This ticket is for an issue I discovered while working on T374170:

In T374170#10127410, @Od1n wrote:

I have just discovered another bug. Per regex101.com:

A repeated capturing group will only capture the last iteration. Put a capturing group around the repeated group to capture all iterations or use a non-capturing group instead if you're not interested in the data

Therefore, the (\\\\\\\\)* group (for 2 backslashes, but PHP-escaped + regex-escaped, totaling 8 backslashes to type) would match all pairs of backslashes (i.e. escaped backslashes) that precede the slash (escaped or not), which is what we want, BUT would capture and restitute only the last pair in the result.

The existing FilterEvaluator->mungeRegexp() is affected, and the one I'm adding in this PR.