qf_guess_filepath(qf_list_T *qfl, char_u *filename)
{
    struct dir_stack_T     *ds_ptr;
    struct dir_stack_T     *ds_tmp;
    char_u		   *fullname;

    // no dirs on the stack - there's nothing we can do
    if (qfl->qf_dir_stack == NULL)
	return NULL;

    ds_ptr = qfl->qf_dir_stack->next;
    fullname = NULL;
    while (ds_ptr)
    {
	vim_free(fullname);
	fullname = concat_fnames(ds_ptr->dirname, filename, TRUE);

	// If concat_fnames failed, just go on. The worst thing that can happen
	// is that we delete the entire stack.
	if ((fullname != NULL) && (mch_getperm(fullname) >= 0))
	    break;

	ds_ptr = ds_ptr->next;
    }

    vim_free(fullname);

    // clean up all dirs we already left
    while (qfl->qf_dir_stack->next != ds_ptr)
    {
	ds_tmp = qfl->qf_dir_stack->next;
	qfl->qf_dir_stack->next = qfl->qf_dir_stack->next->next;
	vim_free(ds_tmp->dirname);
	vim_free(ds_tmp);
    }

    return ds_ptr == NULL ? NULL : ds_ptr->dirname;
}