Implement NoCell, IntoBytes and possibly other traits for std::convert::Infallible

[mseravalli]

What is the name of your project?
Fuchsia netstack3

Please provide a link to your project (GitHub repository, crates.io page, etc).
https://cs.opensource.google/fuchsia/fuchsia/+/main:src/connectivity/

What features would you like from zerocopy?
It might be useful to implement NoCell, IntoBytes and possibly other traits for std::convert::Infallible so that it can be used e.g. in associated types. This would improve how specific invariants are enforced and would allow use Infallible instead of () or a custom defined type with the same behavior of Infallible.

[joshlf]

Thanks for this, @mseravalli!

Just a heads up that, thanks to #1292, we won't be able to vendor new versions of zerocopy (including any that would include an implementation of this issue) into Fuchsia until rust-lang/rust#45713 is fixed, published in a new Rust toolchain version, and that version is vendored into Fuchsia. I discovered the issue when trying to vendor (see my WIP CL stack here), and so far the only problem I've found is in packet-formats. Since you guys own that library, you could potentially work around it by changing the visibility of some types if you care about getting this in on a particular timeline; feel free to reach out internally if you would like guidance on how to do that.