Another question: if we modify Cargo so that it can use locally-available rlibs, as packaged by the distro, then the distro is going to accumulate a bunch of rlibs in /usr/lib. Because of the way rustc works now those will all be invalidated when rustc is upgraded - rustc will not be able to use them at all, and will likely just pretend they don't exist because they 'belong' to another compiler. The obvious way I see to fix this is to make all Rust crate packages depend on a specific version of the compiler. I know that sucks, but is it doable?
Edit: oh, @gus I see that in your previous thread, you said that rust packages would include the source in Debian, not just the rlibs, and I also recall this was a subject of the anti-vendoring thread in Fedora. I would not expect distro packages of crates to include the source, but instead the rlibs, just globally invalidated in some way when the compiler version changes. Is this difficult to do?
If Debian packages simply dropped the source code onto the system with the expectation that Cargo rebuilds it every time its needed then there will be lots of extra builds.
Does Debian really want to package the source code, and not the rlibs? If it packages the source code where would it put it on the local system for Cargo to reuse? Either way is going to require cargo and/or rustc changes.
Any other distro maintainers have opinions about - given Rust's compilation model and ABI limitations - whether their packages of Cargo crates will simply install the source code, or the rlibs?