There are actually two:
Back in the days we had a dedicated jenkins instance running. The Problem is that some plugins require the sdk to compile against (others which are only add-in-libraries only need the engine). Unfortunately the SDK needs much diskspace and time to build. Since we don’t distribute the buildfiles, every plugin has to rebuild the whole sdk.
Back in the days, each plugin was just a subfolder to the sdk and jenkins called them, but for travis this doesn’t work. For this we have the “meta-plugin/bootstrapper/w.e.” https://github.com/MeFisto94/nbproject
You can see the build.gradle file, which downloads netbeans and copies engine libs.
As far as I remember it was only made to build engine-requiring libs like https://github.com/MeFisto94/av-capture
There is no documentation and I don’t remember it myself, however the two commits of av-capture show what is required to build a plugin. Especially https://github.com/MeFisto94/av-capture/blob/a074167d2889eacf18d62e9fa197bfde2db8d203/suite_bootstrap.gradle
However we still need something like a webserver to easily access these files (because I dislike abusing a github repo)