Currently make distcheck is broken because of an include in the panel-plugin. This regression was introduced with 4244c8fec53f0f4f8c5ac6d12569fdfc34100a85
Created attachment 7483 Move common code to the library in order to fix distcheck In these cases I just move common code to special static library. I did the same thing for xfwm.
Viktor Odintsev referenced this bugreport in commit 92f248713f95aaec2709492b3edc988af56174dd Move common code to the library in order to fix distcheck (Bug #14078) https://git.xfce.org/apps/xfce4-notifyd/commit?id=92f248713f95aaec2709492b3edc988af56174dd
Thanks Viktor, makes sense to do it that way!