bug#59862: quit-restore per window buffer

[martin rudalics via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

 > I checked that prev-buffers is nil in both frame and tab cases,
 > so everything is correct here.

It's not correct in the sense that in the tab case the window showing
*info* had a previous buffer - *scratch*.  Think of users working on
some buffer who want to consult Info on something in that buffer with
the intention to turn back to that buffer as soon as they are done.
While consulting *info* they hit C-h e.  Now quitting *info* would
delete the window showing *info* and leave them with a window showing
*Messages* instead.  Is that really the behavior you have in mind?  How
would a user go back to the original buffer?

 > The difference between frame and tab case is that the frame branch
 > calls 'window--delete' that decides whether to delete the frame,
 > or just delete the window.  But in the tab case it either
 > closes the tab, or does nothing.  So in the tab case
 > it should call 'window--delete' as well, that will decide
 > whether to close the tab, or just delete the window.
 >
 > Then 'window--delete' should do something like this:
 >
 >     (unless (and dedicated-only (not (window-dedicated-p window)))
 >       (let ((deletable (window-deletable-p window)))
 >         (cond
 > +       ((eq deletable 'tab)
 > +        (tab-bar-close-tab)
 > +        'tab)
 >          ((eq deletable 'frame)
 >   	(let ((frame (window-frame window)))
 >   	  (cond
 >
 > Then maybe 'seq-count' with (window-parameter w 'quit-restore)
 > should be moved to 'window-deletable-p'.

IIUC when 'display-buffer-record-window' installs a 'quit-restore'
parameter of the 'tab' type, it assumes full responsibility for all
windows on that frame as long as the corresponding tab has not been
closed.  This means that the tab code has to assure a coherent state of
the frame's windows after the tab has been closed.  If you can guarantee
that, feel free to move that check wherever you want.

martin