Leave Terminal Contents Intact and Exit Cleanly

[ditsuke]

We should be using the alternate screen buffer to leave the existing contents of the terminal intact and also exit cleanly (without leaving behind a zulip-term view rendered on the terminal).

[ditsuke]

I'd like to work on this once given a go-ahead.

[neiljp]

@ditsuke This feels like a feature that urwid should be providing, rather than ourselves?

That said, this doesn't seem to be a problem for me on my main development terminals, but does on some others.

Which terminal emulator are you using?

[ditsuke]

@ditsuke This feels like a feature that urwid should be providing, rather than ourselves?

That said, this doesn't seem to be a problem for me on my main development terminals, but does on some others.

Which terminal emulator are you using?

@neiljp
I'm on Windows Terminal. After investigation, it looks its reproducible in non-libVTE based terminals (Alacritty, WT et al).

I think you're right about this being an issue upstream¹ in urwid.

[ditsuke]

Interestingly, I cannot reproduce the unwanted behavior if I use zulip-term in a tmux instance.

[neiljp]

@ditsuke The upstream issue you linked does seem relevant (explicitly, urwid/urwid#396), though there is a lot of discussion there that could be confusing. Specifically, it seems the issue author is/was seeking the option to not use the alternate screen buffer - at least originally? I think that's what the the other person meant when suggesting there was an additional issue, which is maybe the issue you're wanting to resolve here?

[ditsuke]

@ditsuke The upstream issue you linked does seem relevant (explicitly, urwid/urwid#396), though there is a lot of discussion there that could be confusing. Specifically, it seems the issue author is/was seeking the option to not use the alternate screen buffer - at least originally? I think that's what the the other person meant when suggesting there was an additional issue, which is maybe the issue you're wanting to resolve here?

The issue was urvid clearing the contents of the original buffer when the CLI application exits. In particular the application and issue referred in the urwid issue is pazz/alot#1469. It appears that urwid has this problem only when using the raw_display rendering backend (which happens to be what we're using in Zulip Terminal) while the ncurses backend for urwid does not have this issue.

I think as a gist our current issue is:

• zulip-term enters the alternate screen buffer.
• When exiting, zulip-term exits the alternate screen buffer, clears the original buffer and renders again* (?) on the original buffer before finally terminating.

* I'm not entirely sure what happens but after exiting, an almost complete zulip-term view is left on the original buffer. When manually switching to the alternate screen buffer with tput smcup or echo -e '\e[?1049h' I see the top 3 lines of the zulip-term view still rendered on top.

---

A commenter left a (hacky) workaround using the blessed terminal library.

[neiljp]

I closed #1193 as a duplicate of this and am adding a label specifically for this kind of issue.

[neiljp]

@AnonymouX47 Thanks for the upstream contribution; hoping this will be able to resolve this issue :)

[AnonymouX47]

It's a pleasure 🙏🏾 🙇🏾‍♂️ ... and yeah, it should resolve this. 😃

See also: urwid/urwid#521 (comment)

[neiljp]

Looks like this will be fixed when we upgrade to urwid 2.2+ 🎉