Run ./generate.py and then open this directory in IntelliJ.
From there you can launch the Android Studio run configuration as usual.
See the IntelliJ README for IDE build configuration tips.
If you change the project structure (e.g. module dependencies) of either Studio or IntelliJ, then you will need to re-run generate.py for those changes to take effect in the monobuild.
The generate.py script is expected to break occasionally, such as when there are new conflicts between Studio/IntelliJ configuration files. Please spend a few minutes debugging to see if it is an easy fix. Otherwise, file a bug.
If you are running generate.py frequently, but not changing the IntelliJ project structure, then you can use --recycle-intellij-source-map to speed up iteration times.
To test code changes in generate.py, you should diff the generated output against previous runs. You can utilize git diff --no-index <before> <after> for this.
You can use the “Load/Unload Modules” action in the IDE to exclude any broken modules (assuming these modules are not needed by the run configurations you care about).