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[PR #5683] Make sure that EraseAll moves the Terminal viewport #26420

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opened 2026-01-31 09:15:57 +00:00 by claunia · 0 comments
claunia commented 2026-01-31 09:15:57 +00:00
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Original Pull Request: https://github.com/microsoft/terminal/pull/5683

State: closed
Merged: Yes

The Erase All VT sequence (^[[2J) is supposed to erase the entire
contents of the viewport. The way it usually does this is by shifting
the entirety of the viewport contents into scrollback, and starting the
new viewport below it.

Currently, conpty doesn't propagate that state change correctly. When
conpty gets a 2J, it simply erases the content of the connected
terminal's viewport, by writing over it with spaces. Conpty didn't
really have a good way of communicating "your viewport should move", it
only knew "the buffer is now full of spaces".

This would lead to bugs like #2832, where pressing ctrl+L in
bash would delete the current contents of the viewport, instead of
moving the viewport down.

This PR makes sure that when conpty sees a 2J, it passes that through
directly to the connected terminal application as well. Fortunately, 2J
was already implemented in the Windows Terminal, so this actually fixes
the behavior of ctrl+L/clear in WSL in the Terminal.

References

  • #4252 - right now this isn't the most optimal scenario, we're
    literally just printing a 2J, then we'll perform "erase line" height
    times. The erase line operations are all redundant at this point - the
    entire viewport is blank, but conpty doesn't really know that.
    Fortunately, #4252 was already filed for me to come through and
    optimize this path.

PR Checklist

Validation Steps Performed

  • ran tests
  • compared ctrl+L with its behavior in conhost
  • compared clear with its behavior in conhost
**Original Pull Request:** https://github.com/microsoft/terminal/pull/5683 **State:** closed **Merged:** Yes --- The Erase All VT sequence (`^[[2J`) is supposed to erase the entire contents of the viewport. The way it usually does this is by shifting the entirety of the viewport contents into scrollback, and starting the new viewport below it. Currently, conpty doesn't propagate that state change correctly. When conpty gets a 2J, it simply erases the content of the connected terminal's viewport, by writing over it with spaces. Conpty didn't really have a good way of communicating "your viewport should move", it only knew "the buffer is now full of spaces". This would lead to bugs like #2832, where pressing <kbd>ctrl+L</kbd> in `bash` would delete the current contents of the viewport, instead of moving the viewport down. This PR makes sure that when conpty sees a 2J, it passes that through directly to the connected terminal application as well. Fortunately, 2J was already implemented in the Windows Terminal, so this actually fixes the behavior of <kbd>ctrl+L</kbd>/`clear` in WSL in the Terminal. ## References * #4252 - right now this isn't the _most_ optimal scenario, we're literally just printing a 2J, then we'll perform "erase line" `height` times. The erase line operations are all redundant at this point - the entire viewport is blank, but conpty doesn't really know that. Fortunately, #4252 was already filed for me to come through and optimize this path. ## PR Checklist * [x] Closes #2832 * [x] I work here * [x] Tests added/passed * [n/a] Requires documentation to be updated ## Validation Steps Performed * ran tests * compared <kbd>ctrl+L</kbd> with its behavior in conhost * compared `clear` with its behavior in conhost
claunia added the pull-request label 2026-01-31 09:15:57 +00:00
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Reference: starred/terminal#26420
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