bug#23292: 24.5; Combining characters do not reliably combine

[Eli Zaretskii <eliz@gnu.org>]

> Date: Thu, 14 Apr 2016 15:26:03 -0400
> From: Honore Doktorr <hdfssk@gmail.com>
> 
> Combining characters often do not render combined in emacs 24.5.
> For example, the combining short solidus overlay (0x337, o̷) appears
> following the character it's meant to combine with---although they are
> both highlighted together and so forth.
> 
> cf. https://i.imgsafe.org/8369941.jpeg for a visual reference.
> 
> This seems similar to bug 17261, but both characters are from the same
> font, DejaVu Sans Mono.

Was your Emacs built with libotf and other libraries mentioned in
INSTALL under "Complex Text Layout"?

When I arrange for Emacs to use a font that supports both 'o' and the
solidus, the sequence you show does display as a single glyph.  (My
default font doesn't have the solidus, so I need that special
arrangement.)

The fact that Emacs displays a cursor on both of the characters
clearly shows that Emacs did combine them, but the font and/or the
shaping engine didn't display them overlaid.  Not sure why, perhaps
upgrade your libotf and related libraries?