I installed Arch Linux along with GNOME 3 yesterday. I have a git repository to keep all my settings the same across all devices.

This is how my .Xresources looks like:

#include "Xresources.d/xterm"
#include "Xresources.d/Xft"

I use different files for each application settings and #include them into the main .Xresources file. That’s works just fine.

However, it seems that GDM ignores all #include-s in .Xresources file. I didn’t have such issues in Fedora, so I assume this is Arch Linux specific thing.

After some investigation I found that /etc/gdm/Xsession has the following code:

if [ -f "$userresources" ]; then
    xrdb -nocpp -merge "$userresources"

According to man xrdb:

-nocpp  This option indicates that xrdb should not run the  input  file
        through a preprocessor before loading it into properties.

It means, that cpp preprocessor doesn’t get called and that’s why included files were not loaded.

The fix is simple: just edit the /etc/gdm/Xsession file and remove -nocpp option from the command that loads .Xresources:

if [ -f "$userresources" ]; then
    xrdb -merge "$userresources"

Maintainers decided to use -nocpp flag because of performance. It seems that calling the cpp preprocessor is quite expensive operation. Most of users don’t use #include, #define, etc. in their .Xresources file. By using -nocpp you can decrease startup time of your graphic environment.