TUI programs that want to use features that are not backwards-compatible can do so by querying for support (via XTGETTCAP for example) and awaiting the terminals reply.
A terminal that doesn't support a certain feature may fail to reply. A good workaround is to follow-up the initial query with another query that is expected to get a reply. Primary DA is the de-facto standard query to use. It is implemented by every terminal I know, including Terminal.app, st, Putty. In absence of a reply, - TUI framework [notcurses] will hang forever - TUI framwork [libvaxis] will block with a 1 second timeout - fish shell will do either (currently hangs until ctrl-c is pressed) So far, among relevant terminal-like programs, I found only dvtm (and pexpect) to be missing Primary DA. Pretend we are a VT102 (see https://invisible-island.net/xterm/ctlseqs/ctlseqs.html) because that's what st uses. I believe this should be fine in practice but if there are concerns that programs might make invalid assumptions based on that, we can invent a new user agent. st allows to configure this string; that would be fine too although I have not found out why one would want to. Alternatively, we could forward the request to stdout (i.e. do "printf '\033[0c'") which would cause dvtm's parent terminal to reply. I think this would be more technically-correct, but since it doesn't look like we directly forward any other query, I'd stick to this safer option for now. [notcurses]: https://github.com/dankamongmen/notcurses/blob/da7151929d9f87a73cabb4c5b54668b3a42cfcaf/TERMINALS.md?plain=1#L35-L37 [libvaxis]: https://github.com/rockorager/libvaxis --- vt.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/vt.c b/vt.c index 15dabc1..3a2afe3 100644 --- a/vt.c +++ b/vt.c @@ -1078,6 +1078,13 @@ static void interpret_csi(Vt *t) case 'Z': /* CBT: cursor backward tabulation */ puttab(t, param_count ? -csiparam[0] : -1); break; + case 'c': + if (param_count == 0 || (param_count == 1 && csiparam[0] == 0)) { + // Primary Device Attribute. + const char* vtiden = "\033[?6c"; + vt_write(t, vtiden, strlen(vtiden)); + } + break; case 'g': /* TBC: tabulation clear */ switch (param_count ? csiparam[0] : 0) { case 0: -- 2.48.1
