[dialog] portal stays "mounted" when popup is removed

[KingSora]

Bug report

Its a bit hard to explain, but I've created an example here: https://codesandbox.io/p/devbox/pedantic-grass-22zl8v?workspaceId=ws_9E7g8meGhxx9KyReSrgWiy

Steps to reproduce:

• Create a dialog where the Dialog.Popup is dynamically rendered depending on the open state
• When the dialog is dismissed and the Dialog.Popup is switched out with anything else (in the examle its null)
• After the Dialog.Popup disappears the Dialog.Portal stays around indefinitely

Current behavior

The Dialog.Portal stays around even when the Dialog.Popup is gone and thus no transition / animation can occur to unmount the Dialog.Popup.

Expected behavior

The Dialog.Portal should not wait for any animations to complete when there is no Dialog.Popup to perform any animations.

Reproducible example

https://codesandbox.io/p/devbox/pedantic-grass-22zl8v?workspaceId=ws_9E7g8meGhxx9KyReSrgWiy

Base UI version

1.0.0-beta.0

Which browser are you using?

Firefox 139.0.4 (64-Bit)

Which OS are you using?

Windows 11

Additional context

Provide any additional context that might help us identify the problem and find a solution.

[atomiks]

Why not conditionally render the whole portal element tree instead?

Also: the devbox is private

[KingSora]

@atomiks sorry, the devbox should be available now

Why not conditionally render the whole portal element tree instead?

To give a bit more context, a dialog in the codebase I'm working in is implemented like this:

<Dialog content={<DialogPopupImplementation />} />

The DialogPopupImplementation component internally uses the Dialog.Popup element and the Dialog component provides the needed Dialog.Portal element for it. With this structure the Dialog component provides "the needed infrastructure" and its content prop is the visual implementation. Some more complex dialogs can change their content prop depending on some state (also the close state), and thus content can also be just null since the content prop can be any ReactNode.

I recognize that this is an edge case, but I would also expect that a dialog is not stuck in this state where I can't interact with the rest of the page (as you can see in the devbox which is now available)