I think we should do this refactoring either way, but if removing the &mut vmctx syntax from the lucet_hostcalls! macro would make rustfmt work, then let's do that as well.

Unfortunately, removing the &mut vmctx syntax to make it valid Rust doesn't help much.
Everything in the macro is seen as an unstructured blob of text.

But the wrappers are fine. It's actually very convenient to have all of the public definitions in a single file, while having some flexibility for the actual implementations.

Gotcha, that's what I thought, which is why I wasn't worrying too much about messing with the syntax. It definitely is a major downside of using this kind of macro. Eventually it'd be nice to make it a proc macro so that we can use attribute syntax instead.

I totally agree about the separation.

Procedural macros are going to make a lot of things way easier and cleaner.

Looking forward to them being stabilized some day...

They are stable, or at least enough of them that we could do this. I just didn't have the time to dig in and do it properly when implementing the macro the first time around.

I've only made a brief skim through the code here, but it looks good to me as a base to build on!

Thanks a ton for your review, Dan!