Scala Binary Compatibility validation tool – "MiMa" for short
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Migration Manager for Scala

The Migration Manager for Scala (MiMa in short) is a tool for diagnosing binary incompatibilities for Scala libraries.

What it is

The Migration Manager (MiMa in short) can report binary modifications that may lead the JVM throwing a java.lang.LinkageError (or one of its subtypes, like AbstractMethodError) at runtime. Linkage errors are usually the consequence of modifications in classes/members signature.

MiMa compares all classfiles of two released libraries and reports all source of incompatibilities that may lead to a linkage error. MiMa provides you, the library maintainer, with a tool that can greatly automates and simplifies the process of ensuring the release-to-release binary compatibility of your libraries.

A key aspect of MiMa to be aware of is that it only looks for syntactic binary incompatibilities. The semantic binary incompatibilities (such as adding or removing a method invocation) are not considered. This is a pragmatic approach as it is up to you, the library maintainer, to make sure that no semantic changes have occurred between two binary compatible releases. If a semantic change occurred, then you should make sure to provide this information as part of the new release's change list.

In addition, it is worth mentioning that binary compatibility does not imply source compatibility, i.e., some of the changes that are considered compatible at the bytecode level may still break a codebase that depends on it. Interestingly, this is not an issue intrinsic to the Scala language. In the Java language binary compatibility does not imply source compatibility as well. MiMa focuses on binary compatibility and currently provides no insight into source compatibility.

The current version of MiMa provides an aggressive reporting module for finding all potential binary incompatibilties.


The sbt plugin is released for sbt versions 0.13.x and 1.x. To try it, do the following:

Add the following to your project/plugins.sbt file:

addSbtPlugin("com.typesafe" % "sbt-mima-plugin" % "0.3.0")

Add the following to your build.sbt file:

mimaPreviousArtifacts := Set("com.jsuereth" % "scala-arm_2.9.1" % "1.2") // replace with your old artifact id

Run mimaReportBinaryIssues. You should see something like the following:

[info] Found 4 potential binary incompatibilities
[error]  * method rollbackTransactionResource()resource.Resource in object resource.Resource does not have a   correspondent in new version
[error]  * method now()scala.util.continuations.ControlContext in trait resource.ManagedResourceOperations does not    have a correspondent in old version
[error]  * abstract method now()scala.util.continuations.ControlContext in interface resource.ManagedResource does not have a correspondent in old version
[error]  * method rollbackTransactionResource()resource.Resource in trait resource.MediumPriorityResourceImplicits does not have a correspondent in new version
[error] {file:/home/jsuereth/project/personal/scala-arm/}scala-arm/*:mima-report-binary-issues: Binary compatibility check failed!
[error] Total time: 15 s, completed May 18, 2012 11:32:29 AM

Advanced Usage (Filtering Binary Incompatibilities)

Sometimes you may want to filter out some binary incompatibility. For instance, because you warn your users to never use a class or method marked with a particular annotation (e.g., @experimental - note, this annotation is not part of the Scala standard library), you may want to exclude all classes/methods that use such annotation. In MiMa you can do this by explicitly list each binary incompatibility that you want to ignore (unfortunately, it doesn't yet support annotation-based filtering - PR is welcomed! :)).

Open your build.sbt file, and

  1. List the binary incompatibilities you would like to ignore
val ignoredABIProblems = {
  1. Configure MiMa to include the defined binary incompatibility ignores
mimaPreviousArtifacts := Set("com.jsuereth" % "scala-arm_2.9.1" % "1.2") // replace with your old artifact id
mimaBinaryIssueFilters ++= ignoredABIProblems


java.lang.OutOfMemoryError - Java heap space: If you are experiencing out of memory exception you may need to increase the VM arguments for the initial heap size and the maximum heap size. The default values are -Xms64m for for the initial heap size and -Xmx256m for the maximum heap size.