Developing

Ensure you have Java 8 SDK newer than Java 8.112 (newer than what IntelliJ displays in "About IntelliJ IDEA" dialog)
clone the repository
run ./gradlew runIde - for the first time, this will take quite a while, as it downloads IntelliJ.
First, go to "Configure -> Project Defaults -> Project Structure" (or "File -> Project Structure"), then ensure underneath "Platform Settings" -> "SDKs", there is a SDK for the JDK 1.8 version you have. If not, create it.
to open the project in IntelliJ, Use "File -> Open" in IntelliJ and select the "build.gradle" in here.
- then, select "Use Auto-Import"; and select JDK 1.8 (newer than rev 112).
to run the project from within IDEA, go to "View -> Tool Windows -> Gradle", and in the Gradle tool window, do the following:
- expand "Tasks -> intellij -> runIde"
- right-click it and select "Run"
- (you can also select "debug" to run it in debug mode!)
in debug mode, you can hot-reload classes by choosing "Run -> Reload changed classes" as explained on https://www.jetbrains.com/help/idea/2016.3/reloading-classes.html
have fun developing :)

Development Tips and Tricks

install GrammarKit if you want to work on the parser
to log, use NeosProjectComponent.getLogger().warn("Foo") and run tail -f build/idea-sandbox/system/log/idea.log.
If you use debug level, you have to add the "Neos" debug category via Help > Debug Log Settings.