edit.c: disable multiline editing on invalid $TERM

Reproducer: set TERM to an unknown terminal or one that does not
support cursor movement, and watch multiline editing go haywire.
Multiline editing should be auto-disabled under such conditions.

src/cmd/ksh93/edit/edit.c:
- Rename CURSOR_UP and ERASE_EOS to use lowercase names as they
  are not macros.
- get_tput(): Tweaks. Forget pre-existing escape sequences when
  tput(1) currently cannot provide them.
- ed_setup(): If e_multiline is on, and getting the tput(1) escape
  sequences upon a $TERM change fails, then disable e_multiline.
  To make this work correctly, we have to move this whole block
  to immediately before the code that adjusts the window size for
  single-line editing.
- ed_read(): Tweak and correct the code for redrawing the
  command-line on SIGWINCH in multiline mode. Using e_cur (the
  current position) as a factor in determining the number of lines
  to move up was incorrect, as that is the current position, not
  the total line length; for that, we need e_peol. (re: bb4f23e)

src/cmd/ksh93/features/cmds:
- Modernise a couple of old Bourne shell usages. POSIX shells can
  remove initial and final " with parameter expansion operators.

src/cmd/ksh93/include/edit.h:
- Remove two global vars that are unused after the above ed_setup()
  change; a locally scoped static variable is better here.

src/cmd/ksh93/tests/pty.sh:
- Four tests started failing because they depend on the specific
  behaviour of the multiline editor, which is now disabled because
  the pty tests are run with TERM=dumb so tput(1) will not return
  any escape sequences. Use TERM=vt100 for those (the DEC VT100 was
  pretty much the original ANSI escape sequence terminal, so it
  should be known about by just about every operating system).

NEWS

@@ -6,6 +6,11 @@ Uppercase BUG_* IDs are shell bug IDs as used by the Modernish shell library.
 
 - Fixed command line redrawing on resizing the window with --multiline off.
 
+- Multiline editing is now automatically disabled if and when the TERM
+  environment variable is unset, not exported, or set to a terminal type
+  that does not support the necessary operations. It is automatically
+  reenabled when the TERM variable is corrected and --multiline is on.
+
 2023-04-08:
 
 - Fixed a termcap(5) detection bug that broke multiline editing on FreeBSD.

src/cmd/ksh93/edit/edit.c

@@ -45,8 +45,8 @@
 #include	"edit.h"
 #include	"shlex.h"
 
-static char *CURSOR_UP = Empty;  /* move cursor up one line */
-static char *ERASE_EOS = Empty;  /* erase to end of screen */
+static char *cursor_up;  /* move cursor up one line */
+static char *erase_eos;  /* erase to end of screen */
 #if _tput_terminfo
 #define E_MULTILINE	ep->e_multiline
 #define TPUT_CURSOR_UP	"cuu1"
@@ -415,7 +415,7 @@ void ed_ringbell(void)
 
 #if SHOPT_ESH || SHOPT_VSH
 
-#ifdef _pth_tput
+#if defined(_pth_tput) && (_tput_terminfo || _tput_termcap)
 /*
  * Get or update a tput (terminfo or termcap) capability string.
  */
@@ -427,19 +427,27 @@ static void get_tput(char *tp, char **cpp)
 	sh_offoption(SH_RESTRICTED);
 	sh_offoption(SH_VERBOSE);
 	sh_offoption(SH_XTRACE);
-	sfprintf(sh.strbuf,".sh.value=$(" _pth_tput " %s 2>/dev/null)",tp);
+	sfprintf(sh.strbuf,".sh.value=${ " _pth_tput " %s 2>/dev/null;}",tp);
 	sh_trap(sfstruse(sh.strbuf),0);
 	if((cp = nv_getval(SH_VALNOD)) && (!*cpp || strcmp(cp,*cpp)!=0))
 	{
-		if(*cpp && *cpp!=Empty)
+		if(*cpp)
 			free(*cpp);
-		*cpp = *cp ? sh_strdup(cp) : Empty;
+		*cpp = *cp ? sh_strdup(cp) : NULL;
+	}
+	else
+	{
+		if(*cpp)
+			free(*cpp);
+		*cpp = NULL;
 	}
 	nv_unset(SH_VALNOD);
 	sh.options = o;
 	sigrelease(SIGINT);
 }
-#endif /* _pth_tput */
+#else
+#define get_tput(tp,cpp)  /* empty */
+#endif /* defined(_pth_tput) && (_tput_terminfo || _tput_termcap) */
 
