From 44a3f3353e0407e9fffee138125a6927d1c9e7e5 Mon Sep 17 00:00:00 2001
From: Bram Moolenaar <Bram@vim.org>
Date: Mon, 6 Jun 2022 15:38:21 +0100
Subject: [PATCH] patch 8.2.5063: error for a command may go over the end of
 IObuff

Problem:    Error for a command may go over the end of IObuff.
Solution:   Truncate the message.
---
 src/ex_docmd.c               | 12 ++++++++++--
 src/testdir/test_cmdline.vim |  5 +++++
 2 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/src/ex_docmd.c b/src/ex_docmd.c
index 1644573..7c00a26 100644
--- a/src/ex_docmd.c
+++ b/src/ex_docmd.c
@@ -3098,9 +3098,17 @@ checkforcmd(
     static void
 append_command(char_u *cmd)
 {
-    char_u *s = cmd;
-    char_u *d;
+    size_t  len = STRLEN(IObuff);
+    char_u  *s = cmd;
+    char_u  *d;
 
+    if (len > IOSIZE - 100)
+    {
+	// Not enough space, truncate and put in "...".
+	d = IObuff + IOSIZE - 100;
+	d -= mb_head_off(IObuff, d);
+	STRCPY(d, "...");
+    }
     STRCAT(IObuff, ": ");
     d = IObuff + STRLEN(IObuff);
     while (*s != NUL && d - IObuff + 5 < IOSIZE)
diff --git a/src/testdir/test_cmdline.vim b/src/testdir/test_cmdline.vim
index 2588a0d..735b0a5 100644
--- a/src/testdir/test_cmdline.vim
+++ b/src/testdir/test_cmdline.vim
@@ -930,4 +930,9 @@ func Test_cmdline_expr_register()
   exe "sil! norm! ?\<C-\>e0\<C-R>0\<Esc>?\<C-\>e0\<CR>"
 endfunc
 
+func Test_long_error_message()
+  " the error should be truncated, not overrun IObuff
+  silent! norm Q00000000000000     000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000                                                                                                                                                                                                                        
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab
-- 
1.8.3.1

