make distcheck is broken on xfce4-panel when "vala" is present on the system due to the introduction of vala binding generation in commits 3d6d1dd39864d013e96072ce63e8e0c4dfff9a2d and following. By reading https://cgit.freedesktop.org/accountsservice/commit/?id=17af4612e877c3a5c6bff67064d648f0eb2ea0cc , https://wiki.gnome.org/Projects/Vala/FAQ#Is_having_a_local_copy_of_a_.vapi_in_my_project_good_practice.3F and https://wiki.gnome.org/Projects/Vala/UpstreamGuide#Autotools_Integration , we don't need to provide the vapi in release tarballs. So I propose to add --enable-vala=no in DISTCHECK_CONFIGURE_FLAGS . Patch incoming (with other small fixes for distcheck) The other solution is to remove the vala thing from the code.
Created attachment 7456 Fix make distcheck
While fixing typos in your commit message I also managed to sneak one in... :( https://git.xfce.org/xfce/xfce4-panel/commit/?id=628624b41908eb70264b4ea491394834af5783ef Thanks for the patch!