The primary challenge in having a stable ABI is that we have generics. So, even if we never changed the calling conventions, an ABI is not as simple as exporting a symbol with the right name. We implement generics by providing MIR (our main intermediate representation) that gets compiled by the linking program for each instantiation of a generic.

Swift handles this through the equivalent of Rust's `dyn`. We could have a stable ABI that's based entirely on `dyn`. Such an ABI would have some limitations, since there are traits `dyn` can't represent (anything that's generic over something other than the type that implements the trait, which is quite common), though we're working on some of those.

Essentially, you wouldn't be able to have a `Vec<T>` in your ABI without either pinning down T or using something like `Vec<Box<dyn Trait>>`. Which is possible, but kind of awful.

We're still planning to ship a stable ABI at some point, but that gives a flavor for some of the kinds of problems we'd need to solve in order for that stable ABI to be useful.

(C++ typically handles generics by having types defined in header files, and those get compiled with the program consuming the library, which is effectively the same situation Rust is in. You could export symbols from a shared library for specific instantiation of a template, but people rarely do that.)

We have it: unsafe extern "C" { }.

An actual stable native Rust ABI sounds like a forward compatibility nightmare.

Follow or contribute to efforts on a minimal crABI:

https://github.com/joshtriplett/rfcs/blob/crabi-v1/text/3470...

I don't think a stable ABI has enough advantages to be worth it. C++, IMHO, is a great examples of the downsides of a stable-enough ABI, where stability was never guaranteed, but is now so entrenched that it'll likely never be broken again (limiting the language & the usability in a bunch of ways).

It might make sense to have a subset Swift-style stable ABI, but that's a huge engineering effort, has lots of overhead and is also likely not worth it IMHO.

stable ABI sounds great, but anything/everything that reduces build times is what I really want

Why the yearning for prebuilt Rust libraries? Seems like a nightmare which does not need to happen.