https://github.com/vim-jp/issues/issues/467

eval.c.diff

diff --git a/src/eval.c b/src/eval.c
--- a/src/eval.c
+++ b/src/eval.c
@@ -7972,8 +7972,8 @@
     {"iconv",		3, 3, f_iconv},
     {"indent",		1, 1, f_indent},
     {"index",		2, 4, f_index},
-    {"input",		1, 3, f_input},
-    {"inputdialog",	1, 3, f_inputdialog},
+    {"input",		1, 4, f_input},
+    {"inputdialog",	1, 4, f_inputdialog},
     {"inputlist",	1, 1, f_inputlist},
     {"inputrestore",	0, 0, f_inputrestore},
     {"inputsave",	0, 0, f_inputsave},
@@ -13022,6 +13022,7 @@
     char_u	*defstr = (char_u *)"";
     int		xp_type = EXPAND_NOTHING;
     char_u	*xp_arg = NULL;
+    list_T	*ret_list = NULL;
 
     rettv->v_type = VAR_STRING;
     rettv->vval.v_string = NULL;
@@ -13060,24 +13061,38 @@
 	    if (defstr != NULL)
 		stuffReadbuffSpec(defstr);
 
-	    if (!inputdialog && argvars[2].v_type != VAR_UNKNOWN)
-	    {
-		char_u	*xp_name;
-		int	xp_namelen;
-		long	argt;
-
-		/* input() with a third argument: completion */
-		rettv->vval.v_string = NULL;
-
-		xp_name = get_tv_string_buf_chk(&argvars[2], buf);
-		if (xp_name == NULL)
-		    return;
-
-		xp_namelen = (int)STRLEN(xp_name);
-
-		if (parse_compl_arg(xp_name, xp_namelen, &xp_type, &argt,
-							     &xp_arg) == FAIL)
-		    return;
+	    if (argvars[2].v_type != VAR_UNKNOWN)
+	    {
+		if (argvars[3].v_type == VAR_LIST)
+		{
+		    if ((ret_list = argvars[3].vval.v_list) != NULL
+			    && tv_check_lock(ret_list->lv_lock,
+						 (char_u *)_("add() argument")))
+			ret_list = NULL;
+		}
+
+		if (!inputdialog)
+		{
+		    char_u	*xp_name;
+		    int	xp_namelen;
+		    long	argt;
+
+		    /* input() with a third argument: completion */
+		    rettv->vval.v_string = NULL;
+
+		    xp_name = get_tv_string_buf_chk(&argvars[2], buf);
+		    if (xp_name == NULL)
+			return;
+
+		    xp_namelen = (int)STRLEN(xp_name);
+
+		    if (xp_namelen > 0 || ret_list == NULL)
+		    {
+			if (parse_compl_arg(xp_name, xp_namelen, &xp_type, &argt,
+								&xp_arg) == FAIL)
+			    return;
+		    }
+		}
 	    }
 	}
 
@@ -13099,6 +13114,13 @@
 		&& argvars[2].v_type != VAR_UNKNOWN)
 	    rettv->vval.v_string = vim_strsave(get_tv_string_buf(
 							   &argvars[2], buf));
+	if (ret_list)
+	{
+	    if (rettv->vval.v_string)
+		list_append_tv(ret_list, rettv);
+	    else
+		list_append_number(ret_list, 0);
+	}
 
 	vim_free(xp_arg);