The given library example uses rust-foo for the srpm and rust-foo-devel.

Also, what happens if a library-only or binary-only crate later becomes dual-purpose?

as in other ecosystems, we rename it

Most ecosystems have main generic package name, and everything is subpackages underneath. That way, you can avoid the renaming process.

So I would go with the source package being rust-foo in all cases.

I would suggest an inline example here.

What about guidelines for how BuildRequires for crates should be structured? It seems like a specific case of what we do for Dependencies.

Alternatively, I think it might make sense to fold in BuildRequires section into Dependencies in general. It's really a subtopic of it anyway...

I suggest source package name should always be rust-%{crate} for this case.

I think we should use Google docs instead of git for faster collaboration, since we have only one week to prepare these guidelines. Of course I expect to switch back after we are done.

We are discussing changes for this PR here, if you want to contribute:
https://docs.google.com/document/d/1yx6TmybWdu82geF7H47JjowYf6_x6NaIT2UJ_znUtYM/edit?usp=sharing