Negative lookahead unsupported

Created by: majapw

• Sourcegraph version: 2.12.2

Steps to reproduce:

1. Try to use negative lookahead, e.g. foo(?!bar) in the search bar

Expected behavior:

Search returns matches on foo but not foobar

Actual behavior:

I get an error saying Type error at character 43: error parsing regexp: invalid or unsupported Perl syntax: '(?!'

Is there any intention to support negative lookahead in the future? That would be super helpful! :)