> Anytime you already have the C or C++ code but not the WUFFS.

But we literally do already have WebP for WUFFS.

> Like what?

Take a recent (September) double-free in the C codec, it's easy to write that in C. We have a Thing, we sometimes make an alias to the Thing, and then later we free both the alias and the original Thing. In Rust when you try to write this the compiler is unhappy. We can either have the same realisation which led to that being fixed (we do not need this alias, it should not be created) -- which I'd say is likely for a competent Rust programmer or we can clone the Thing, and then free both the clone and original, which is not a bug unlike the C library but is a waste of performance.