Control characters printed in initial buffer when using Neovim over ssh

[ddickstein]

Problem

When starting up Neovim, I'm seeing control characters printed in the initial buffer.

These look somewhat similar to the control characters that were emitted on exit in 0.7.0, but with 4;2m instead of 4;0m at the end. Just mentioning this in case the issues have similar causes.

Steps to reproduce

Open Neovim (still reproduces with --clean). See the details below for version information. Please let me know if you need me to check additional information, e.g., something in terminfo.

Expected behavior

No control characters printed

Neovim version (nvim -v)

v0.10.0-dev-497+g4229bbe51

Vim (not Nvim) behaves the same?

N/A

Operating system/version

Rocky Linux 8.6

Terminal name/version

xfce4-terminal 1.0.4

$TERM environment variable

xterm-256color

Installation

appimage

[ddickstein]

I am ssh'd (double hop) when accessing the host that is running Neovim, for corporate networking reasons. While (for those reasons) I can't download and run the appimage on my local host, from a built-from-source version of Neovim 0.9.1 on my local host I can confirm that (1) the issue does not appear when I just open Neovim 0.9.1, and (2) the issue does appear when I ssh into the same box and open Neovim 0.9.1. I updated the issue title to reflect this.

[justinmk]

#18172 mentions that 4;2 is OSC 4

Posting terminal debug info from nvim -V1 can be helpful.

[gpanders]

#18172 mentions that 4;2 is OSC 4

Posting terminal debug info from nvim -V1 can be helpful.

OSC codes use ESC ], this is ESC [ which is a CSI (Control Sequence Introducer). Specifically, ESC [>4;2m is the escape sequence to enable the modifyOtherKeys Xterm mode.

@ddickstein This could be a bug with xfce4-terminal. Could you also open an issue with them with your reproduction steps?

EDIT: Although, in light of this:

I can confirm that (1) the issue does not appear when I just open Neovim 0.9.1, and (2) the issue does appear when I ssh into the same box and open Neovim 0.9.1.

That seems unlikely. Still might be worth mentioning it to the xfce4 folks, if nothing else to have them confirm it's not an issue on their end.

[ddickstein]

I'm not sure if this is what you meant by terminal debug info -- the only output I see from passing -V1/tmp/debug is:

  1: ~/vim/_editor.lua
  2: ~/neovim/squashfs-root/usr/share/nvim/runtime/ftplugin.vim
  3: ~/neovim/squashfs-root/usr/share/nvim/runtime/indent.vim
  4: ~/neovim/squashfs-root/usr/share/nvim/runtime/filetype.lua
  5: ~/neovim/squashfs-root/usr/share/nvim/runtime/syntax/syntax.vim
  6: ~/neovim/squashfs-root/usr/share/nvim/runtime/syntax/synload.vim
  7: ~/neovim/squashfs-root/usr/share/nvim/runtime/plugin/gzip.vim
  8: ~/neovim/squashfs-root/usr/share/nvim/runtime/plugin/matchit.vim
  9: ~/neovim/squashfs-root/usr/share/nvim/runtime/pack/dist/opt/matchit/plugin/matchit.vim
 10: ~/neovim/squashfs-root/usr/share/nvim/runtime/plugin/matchparen.vim
 11: ~/neovim/squashfs-root/usr/share/nvim/runtime/plugin/netrwPlugin.vim
 12: ~/neovim/squashfs-root/usr/share/nvim/runtime/plugin/rplugin.vim

I can also confirm that this problem does not happen for me under tmux, nor does it happen with some other terminal emulators (xterm, kitty) but it does happen with gnome-terminal. @catern pointed out that both gnome-terminal and xfce4-terminal are based on libvte - maybe the bug is there?

[gpanders]

@catern pointed out that both gnome-terminal and xfce4-terminal are based on libvte - maybe the bug is there?

That seems likely. AFAIK libvte is responsible for parsing the terminal codes. We already have a check on the libvte version. Maybe that range needs to be adjusted.

[ddickstein]

@TyOverby noticed that we are dropping VTE_VERSION over ssh, which is causing us to fall into that check when we otherwise wouldn't. So I think all the behavior we were seeing is now explained!

[TyOverby]

I think it's worth re-evaluating the missing vte version check. If my current reading of the code is correct, it's saying that "if you can't read the vte version, assume that it is is using vte, and that it's using a new version", which may be a mistake.