notebooks: incorrect handling of control characters if both stdout and stderr are used

[bvenreply]

Bug Description:

When both stdout and stderr streams are used in an output cell of a notebook, erasing the last line using backspaces doesn't work; instead, the backspaces are ignored and the subsequent output is placed on a new line. Here's an example of this occurring in the Keras model training progress reporting UI:

Steps to Reproduce:

You can use the browser example app to reproduce this:

• Install the necessary vscode plugins:

  • ms-python.python (https://open-vsx.org/extension/ms-python/python)
  • ms-toolsai.jupyter (https://open-vsx.org/extension/ms-toolsai/jupyter)
  • vscode builtins (https://open-vsx.org/extension/eclipse-theia/builtin-extension-pack)

• Create a file with extension .ipynb and open it; it should be rendered as a notebook

• Create a code cell with the following code and run it:

  import time
  import sys
  
  msg = "abcdef"
  print("spoiler!", flush=True, file=sys.stderr)
  
  for i in range(5):
      print(msg, end="", flush=True)
      time.sleep(1)
      for j in msg:
          print("\b", end="", flush=True)
      time.sleep(0.5)

• Observe the incorrect output. The line should be erased and printed again, here compared with vscode on the right:

Additional Information

• Theia Version: The PR ported the full output optimization code from VSCode #13137 fixes a bug that prevented this other issue from manifesting. As soon as it is merged this issue will reproduce on master
• Operating system: Debian 6.1.55-1 (2023-09-29) x86_64 GNU/Linux
• Browser: Chromium version 119.0.6045.159

cc: @jonah-iden

[jonah-iden]

Hi, I found the issue, the fix was super simple just very hard to spot. Added it t the Original PR since its just one modified line of code

[bvenreply]

I tested the new code, it's working great! Thanks a lot @jonah-iden