Add comment explaining compl_func_args

plugins/available/alias-completion.plugin.bash

@@ -63,9 +63,13 @@ function alias_completion {
             local compl_func="${new_completion/#* -F /}"; compl_func="${compl_func%% *}"
             # avoid recursive call loops by ignoring our own functions
             if [[ "${compl_func#_$namespace::}" == $compl_func ]]; then
+                # the completion function stored in compl_func may need argument(s),
+                # in which case they should be provided in compl_func_args (see #1497)
+                local compl_func_args=
                 if [[ $compl_func == _filedir_xspec ]]; then
                     compl_func_args=$alias_cmd
                 fi
+
                 local compl_wrapper="_${namespace}::${alias_name}"
                     echo "function $compl_wrapper {
                         (( COMP_CWORD += ${#alias_arg_words[@]} ))