Scrollbars may trap the mouse if hidden while the user is scrolling about textual HOT 6 OPEN

I'm sure the maintainers are way ahead of me on this, but posting my findings anyway in case it helps...

The ScrollBar does already release the mouse on a Hide event, but perhaps related is #3460 where what Hide means exactly needs some clarification.

But more importantly this issue isn't only with scrollbars, but any widget which captures the mouse. For example, if you start a mouse selection with the TextArea which is then hidden, you'll see the same behaviour.

from textual.

Digging deeper, what is interesting is the other contents do get a Hide message, which further suggests that the issue here isn't that Hide isn't getting posted, it's that a scrollbar isn't taken into account when sending such messages. For example, the problem documented here is fixed with:

diff --git a/src/textual/screen.py b/src/textual/screen.py
index f9674a47..1cee5b11 100644
--- a/src/textual/screen.py
+++ b/src/textual/screen.py
@@ -793,6 +793,8 @@ class Screen(Generic[ScreenResultType], Widget):
 
                 for widget in hidden:
                     widget.post_message(Hide())
+                    if widget.vertical_scrollbar is not None:
+                        widget.vertical_scrollbar.post_message(Hide())
 
                 # We want to send a resize event to widgets that were just added or change since last layout
                 send_resize = shown | resized

while likely not the actual fix to go with, I think it does suggest that it isn't down to a specific event not being posted, it's just that it isn't being posted as widely as it should.

from textual.

At a guess, I suspect it is the mouse capture system not "releasing" the mouse, if the scrollbar is made invisible.

Feels like an easy fix.

from textual.

Just to confirm things: I think @TomJGooding has perfectly summed up the issue here. The situation presented with the MRE above won't result in a Hide event being posted, which does feed back into #3460.

from textual.