bug#31880: 26.1; VC mode line popup when clicked is off screen

[martin rudalics <rudalics@gmx.at>]

 > When I use Emacs via the GUI and I maximize the window, clicking on a
 > git branch in the mode line of a buffer produces the actions popup, but
 > it is unusable because it is either squished at the bottom of the screen
 > or it extends off the buttom of the screen. If I make the Emacs frame
 > smaller so that the bottom of the frame is not at the bottom of the
 > screen, then I get a usable scrollable list of VC actions when I click
 > the git branch information in the mode line.
 >
 > It seems like this popup always popups up below/beneath/downward of the
 > Emacs frame. Instead, if the bottom of the frame is at the bottom of the
 > screen (or close to it even, maybe?), then the VC popup should display
 > above/upwards.
 >
 >
 > In GNU Emacs 26.1 (build 2, x86_64-pc-linux-gnu, GTK+ Version 3.22.30)
 >   of 2018-05-29 built on lcy01-amd64-029
 > Windowing system distributor 'The X.Org Foundation', version 11.0.11906000
 > System Description:	Pop!_OS 18.04 LTS

Thank you for your report.  Similar problems have been mentioned in
bugs 24084, 25064, 26130, 26855 and 27131, most of them for Emacs 25
and GTK 3.22.  Can you see related GTK error messages when running
Emacs from a console?  Are you using multiple monitors, a high
resolution display or any other peculiar configuration that has been
mentioned in those reports?

martin