To work on your own plugin, you can use either the Community or the Ultimate Edition of IntelliJ IDEA; both these editions are well-suited to plugin development. To be able to debug IDEA's core code though, you will need to use the Community Edition and have the Community Edition sources available on the source path of the plugin project. It's not mandatory for the plugin development process but can sometimes be useful. To get the Community Edition source, we need to pull it out from the repository; it's open source. Take note that the size of the sources will be more than one gigabyte, so make sure you have plenty of free space on your drive.

To pull out the source from the repository, use the Git pull command in the shell of your operating system:

git clone git://git.jetbrains.org/idea/community.git idea