Support OSC 9 or OSC 777;notify

[Hello71]

It is useful over SSH. It was bikeshedded to death in https://bugzilla.gnome.org/show_bug.cgi?id=711059 due to excessive focus on detection of command completion, but I think the feature is good.

[kovidgoyal]

It would be helpful if you pointed to some document describing what
these escape codes are supopsed to do and what software uses them.

[Hello71]

https://chromium.googlesource.com/apps/libapps/+/master/hterm/doc/ControlSequences.md#OSC

According to that document, iTerm2 supports OSC 9 and urxvt supports OSC 777. I also read in the vte bug that Terminator supports OSC 777;notify.

[kovidgoyal]

OSC 777 seems like a urxvt specific "random command to terminal emulator for extension plugins" thing. So I am not going to implement that.

OSC 9 seems more sensible. How is the notification supposed to be encoded? as UTF-8 text? @gnachman since this scheme comes from iTerm2 could you comment? Are there any facilites for setting subtitles? Icons? Is it allowed for users to turn this off at a terminal level? Is there any detection mechanism? Is the protocol extensible in some way?

[gnachman]

It's in the session's encoding, which is UTF-8 for most people. No subtitles or icons. There is a per-profile preference to disable it. This is a really old control sequence dating to before my stewardship of iTerm; if you're going to build something new, it should be more powerful or at least have room for extension in the future.

[egmontkob]

Let's work out a specification (terminal-wg specifications 13) first.

[kovidgoyal]

I'm going to close this issue. If an when a spec is worked out, I will
be happy to implement it in kitty.

[kovidgoyal]

Since, there is no movement in terminal-wg, I went ahead and implemented the OSC 99 protocol I proposed there, with some modifications based on feedback. ANd I also added support to kitty for OSC 9 for backwards compat. THe new protocol is documented in the kitty protocol extensions page. https://github.com/kovidgoyal/kitty/blob/master/docs/protocol-extensions.rst#desktop-notifications

If any one has any useful feedback on the protocol (modulo bike shedding about escape code design) feel free to comment.