bug#51883: 29.0.50; Command to get accidentally deleted frames back

[Juri Linkov]

> Maybe having it in C would be better - I don't know.

To avoid implementing the whole function in C,
'delete-frame' could call a hook with the frame as its arg,
then you can add your code to the hook.

> A more convenient access to frames killed earlier than the last one,
> instead of using the prefix arg like above, might be appropriate (making
> the command repeatable, maybe?)  Apart from these details the above is
> a start and could just go to frameset.el.  Opinions?

Very useful feature.  And like tab-undo is bound to 'C-x t u',
the frame closing undo could be bound to 'C-x 5 u'.

I haven't yet tested whether your implementation restores the tab-bar
as well, or maybe it would require more handling.  I suspect that
instead of framesets you might need to use window-state-get/window-state-put
like it's used in 'clone-frame'.  This means that code could go to frame.el.