bug#17261: Some combining characters don't combine (Emacs 24 regression)

[Stefan Kangas]

Eli Zaretskii <eliz@gnu.org> writes:

>> Date: Sun, 13 Apr 2014 10:49:44 -0500
>> From: Max Shinn <max@maxshinnpotential.com>
>>
>> Certain combining characters---such as the combining vector
>> arrow (0x20D7, a⃗) and the combining circle (0x20DD, a⃝)---do not
>> combine properly under most fonts on Emacs 24.3.1 under Debian GNU/Linux
>> x86_64, GTK 3.4.2.  In Emacs 23.3.1, these characters worked properly
>> under several fonts (for instance, Droid Sans Mono), whereas in Emacs
>> 24, they only work properly with the FreeMono font.  The precise
>> behavior I am observing on Emacs 24 is where the base character and the
>> combining character sit side-by-side instead of superimposed on one
>> another.
>
> Looks like some side effect of changes in how we select fonts.  Where
> Emacs 23 would force the base character to use the font that could
> display the combining character, Emacs 24 now does not, which disables
> auto-composition because Emacs can only compose characters that come
> from the same font.  So the only way to display those characters as
> composed is to select a buffer font that can display them.

Does that mean that the behaviour is not a bug, or should it be fixed?

Best regards,
Stefan Kangas