commit 98610fcd37f655d44586323dc86c1d013c2798ce
from: Johannes Altmanninger <aclopte@gmail.com>
via: Hiltjo Posthuma <hiltjo@codemadness.org>
date: Thu Jan 30 16:50:37 2025 UTC

Do not interpret CSI ? u as DECRC

The kitty keyboard protocol docs recommend CSI ? u to query support for
that protocol, see https://sw.kovidgoyal.net/kitty/keyboard-protocol/

For better or worse, fish shell uses this query to work around bugs
in other terminals triggered by requesting that protocol via CSI = 5 u.

Unfortunately, st interprets CSI ? u as DECRC (restore cursor
position). reproduce with 'printf "\x1b[?u"; cat'.

fish could work around this by switching to the alternate screen
before running this query; but that might cause tearing on terminals
that don't support Synchronized Output. I'm not sure.

In the meantime, let's correct our parser.

This adds a redundant else-after-return, for consistency with the
surrounding code.

commit - 6009e6e25bdff9548f085e9ae562b1ca305d3a0b
commit + 98610fcd37f655d44586323dc86c1d013c2798ce
blob - 2e3800e437ecda60d015a16da9f468c576337bb4
blob + 03b9bc88b1b8335bd82c9a98c630abd99fd642db
--- st.c
+++ st.c
@@ -1801,7 +1801,11 @@ csihandle(void)
 		tcursor(CURSOR_SAVE);
 		break;
 	case 'u': /* DECRC -- Restore cursor position (ANSI.SYS) */
-		tcursor(CURSOR_LOAD);
+		if (csiescseq.priv) {
+			goto unknown;
+		} else {
+			tcursor(CURSOR_LOAD);
+		}
 		break;
 	case ' ':
 		switch (csiescseq.mode[1]) {