On some Windows terminals, if TIOCWINSZ does not return xpixel and

ypixel (they are zero), if this is the case then try the query escape
sequences. From Dmitry Galchinsky in GitHub issue 4099.

tmux.h

@@ -1474,6 +1474,7 @@ struct tty {
 #define TTY_HAVEXDA 0x200
 #define TTY_SYNCING 0x400
 #define TTY_HAVEDA2 0x800 /* Secondary DA. */
+#define TTY_WINSIZEQUERY 0x1000
 #define TTY_ALL_REQUEST_FLAGS \
 	(TTY_HAVEDA|TTY_HAVEDA2|TTY_HAVEXDA)
 	int		 flags;
@@ -2307,6 +2308,7 @@ typedef void (*job_free_cb) (void *);
 #define JOB_NOWAIT 0x1
 #define JOB_KEEPWRITE 0x2
 #define JOB_PTY 0x4
+#define JOB_DEFAULTSHELL 0x8
 struct job	*job_run(const char *, int, char **, struct environ *,
 		     struct session *, const char *, job_update_cb,
 		     job_complete_cb, job_free_cb, void *, int, int, int);
@@ -2369,6 +2371,7 @@ void	tty_cell(struct tty *, const struct grid_cell *,
 int	tty_init(struct tty *, struct client *);
 void	tty_resize(struct tty *);
 void	tty_set_size(struct tty *, u_int, u_int, u_int, u_int);
+void	tty_invalidate(struct tty *);
 void	tty_start_tty(struct tty *);
 void	tty_send_requests(struct tty *);
 void	tty_repeat_requests(struct tty *);

tty-keys.c

@@ -654,6 +654,74 @@ tty_keys_next1(struct tty *tty, const char *buf, size_t len, key_code *key,
 	return (-1);
 }
 
+/* Process window size change escape sequences. */
+static int
+tty_keys_winsz(struct tty *tty, const char *buf, size_t len, size_t *size)
+{
+	struct client	*c = tty->client;
+	size_t		 end;
+	char		 tmp[64];
+	u_int		 sx, sy, xpixel, ypixel, char_x, char_y;
+
+	*size = 0;
+
+	/* If we did not request this, ignore it. */
+	if (!(tty->flags & TTY_WINSIZEQUERY))
+		return (-1);
+
+	/* First two bytes are always \033[. */
+	if (buf[0] != '\033')
+		return (-1);
+	if (len == 1)
+		return (1);
+	if (buf[1] != '[')
+		return (-1);
+	if (len == 2)
+		return (1);
+
+	/*
+	 * Stop at either 't' or anything that isn't a
+	 * number or ';'.
+	 */
+	for (end = 2; end < len && end != sizeof tmp; end++) {
+		if (buf[end] == 't')
+			break;
+		if (!isdigit((u_char)buf[end]) && buf[end] != ';')
+			break;
+	}
+	if (end == len)
+		return (1);
+	if (end == sizeof tmp || buf[end] != 't')
+		return (-1);
+
+	/* Copy to the buffer. */
+	memcpy(tmp, buf + 2, end - 2);
+	tmp[end - 2] = '\0';
+
+	/* Try to parse the window size sequence. */
+	if (sscanf(tmp, "8;%u;%u", &sy, &sx) == 2) {
+		/* Window size in characters. */
+		tty_set_size(tty, sx, sy, tty->xpixel, tty->ypixel);
+
+		*size = end + 1;
+		return (0);
+	} else if (sscanf(tmp, "4;%u;%u", &ypixel, &xpixel) == 2) {
+		/* Window size in pixels. */
+		char_x = (xpixel && tty->sx) ? xpixel / tty->sx : 0;
+		char_y = (ypixel && tty->sy) ? ypixel / tty->sy : 0;
+		tty_set_size(tty, tty->sx, tty->sy, char_x, char_y);
+		tty_invalidate(tty);
+
+		tty->flags &= ~TTY_WINSIZEQUERY;
+		*size = end + 1;
+		return (0);
+	}
+
+	log_debug("%s: unrecognized window size sequence: %s", c->name, tmp);
+	return (-1);
+}
+
+
 /* Process at least one key in the buffer. Return 0 if no keys present. */
 int
 tty_keys_next(struct tty *tty)
@@ -754,6 +822,17 @@ tty_keys_next(struct tty *tty)
 		goto partial_key;
 	}
 
+	/* Check for window size query */
+	switch (tty_keys_winsz(tty, buf, len, &size)) {
+	case 0:		/* yes */
+		key = KEYC_UNKNOWN;
+		goto complete_key;
+	case -1:	/* no, or not valid */
+		break;
+	case 1:		/* partial */
+		goto partial_key;
+	}
+
 first_key:
 	/* Try to lookup complete key. */
 	n = tty_keys_next1(tty, buf, len, &key, &size, expired);

tty.c

@@ -42,7 +42,6 @@ static void	tty_cursor_pane(struct tty *, const struct tty_ctx *, u_int,
 		    u_int);
 static void	tty_cursor_pane_unless_wrap(struct tty *,
 		    const struct tty_ctx *, u_int, u_int);
-static void	tty_invalidate(struct tty *);
 static void	tty_colours(struct tty *, const struct grid_cell *);
 static void	tty_check_fg(struct tty *, struct colour_palette *,
     		    struct grid_cell *);
@@ -135,6 +134,14 @@ tty_resize(struct tty *tty)
 			ypixel = 0;
 		} else
 			ypixel = ws.ws_ypixel / sy;
+
+		if ((xpixel == 0 || ypixel == 0) &&
+		    tty->out != NULL &&
+		    !(tty->flags & TTY_WINSIZEQUERY) &&
+		    (tty->term->flags & TERM_VT100LIKE)) {
+			tty_puts(tty, "\033[18t\033[14t");
+			tty->flags |= TTY_WINSIZEQUERY;
+		}
 	} else {
 		sx = 80;
 		sy = 24;
@@ -2247,7 +2254,7 @@ tty_reset(struct tty *tty)
 	memcpy(&tty->last_cell, &grid_default_cell, sizeof tty->last_cell);
 }
 
-static void
+void
 tty_invalidate(struct tty *tty)
 {
 	memcpy(&tty->cell, &grid_default_cell, sizeof tty->cell);