[Feature] TabClosePre autocmd

[zoumi]

Is your feature request about something that is currently impossible or hard to do? Please describe the problem.
I'm using tab page as project's "working space". I want to save t: vars and use :mksession to save windows in the tab page when tab page is going to close. I can not achieve these without TabClosePre autocmd.

Describe the solution you'd like
Provide a TabClosePre autocmd so I can do something before the tab is going to be closed.
(Only trigger this autocmd when tab can be closed)

[chrisbra]

You can possibly use a WinClosed autocommand and check for winnr('$') == 1, in which case the tabpage should also be closed. (Not saying that we shouldn't add this)

[ZMProHelper]

No, if only one window left, it's too late to :mksession. When I load session later, I can only recover the only one buffer window.