Bash-completion is written with FHS in mind where completion scripts
all get added to /usr/share/bash-completion/completions and are picked
up by the dynamic completion loader from there---whether they are
part of bash-completion or installed by another package.

On Guix systems, we want not only to search within bash-completion's own
directory, but also in the user's profile and in the system profile.
This is what this patch does.

--- a/bash_completiong	2016-08-03 10:23:02.356782287 +0200
+++ b/bash_completion	2016-08-03 10:27:50.120140403 +0200
@@ -1960,7 +1960,13 @@
 
 __load_completion()
 {
-    local -a dirs=( ${BASH_COMPLETION_USER_DIR:-${XDG_DATA_HOME:-$HOME/.local/share}/bash-completion}/completions )
+    local -a dirs=(
+        "$HOME/.guix-profile/share/bash-completion/completions/$base"
+        "$HOME/.guix-profile/etc/bash_completion.d/$base"
+        "/run/current-system/profile/share/bash-completion/completions/$base"
+        "/run/current-system/profile/etc/bash_completion.d/$base"
+        ${BASH_COMPLETION_USER_DIR:-${XDG_DATA_HOME:-$HOME/.local/share}/bash-completion}/completions )
+
     local OIFS=$IFS IFS=: dir cmd="$1" compfile
     for dir in ${XDG_DATA_DIRS:-/usr/local/share:/usr/share}; do
         dirs+=( $dir/bash-completion/completions )