Comment 1 for bug 1258962

> Nuvolaplayer 2.0.4 compiles without error messages. Are there other dependencies necessary ?

No, new Valac versions often introduce backward incompatible changes
in VAPI files and break software that perfectly builds with older
Valac versions :-(

> Loaded package `/usr/share/vala-0.22/vapi/libnotify.vapi'
> Compilation failed: 4 error(s), 9 warning(s)
> glib-2.0.vapi:3322.118-3322.139: warning: parameter without default follows parameter with default
> /home/martin/rpmbuild/BUILD/nuvolaplayer-2.2.0/src/nuvola/extensions/notifications.vala:109.24-109.62: error: Invalid assignment from owned expression to unowned variable
> unowned List<string> capabilities = Notify.get_server_caps();
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Here is the villain, a signature of method Notify.get_server_caps()
has changed in an incompatible way.

Could you try to add attached file (libnotify.vapi from Valac 0.18.1) to the directory /external/vala-0.18 in the source directory and try to rebuild Nuvola Player once again?