No subset, all of crates.io gets built for every beta amd then stable right before release looking for any changes from the prior stable.
Note that this is not all Rust code that exists, but it does help a lot.
> If you believe that you won't run into a compiler bug
I never made anything like that claim. Nor was I making any comment about the utility of something like crates.io.
I was just relating my personal real-world experience working with code. Interesting that I got downvoted, as if what I've experienced in my career was somehow wrong. I certainly wouldn't claim that devs reporting the opposite experience from mine are wrong. It's just that the difference is stark, and I was curious as to why.
If you believe that you won't run into a compiler bug in a large enough sampling of C++ code to build against you are misrepresenting reality or haven't ever looked at the gcc or clang bug trackers.
Rust actually does a really nice job along these lines by continuously building and running test for some subset of crates in crates.io
The only thing maybe even close to that with gcc/clang involved I've seen is nixos's hydra.