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.

1 files changed, 5 insertions, 1 deletions

diff --git a/st.c b/st.c
index 2e3800e..03b9bc8 100644
--- a/st.c
+++ b/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]) {