When preview window gets closed (rather than autoclose), the popup should disappear

[wookayin]

The preview window would usually get auto-closed, but in some cases it is not "automatically" closed when a user move their focus onto it (#9) and close manually, or when any other vim functions/commands are executed that close the preview window --- there remains only a floating window that draws the border without the content which is already closed.

Since the border window is not focusable and there is no way to close this popup border window, it would remain forever. Using a sort of autocmd (WinClose, etc. --- but not sure), we need to make sure they are cleaned up when the main preview window is lost.

[skywind3000]

fine

[skywind3000]

I was going to look at it today. But there isn't a WinClose event, and quickui can't detect the right moment to close the background window.

It seems that no reliable way to detect window close, see here:
vim/vim#742

What about setup some local keymaps like <c-w>c in the popup window ? And quickui can close background window when people press <c-w>c ??

And another way for this is:

:call quickui#preview#close()

This will close both background and foreground window.