:terminal text clipped after resize

[khughitt]

• nvim --version: NVIM v0.1.5-508-g47a15d0
• Vim (version: ) behaves differently? N/A
• Operating system/version: Arch Linux (64-bit Linux 4.6.3-1)
• Terminal name/version: rxvt-unicode v9.22
• $TERM: rxvt-256color

Actual behaviour

Text in Neovim terminal becomes clipped on the right side after reducing window size to a width smaller than what is displayed.

Expected behaviour

Terminal text return to its original unclipped after the window is temporarily narrowed.

Steps to reproduce using nvim -u NORC

1. nvim -u NORC
2. Open a terminal using :term and then print some long line to the screen. Initially the entire text will be displayed:

$ echo "abcdefg hijklmn opqrstuv xzy abcdefg hijklmn opqrstuv xzy abcdefg hijklmn opqrstuv xzy abcdefg hijklmn opqrstuv xzy"                                               
abcdefg hijklmn opqrstuv xzy abcdefg hijklmn opqrstuv xzy abcdefg hijklmn opqrstuv xzy abcdefg hijklmn opqrstuv xzy 

If the screen is then resized (e.g. 50% width), and then resized back to 100% width, the text is now clipped at the position where it was hidden when the terminal size was reduced:

$ echo "abcdefg hijklmn opqrstuv xzy abcdefg hijklmn opqrstuv xzy abcdefg hijklmn op                                                                                       
abcdefg hijklmn opqrstuv xzy abcdefg hijklmn opqrstuv xzy abcdefg hijklmn opqrstuv xzy 

(Thanks @jalvesaq for coming up with this simple example to reproduce the issue).

[justinmk]

This is because of #4929 (comment).

As I mentioned there, instead of forcing the resize at every BufEnter/WinEnter, I think instead the terminal resize should only happen on :redraw! / <C-L> .

Those who want to force it unconditionally can set up a handler:

au TermOpen * au <buffer> BufEnter,WinEnter redraw!

But in most cases I think the terminal size should never be reduced, because it loses data. At least until (if ever) libvterm gains the ability to remember off-screen text.

edit: @leonerd mentioned in gitter that this is currently the expected libvterm behavior.

[khughitt]

That makes sense. I agree with your suggestions about the default redraw behavior.

Thanks for the explanation!

[justinmk]

@mhinz Also I think totally reverting #4929 is not necessary. Perhaps it could be modified to resize only if the target size is greater than the previous size. That way #4820 and #3864 won't regress.

[mhinz]

But then it would be possible that you don't even see the prompt if you switch back to a smaller window with the same terminal.

Basically we only have these options:

• old way: Resize the terminal to the smallest embedding window which renders excess space in bigger windows unusable.
• new way: Make the terminal dimensions fit into the current window. Problem: If you came from a smaller window, text will be lost due to the also smaller terminal text buffer.

In hindsight, I'd vote for the old way (so a full merge revert), but making :redraw!/<c-l> fitting a potential terminal into the current window + making terminal_resize() aware of the {number,sign,fold} column.

[sprice-janrain]

I still experience this with v0.3.0-1233-gde7a0bdc3. Vim 8.1 was released today, and I noticed that it also has :terminal now. It works a bit differently, but I did see that scrollback text is not clipped when you resize windows. It's also using a customized libvterm, right? what's different here?

[justinmk]

@sprice-janrain It does clip text, I just tried in vim8.1:

:term
ls
ctrl-w N
ctrl-w v
i

[sprice-janrain]

Ok, to clarify, i do see clipping, but if I switch back to that original terminal and then switch to Normal mode with ctrl-w ctrl-n, I see the text restored.

[justinmk]

related: #2514

[Shougo]

Hi. I have tested it and :redraw! does not fix the problem unfortunately.

[clason]

You can try building from master with reflow enabled: #20222 (comment)

Testing this feature and reporting on any issues with it (or lack thereof) will help with this.

[nyngwang]

@clason Not sure if it's appropriate to ask you here: Is that "inserting a line into the neovim/src/nvim/terminal.c" the only way to apply the patch or do we have some flag(?) to do this? Anyway, always appreciate your (huge!) contributions to Neovim :)

[clason]

Yes, that's the only way (or check out the linked PR).

[nyngwang]

Can I call this a success? NVIM v0.10.0-dev-241+g26cc94622-dirty:

note: but if I resize it "too much", the problem of OP seems to still persist (lines got truncated).

Screen.Recording.2023-05-02.at.1.18.57.AM.mov

[clason]

Yes, as explained in the PR, the scrollback buffer does not reflow.

[nyngwang]

I just tried stretching the output of cat src/nvim/terminal.c and it works perfectly (I resized it such that the terminal-buffer split disappeared entirely, and all contents got recovered after I stretched it back to the original width). I hope this quick test might help a little bit. Thanks for your help!