fix(text area): fix initial flicker in rendering

[TomJGooding]

Fix initial flicker in the TextArea, where for a brief moment each character is rendered on a new line before the size is settled.

The width for the WrappedDocument is slightly confusing where zero means no wrapping, but the current negative wrap width looks like the bug.

Fixes #5841

Please review the following checklist.

• Docstrings on all new or modified functions / classes
• Updated documentation
• Updated CHANGELOG.md (where appropriate)

[TomJGooding]

I've tested manually obviously with the examples in the linked issue, but I'm not sure it's possible to add a regression test for this flicker.

[lyovushka]

I think there is still a flickering even when soft_wrap=False.

[TomJGooding]

I think there is still a flickering even when soft_wrap=False.

Strange, I don't see the same flicker with this change. Do you mean a different kind of flicker, or do you have an example to demonstrate?

Running your example with some debug logs, here's extracts from the console before and after this change.

Before

[15:02:19] DEBUG                                              screen.py:1027
Button() was focused
────────────────────────────────────────────────────────────────────────────
[15:02:20] DEBUG                                          _text_area.py:1309
render_line(0): L                                                           
[15:02:20] DEBUG                                          _text_area.py:1309
render_line(1): o                                                           
[15:02:20] DEBUG                                          _text_area.py:1309
render_line(2): r                                                           

...

[15:02:20] DEBUG                                          _text_area.py:1309
render_line(27): m                                                          
[15:02:20] DEBUG                                          _text_area.py:1309
render_line(28): e                                                          
[15:02:20] DEBUG                                          _text_area.py:1309
render_line(29): t                                                          
[15:02:20] DEBUG                                          _text_area.py:1309
render_line(0): Lorem ipsum dolor sit amet                                  
────────────────────────────────────────────────────────────────────────────

After

[15:12:00] DEBUG                                              screen.py:1027
Button() was focused
────────────────────────────────────────────────────────────────────────────
[15:12:02] DEBUG                                          _text_area.py:1309
render_line(0): Lorem ipsum dolor sit amet                                  
────────────────────────────────────────────────────────────────────────────

[lyovushka]

No the letters don't appear to be rendered individually with soft_wrap=False. But there is still a flicker. I've attached a screencast (this is without soft_wrap). The TextArea initially has a larger height before snapping to a single line. It also makes the vertical scroll visible momentarily.

Screencast.From.2025-06-05.15-36-55.mp4

[TomJGooding]

Sorry I think I understand what you mean now - you've not tested with this change but just setting soft_wrap to False?

Good catch - it looks like the wrap_width is being called before this is set!

[TomJGooding]

Fixed in 4653f30 by ensuring the attribute is assigned before trying to wrap the document.

Again tested manually but don't think it's possible to add a regression test for this.

[willmcgugan]

LGTM.