Added definitions to the glossary

[adfernandes]

Specifically:

• regulatory approach
• memory safety (spatial and temporal)
• mc/dc coverage
• integer overflow
• functional purity

as per this issue

[RalfJung]

Thanks for the PR! However, most of these I don't think fit this repo. I have also never seen that issue you are referring to. We don't have a "regulatory approach" in this repo nor are we specifically considering coverage, and the definition of an integer overflow is sufficiently simple that I see no reason to carry it in our glossary. I am not sure why we would define "pure function" here, either.

We could add a definition of memory safety, but I think splitting memory safety into subclasses such as spatial and temporal is largely not useful, so I don't agree with the definition you have added here. In my view, memory safety in the context of Rust simply means "the program has no UB". For instance, there is no meaningful way in which a program with data races (in a language like Rust where data races are UB) is memory safe.

[adfernandes]

Thanks for the comments, @RalfJung - in retrospect, I think I agree with you.

If I could as not to close this issue quite yet, I'm going to bring this up to the committee, because I think there's a fair bit of conflation between "Unsafe Rust" and "Safety-Critical Unsafe Rust".

Needs some thought...