 /*	ED_SETUP( max_prompt_size )
  *
@@ -620,6 +628,28 @@ void	ed_setup(Edit_t *ep, int fd, int reedit)
 	if(pp-ep->e_prompt > qlen)
 		ep->e_plen = pp - ep->e_prompt - qlen;
 	*pp = 0;
+	if(E_MULTILINE)
+	{
+		static char *oldterm;
+		Namval_t *np = nv_search("TERM",sh.var_tree,0);
+		char *term = NULL;
+		if(nv_isattr(np,NV_EXPORT))
+			term = nv_getval(np);
+		if(!term)
+			term = "";
+		if(!oldterm || strcmp(term,oldterm))
+		{
+			get_tput(TPUT_CURSOR_UP,&cursor_up);
+			get_tput(TPUT_ERASE_EOS,&erase_eos);
+			if(oldterm)
+				free(oldterm);
+			oldterm = sh_strdup(term);
+		}
+		if(cursor_up && erase_eos)
+			ep->e_wsize = MAXLINE - (ep->e_plen + 1);
+		else
+			ep->e_multiline = 0;
+	}
 	if(!E_MULTILINE && (ep->e_wsize -= ep->e_plen) < 7)
 	{
 		int shift = 7-ep->e_wsize;
@@ -648,21 +678,6 @@ void	ed_setup(Edit_t *ep, int fd, int reedit)
 		sfset(sfstderr,SF_READ,1);
 	sfwrite(sfstderr,ep->e_outptr,0);
 	ep->e_eol = reedit;
-	if(E_MULTILINE)
-	{
-#ifdef _pth_tput
-		char *term;
-		if(!ep->e_term)
-			ep->e_term = nv_search("TERM",sh.var_tree,0);
-		if(ep->e_term && (term=nv_getval(ep->e_term)) && strlen(term)<sizeof(ep->e_termname) && strcmp(term,ep->e_termname))
-		{
-			get_tput(TPUT_CURSOR_UP,&CURSOR_UP);
-			get_tput(TPUT_ERASE_EOS,&ERASE_EOS);
-			strcopy(ep->e_termname,term);
-		}
-#endif /* _pth_tput */
-		ep->e_wsize = MAXLINE - (ep->e_plen+1);
-	}
 	if(ep->e_default && (pp = nv_getval(ep->e_default)))
 	{
 		n = strlen(pp);
@@ -730,20 +745,25 @@ int ed_read(void *context, int fd, char *buff, int size, int reedit)
 			int	n, newsize;
 			char	*cp;
 			sh_winsize(NULL,&newsize);
+			ed_putchar(ep,'\r');
 			/*
 			 * Try to move cursor to start of first line and pray it works... it's very
 			 * failure-prone if the window size changed, especially on modern terminals
 			 * that break the whole terminal abstraction by rewrapping lines themselves :(
 			 */
 			if(E_MULTILINE)
 			{
-				n = (ep->e_plen + ep->e_cur) / newsize;
-				while(n--)
-					ed_putstring(ep,CURSOR_UP);
+				n = (ep->e_plen + ep->e_peol) / ep->e_winsz;
+				while(n-- > 0)
+					ed_putstring(ep,cursor_up);
+				/* clear the current command line */
+				ed_putstring(ep,erase_eos);
+			}
+			else
+			{
+				ed_nputchar(ep,newsize-1,' ');
+				ed_putchar(ep,'\r');
 			}
-			ed_putchar(ep,'\r');
-			/* clear the current command line */
-			ed_putstring(ep,ERASE_EOS);
 			ed_flush(ep);
 			/* show any buffered 'set -b' job notification(s) */
 			if(sh.notifybuf && (cp = sfstruse(sh.notifybuf)) && *cp)
@@ -1127,7 +1147,7 @@ int ed_setcursor(Edit_t *ep,genchar *physical,int old,int new,int first)
 		{
 			int n,pline,plen=ep->e_plen;
 			for(;ep->e_curpos.line > newpos.line; ep->e_curpos.line--)
-				ed_putstring(ep,CURSOR_UP);
+				ed_putstring(ep,cursor_up);
 			pline = plen/(ep->e_winsz+1);
 			if(newpos.line <= pline)
 				plen -= pline*(ep->e_winsz+1);
@@ -1150,7 +1170,7 @@ int ed_setcursor(Edit_t *ep,genchar *physical,int old,int new,int first)
 							ed_putchar(ep,physical[m++]);
 					}
 					ed_nputchar(ep,n,' ');
-					ed_putstring(ep,CURSOR_UP);
+					ed_putstring(ep,cursor_up);
 				}
 			}
 		}

