re.compile() cannot identify operator "(?<"

[xiaxinmeng]

In the following example, re.compile fails to match "(?<"

test.py:

import re
p=re.compile('(?<!abc)(def)')
p.search('abcddef') 

Error message:

error: invalid perl operator: (?<

Raised from: std.re.compile:0
/home/xxm/Desktop/IFuzzer/experiment_on_different_interpreter/codon/codon-linux-x86_64/codon-deploy/lib/codon/stdlib/re.codon:104:9
Aborted (core dumped)

Reproduce:
'codon/codon-linux-x86_64/codon-deploy/bin/codon' run -release test.py

Behavior on CPython 3.10.8: work well
Environment:
codon: v0.15.5 on Feb 6
Ubuntu 18.04

[xiaxinmeng]

"\" also fails. For example:

import re
match = re.compile('((a)|b\\2)*')

output:

error: invalid escape sequence: \2

Raised from: std.re.compile:0
/home/xxm/Desktop/IFuzzer/experiment_on_different_interpreter/codon/codon-linux-x86_64/codon-deploy/lib/codon/stdlib/re.codon:104:9
Aborted (core dumped)

[arshajii]

This is because Codon uses Google's re2 under the hood for regular expressions, which is faster but has some limitations. What we want to do at some point is also incorporate Python's regex engine and choose at compile time whether to go with Python or re2 (since the regex is normally known at compile time anyway).

[inumanag]

Merging into #608 .