CSI 2 J works in unexpected way

[Luit]

In VS Code I've noticed the behavior of Ctrl-L being different from what I was used to. Mainly compared to Gnome Terminal, but I've never really noticed terminal emulators handling this differently.

Ctrl-L or tput -x clear (or clear -x) run CSI H followed by CSI 2 J. In Gnome Terminal this results in everything that's in the current display to be scrolled out of view. In VS Code this results in everything in the current view being erased from the scrollback instead.

Details

• Browser and browser version: Electron (VS Code 1.44.2)
• OS version: Linux
• xterm.js version: VS Code 1.44.2 (not exactly sure which xterm.js version that is)

Steps to reproduce

1. In a new terminal, run clear -x/tput -x clear
2. Scroll up.

In Gnome terminal, the line with clear -x/tput -x clear is there on the scrollback. In xterm.js, there's nothing there.

If it's not a new terminal (e.g. run seq 100 first) the last line found in the scrollback will be the last line that was out of view before the clear ran.

[theflyingape]

I think it matters to what your environment TERM is set as, i.e., vt220 behaves differently than xterm and xterm-256color.

[Luit]

In all of the situations described above, TERM=xterm-256color. To make sure I've also tried sending the CSI directly with echo -ne "\033[H\033[2J", yielding the same results.

[Luit]

In Gnome Terminal the CSI H CSI J sequence (tput -Tvt220 -x clear) appears to work identically to CSI H CSI 2 J in xterm.js, clearing everything in display, leaving any scrollback intact.

[Tyriar]

duplicate of #1727