tmux compatibility

- New allowclipboard config flag (default on) so OSC 52 works without
  enabling all window ops. tmux set-clipboard was silently dropped before.
- DA2 (CSI >c) and DA3 (CSI =c) answered; tmux fingerprints with these.
- DSR 996 reports the colour scheme (dark/light) from the background.
- DECRQM 2031 reported as permanently reset.
- Unknown DCS sequences (DCS tmux; passthrough, XTGETTCAP) are discarded
  until ST instead of having their body interpreted as text/CSI.
- Private mode 7727 (extended keys) silently ignored.
- st.info: add RGB, Smulx, Setulc, kxIN, kxOUT and Hls so tmux and
  ncurses apps use truecolor, styled underlines, focus events and links.

config.def.h

@@ -90,6 +90,10 @@ int allowaltscreen = 1;
    setting the clipboard text */
 int allowwindowops = 0;
 
+/* allow programs to set the clipboard via OSC 52. This is what tmux uses
+   for set-clipboard, and what remote programs use to copy over ssh. */
+int allowclipboard = 1;
+
 /*
  * draw latency range in ms - from new content/keypress/etc until drawing.
  * within this range, st draws when content stops arriving (idle). mostly it's

config.h

@@ -90,6 +90,10 @@ int allowaltscreen = 1;
    setting the clipboard text */
 int allowwindowops = 0;
 
+/* allow programs to set the clipboard via OSC 52. This is what tmux uses
+   for set-clipboard, and what remote programs use to copy over ssh. */
+int allowclipboard = 1;
+
 /*
  * draw latency range in ms - from new content/keypress/etc until drawing.
  * within this range, st draws when content stops arriving (idle). mostly it's

st.c

@@ -117,6 +117,7 @@ enum escape_state {
 	#if SIXEL_PATCH
 	ESC_DCS        =128,
 	#endif // SIXEL_PATCH
+	ESC_DCS_IGNORE =256, /* discarding an unknown DCS until ST */
 };
 
