bug#42147: 28.0.50; pure vs side-effect-free, missing optimizations?

[Stefan Monnier]

> Regarding package-get-version: perhaps we should drop the 'pure' property
> and just let callers wrap it in eval-when-compile?

I'd rather not: the benefit is too subtle, I'd expect most users won't
know/bother to use `eval-when-compile` around it even though I'd expect
a vast majority of the uses can benefit from compile-time evaluation.
In contrast the cases where the impurity will get in the way
should be rare.  Feel free to add a `save-match-data` if you think it's
worth the trouble (but please include a comment explaining it's only
there in order to satisfy the `pure` annotation).


        Stefan