TextArea code editor freezes the app

[Klavionik]

Hey again. :)

Mounting the TextArea code editor with any code other than the comment freezes my terminal. I tried several versions of Textual, I tried running it both on Mac and Linux and using Python 3.10 and 3.12. It freezes every time. I then tried an example from the docs and it freezes too.

An MRE:

from textual.app import App, ComposeResult
from textual.widgets import TextArea

# OK_TEXT = "# OK"
FAIL_TEXT = "x = 1"


class CodeApp(App):
    def compose(self) -> ComposeResult:
        yield TextArea.code_editor(FAIL_TEXT, language="python")


if __name__ == "__main__":
    app = CodeApp()
    app.run()

If you replace usage of FAIL_TEXT with OK_TEXT, it doesn't freeze. Somehow it doesn't freeze with FAIL_TEXT too if you set show_line_numbers=False.

I tried investigating it a bit myself and I found out that the freeze happens because of the while True loop in rich.segment.Segment._split_cells: it keeps counting pos down and never stops. I'm not sure why, though. And I still don't know why the comment works alright even with the line numbers.

Textual Diagnostics

Versions

Name	Value
Textual	0.83.0
Rich	13.9.2

Python

Name	Value
Version	3.12.3
Implementation	CPython
Compiler	GCC 11.4.0
Executable	/home/jediroman/Desktop/textarea-mre/.venv/bin/python

Operating System

Name	Value
System	Linux
Release	5.15.0-122-generic
Version	#132-Ubuntu SMP Thu Aug 29 13:45:52 UTC 2024

Terminal

Name	Value
Terminal Application	WezTerm (20230712-072601-f4abf8fd)
TERM	xterm-256color
COLORTERM	truecolor
FORCE_COLOR	Not set
NO_COLOR	Not set

Rich Console options

Name	Value
size	width=105, height=25
legacy_windows	False
min_width	1
max_width	105
is_terminal	True
encoding	utf-8
max_height	25
justify	None
overflow	None
no_wrap	False
highlight	None
markup	None
height	None

[github-actions]

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[darrenburns]

Hi, thanks for the report. I can't reproduce this.

Could you please share the full error output?

[TomJGooding]

@darrenburns This freeze only seems to happen with the latest rich version 13.9.2.

I suspect related to Textualize/rich#3532?

[darrenburns]

Yeah, I tried with Rich 13.9.2 and Textual v0.83.0 (and main). There must be some specific condition causing the crash. The width of the TextArea maybe? 🤷

Edit: tried with various sizes and can't reproduce 🤔
Edit2: This is almost certainly an environment issue on my part 🤦 No idea what's happening...
Edit3: pip freeze says rich==13.9.2, and poetry show says rich==13.9.2.
Edit4: Got it!

[willmcgugan]

I'll look in to this today.

[darrenburns]

Ok apparently this bug only happens if the first character in the text area is e.g. w, x, y or z.

a is fine.

It seems to be when line_numbers=True and soft_wrap=False. Also, seems unrelated to it actually being the "code editor". It happens with syntax highlighting off too.

Will has a PR which fixes it but we don't know why 😂

[github-actions]

Don't forget to star the repository!

Follow @textualizeio for Textual updates.

[TomJGooding]

Bizarre! After testing working through the alphabet, "o" doesn't seem to crash but "p" does...

[TomJGooding]

After being nerd sniped by this, I couldn't help trying to dig a bit deeper. I found this line in rich/rich/cells.py:

_is_single_cell_widths = re.compile("^[\u0020-\u006f\u00a0\u02ff\u0370-\u0482]*$").match

This might explain why this only seems to occur with certain characters, since this doesn't seem to include lowercase p-z?

[willmcgugan]

Bravo, Tom!

[darrenburns]

Thank you Tom, I will sleep tonight!!

[willmcgugan]

How did you get there so fast @TomJGooding ? We were bamboozled by this.

[TomJGooding]

Haha, definitely a team effort!