I am in the process of making a fairly minimalistic XFCE-based distribution. We use Thunar as the file manager, and one of the packages we would like to put on the system uses xdg-desktop-menu to install its ".desktop" file.
However, the file is never placed in /usr/share/applications, because the xdg-desktop-menu script errors out:
"No writable system menu directory found."
The issue is we don't have anything that installs a /usr/share/desktop-directories directory. Creating one causes the script to run properly and install the ".desktop" file in /usr/share/applications. However, the desktop-directories directory still remains empty.
The bug is that I can't see any reason why xdg-desktop-menu should error out when /usr/share/desktop-directories does not exist. It installs the ".desktop" file in /usr/share/applications anyway.