I just peaked at the crates.io dependencies in the standard library. There's three dependencies to high-quality libraries in the rust-lang GitHub organization:

I just peaked at the crates.io dependencies in the standard library. There's three dependencies to high-quality libraries in the rust-lang GitHub organization: a macro to make conditional compilation easier (cfg_if), a port of Google's SwissTable hashmap library (hashbrown), and bindings to libc. These all have maintainers in common with the standard library. The rust standard library hashmap is (zero cost) wrapper around a hashbrown hashmap with a subset of hashbrown's methods. cfg_if is probably used just for the convenience. I guess they're not ready to commit to stabilizing that macro in the standard library for some reason. libc was originally autogenerated from the c header files, but if I recall correctly updating it involves a bunch of annoying manual processes necessary to ensure perfect compatibility. It's obvious used in the implementation of standard library features. Then there's a handful of dependenencies for the optional but enabled-by-default backtrace feature like a symbol demangler and a zlib encoder/decoder. I'm not familiar with their quality, but I don't think it's as excellent as the other dependencies.