Hi,

according to describe-function, `sort' modifies its input list, but not
in any way that the programmer can rely on. (For example, '(2 1 3)
becomes '(2 3)). I assume the precise thing that ends up in the original
list is an implementation detail and being able to "destroy" the
original list has some performance benefits.

Personally, I find this behavior very surprising and think it would make
more sense to either set the input list to the final sorting result (in
addition to returning it) or not to modify the input. In the current
situation, one basically has to do something like (setq foo (sort foo))
anyway if one wants to continue using foo (or pass a copy of foo to sort
instead), which would no longer be necessary after this change (modulo
backwards compatibility).

Is there some rationale for sort working the way it does, that I am
missing here?

Cheers,
Daniel