 typedef struct {
@@ -2100,6 +2101,7 @@ tmodestatus(int priv, int mode)
 		#if SYNC_PATCH
 		case 2026: return su ? 1 : 2;
 		#endif // SYNC_PATCH
+		case 2031: return 4; /* theme change notifications: not supported */
 		#if SIXEL_PATCH
 		case 80:   return IS_SET(MODE_SIXEL_SDM) ? 1 : 2;
 		case 8452: return IS_SET(MODE_SIXEL_CUR_RT) ? 1 : 2;
@@ -2174,6 +2176,8 @@ tsetmode(int priv, int set, const int *args, int narg)
 			case 1004: /* 1004: send focus events to tty */
 				xsetmode(set, MODE_FOCUS);
 				break;
+			case 7727: /* 7727: extended keys (tmux/mintty), not supported */
+				break;
 			case 1006: /* 1006: extended reporting mode */
 				xsetmode(set, MODE_MOUSESGR);
 				break;
@@ -2328,6 +2332,22 @@ csihandle(void)
 		}
 		break;
 	case 'c': /* DA -- Device Attributes */
+		if (csiescseq.prefix == '>') {
+			/*
+			 * DA2 -- Secondary Device Attributes: CSI > Pp ; Pv ; Pc c
+			 * Pp = 0 (VT100 class), Pv = firmware version, Pc = 0.
+			 * tmux and others use this to fingerprint the terminal.
+			 */
+			if (csiescseq.arg[0] == 0)
+				ttywrite("\033[>0;95;0c", 10, 0);
+			break;
+		}
+		if (csiescseq.prefix == '=') {
+			/* DA3 -- Tertiary Device Attributes: unit id, all zeroes */
+			if (csiescseq.arg[0] == 0)
+				ttywrite("\033P!|00000000\033\\", 14, 0);
+			break;
+		}
 		if (csiescseq.arg[0] == 0)
 			ttywrite(vtiden, strlen(vtiden), 0);
 		break;
@@ -2634,6 +2654,18 @@ csihandle(void)
 			               term.c.y+1, term.c.x+1);
 			ttywrite(buffer, len, 0);
 			break;
+		case 996: /* colour scheme (dark/light) report: CSI ? 997 ; Ps n */
+			if (csiescseq.priv) {
+				unsigned char r, g, b;
+				int dark = 1;
+				if (!xgetcolor(defaultbg, &r, &g, &b))
+					dark = (299*r + 587*g + 114*b) / 1000 < 128;
+				len = snprintf(buffer, sizeof(buffer), "\033[?997;%dn",
+				               dark ? 1 : 2);
+				ttywrite(buffer, len, 0);
+				break;
+			}
+			goto unknown;
 		default:
 			goto unknown;
 		}
@@ -2871,7 +2903,7 @@ strhandle(void)
 				#endif // CSI_22_23_PATCH
 			return;
 		case 52:
-			if (narg > 2 && allowwindowops) {
+			if (narg > 2 && (allowwindowops || allowclipboard)) {
 				dec = base64dec(strescseq.args[2]);
 				if (dec) {
 					xsetsel(dec);
@@ -3369,9 +3401,13 @@ dcshandle(void)
 	switch (csiescseq.mode[0]) {
 	default:
 	unknown:
-		fprintf(stderr, "erresc: unknown csi ");
+		/*
-		csidump();
+		 * An unknown DCS, e.g. the "DCS tmux;" passthrough wrapper or
-		/* die(""); */
+		 * XTGETTCAP. Its body must not be interpreted, so discard every
+		 * byte until the terminating ST. Note the body may contain ESC ESC
+		 * (tmux doubles them), which must not end the string.
+		 */
+		term.esc |= ESC_DCS_IGNORE;
 		break;
 	#if SYNC_PATCH
 	case '=':
@@ -3541,6 +3577,23 @@ tputc(Rune u)
 	 * receives a ESC, a SUB, a ST or any other C1 control
 	 * character.
 	 */
+	if (term.esc & ESC_DCS_IGNORE) {
+		static int sawesc;
+		if (sawesc) {
+			sawesc = 0;
+			if (u == '\\') {
+				term.esc = 0;
+				return;
+			}
+			/* ESC ESC or ESC <other>: still inside the payload */
+			if (u != 033)
+				return;
+		}
+		if (u == 033)
+			sawesc = 1;
+		return;
+	}
+
 	if (term.esc & ESC_STR) {
 		if (u == '\a' || u == 030 || u == 032 || u == 033 ||
 		   ISCONTROLC1(u)) {

st.h

@@ -415,6 +415,7 @@ extern wchar_t *kbds_ldelim;
 #endif // KEYBOARDSELECT_PATCH
 extern int allowaltscreen;
 extern int allowwindowops;
+extern int allowclipboard;
 extern char *termname;
 extern unsigned int tabspaces;
 extern unsigned int defaultfg;

st.info

@@ -199,11 +199,20 @@ st-mono| simpleterm monocolor,
 #	rep=%p1%c\E[%p2%{1}%-%db,
 # tmux extensions, see TERMINFO EXTENSIONS in tmux(1)
 	Tc,
+	RGB,
 	Ms=\E]52;%p1%s;%p2%s\007,
 	Se=\E[2 q,
 	Ss=\E[%p1%d q,
 # sync patch / SYNC_PATCH
 	Sync=\EP=%p1%ds\E\\,
+# undercurl patch / UNDERCURL_PATCH: styled and coloured underlines
+	Smulx=\E[4:%p1%dm,
+	Setulc=\E[58:2::%p1%{65536}%/%d:%p1%{256}%/%{255}%&%d:%p1%{255}%&%dm,
+# focus events (mode 1004), used by tmux focus-events
+	kxIN=\E[I,
+	kxOUT=\E[O,
+# hyperlinks / OSC7_OSC8_PATCH
+	Hls=\E]8;id=%p1%s;%p2%s\E\\,
 
 st| simpleterm,
 	use=st-mono,