utils.str: Handle \0 in perlReToReplacer

[tatokis]

It is required to use \g<0> as otherwise Python will process \0 as a 0 byte.

Previous behaviour:

<User> @re "s/hello/\0 world/" "hello"
<Bot> '\x00 world'

[jlu5]

I did some testing and it seems that \0 is not a particularly standard construct among regex implementations. Some will treat it as NUL, some will treat it as the a backreference for the whole string, while others will see it as an error entirely: https://regex101.com/r/SCfTW4/1

I think in these cases it's better to preserve the Python behaviour to avoid introducing inconsistencies, and use \g<0> explicitly in your regexps as needed.

<jlu5_> re "s/o/\0\0/" "hello"
-bitmonster- 'hell\x00\x00'
<jlu5_> re "s/o/\g<0>\g<0>/" "hello"
-bitmonster- helloo

Interestingly it seems perl also treats \0 as NUL:

$ perl -p -e 's/(o)/\0/g' <<< foobar | hexdump -c
0000000   f  \0  \0   b   a   r  \n                                    
0000007

[progval]

this line looks redundant

[progval]

Some will treat it as NUL

this one doesn't really make sense on IRC

[jlu5]

Some will treat it as NUL

this one doesn't really make sense on IRC

Given the nested commands support though, not all command output is necessarily made to be displayed.