bug#3285: 23.0.91; Messaging propertized text increases minibuffer height unnecessarily

[Drew Adams]

> > > Notice that the height changes to 2 lines.
> > >
> > > The maximum height of the regular sized font versus of 
> > > the bold font can NOT be so different as to cause the
> > > minibuffer have to increase in height from 1 line to 2 lines.
> >
> > I'm afraid I don't observe this.  Use a bold font does not 
> > resize the minibuffer.  What font are you using?
> 
> I'm using xft with the "Bitstream Vera Sans Mono-9" font.

I suspect this is the known problem, reported long ago, that if a face makes a
character slightly taller, then an extra line is allocated to handle the extra 1
or 2 pixels in height. 

I see this too, because I use a face with `box' for one character sometimes in
the minibuffer (before the prompt), and that causes the minibuffer height to
increase by a whole character height. The box outline is only 1 pixel thick, but
those 2 pixels (box top + bottom) are enough to cause the faced character to be
larger than the one character height allocated.

Maybe (dunno) the same thing happens for bold - maybe the bold characters are a
pixel or two taller.

This was discussed in Emacs Devel long ago, but never fixed. Maybe there is no
easy fix, as long as the minibuffer must be an integral number of chars high.
Dunno.

Yes, it is annoying. We accommodate ascenders and descenders (e.g. in p and d)
as part of the character height, but we don't account for box outlines or
(apparently?) for the thickness of bolding.

HTH.