From 527f66ed23a88a59fb3d8c1972336f55612059bf Mon Sep 17 00:00:00 2001
From: Nicholas Marriott <nicholas.marriott@gmail.com>
Date: Fri, 24 Apr 2020 15:52:44 +0100
Subject: [PATCH] Instead of having a default set of terminals in
 terminal-overrides that get XT added and using that as a marker for
 xterm(1)-like, assume that if the terminfo(5) entry already has XT or the
 clear capability starts with CSI then the terminal is VT100-like and it
 should be safe to send DA requests. The DA responses trigger additional
 features being added.

This is all to detect extensions if terminfo(5) is wrong or inadequate. If it
fails, tmux will just fall back to using the capabilities in the terminfo(5)
entry alone.
---
 options-table.c |  2 +-
 tmux.h          |  1 +
 tty-term.c      | 22 ++++++++++++++++++----
 tty.c           |  6 +++---
 4 files changed, 23 insertions(+), 8 deletions(-)

diff --git a/options-table.c b/options-table.c
index 35d6b086..d593eff6 100644
--- a/options-table.c
+++ b/options-table.c
@@ -260,7 +260,7 @@ const struct options_table_entry options_table[] = {
 	  .type = OPTIONS_TABLE_STRING,
 	  .scope = OPTIONS_TABLE_SERVER,
 	  .flags = OPTIONS_TABLE_IS_ARRAY,
-	  .default_str = "tmux*:XT,rxvt*:XT,screen*:XT,xterm*:XT",
+	  .default_str = "",
 	  .separator = ","
 	},
 
diff --git a/tmux.h b/tmux.h
index 2eb17ae0..fcf39bfb 100644
--- a/tmux.h
+++ b/tmux.h
@@ -1202,6 +1202,7 @@ struct tty_term {
 #define TERM_DECSLRM 0x4
 #define TERM_DECFRA 0x8
 #define TERM_RGBCOLOURS 0x10
+#define TERM_VT100LIKE 0x20
 	int		 flags;
 
 	LIST_ENTRY(tty_term) entry;
diff --git a/tty-term.c b/tty-term.c
index 4217d6d6..dd65e1e7 100644
--- a/tty-term.c
+++ b/tty-term.c
@@ -561,16 +561,30 @@ tty_term_create(struct tty *tty, char *name, int *feat, int fd, char **cause)
 		goto error;
 	}
 
+	/*
+	 * If TERM has XT or clear starts with CSI then it is safe to assume
+	 * the terminal is derived from a VT100. This controls whether device
+	 * attributes requests are sent to get more information.
+	 *
+	 * This is a bit of a hack but there aren't that many alternatives.
+	 * Worst case tmux will just fall back to using whatever terminfo(5)
+	 * says without trying to correct anything that is missing.
+	 *
+	 * Also add few features that VT100-like terminals should either
+	 * support or safely ignore.
+	 */
+	s = tty_term_string(term, TTYC_CLEAR);
+	if (tty_term_flag(term, TTYC_XT) || strncmp(s, "\033[", 2) == 0) {
+		term->flags |= TERM_VT100LIKE;
+		tty_add_features(feat, "bpaste,focus,title", ",");
+	}
+
 	/* Add RGB feature if terminal has RGB colours. */
 	if ((tty_term_flag(term, TTYC_TC) || tty_term_has(term, TTYC_RGB)) &&
 	    (!tty_term_has(term, TTYC_SETRGBF) ||
 	    !tty_term_has(term, TTYC_SETRGBB)))
 		tty_add_features(feat, "RGB", ",");
 
-	/* Add some features if terminal has XT. */
-	if (tty_term_flag(term, TTYC_XT))
-		tty_add_features(feat, "bpaste,focus,title", ",");
-
 	/* Apply the features and overrides again. */
 	tty_apply_features(term, *feat);
 	tty_term_apply_overrides(term);
diff --git a/tty.c b/tty.c
index 75942d2d..016ce399 100644
--- a/tty.c
+++ b/tty.c
@@ -334,7 +334,7 @@ tty_start_tty(struct tty *tty)
 		tty->flags |= TTY_FOCUS;
 		tty_raw(tty, tty_term_string(tty->term, TTYC_ENFCS));
 	}
-	if (tty_term_flag(tty->term, TTYC_XT))
+	if (tty->term->flags & TERM_VT100LIKE)
 		tty_puts(tty, "\033[?7727h");
 
 	evtimer_set(&tty->start_timer, tty_start_timer_callback, tty);
@@ -357,7 +357,7 @@ tty_send_requests(struct tty *tty)
 	if (~tty->flags & TTY_STARTED)
 		return;
 
-	if (tty_term_flag(tty->term, TTYC_XT)) {
+	if (tty->term->flags & TERM_VT100LIKE) {
 		if (~tty->flags & TTY_HAVEDA)
 			tty_puts(tty, "\033[>c");
 		if (~tty->flags & TTY_HAVEXDA)
@@ -420,7 +420,7 @@ tty_stop_tty(struct tty *tty)
 		tty->flags &= ~TTY_FOCUS;
 		tty_raw(tty, tty_term_string(tty->term, TTYC_DSFCS));
 	}
-	if (tty_term_flag(tty->term, TTYC_XT))
+	if (tty->term->flags & TERM_VT100LIKE)
 		tty_raw(tty, "\033[?7727l");
 
 	if (tty_use_margin(tty))