bug#14461: 24.3.50; bad display for 'space' + (U+0336) unicode combination

[Stephen Berman]

On Sat, 17 Aug 2019 15:00:18 +0300 Eli Zaretskii <eliz@gnu.org> wrote:

>> From: Stephen Berman <stephen.berman@gmx.net>
>> Date: Thu, 15 Aug 2019 14:29:08 +0200
>> Cc: 14461@debbugs.gnu.org, Lars Ingebrigtsen <larsi@gnus.org>
>>
>> ... I assume combining characters are always displayed after a space
>> instead of over it -- at least that's what I see with e.g. U+0301
>> (COMBINING ACUTE ACCENT) and U+0302 (COMBINING CIRCUMFLEX ACCENT).
>> That makes sense to me (otherwise, you couldn't visually distinguish
>> e.g. the sequence 'aU+0301U+0302' from the sequence 'aU+0301 U+0302')
>
> I don't see why: the former should be displayed as a single grapheme
> cluster, with both diacritics on top of a, whereas the latter should
> be displayed as 2 grapheme clusters, with U+0302 on top of the SPC
> character instead of on top of a.

Hm, I chose COMBINING ACUTE ACCENT and COMBINING CIRCUMFLEX ACCENT more
or less at random, but I do indeed see the sequence 'aU+0301U+0302' as
two grapheme clusters (also with -Q): 'a' with an acute accent over it
followed by a circumflex.  In contrast, the sequences 'aU+0301U+0317'
and 'aU+0302U+0317' are displayed as single grapheme clusters (317 is
COMBINING ACUTE ACCENT BELOW).  I also noticed that the seqence
'-U+0301U+0302' is displayed as a dash followed by a single grapheme
cluster of an acute accent and a circumflex; this holds for all
nonalphabetic ASCII characters I tried and for some but not all
non-ASCII alphabetic characters.  So there seems to be some
inconsistency in the display of combining characters.

Steve Berman