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.

--- bash-completion-2.1/bash_completion	2015-03-11 09:45:45.056846446 +0100
+++ bash-completion-2.1/bash_completion	2015-03-11 09:52:43.248159504 +0100
@@ -1928,9 +1928,20 @@ _completion_loader()
     local compfile=./completions
     [[ $BASH_SOURCE == */* ]] && compfile="${BASH_SOURCE%/*}/completions"
     compfile+="/${1##*/}"
+    local base="${1##*/}"
 
+    # Look for completion files in the user and global profiles and
+    # lastly in 'bash-completion' itself.
+    for file in                                                                 \
+        "$HOME/.guix-profile/share/bash-completion/completions/$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"               \
+        "$compfile"
+    do
     # Avoid trying to source dirs; https://bugzilla.redhat.com/903540
-    [[ -f "$compfile" ]] && . "$compfile" &>/dev/null && return 124
+        [[ -f "$file" ]] && . "$file" &>/dev/null && return 124
+    done
 
     # Need to define *something*, otherwise there will be no completion at all.
     complete -F _minimal "$1" && return 124