But moreover, you stumbled upon one of the worst cases, a soundness problem that has yielded a lot of discussion because of that crate specifically: https://github.com/rust-lang/rust/issues/50781
The issue here is that the typemap crate was found to be relying on a compiler bug. The compiler bug could be exploited to write transmute in safe code: in other words, all the safety guarantees of Rust go out the window unless we break that crate. It's a bad situation, but I don't know what we could have done differently. I think everyone agrees it's not worth sacrificing all the safety properties of Rust to keep typemap building.
But as a possible example, typemap [1] which is a library featured on Awesome Rust [2] ("curated list of Rust code and resources").
Project uses cargo. Has a lock file with two deps. Last code commit was May 2017. And I can't get it to compile.
[1] https://github.com/reem/rust-typemap
[2] https://github.com/rust-unofficial/awesome-rust