Add an option to set the key sent by backspace for those whose system

uses ^H rather than ^?. GitHub issue 1969.

input-keys.c

@@ -43,9 +43,6 @@ struct input_key_ent {
 };
 
 static const struct input_key_ent input_keys[] = {
-	/* Backspace key. */
-	{ KEYC_BSPACE,		"\177",		0 },
-
 	/* Paste keys. */
 	{ KEYC_PASTE_START,	"\033[200~",	0 },
 	{ KEYC_PASTE_END,	"\033[201~",	0 },
@@ -180,6 +177,13 @@ input_key(struct window_pane *wp, key_code key, struct mouse_event *m)
 		return;
 	}
 
+	/* Is this backspace? */
+	if ((key & KEYC_MASK_KEY) == KEYC_BSPACE) {
+		key = options_get_number(global_options, "backspace");
+		if (key >= 0x7f)
+			key = '\177';
+	}
+
 	/*
 	 * If this is a normal 7-bit key, just send it, with a leading escape
 	 * if necessary. If it is a UTF-8 key, split it and send it.

key-string.c

@@ -159,7 +159,7 @@ key_string_get_modifiers(const char **string)
 key_code
 key_string_lookup_string(const char *string)
 {
-	static const char	*other = "!#()+,-.0123456789:;<=>?'\r\t";
+	static const char	*other = "!#()+,-.0123456789:;<=>'\r\t";
 	key_code		 key;
 	u_int			 u;
 	key_code		 modifiers;
@@ -196,7 +196,7 @@ key_string_lookup_string(const char *string)
 	/* Is this a standard ASCII key? */
 	if (string[1] == '\0' && (u_char)string[0] <= 127) {
 		key = (u_char)string[0];
-		if (key < 32 || key == 127)
+		if (key < 32)
 			return (KEYC_UNKNOWN);
 	} else {
 		/* Try as a UTF-8 key. */
@@ -226,6 +226,8 @@ key_string_lookup_string(const char *string)
 			key -= 64;
 		else if (key == 32)
 			key = 0;
+		else if (key == '?')
+			key = 127;
 		else if (key == 63)
 			key = KEYC_BSPACE;
 		else
@@ -329,7 +331,7 @@ key_string_lookup_key(key_code key)
 	}
 
 	/* Invalid keys are errors. */
-	if (key == 127 || key > 255) {
+	if (key > 255) {
 		snprintf(out, sizeof out, "Invalid#%llx", key);
 		return (out);
 	}
@@ -343,7 +345,9 @@ key_string_lookup_key(key_code key)
 	} else if (key >= 32 && key <= 126) {
 		tmp[0] = key;
 		tmp[1] = '\0';
-	} else if (key >= 128)
+	} else if (key == 127)
+		xsnprintf(tmp, sizeof tmp, "C-?");
+	else if (key >= 128)
 		xsnprintf(tmp, sizeof tmp, "\\%llo", key);
 
 	strlcat(out, tmp, sizeof out);

options-table.c

@@ -147,6 +147,12 @@ static const char *options_table_status_format_default[] = {
 /* Top-level options. */
 const struct options_table_entry options_table[] = {
 	/* Server options. */
+	{ .name = "backspace",
+	  .type = OPTIONS_TABLE_KEY,
+	  .scope = OPTIONS_TABLE_SERVER,
+	  .default_num = '\177',
+	},
+
 	{ .name = "buffer-limit",
 	  .type = OPTIONS_TABLE_NUMBER,
 	  .scope = OPTIONS_TABLE_SERVER,

spawn.c

@@ -217,6 +217,7 @@ spawn_pane(struct spawn_context *sc, char **cause)
 	u_int			  hlimit;
 	struct winsize		  ws;
 	sigset_t		  set, oldset;
+	key_code		  key;
 
 	spawn_log(__func__, sc);
 
@@ -378,13 +379,17 @@ spawn_pane(struct spawn_context *sc, char **cause)
 
 	/*
 	 * Update terminal escape characters from the session if available and
-	 * force VERASE to tmux's \177.
+	 * force VERASE to tmux's backspace.
 	 */
 	if (tcgetattr(STDIN_FILENO, &now) != 0)
 		_exit(1);
 	if (s->tio != NULL)
 		memcpy(now.c_cc, s->tio->c_cc, sizeof now.c_cc);
-	now.c_cc[VERASE] = '\177';
+	key = options_get_number(global_options, "backspace");
+	if (key >= 0x7f)
+		now.c_cc[VERASE] = '\177';
+	else
+		now.c_cc[VERASE] = key;
 	if (tcsetattr(STDIN_FILENO, TCSANOW, &now) != 0)
 		_exit(1);
 

tmux.1

@@ -2925,6 +2925,10 @@ omitted to toggle).
 .Pp
 Available server options are:
 .Bl -tag -width Ds
+.It Ic backspace Ar key
+Set the key sent by
+.Nm
+for backspace.
 .It Ic buffer-limit Ar number
 Set the number of buffers; as new buffers are added to the top of the stack,
 old ones are removed from the bottom if necessary to maintain this maximum