Regex hang - enormous memory consumption

[paulprocacci]

The Problem

Given the following:

my $line = '      media: Ethernet autoselect (1000baseT <full-duplex>)';
say $<media> if $line ~~ / ^ \s+ 'media: ' $<media> = [ <![\(]>+ ] $ /;

Raku is spinning spinning spinning.

Expected Behavior

I expect raku surely not to hang spinning on ~20 characters is needs to go through.

Actual Behavior

After just 5 seconds of runtime for the above:

PID USERNAME THR PRI NICE SIZE RES STATE C TIME WCPU COMMAND
97367 root 2 129 0 1385M 1139M CPU6 6 0:22 100.07% rakudo

Steps to Reproduce

Run what I've provided.

Environment

• Operating system:
  FreeBSD 14.0-RELEASE

• Compiler version (rakudo -v or raku -v):
  raku -v
  Welcome to Rakudo™ v2024.01.
  Implementing the Raku® Programming Language v6.d.
  Built on MoarVM version 2024.01.

Note the same thing happened w/ the last 2023 release.

It shall be known that what I provided <![(]+> should have been <-[(]]+>.
I understand this. I'm documenting the behavior, not the syntax.

[lizmat]

I guess it's one of those cases where the regex engine gets into an infiniloop. It's my hope we will be able to catch those cases in RakuAST.