bash-completion: handle comma-separated options in findmnt

index cf66565..3ad9147 100644
@@ -43,15 +43,23 @@ _findmnt_module()
 			return 0
 			;;
 		'-o'|'--output')
-			# FIXME: how to append to a string with compgen?
-			local OUTPUT
-			OUTPUT="SOURCE TARGET FSTYPE OPTIONS VFS-OPTIONS
+			local prefix realcur OUTPUT_ALL OUTPUT
+			realcur="${cur##*,}"
+			prefix="${cur%$realcur}"
+
+			OUTPUT_ALL="SOURCE TARGET FSTYPE OPTIONS VFS-OPTIONS
 				FS-OPTIONS LABEL UUID PARTLABEL PARTUUID
 				MAJ\:MIN ACTION OLD-TARGET OLD-OPTIONS
 				SIZE AVAIL USED USE% FSROOT TID ID
 				OPT-FIELDS PROPAGATION FREQ PASSNO"
+
+			for WORD in $OUTPUT_ALL; do
+				if ! [[ $prefix == *"$WORD"* ]]; then
+					OUTPUT="$WORD $OUTPUT"
+				fi
+			done
 			compopt -o nospace
-			COMPREPLY=( $(compgen -W "$OUTPUT" -S ',' -- $cur) )
+			COMPREPLY=( $(compgen -P "$prefix" -W "$OUTPUT" -S ',' -- $realcur) )
 			return 0
 			;;
 		'-t'|'--types')