Difftastic is written in Rust, so I was surprised to get a user report of a segfault.
After some investigation, it turns out that it's a segfault in git itself, which has existed since 2014! https://lore.kernel.org/git/CAFXAjY7XcL1APhLRXU8TO96z=f7957f2ieK56dHVsXUay55vpg@mail.gmail.com/T/#u
(Upstream has already kindly written a patch.)