bug#17973: Thin space not thin at all

[Stefan Monnier]

Package: Emacs
Version: 24.3.92
Severity: important


   % emacs-24/src/emacs -Q -fn '-misc-fixed-*-r-semicondensed--13-*-*-*-*-*-*'
   M-< C-f C-x SPC

At this point I should see a thin space before the cursor (highlighted
with the region face).  Instead I see a full space.

   C-u C-x =

indeed shows that there's an overlay at point with an after-string of:

   #(" " 0 1 (face (region (:height 0.2))))

Now admittedly, ":height 0.2" does not specify a width, but Emacs should
be able to find a font that's about 2½ pixels high but not
6 pixels wide.

This is related to bug#16403, in that this is probably a long-standing
bug, but the new rectangular region makes it more visible.
Maybe it's actually the same bug as bug#9787 as well, which is also more
visible since *VC-log* uses such a "thin line" to separate the header
from the body.


        Stefan