With the deprecation of the menu files in Debian per
CTTE #741573 the desktop file and associated icons have become much more important, but the spatialite-gui build system does not install them.
The attached desktop-file.patch updates the spatialite-gui.desktop file included in the gnome_resource subdirectory, it removes the shebang which is not required, and adds Exec variables for the file argument supported on the commandline, and adds Keywords to assist desktop searching. `desktop-file-validate gnome_resource/spatialite-gui.desktop` only hints at the duplicate categories now, that does not need to be changed.
The complementary install-icons.patch updates gnome_resource/Makefile.am to install the desktop file and the associated application icon for various sizes in the hicolor theme per the
Icon Theme Specification.
Because support for binary files in patches still sucks this day and age, you need to extract the icons directory from the spatialite-gui-icons.tar.xz into the gnome_resource directory. The existing gnome_resource/spatialite-gui.png can be removed, it's not a valid icon size for the Icon Theme Specification (48x42 instead of 48x48).
The various sized icons > 128x128 were created from the win_resource/spatialite-icon.png because it's the highest resolution (693x613), the > 48x48 <= 128x128 were created from icons/icon_info.xpm, and the <= 48x48 icons from gnome_resource/spatialite-gui.png.
Ideally the source icon is in SVG format, which can then also be installed in $prefix/share/icons/hicolor/scalable/apps to have it available for any size, but as far as I can tell there is no SVG for the spatialite-gui icon.
My autotools-fu is not that great, so there is room for improvement of the changes in install-icons.patch. You probably want to skip the icon installation on OSX & Windows for example.
Kind Regards,
Bas