Detect and Fix Overscope unsafe Block

[tczajka]

@afetisov

IDEs can already trivially mark all unsafe operations in your code. That "unsure what part is truly unsafe" in a non-issue in practice, unless you don't use an IDE (in which case you'll have plenty of other issues, like non-obvious type inference).

I think Rust is supposed to be usable without an IDE. I often look at Rust code without an IDE. doc.rust-lang.org generates links to pure text source code on a website. Code reviews are often done on text diffs, not in an IDE.

I always prefer minimal unsafe blocks. I'd much prefer if individual function calls could be directly marked.

@afetisov

They should be used to mark blocks of code which share specific safety preconditions and postconditions.

Every unsafe function call should be checked to see if the function's preconditions are satisfied as documented by the function.