miniPerl VS unsafe-code-guidelines

Using "mini" to mean a subset of the language rather than a version for small systems has precedent. For example in the Perl community, miniperl is a subset of Perl. It's mostly used to bootstrap builds of the full language, but in theory can be used separately as a restricted programming language. It's also the name of a module, ExtUtils::Miniperl, for Perl (https://metacpan.org/pod/ExtUtils::Miniperl) that builds miniperlmain.c and perlmain.c files to bootstrap the compilation of the language system. This is not to be confused with the Raku project on Github called "miniPerl" (https://github.com/grondilu/miniPerl) which compiles subsets of Perl via the Lambda calculus to JavaScript output.

I'd personally pretty much always expect "mini" or "r" (as in "rperl", a restricted subset of Perl with C++ connections) versions of a language to be restricted subsets for some purpose (rperl's is to give away flexibility for performance while maintaining a good portion of the original language).

I've seen an "e" or "emb" prefix or a "small", "tiny", "micro" or "µ" (or "u") prefix to mean a small toolchain version several places, like SmallC or uclibc or Mikroe's mikroC. It wouldn't surprise me to see a "nano" version of a language tool either. Sometimes these are subsets as well, but to fit the size constraints of the target rather than for constraining the input for its own sake.

Useful context on the Rust side is this issue [1]. It sounds like some of the author's concerns are addressed already.

[1]: https://github.com/rust-lang/unsafe-code-guidelines/issues/4...

Is this captured by one of the known soundness conflicts? If not then should consider adding it to the list.

There are some competing proposals for different memory models. Stacked borrows is the current proposal, but there are more work in the approproate WG.

Thank you /u/RalfJung for bringing formal methods to Rust, both through models like Stacked Borrows, by developing miri, and by working on unsafe-code-guidelines which aims to specify exactly what is and isn't allowed in unsafe code (surprisingly, it's an open question as 2023!)

You could imagine some way to make this safe for example automatically convert &'short &'long mut T to &'short &'short T, but it's non-trivial to prove they are safe at all, not to mention ensuring this is correctly implemented in the compiler. If you're interested there's also a discussion on whether the opposite (& & T to & &mut T) is sound here.

Agreed! MIRI is so good, it still feels like magic to me. It also comforts me that the Rust team takes improving unsafe semantics seriously, with the past Unsafe Code Guidelines WG and today's operational semantics team (t-opsem).

I think there are some aspects of this rule that are still undecided. See for example:

- https://github.com/rust-lang/unsafe-code-guidelines/issues/8...

- https://github.com/rust-lang/miri/issues/2732

C is much better specified than unsafe Rust. Some things are just not worked out yet in Rust. This may sometimes even bite very experienced devs, such as this issue with Box's aliasing semantics, which tripped up the author of left-right.