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.

diff --git a/st.c b/st.c
index 2e3800e437ecda60d015a16da9f468c576337bb4..03b9bc88b1b8335bd82c9a98c630abd99fd642db 100644 (file)
--- 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]) {