bug#31020: 27.0; Please provide a way to know about menu-bar wrapping

[martin rudalics <rudalics@gmx.at>]

 > I don't understand why you think that the menu-bar-lines parameter
 > should not be it.  AFAIU, the problem with setting it (or any other
 > frame parameter) to the actual value is that with many toolkits Emacs
 > simply doesn't know the correct value.  But maybe Martin will have
 > some trick up his sleeves.

I am not aware of any toolkit telling us that number or whether the
current menu bar was wrapped at all.  It's nowhere in the various API
descriptions and I suppose the information usually gets lost somewhere
in between calculations of which font the user's theme wants for the
menu bar and how that affects wrapping.  I'm not even sure whether
some toolkit would deliberately truncate our menu bar when it doesn't
fit into one line.  And lets not talk about GTK auto-resizing our
frame when the menu bar gets too long.

So what you can do is the following: Make a frame with a _visibly
unwrapped_ menu bar, get the menu bar height via

(cddr (assq 'menu-bar-size (frame-geometry)))

Do the same for a frame with a _visibly wrapped_ two-lines menu bar.
You can now derive the height of the single-line and any additional
menu bar line and use these values together with 'frame-geometry' for
getting the actual number of lines.

Obviously, this will work only as long as you do not change themes,
the menu bar height of the current theme or the resolution of your
screen or whatever else could affect this.  And since you have to
visuallly check the "wrappedness" of the menu bar, this work cannot be
reasonably done from within Emacs.

martin