Feature: Add support for Infinite Scrollback

[iancward]

Summary of the new feature/enhancement

I know at least gnome-terminal supports infinite scrollback as a checkbox option in profile settings; it would be great to have that here (I'd love to be able to replace X server+gnome-terminal for WSL).

I checked to make sure that there wasn't an issue for this already, and I saw that you have a TODO comment in the code for this, so I figured I'd open a GitHub issue so that you can use the 👍 to figure out how to rank it.

Proposed technical implementation details (optional)

Looks like the plan is for users to set HistorySize to -1

terminal/src/cascadia/TerminalCore/Terminal.cpp

Line 88 in 900d0c3

// TODO:MSFT:20642297 - Support infinite scrollback here, if HistorySize is -1

[JushBJJ]

Would the buffer content be stored inside a file?

[egmontkob]

In GNOME Terminal (VTE) we store the scrollback in a compressed and encrypted file. Storing it in memory could easily result in heavy swapping, followed by the OOM killer kicking in. We store it on disk even if it's configured to have a finite size.

The file is unlinked immediately after creating it, so it's freed up in the unlikely case that gnome-terminal (or another VTE-based terminal) crashes. During normal operation, the file handle is released (and thus the file contents get freed up) and encryption key is explicitly zeroed out in the memory when the terminal tab/window is closed.

We used to store it in unencrypted file, but people were worried about privacy / data leakage issues e.g. if the computer gets stolen, see e.g. a generic security report and the tracking bug. (A nice extension would be if we could detect if the file system is encrypted and then skip this step.)

Konsole, on the other hand, warns you in its config dialog that "When using [unlimited scrollback], the scrollback data will be written unencrypted to temporary files." If fixed scrollback is configured, Konsole stores it in memory (and again, informs the user about it and the corresponding risks).