GNU bug report logs - #66664
On modified lines containing 🌐︎ and Unicode VS15 in text mode emacs does not show the real content of the lines

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Subject: On modified lines containing =?UTF-8?Q?=F0=9F=8C=90=EF=B8=8E?= and
 Unicode VS15 in text mode emacs does not show the real content of the lines
From: =?UTF-8?Q?=D0=94=D0=B8=D0=BB=D1=8F=D0=BD_?=
 =?UTF-8?Q?=D0=9F=D0=B0=D0=BB=D0=B0=D1=83=D0=B7=D0=BE=D0=B2?=
 <dilyan.palauzov@HIDDEN>
To: bug-gnu-emacs@HIDDEN
Date: Sat, 21 Oct 2023 14:07:52 +0200
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Hello,

I have a text unix file u.txt where I insert this line:


t.add('=F0=9F=8C=90=EF=B8=8E ' + 'abcd')

That is a globe U+1F310 followed by Unicode Variation Selector 15 to remove=
 the colour of the globe.

$ hexdump -C  u.txt
00000000  74 2e 61 64 64 28 27 f0  9f 8c 90 ef b8 8e 20 27  |t.add('.......=
 '|
00000010  20 2b 20 27 61 62 63 64  27 29 0a                 | + 'abcd').|
0000001b

I open the file in text mode, emacs-fedora-28.3 -nw, and press the right ar=
row repeatedly to go over c.  Then I press x.  emacs shows that c is delete=
d and on its place appears x. I press Ctrl+L to refresh.  Now c appears bef=
ore x.

I close emacs, repeat the above steps and get consistent results.  I try th=
is on a different system with self-compiled emacs 29.1, same results.

The problem report is that when that character sequence is contained in a t=
ext file, modifying more complex lines gets practically impossible with ema=
cs, as the latter stops showing the actual text.  I have to refresh, close,=
 open emacs several times in order to get modifications correctly on the li=
nes, containing the above sequence.  I literally  cannot see what I am chan=
ging on such lines, as what is displayed is different to what is actually m=
odified.

Kind regards
  Dilyan