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

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.

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

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)

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('+', '-')

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

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:

• define the intended compatibility level of the next release, and check that the changes applied to the project do not violate it,
• or, let the project evolve freely and, at the time of the release, compute the release version according to the level of incompatibilities introduced in the project.

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.

• check that incoming pull requests do not violate the intended compatibility level (detailed documentation)
  1. set the intended compatibility level of the next release with the setting versionPolicyIntention
  2. run sbt versionPolicyCheck in your CI pipeline:

     steps
       - name: Check compatibility
         run: sbt versionPolicyCheck

• compute the next release version according to its compatibility guarantees
  1. set the key releaseVersion as follows:

     import sbtversionpolicy.withsbtrelease.ReleaseVersion
     releaseVersion := ReleaseVersion.fromCompatibility(versionPolicyIntention.value)

     The releaseVersion function bumps the release version according to the compatibility guarantees defined by versionPolicyIntention. 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").
  2. Reset versionPolicyIntention to Compatibility.BinaryAndSourceCompatible after every release. This can be achieved by managing the setting versionPolicyIntention in a separate file (like sbt-release manages the setting version in a separate file, by default), and by adding a step that overwrites the content of that file and commits it.

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.

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.

We demonstrate the “unconstrained” mode in this example.

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"'

The versionPolicyCheck task:

• checks that there are no binary or source incompatibilities between the current state of the project and the previous release (it uses mimaReportBinaryIssues under the hood),
• and, that no dependencies of your project have been removed or bumped in an incompatible way (it uses a subtask versionPolicyReportDependencyIssues under the hood).

The task versionPolicyCheck fails if any of these checks fails.

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:

• if it contains "metadata" (anything after a +, including the + itself), drop the metadata part
  • if the resulting version contains only zeros (like 0.0.0), leave mimaPreviousArtifacts empty,
  • else if the resulting version does not contain a qualifier (see below), it is used in mimaPreviousArtifacts. For instance, if version is 1.0.0+3-abcd1234, then mimaPreviousArtifacts will contain the artifacts of version 1.0.0.
• else, drop the qualifier part, that is any suffix like -RC1 or -M2 or -alpha or -SNAPSHOT
  • if the resulting version ends with .0.0, which corresponds to a major version bump like 1.0.0, or 2.0.0, mimaPreviousArtifacts is left empty,
  • else, this is a minor or patch version bump, so the last numerical part of this version is decreased by one, and used in mimaPreviousArtifacts. For instance, if version is 1.2.0, then mimaPreviousArtifacts will contain the artifacts of version 1.1.0, and if version is 1.2.3, then mimaPreviousArtifacts will contain the artifacts of version 1.2.2.

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

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.

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.

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:

• early-semver: assumes the matched modules follow a variant of Semantic Versioning that enforces compatibility within 0.1.z,
• semver-spec: assumes the matched modules follow semantic versioning,
• pvp: assumes the matched modules follow package versioning policy (quite common in Scala),
• always: assumes all versions of the matched modules are compatible with each other,
• strict: requires exact matches between the wanted and the selected versions of the matched modules.

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).

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

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
}

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