Collapsible: title formatting is not updated unless title text actually changes

[xavierog]

• Have you checked closed issues? (https://github.com/Textualize/textual/issues?q=is%3Aissue+is%3Aclosed)

• Have you checked against the most recent version of Textual? (https://pypi.org/search/?q=textual)

The bug

MRE

#!/usr/bin/env python3
from textual.app import App, ComposeResult
from textual.widgets import Label, Collapsible

INSTRUCTIONS = """[u]Instructions:[/u]
1. Wait for 2 seconds
2. The label inside the collapsible changes, this is good
3. The collapsible title remains unchanged, this is problematic
4. Wait for 2 seconds again
5. Both label and title change.
"""
COLLAPSIBLE_TITLE_1 = '[#ff0000]title[/]'
COLLAPSIBLE_TITLE_2 = '[#00ff00]title[/]' # color change
COLLAPSIBLE_TITLE_3 = '[#00ff00]TITLE[/]' # color and text change

class Textual3Collapsible(App):
	def compose(self) -> ComposeResult:
		yield Label(INSTRUCTIONS)
		with Collapsible(title=COLLAPSIBLE_TITLE_1, collapsed=False):
			yield Label(COLLAPSIBLE_TITLE_1)

	def change(self, new_title) -> None:
		self.query_one('Collapsible', Collapsible).title = new_title
		self.query_one('Collapsible Label', Label).update(new_title)

	def on_ready(self) -> None:
		self.set_timer(2, self.change_1)

	def change_1(self) -> None:
		self.change(COLLAPSIBLE_TITLE_2)
		self.set_timer(2, self.change_2)

	def change_2(self) -> None:
		self.change(COLLAPSIBLE_TITLE_3)


if __name__ == "__main__":
	app = Textual3Collapsible()
	app.run()

At t=0: ok:

At t=2: not ok, the collapsible title remains unchanged:

At t=4: ok, the collapsible title changed

Additionally, Collapsible's title reactive is a string whereas CollapsibleTitle's label reactive is a ContentText created using Content.from_text(). It would be nice if we could pass a ContentText to Collapsible without vexing mypy.
Alternatively, being able to import CollapsibleTitle would allow mypy to understand what is happening when working on a CollapsibleTitle widget obtained through query_one().

Textual Diagnostics

Versions

Name	Value
Textual	3.2.0
Rich	14.0.0

Python

Name	Value
Version	3.13.3
Implementation	CPython
Compiler	GCC 14.2.0
Executable	/path/to/my/venv/bin/python3

Operating System

Name	Value
System	Linux
Release	6.12.25-amd64
Version	#1 SMP PREEMPT_DYNAMIC Debian 6.12.25-1 (2025-04-25)

Terminal

Name	Value
Terminal Application	tmux (3.5a)
TERM	tmux-256color
COLORTERM	truecolor
FORCE_COLOR	Not set
NO_COLOR	Not set

Rich Console options

Name	Value
size	width=106, height=57
legacy_windows	False
min_width	1
max_width	106
is_terminal	False
encoding	utf-8
max_height	57
justify	None
overflow	None
no_wrap	False
highlight	None
markup	None
height	None

[github-actions]

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This is an automated reply, generated by FAQtory

[TomJGooding]

The problem is that Content objects are defined as equal if they have the same plain text, so because the reactive value hasn't changed the watch method is never called.

It looks like there's a similar problem in the Button (and maybe other widgets?) where the "smart refresh" isn't invoked when the new content only updates the style.

I'm not sure what the correct fix is here, perhaps these reactives need marking as always_update=True?

from textual.app import App, ComposeResult
from textual.widgets import Button, Static

CONTENT_PLAIN = "Update styles"
CONTENT_MARKUP = f"[magenta on yellow]{CONTENT_PLAIN}[/]"


class ExampleApp(App):
    def compose(self) -> ComposeResult:
        yield Button(CONTENT_PLAIN)
        yield Static(CONTENT_PLAIN)

    def on_button_pressed(self) -> None:
        # This works...
        self.query_one(Static).update(CONTENT_MARKUP)
        # ...but this doesn't
        self.query_one(Button).label = CONTENT_MARKUP


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