…and a bonus: one promising change not to try just yet.

Enable runtime @NotNull checks

To enable these checks you need to tell MPS that you want your Java code compiled using the IntelliJ compiler.

  1. In the project structure settings, find or add a java options node.
  2. Change the compiler to IntelliJ.
  3. Define idea_home folder macro, set it to the MPS home (mps_home or mps.home variable).

The result should look like this:

This will change the generated build script to use JetBrains-specific Ant task called javac2 instead of the default javac task. The javac2 task wraps javac, adding not-null checks and some (unrelated) IntelliJ IDEA GUI Designer form functionality.

Enable copying of resources to avoid problems with images

MPS defaults to not copying resources (non-Java files) generated by a build into JAR files. This default is, in my opinion, unfortunate and should be fixed1. Until it is fixed though, enable the copying of resources manually:

  1. In the project structure settings, find or add a java options node.
  2. Make sure copy resources is set to true.

Enabling copy resources reveals resource patterns option. Unless you have specific reasons to change it, leave it at its default setting (<all non-java files>).

The final result should look like this:

Move the tests build into a separate solution

The MPS build will package complete solutions into the final artifact. The build solution often needs to be packaged as well. To avoid tests leaking into the final product, it therefore makes sense to move the tests build script into a separate solution.

On the other side, two build solutions for a small project may be overkill. Packaging a build script that refers to some modules but not packaging those modules is actually harmless, in that it will not cause any errors or compilation failures (assuming that the consumer does not reference the test build script). The problem is merely too much disclosure, so decide for yourself.

BONUS: Avoiding double Java compilation… but not yet

MPS 2021.3.1 and above offer an experimental feature in the inspector of the mps plugin:

The reason for existence of this feature is the fact that by default MPS will compile your Java code twice. Once as part of the MPS make process trigggered by the generate Ant task, and a second time before assembling the artifact by a standard javac task (or IntelliJ-specific javac2 task, if you enable the IntelliJ compiler as described above).

Enabling “single MPS Make task” will replace the generate task with a rather similar but better named mps.make task and disable the second compilation, slightly improving the build times. However, as of early 2023, the mps.make task is quite buggy in all currently released MPS versions. So, keep an eye on the bugs, vote for the ones important to you, and once they are fixed, give it a try.

  1. Vote for MPS-25087 ↩︎