TextArea modal crashes: KeyError 'text-area--gutter' in apply_css (8.2.x) #6528

Summary

Mounting a TextArea inside a ModalScreen crashes on first render with KeyError: "No 'text-area--gutter' key in COMPONENT_CLASSES". _text_area_theme.apply_css calls get_component_rich_style("text-area--gutter") but TextArea's COMPONENT_CLASSES doesn't declare that name.

Versions

• Textual 8.2.x (latest at time of report)
• Python 3.14
• Ubuntu 24.04 LTS / Ubuntu 26.04 LTS in WSL2 (Microsoft kernel 6.6)

Traceback (truncated to relevant frames)

File ".../textual/widget.py", line 1206, in render_lines
    theme.apply_css(self)
File ".../textual/_text_area_theme.py", line 107, in apply_css
    gutter_style = get_style("text-area--gutter")
File ".../textual/widget.py", line 1194, in get_component_rich_style
    component_styles = self.get_component_styles(*names)
File ".../textual/dom.py", line 618, in get_component_styles
    raise KeyError(f"No {name!r} key in COMPONENT_CLASSES")
KeyError: "No 'text-area--gutter' key in COMPONENT_CLASSES"

The mounted widget is a TextArea(id='creds-text', language=None, show_line_numbers=False).

Minimal repro

from textual.app import App, ComposeResult
from textual.containers import Container
from textual.screen import ModalScreen
from textual.widgets import TextArea


class CredsModal(ModalScreen[None]):
    CSS = """
    #box {
        width: 80;
        height: 20;
        border: heavy white;
    }
    #ta {
        height: 10;
        border: solid white;
    }
    """

    def compose(self) -> ComposeResult:
        with Container(id="box"):
            yield TextArea("", id="ta", language=None, show_line_numbers=False)


class Demo(App):
    def on_mount(self) -> None:
        self.push_screen(CredsModal())


if __name__ == "__main__":
    Demo().run()

Pip install on a clean Python 3.14 environment, run, and the modal blows up on first render.

Workaround

Pin textual<8. Versions 7.x and earlier don't reach the new apply_css code path that requires text-area--gutter.

Notes

• Hit in the wild by users of the Maude WSL sandbox (https://github.com/dirkpetersen/maude) when opening a credentials-entry modal containing a TextArea. We've pinned <8 as a stop-gap (dirkpetersen/maude@2716297).
• Looks like a TextArea component-class declaration was removed (or renamed) without updating _text_area_theme.apply_css. Adding text-area--gutter (and the other text-area--* names referenced in apply_css) to TextArea.COMPONENT_CLASSES, or guarding the lookups with try/except KeyError, should both work.