Created attachment 5283 Adds the missing line, removes the typo Hi, in mousepad-dbus.h is G_BEGIN_DECLS missing, in mousepad-window is a type.
Thanks Jörg for this patch!
Jörg Preiß referenced this bugreport in commit 2876ae562157f704f70ff21fc7d94d9e66e6fae1 Missing line in dbus.h, found typo in window.h (bug #10583) https://git.xfce.org/apps/mousepad/commit?id=2876ae562157f704f70ff21fc7d94d9e66e6fae1
Thanks, pushed !