Follow the Developer Guide intro to install the required software:
and then this tutorial for VS Code (I tried to make Eclipse work with the new build system a while ago without success, but I managed to get VS Code working):
except instead of cloning GitHub - openhab/openhab2-addons: This is an archive of the full history of the openhab2-addons repo. you’ll clone @arctus’ fork or your own fork with his changes.
Then you should be able to make a .jar file with mvn clean package or mvn clean install from the new bundle’s folder.
For HABPanel it should be similar (it is in the GitHub - openhab/openhab-webui: Web UIs of openHAB repo, in the bundles/org.openhab.ui.habpanel folder). But in this case you can either build HABPanel’s .jar (the clean way), or simply clone the repo in the html folder of your configuration, and edit the Javascript source directly - your version will be in a different URL under /static/, see: