It looks like on_hide is not called when a widget is hidden in some way

[davep]

I would expect the following application to crash when the button is pressed:

from textual.app        import App, ComposeResult
from textual.containers import Vertical
from textual.widgets    import Button, Label

class ShouldCrash( Label ):

    def on_hide( self ) -> None:
        _ = 1/0

class NoHideApp( App[ None ] ):

    CSS = """
    Vertical {
        align: center middle;
    }
    """

    def compose( self ) -> ComposeResult:
        with Vertical():
            yield Button( "Press to hide the label below" )
            yield ShouldCrash( "Press the button above me to hide me" )

    def on_button_pressed( self ):
        self.query_one( ShouldCrash ).display = False

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

However, when the button is pressed; it doesn't. It would appear that the Hide message isn't being sent. Looking in the debug console I don't see the event.

The same is true if I attempt to hide the widget using any of:

self.query_one( ShouldCrash ).display = "none"
self.query_one( ShouldCrash ).visible = False
self.query_one( ShouldCrash ).set_class( True, "hidden" ) # With appropriate CSS to back it up.

[aaronst]

I may have this wrong, but I think the issue might be in _compositor.reflow().

It looks like self.widgets = widgets and then hidden_widgets = self.widgets - widgets would mean hidden_widgets is always empty?

Should it maybe be hidden_widgets = old_widgets - new_widgets instead?

[aaronst]

It looks like this was introduced here, where hidden_widgets was set before self.widgets = widgets.

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