src/cmd/ksh93/features/cmds

@@ -10,7 +10,8 @@ tput_terminfo note{ does tput support terminfo codes }end run{
 	export TERM=xterm
 	case ${_pth_tput-} in
 	\"/*/tput\")
-		tput=`echo "${_pth_tput}" | sed 's/^"//; s/"$//'`
+		tput=${_pth_tput#\"}
+		tput=${tput%\"}
 		if	"$tput" ed >/dev/null 2>&1 &&
 			"$tput" cuu1 >/dev/null 2>&1
 		then	echo '#define _tput_terminfo	1	/* tput supports terminfo codes */'
@@ -25,7 +26,8 @@ tput_termcap note{ does tput support termcap codes }end run{
 	export TERM=xterm
 	case ${_pth_tput-} in
 	\"/*/tput\")
-		tput=`echo "${_pth_tput}" | sed 's/^"//; s/"$//'`
+		tput=${_pth_tput#\"}
+		tput=${tput%\"}
 		if	"$tput" cd >/dev/null 2>&1 &&
 			"$tput" up >/dev/null 2>&1
 		then	echo '#define _tput_termcap	1	/* tput supports termcap codes */'

src/cmd/ksh93/include/edit.h

@@ -141,8 +141,6 @@ typedef struct edit
 	int	e_winsz;	/* columns in window */ 
 	Edpos_t	e_curpos;	/* cursor line and column */
 	Namval_t *e_default;	/* variable containing default value */
-	Namval_t *e_term;	/* TERM variable */
-	char 	e_termname[80];	/* terminal name */
 #if SHOPT_EDPREDICT
 	Histmatch_t	**hlist;
 	Histmatch_t	*hfirst;

src/cmd/ksh93/sh.1

@@ -7779,11 +7779,23 @@ Same as
 .B multiline
 The built-in editors will use multiple lines on the screen for lines
 that are longer than the width of the screen.  This may not work
-for all terminals. The option is forced off on systems with neither
-.B terminfo (5)
+for all terminals.
+The shell uses the system's
+.BR tput (1)
+command to obtain the terminal escape codes for the necessary operations.
+Multi-line editing is disabled if this fails.
+On most systems, setting the
+.B TERM
+variable to your terminal's type and exporting it corrects this situation.
+The
+.B multiline
+option is permanently forced off on systems whose
+.BR tput (1)
+command supports neither
+.BR terminfo (5)
 nor
-.B termcap (5)
-support.
+.BR termcap (5)
+capability names.
 .TP 8
 .B noclobber
 Same as

src/cmd/ksh93/tests/pty.sh

@@ -804,7 +804,8 @@ w :\E_
 r ^:test-2: : One\\ "Two Three"\$'Four Five'\.mp3\r\n$
 !
 
-((SHOPT_VSH)) && tst $LINENO <<"!"
+# needs non-dumb terminal for multiline editing
+((SHOPT_VSH)) && TERM=vt100 tst $LINENO <<"!"
 L crash when entering comment into history file (vi mode)
 # https://github.com/att/ast/issues/798
 
@@ -857,7 +858,8 @@ w $'`/dev\t
 r ^:test-5: \$'`/dev[[:blank:]]*\r\n$
 !
 
-((SHOPT_ESH)) && VISUAL=emacs tst $LINENO <<"!"
+# needs non-dumb terminal for multiline editing
+((SHOPT_ESH)) && VISUAL=emacs TERM=vt100 tst $LINENO <<"!"
 L emacs: keys with repeat parameters repeat extra steps
 # https://github.com/ksh93/ksh/issues/292
 
@@ -1083,7 +1085,8 @@ w p\E[AT
 u CORRECT
 !
 
-((SHOPT_ESH)) && mkdir -p fullcomplete/foe && VISUAL=emacs tst $LINENO <<"!"
+# needs non-dumb terminal for multiline editing
+((SHOPT_ESH)) && mkdir -p fullcomplete/foe && VISUAL=emacs TERM=vt100 tst $LINENO <<"!"
 L full-word completion in emacs mode
 # https://github.com/ksh93/ksh/pull/580
 
@@ -1099,7 +1102,8 @@ w true fullcomplete/foi\cb*
 r ^:test-3: true fullcomplete/foi\r\n
 !
 
-((SHOPT_VSH)) && mkdir -p fullcomplete/fov && VISUAL=vi tst $LINENO <<"!"
+# needs non-dumb terminal for multiline editing
+((SHOPT_VSH)) && mkdir -p fullcomplete/fov && VISUAL=vi TERM=vt100 tst $LINENO <<"!"
 L full-word completion in vi mode
 # https://github.com/ksh93/ksh/pull/580