Starcraft AI blog

In Steamhammer 3.5.1 (see the “zerg” section) I added a defense against cannon rushes which exploits the sunken range bug. The bug makes it possible, under specific conditions, for a sunken colony to target an enemy which is outside the sunken’s range. Exploiting the bug is allowed in human tournaments. In fact, it’s a standard defense against cannon rushes, one that players know and use. An example is ASL 11 Semifinal A, Mini vs Queen, game 1—see about 32 minutes into the vod for a complicated sequence where Mini eventually abandons the cannon rush knowing that it has been countered, and notice that casters Nyoken and Scan have little trouble understanding what happened and why.

At the time I wrote “Use of this bug seems to be universally legal,” but today I checked the AIIDE rules more closely. The rules include a list of allowed bugs to exploit, and add “All other bugs/exploits are forbidden.” The sunken range bug is not on the list.

I sent e-mail to Dave Churchill explaining the situation and its complexities. He’s busy and I don’t know if he’ll have time to look into it. Basically, I’m expecting to disable the behavior in Steamhammer for the tournament. I’m adding a configuration setting Config::Skills::UseSunkenRangeBug so I can turn it on and off.

Most likely no AIIDE 2021 protoss will cannon rush at all, so in a way the point is academic. But who knows?

what should the rules say?

It’s complicated!

The range bug is a game behavior, and it can happen unintentionally in real games, just because events happen to trigger its conditions. It’s fairly rare, but I expect all who play regularly have seen it (whether they recognized it or not). Bots should not be penalized for game behavior that they did not intend, and have no reason to even notice.

Steamhammer deliberately attempts to exploit the bug to beat cannon rushes. I have to interpret that as a violation of the AIIDE rules as they are written.

If you’re actively trying to enforce the rule, how would you do it? First, you’d have to examine the games, presumably with replay analysis software since there are too many to watch in person. Then you’d have to decide whether at least one instance of the bug was a deliberate exploit. That likely involves reading the code to be sure. Tournament organizers are not going to go to so much trouble, so probably the only practical enforcement would be for other authors or observers to point out possible infractions after the fact.

Then there’s the point that exploiting the bug is legal in human play, so presumably it should be legal in bot play. But that has a hidden assumption behind it: Humans can’t or don’t exploit the bug in any way that seems unfair, therefore bots won’t either. It might be true, but how sure are you? Bots with perfect timing and simultaneous view of all information might be able to exploit the bug in a way that feels unfair. Then the rules would be unfair.

Maybe it’s right to allow exploiting the range bug unless and until some bot implements an unfair exploitation.

Even if it may be a good idea to change the rules, it’s no good to change them close to the submission deadline. The rules for this year should stay put. Next year’s rules may be open to debate.

Update: I have mail from Dave Churchill. After some flip-flopping, the final ruling is “INTENTIONAL use of this bug via any specific code that invokes it is not allowed.” That follows the original rules.