feature 'extra_paired_delimiters': Please remove U+0706/U+0707 from the list

[HaraldJoerg]

Description

The feature 'extra_paired_delimiters' allows many pairs, at least one of them is likely to cause confusion: U+0706 and U+0707 (SYRIAC COLON SKEWED LEFT and SYRIAC COLON SKEWED RIGHT). These characters have the BIDI property "Right-to-Left Arabic [AL]".
Unicode-aware editors and terminals process this property. The consequence: If a character between the delimiters has a left-to-right property, then everything looks normal. However, if the text between the delimiters has only BIDI neutral characters, then this text including the delimiters is displayed as right-to-left. As a special effect, if one of the characters has a "Mirror" property, then the mirrored character is displayed: a "<" is shown with the glyph ">".

Perl is not confused by this, but humans looking at the code might be. Can we please remove this (and maybe other) right-to-left delimiters from the list?

use utf8;
use feature 'extra_paired_delimiters';

my $alphabetic  = q܆a܇; # this is correct
my $punctuation = q܆.܇; # this is also correct but looks backwards

my $weird = q܆<-܇;
print $weird; # prints "<-", because that's actually the value

Perl configuration

# perl -V output goes here

Summary of my perl5 (revision 5 version 39 subversion 11) configuration:
Local Commit: 2fc32c2
Ancestor: e3f226d
Platform:
osname=linux
osvers=6.5.0-35-generic
archname=x86_64-linux
uname='linux hajbuntu 6.5.0-35-generic #35~22.04.1-ubuntu smp preempt_dynamic tue may 7 09:00:52 utc 2 x86_64 x86_64 x86_64 gnulinux '
config_args='-des -Dusedevel -Dprefix=/home/haj/localperl/ -Dman1dir=none -Dman3dir=none'
hint=recommended
useposix=true
d_sigaction=define
useithreads=undef
usemultiplicity=undef
use64bitint=define
use64bitall=define
uselongdouble=undef
usemymalloc=n
default_inc_excludes_dot=define
Compiler:
cc='cc'
ccflags ='-fwrapv -fno-strict-aliasing -pipe -fstack-protector-strong -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64'
optimize='-O2'
cppflags='-fwrapv -fno-strict-aliasing -pipe -fstack-protector-strong -I/usr/local/include'
ccversion=''
gccversion='11.4.0'
gccosandvers=''
intsize=4
longsize=8
ptrsize=8
doublesize=8
byteorder=12345678
doublekind=3
d_longlong=define
longlongsize=8
d_longdbl=define
longdblsize=16
longdblkind=3
ivtype='long'
ivsize=8
nvtype='double'
nvsize=8
Off_t='off_t'
lseeksize=8
alignbytes=8
prototype=define
Linker and Libraries:
ld='cc'
ldflags =' -fstack-protector-strong -L/usr/local/lib'
libpth=/usr/local/lib /usr/lib/x86_64-linux-gnu /usr/lib /usr/lib64
libs=-lpthread -ldl -lm -lcrypt -lutil -lc
perllibs=-lpthread -ldl -lm -lcrypt -lutil -lc
libc=/lib/x86_64-linux-gnu/libc.so.6
so=so
useshrplib=false
libperl=libperl.a
gnulibc_version='2.35'
Dynamic Linking:
dlsrc=dl_dlopen.xs
dlext=so
d_dlsymun=undef
ccdlflags='-Wl,-E'
cccdlflags='-fPIC'
lddlflags='-shared -O2 -L/usr/local/lib -fstack-protector-strong'

Characteristics of this binary (from libperl):
Compile-time options:
HAS_LONG_DOUBLE
HAS_STRTOLD
HAS_TIMES
PERLIO_LAYERS
PERL_COPY_ON_WRITE
PERL_DONT_CREATE_GVSV
PERL_HASH_FUNC_SIPHASH13
PERL_HASH_USE_SBOX32
PERL_MALLOC_WRAP
PERL_OP_PARENT

[khwilliamson]

Thank you for reporting this. Of course you are right; I just hadn't thought of issues with R-to-L scripts. I added an exclusion for all characters in such scripts, and the ones you mentioned are the only ones that were problematic.

I'm marking this as a release blocker, so that it gets considered for 5.40.

[rjbs]

@HaraldJoerg I echo Karl's sentiment: Thanks for this report