The Stockfish chess engine requires patches to pass a test: it must beat the old version a sufficient proportion of the time.
This introduces an interesting problem: what if a patch set makes it stronger, but applied individually they make it worse?
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I've started keeping a list of particularly interesting bugs and patches that I've worked on: https://github.com/Wilfred/interesting-code
The time that I once removed *a single closing paren* in Emacs is still my favourite.
It's incredibly hard to explain adversarial problems to users. I see gamers sincerely asking "why doesn't the publisher just fix the cheater problem?".
This is exacerbated by the fact that sharing too many details of anticheat can make the problem worse.
It's a small thing, but I'm much happier with the output of --version in the latest version of difftastic.
It shows the release version number, the commit hash, and the commit date. This gives you a sense of the age of release, but you still have a reproducible build (unlike build time).
It also shows OS, arch and compiler, because those are common requirements in bug reports.