patch 8.2.3864: cannot disable requesting key codes from xterm

Problem:    Cannot disable requesting key codes from xterm.
Solution:   Add the 'xtermcodes' option, default on.

runtime/doc/options.txt

@@ -9206,4 +9206,16 @@ A jump table for the options with a short description can be found at |Q_op|.
 	screen.  When non-zero, characters are sent to the terminal one by
 	one.  For debugging purposes.
 
+					   *'xtermcodes'* *'noxtermcodes'*
+'xtermcodes'		boolean	(default on)
+			global
+	When detecting xterm patchlevel 141 or higher with the termresponse
+	mechanism and this option is set, Vim will request the actual termimal
+	key codes and number of colors from the terminal.  This takes care of
+	various configuration options of the terminal that cannot be obtained
+	from the termlib/terminfo entry, see |xterm-codes|.
+	A side effect may be that t_Co changes and Vim will redraw the
+	display.
+
+
  vim:tw=78:ts=8:noet:ft=help:norl:

runtime/doc/term.txt

@@ -556,8 +556,15 @@ request the key codes directly from the xterm.  The responses are used to
 adjust the various t_ codes.  This avoids the problem that the xterm can
 produce different codes, depending on the mode it is in (8-bit, VT102,
 VT220, etc.).  The result is that codes like <xF1> are no longer needed.
-Note: This is only done on startup.  If the xterm options are changed after
+
-Vim has started, the escape sequences may not be recognized anymore.
+One of the codes that can change is 't_Co', the number of colors.  This will
+trigger a redraw.  If this is a problem, reset the 'xtermcodes' option as
+early as possible: >
+	set noxtermcodes
+
+Note: Requesting the key codes is only done on startup.  If the xterm options
+are changed after Vim has started, the escape sequences may not be recognized
+anymore.
 
 							*xterm-true-color*
 Vim supports using true colors in the terminal (taken from |highlight-guifg|

runtime/optwin.vim

@@ -562,14 +562,22 @@ endif
 call <SID>Header(gettext("terminal"))
 call <SID>AddOption("term", gettext("name of the used terminal"))
 call <SID>OptionG("term", &term)
+
 call <SID>AddOption("ttytype", gettext("alias for 'term'"))
 call <SID>OptionG("tty", &tty)
+
 call <SID>AddOption("ttybuiltin", gettext("check built-in termcaps first"))
 call <SID>BinOptionG("tbi", &tbi)
+
 call <SID>AddOption("ttyfast", gettext("terminal connection is fast"))
 call <SID>BinOptionG("tf", &tf)
+
+call <SID>AddOption("xtermcodes", gettext("request terminal key codes when an xterm is detected"))
+call <SID>BinOptionG("xtermcodes", &xtermcodes)
+
 call <SID>AddOption("weirdinvert", gettext("terminal that requires extra redrawing"))
 call <SID>BinOptionG("wiv", &wiv)
+
 call <SID>AddOption("esckeys", gettext("recognize keys that start with <Esc> in Insert mode"))
 call <SID>BinOptionG("ek", &ek)
 call <SID>AddOption("scrolljump", gettext("minimal number of lines to scroll at a time"))

src/option.h

@@ -485,6 +485,7 @@ EXTERN int	p_deco;		// 'delcombine'
 #ifdef FEAT_EVAL
 EXTERN char_u	*p_ccv;		// 'charconvert'
 #endif
+EXTERN int	p_cdh;		// 'cdhome'
 EXTERN char_u	*p_cino;	// 'cinoptions'
 #ifdef FEAT_CMDWIN
 EXTERN char_u	*p_cedit;	// 'cedit'
@@ -1094,7 +1095,7 @@ EXTERN int	p_write;	// 'write'
 EXTERN int	p_wa;		// 'writeany'
 EXTERN int	p_wb;		// 'writebackup'
 EXTERN long	p_wd;		// 'writedelay'
-EXTERN int	p_cdh;		// 'cdhome'
+EXTERN int	p_xtermcodes;	// 'xtermcodes'
 
 /*
  * "indir" values for buffer-local options.

src/optiondefs.h

@@ -2941,6 +2941,9 @@ static struct vimoption options[] =
     {"writedelay",  "wd",   P_NUM|P_VI_DEF,
 			    (char_u *)&p_wd, PV_NONE,
 			    {(char_u *)0L, (char_u *)0L} SCTX_INIT},
+    {"xtermcodes",  NULL,   P_BOOL|P_VI_DEF,
+			    (char_u *)&p_xtermcodes, PV_NONE,
+			    {(char_u *)TRUE, (char_u *)0L} SCTX_INIT},
 
 // terminal output codes
 #define p_term(sss, vvv)   {sss, NULL, P_STRING|P_VI_DEF|P_RALL|P_SECURE, \

src/term.c

@@ -4694,7 +4694,7 @@ handle_version_response(int first, int *arg, int argc, char_u *tp)
 
 	// If xterm version >= 141 try to get termcap codes.  For other
 	// terminals the request should be ignored.
-	if (version >= 141)
+	if (version >= 141 && p_xtermcodes)
 	{
 	    LOG_TR(("Enable checking for XT codes"));
 	    check_for_codes = TRUE;
@@ -6446,8 +6446,7 @@ got_code_from_term(char_u *code, int len)
 	    if (name[0] == 'C' && name[1] == 'o')
 	    {
 		// Color count is not a key code.
-		i = atoi((char *)str);
+		may_adjust_color_count(atoi((char *)str));
-		may_adjust_color_count(i);
 	    }
 	    else
 	    {

src/version.c

@@ -749,6 +749,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    3864,
 /**/
     3863,
 /**/