IntelliJ API to Build Scala Macros Support

Andrey Cheptsov

Today we’ve released a new Scala plugin EAP build. With this build, we’re happy to introduce an API that extends the IDE coding assistance to custom Scala macros.

A macro is executed at compile-time and modifies the AST of your code: e.g. it can extend the class or its companion object with new methods or other code represented by the AST returned by the macro. Since IntelliJ IDEA’s coding assistance is based on static code analysis, the IDE is not aware of AST changes, and can’t provide appropriate code completion and inspections for the generated code.

Since macros are heavily used in some projects and libraries, we’ve added a special API to the platform that lets build IntelliJ plugins supporting particular macros. Using this API, we earlier added support for Monocle, and now Simulacrum:

Now, everyone can use this API to make their macros more friendly to their favorite IDE. To do that, you have to implement SyntheticMembersInjector, and register it in the plugin.xml file:

<extensions defaultExtensionNs="org.intellij.scala">
    <syntheticMemberInjector implementation="org.jetbrains.example.injector.Injector"/>
</extensions>

The Monocle and Simulacrum implementations will help you understand how to use the API. To help you with setting up a project, we’ve prepared a skeleton. You’re welcome to fork it, and add your implementation.

Once you’ve built a working plugin, it can be installed to the IDE via Settings → Plugins → Install plugin from disk…. If you want to share your plugin with other IntelliJ IDEA users, feel free to upload it to our plugin repository.

We’re eager to hear your feedback on the API. Feel free to share it either here in comments, on our discussion forum, or in the issue tracker.

In case you’d like to have particular macros supported by the Scala plugin, send us pull requests.

Develop with Pleasure!