Teach apps activation script to set XDG_DATA_DIRS

This allows systemd to find units, and desktop environments to find
application entries.

1 files changed, 31 insertions, 2 deletions

diff --git a/guides/setups/operating-systems/apps-demo/activate b/guides/setups/operating-systems/apps-demo/activate
index 434924a..fbf522c 100644
--- a/guides/setups/operating-systems/apps-demo/activate
+++ b/guides/setups/operating-systems/apps-demo/activate
@@ -1,12 +1,41 @@
 # Hey Emacs; this is a -*- shell-script -*-.
 # Hopefully invoked by bash 🤞
 
-_apps_dir=$(dirname ${BASH_SOURCE})
+_apps_dir=$(realpath --no-symlinks $(dirname ${BASH_SOURCE}))
 
 _apps_PATH=$(
     shopt -s nullglob
     bins=( "${_apps_dir}"/*/bin )
     IFS=: eval 'echo "${bins[*]}"'
 )
-
 export PATH=${_apps_PATH}:${PATH}
+
+_apps_XDG_DATA_DIRS=$(
+    shopt -s nullglob
+    # We could set globstar and let Bash loose, searching the depths
+    # of _apps_dir for
+    # **/{applications/*.desktop,systemd/user/*.service}
+    # but it seems like asking for trouble.  Make some assumptions
+    # about where applications typically dump their XDG-related files.
+    datadirs=($(
+        {
+            for dkentry in "${_apps_dir}"/*/share/applications/*.desktop
+            do
+                echo ${dkentry%/applications/*.desktop}
+            done
+            for unit in "${_apps_dir}"/*/lib*/systemd/user/*.service
+            do
+                echo ${unit%/systemd/user/*.service}
+            done
+        } | sort -u
+    ))
+    IFS=: eval 'echo "${datadirs[*]}"'
+)
+export XDG_DATA_DIRS=$(
+    if test "${XDG_DATA_DIRS}"
+    then
+        echo "${_apps_XDG_DATA_DIRS}:${XDG_DATA_DIRS}"
+    else
+        echo "${_apps_XDG_DATA_DIRS}"
+    fi
+)