#[derive(Clone)] places unnecessarily restrictive bounds on type parameter

[Ixrec]

It takes a while to really digest why derive bounds are hard just from the issue, so I'd also cite

[lang-team-minutes] private-in-public rules

Note that “perfect derive” is a chimera. It is not actually possible in the general case, because it will overflow for recursive types. Fixing this would imply coinductive matching, which is unsound in general. Given all the things we are trying to achieve with the trait system, adding general purpose coinductive matching feels out of the question to me. (There are interesting papers on combining inductive/coinductive reasoning, but those same papers indicate that it is easy to get surprising, …