Re: Unicode combining characters

[Eli Zaretskii <eliz@gnu.org>]

> Cc: emacs-devel@gnu.org
> From: Clément Pit-Claudel <cpitclaudel@gmail.com>
> Date: Tue, 25 May 2021 15:30:21 -0400
> 
> Based on the screenshot this is an issue with Company.  Company displays its "pop-ups" by putting a replacing 'display property on the text following the point (and on the next few lines).  So if the buffer contains
> 
> ABC XYZ DEF GHI
> JKL MNO PQR STU
> 
> and the point is after XYZ, then company puts a replacing display spec from " DEF" to "STU".
> To display completions "XYZ1233" and "XYZ456", the replacing display spec contains "123| GHI\nJKL XYZ456| STU", so the final display is
> 
> ABC XYZ123| GHI
> JKL XYZ456| STU
> 
> The OP's issue is that "123" and "456" don't have the same length.  As far as I know, there is no way to add extra space after 123 or 456 so that they reach the same X coordinate, given that they are already part of a display spec.

First, the OP said "overlay", and overlay strings can have display
properties.

And second, I'd expect the current code to use string-width to compute
how much whitespace will be needed after each completion candidate,
and string-width already accounts for composed (a.k.a "combined")
characters.  Yes, string-width provides only an approximation for the
true pixel width of the string, but that's not specific to
compositions, and the whole technique is somewhat of a kludge anyway,
for this reason and others.