Hello,
I would like to ask about support for DEC private mode 2026 (Synchronized
Output) in st.
I am running NetBSD 11.0 amd64 with the current st master (commit 04ce0d6,
2026-06-29), built locally against NetBSD's X11R7. I use st as my terminal
emulator and lf as my terminal file manager.
While investigating a large number of error messages printed by st, I found
that lf emits the following sequences when drawing its interface:
CSI ? 2026 h
..
CSI ? 2026 l
A minimal reproduction is:
printf '\033[?2026hHELLO\033[?2026l\n'
This works correctly in xterm, but st reports:
erresc: unknown private set/reset mode 2026
The same messages are produced continuously when navigating in lf.
I initially had the NetBSD/pkgsrc version of lf installed. I then removed it
and built the latest upstream lf from GitHub with Go 1.26.5. The behaviour was
unchanged, so this does not appear to be specific to the packaged version of lf.
I also tested lf with an empty configuration, with the same result.
I checked the existing synchronized-rendering support on the st website. The
"sync" patch is described as having two parts:
auto-sync, which has already been merged upstream;
application-sync, which is available as the historical st-appsync patch.
However, the application-sync patch appears to implement the older DCS protocol:
ESC P = 1 s ESC \
ESC P = 2 s ESC \
rather than the DECSET/DECRST 2026 sequences:
CSI ? 2026 h
CSI ? 2026 l
The existing st application-sync patch therefore does not solve this particular
case.
I also confirmed that the current st master does not handle private mode 2026:
it reaches the "unknown private set/reset mode" error path in tsetmode().
My questions are:
Is there currently any work or patch for supporting DECSET/DECRST 2026 in
st?
Is the older application-sync implementation intentionally considered
sufficient, or is support for the newer CSI ?2026h/l mechanism desirable?
If support for DEC mode 2026 is considered appropriate for st, would a
patch implementing synchronized output at the rendering level be acceptable?
I am particularly interested in the distinction between merely accepting mode
2026 (and suppressing the error) and actually implementing its semantics: while
synchronized output is active, terminal input should still be processed, but
screen updates should not be presented until the corresponding 2026l is
received, with an appropriate timeout as a safeguard.
For reference, my minimal reproduction is simply:
printf '\033[?2026hHELLO\033[?2026l\n'
With xterm, this produces "HELLO" without an error. With current st master, it
produces the "unknown private set/reset mode 2026" diagnostic.
I would appreciate any pointers to existing work, design considerations, or
objections before attempting an implementation for st.
Thanks.
--
Stéphane ORTEGA https://stephaneortega.fr/ +33 (0)684.041.350
GPG Key ID: 0x56F6CF155AB3B3BF/2048R IRC: Well@{libera,oftc}
