lightbend / migration-manager

Scala Binary Compatibility validation tool – "MiMa" for short


Migration Manager for Scala

A tool for diagnosing migration problems for Scala libraries

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

If you don't know how to use MiMa, please read the user documentation.

MiMa's Modules

MiMa is split into Several modules:

  • Core: Classes that are used for detection.
  • Reporter: Raw reporting classes and the command line interface.
  • SBT Plugin: The SBT plugin for usage inside SBT builds.


To use MiMa as an sbt plugin, see the sbt plugin wiki page.


Using sbt:

  $ sbt compile

This will recompile all MiMa's modules.

If you'd like to create distributable jar files for the CLI, run:

  $ sbt assembly

This will create reporter/target/mima-reporter-assembly-....jar jar file that can be used to launch the command line version of MiMa.

Launch MiMa Reporter CLI

Type the following command to run the MiMa Reporter command-line

$ sbt reporter/run

Alternatively, you can use the assembly jar to use the CLI as a standalone application:

    $ java -jar path/to/mima-reporter-assembly-....jar --prev LIB-v1.jar --curr LIB-v2.jar

MiMa Reporter: Functional Tests

The directory containing the MiMa Reporter module ('reporter') there is a 'functional-tests' folder that contains several functional tests exercising the system. All tests are executed as part of the build, therefore when running

$ sbt testFunctional

if one (or more) test fails the build is stop and no jar will not be produced.

To add a new functional test to the suite, create a new folder within 'functional-tests' directory with the following structure:

    | --> <your-new-test-folder> (folder for your new test)
		|-----> problems.txt (the expected list of reported errors - 1 line per error)
		|-----> v1 (folder containing sources @ version 1)
		|-----> v2 (folder containing sources @ version 2)

After doing that, reload if you are in a sbt console session (if that makes no sense to you, it means you are fine and you can run the test as usual).

Tests within the functional-tests folder should always pass.

Note: The problems.txt is the test oracle. Expected errors are declared using the MiMa's reporting output (i.e., the output of the tool and the expected errors should match perfectly). Admittedly, this coupling is an issue since the testing framework is highly coupled with the tool output used to report errors to the user. We should improve this and make the two independent. Until then, mind that by changing the output of the tool you will likely have to update some of the test oracles (i.e., problems.txt file). When running tests against Scala 2.12 or higher, problems-2.12.txt is preferred over problems.txt if the former exists.


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.

Bugs and Feature requests

Use the GitHub project page for filing new tickets.


If you'd like to contribute to the MiMa project, please sign the contributor's licensing agreement.


Copyright 2012-2016 Lightbend, Inc.

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.