Select widget crashes if removed right after selected

[davidbrochart]

The following code used to work, but now it crashes:

from textual import on
from textual.app import App, ComposeResult
from textual.widgets import Header, Select

LINES = """I must not fear.
Fear is the mind-killer.
Fear is the little-death that brings total obliteration.
I will face my fear.
I will permit it to pass over me and through me.""".splitlines()


class SelectApp(App):
    def compose(self) -> ComposeResult:
        self.select = Select((line, line) for line in LINES)
        self.select.watch_value = self.on_select
        yield Header()
        yield self.select

    def on_select(self):
        self.select.remove()


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

╭────────────────────────────────────────────────────── Traceback (most recent call last) ──────────────────────────────────────────────────────╮
│ /home/david/.local/share/hatch/env/virtual/jpterm/N1y3coPp/dev/lib/python3.12/site-packages/textual/widgets/_select.py:537 in update_focus    │
│                                                                                                                                               │
│   534 │   │   async def update_focus() -> None:                                                ╭──── locals ─────╮                            │
│   535 │   │   │   """Update focus and reset overlay."""                                        │ self = Select() │                            │
│   536 │   │   │   self.focus()                                                                 ╰─────────────────╯                            │
│ ❱ 537 │   │   │   self.expanded = False                                                                                                       │
│   538 │   │                                                                                                                                   │
│   539 │   │   self.call_after_refresh(update_focus)  # Prevents a little flicker                                                              │
│   540                                                                                                                                         │
│                                                                                                                                               │
│ /home/david/.local/share/hatch/env/virtual/jpterm/N1y3coPp/dev/lib/python3.12/site-packages/textual/widgets/_select.py:496 in _watch_expanded │
│                                                                                                                                               │
│   493 │                                                                                        ╭────── locals ───────╮                        │
│   494 │   def _watch_expanded(self, expanded: bool) -> None:                                   │ expanded = False    │                        │
│   495 │   │   """Display or hide overlay."""                                                   │     self = Select() │                        │
│ ❱ 496 │   │   overlay = self.query_one(SelectOverlay)                                          ╰─────────────────────╯                        │
│   497 │   │   self.set_class(expanded, "-expanded")                                                                                           │
│   498 │   │   if expanded:                                                                                                                    │
│   499 │   │   │   overlay.focus()                                                                                                             │
╰───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────╯
NoMatches: No nodes match <DOMQuery query='SelectOverlay'> on Select()

It seems that a check is needed before trying to hide the choices, in case the widget was removed.

Textual Diagnostics

Versions

Name	Value
Textual	0.73.0
Rich	13.7.1

Python

Name	Value
Version	3.12.4
Implementation	CPython
Compiler	GCC 12.3.0
Executable	/home/david/.local/share/hatch/env/virtual/jpterm/N1y3coPp/dev/bin/python

Operating System

Name	Value
System	Linux
Release	6.8.0-38-generic
Version	#38-Ubuntu SMP PREEMPT_DYNAMIC Fri Jun 7 15:25:01 UTC 2024

Terminal

Name	Value
Terminal Application	WezTerm (20240203-110809-5046fc22)
TERM	xterm-256color
COLORTERM	truecolor
FORCE_COLOR	Not set
NO_COLOR	Not set

Rich Console options

Name	Value
size	width=145, height=34
legacy_windows	False
min_width	1
max_width	145
is_terminal	True
encoding	utf-8
max_height	34
justify	None
overflow	None
no_wrap	False
highlight	None
markup	None
height	None

[willmcgugan]

self.select.watch_value = self.on_select

Whats the thinking behind monkey patching here? You may be right about the fix, but I wouldn't recommend adding a watcher like that.

[davidbrochart]

Right, this is the only way I could reproduce the bug in a minimal reproducible example. But I also saw it in a bigger project that is using @on(Select.Changed) and I had to add this logic as a workaround:

    @on(Select.Changed)
    async def select_changed(self, event: Select.Changed) -> None:
        while True:
            await asyncio.sleep(0)
            if not self.select.expanded:
                break
        self.select.remove()

[willmcgugan]

Got it. I'll have a fix for the next release. In the meantime, I'd recommend this as a workaround:

    def on_select(self):
        self.call_later(self.select.remove)

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